United States
Department of
Agriculture
Natural
Resources
Conservation
Service
Agriculture
Handbook
Number 590
Ponds —
Pla...
i
Ponds—Planning, Design, ConstructionAgriculture Handbook 590
Preface
This handbook describes the requirements for buildi...
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Ponds—Planning, Design, ConstructionAgriculture Handbook 590
Acknowledgments
The first version of this handbook was pre...
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Ponds—Planning, Design, ConstructionAgriculture Handbook 590
Introduction 1
Water needs 2
Livestock .....................
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Embankment ponds 24
Detailed soils investigation.............
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Tables Table 1 Runoff curve numbers for urban areas 14
Tabl...
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Figures Figure 1 Typical embankment and reservoir 1
Figure...
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Figure 16 Time of concentration (Tc) nomograph 20
Figure ...
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Figure 33 The sod and topsoil in a pond construction are...
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Ponds—Planning, Design, ConstructionAgriculture Handbook 590
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Ponds—Planning, Design, ConstructionAgriculture Handbook 590
Issued June 1982
Revised November 1997
The United States De...
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Ponds—Planning, Design, ConstructionAgriculture Handbook 590
Figure 1 Typical embankment and reservoir
An embankment pon...
Ponds—Planning, Design, Construction
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Water needs
Livestock
Clean water and ample forage are equ...
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Ponds—Planning, Design, ConstructionAgriculture Handbook 590
Irrigation
Farm ponds are now an important source of irriga...
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Field and orchard spraying
You may wish to provide water f...
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Ponds—Planning, Design, ConstructionAgriculture Handbook 590
Figure 5 A dry hydrant is needed when a pond is close enoug...
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Recreation
A pond can provide many pleasant hours of swimm...
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Ponds—Planning, Design, ConstructionAgriculture Handbook 590
Figure 8 Waterfowl use ponds as breeding, feeding, watering...
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Regardless of its purpose, a pond’s appearance can be
impr...
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Preliminary investigations
General considerations
Selecting...
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tics, such as amount, intensity, and duration of rainfall...
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Ponds—Planning, Design, ConstructionAgriculture Handbook 590
Drainage area protection
To maintain the required depth an...
Ponds—Planning, Design, Construction
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Landscape evaluation
Alternative pond sites should be eva...
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Ponds—Planning, Design, ConstructionAgriculture Handbook 590
Estimating storm runoff
The amount of precipitation, wheth...
Ponds—Planning, Design, Construction
14
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Table 1 Runoff curve numbers for urban areas 1/
Cover des...
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Table 2 Runoff curve numbers for agricultural lands 1/
Cov...
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Table 3 Runoff curve numbers for other agricultural lands...
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Table 4 Runoff curve numbers for arid and semiarid rangela...
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Volume of storm runoff
Often knowing how much water runs ...
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Rainfall amounts and expected
frequency
Maps in U.S. Weath...
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Peak discharge rate
The slope of the land above the pond ...
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Average watershed slope
The average watershed slope (Y) is...
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Estimating peak discharge rates
The unit peak discharge (...
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Ponds—Planning, Design, ConstructionAgriculture Handbook 590
Figure 17a Unit peak discharge (qu) for Type I storm
distr...
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Embankment ponds
Detailed soils investigation
Soils in th...
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Soil borings help to investigate thoroughly the founda-
ti...
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Agriculture Handbook 590
length of time they stay in suspension in still water.
Hi...
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Ponds—Planning, Design, ConstructionAgriculture Handbook 590
The principal spillway normally is sized to control the
ru...
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Table 8 Permissible velocity for vegetated spillways 1/
V...
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Figure 20 Plan, profile, and cross section of a natural sp...
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Table 10 Hp discharge and velocities for natural vegetate...
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The following example shows how to use table 10:
Given:
Ve...
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For retardance C, enter table 11 from left at
maximum vel...
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Figure 21 Excavated earth spillway
,,,,,,
,, ,,,Exit chann...
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Table 11 Depth of flow (Hp) and slope range at retardance...
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Table 11 Depth of flow (Hp) and slope range at retardance ...
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Pipes through the dam
Pipe spillways—Protect the vegetati...
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Figure 23 Drop-inlet pipe spillways
(a) With sand-gravel f...
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Table 12 Discharge values for smooth pipe drop inlets 1/
...
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Hood-inlet pipe spillway—A hood-inlet consists of a
pipe l...
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Figure 25 Pipe inlet spillways that have trash rack and a...
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Ponds—Planning, Design, ConstructionAgriculture Handbook 590
The required diameter for a hood-inlet pipe can be
selecte...
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Table 15 Minimum head, h (ft), required above the invert ...
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with pipe spillways for many years. More fabricated
materi...
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Figure 26 Water is piped through the dam’s drainpipe to a...
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Ponds, planning, design, construction

This handbook describes the requirements for building a pond. It is useful to the landowner for general information and serves as a reference for the engineer, technician, and contractor
Published on: Mar 4, 2016
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Transcripts - Ponds, planning, design, construction

  • 1. United States Department of Agriculture Natural Resources Conservation Service Agriculture Handbook Number 590 Ponds — Planning, Design, Construction
  • 2. i Ponds—Planning, Design, ConstructionAgriculture Handbook 590 Preface This handbook describes the requirements for building a pond. It is useful to the landowner for general information and serves as a reference for the engineer, technician, and contractor. In fulfilling their obligation to protect the lives and property of citizens, most states and many other government entities have laws, rules, and regulations governing the installation of ponds. Those responsible for planning and designing ponds must comply with all such laws and regula- tions. The owner is responsible for obtaining permits, performing necessary maintenance, and having the required safety inspections made.
  • 3. ii Ponds—Planning, Design, ConstructionAgriculture Handbook 590 Acknowledgments The first version of this handbook was prepared under the guidance of Ronald W. Tuttle, national landscape architect for the USDA, Natural Resources Conservation Service (NRCS), and Gene Highfill, national agricultural engineer (retired), NRCS, Washington, DC. This version of the handbook was prepared by Clifton Deal, soil mechanic engineer, NRCS Portland, Oregon; Jerry Edwards, hydraulic engineer (retired), NRCS, Columbia, Missouri; Neil Pellmann, agricultural engineer, NRCS, Columbia, Missouri; Ronald W. Tuttle; and under the guidance of Donald Woodward, national hydrologist, NRCS, Washington, DC. The appendixes material was originally prepared for Landscape Architec- ture Note 2—Landscape Design: Ponds by Gary Wells, landscape architect, NRCS, Lincoln, Nebraska. Mary R. Mattinson, editor; Lovell S. Glasscock, editor; John D. Massey, visual information specialist; and Wendy R. Pierce, illustrator; NRCS, Fort Worth, Texas, provided valuable assistance in preparing the document for publishing.
  • 4. iii Ponds—Planning, Design, ConstructionAgriculture Handbook 590 Introduction 1 Water needs 2 Livestock ............................................................................................................ 2 Irrigation ............................................................................................................ 3 Fish production ................................................................................................. 3 Field and orchard spraying .............................................................................. 4 Fire protection .................................................................................................. 4 Recreation.......................................................................................................... 6 Waterfowl and other wildlife ........................................................................... 6 Landscape quality ............................................................................................. 6 Multiple purposes ............................................................................................. 8 Preliminary investigations 9 General considerations .................................................................................... 9 Area adequacy of the drainage ........................................................................ 9 Minimum pond depth ..................................................................................... 10 Drainage area protection ............................................................................... 11 Pond capacity .................................................................................................. 12 Landscape evaluation ..................................................................................... 12 Estimating storm runoff 13 Hydrologic groupings of soils........................................................................ 13 Runoff curve numbers.................................................................................... 13 Volume of storm runoff .................................................................................. 18 Rainfall amounts and expected frequency .................................................. 19 Rainfall distribution ........................................................................................ 19 Peak discharge rate ........................................................................................ 20 Time of concentration .................................................................................... 20 Average watershed slope ............................................................................... 21 Flow length ...................................................................................................... 21 Ia /P ratio.......................................................................................................... 21 Estimating peak discharge rates ................................................................... 22 Site surveys 24 Contents Ponds — Planning, Design, Construction Agriculture Handbook 590
  • 5. iv Ponds—Planning, Design, ConstructionAgriculture Handbook 590 Embankment ponds 24 Detailed soils investigation............................................................................ 24 Spillway requirements .................................................................................... 26 Pipes through the dam ................................................................................... 36 Planning an earthfill dam ............................................................................... 45 Staking for construction ................................................................................ 53 Building the pond............................................................................................ 53 Excavated ponds 57 Soils .................................................................................................................. 57 Spillway and inlet requirements.................................................................... 58 Planning the pond ........................................................................................... 58 Building the pond............................................................................................ 61 Sealing the pond 62 Compaction ..................................................................................................... 62 Clay blankets ................................................................................................... 63 Bentonite.......................................................................................................... 63 Chemical additives.......................................................................................... 64 Waterproof linings .......................................................................................... 65 Establishing vegetation 66 Protecting the pond ........................................................................................ 66 Wave action ..................................................................................................... 66 Livestock .......................................................................................................... 67 Operating and maintaining the pond 68 Pond safety 69 Before construction ........................................................................................ 69 During construction........................................................................................ 69 After completion ............................................................................................. 69 References 70 Glossary 71 Appendixes 75 Appendix A: Estimating the Volume of an Excavated Pond ..................... 75 Appendix B: Flood-Tolerant Native Trees and Shrubs .............................. 79
  • 6. v Ponds—Planning, Design, ConstructionAgriculture Handbook 590 Tables Table 1 Runoff curve numbers for urban areas 14 Table 2 Runoff curve numbers for agricultural lands 15 Table 3 Runoff curve numbers for other agricultural lands 16 Table 4 Runoff curve numbers for arid and semiarid rangelands 17 Table 5 Runoff depth, in inches 18 Table 6 Ia values for runoff curve numbers 21 Table 7 Minimum spillway design storm 27 Table 8 Permissible velocity for vegetated spillways 28 Table 9 Guide to selection of vegetal retardance 28 Table 10 Hp discharge and velocities for natural vegetated 30 spillways with 3:1 end slope (Z1 ) Table 11 Depth of flow (Hp) and slope range at retardance 34 values for various discharges, velocities, and crest lengths Table 12 Discharge values for smooth pipe drop inlets 38 Table 13 Discharge values for corrugated metal pipe drop inlets 38 Table 14 Minimum head, h (ft), required above the invert of 41 hood inlets to provide full flow, Q (ft3 /s), for various sizes of smooth pipe and values of total head, H Table 15 Minimum head, h (ft), required above the invert of 42 hood inlets to provide full flow, Q (ft3 /s), for various sizes of corrugated pipe and values of total head, H Table 16 Recommended side slopes for earth dams 46 Table 17 End areas in square feet of embankment sections 48 for different side slopes and top widths Table 18 Volume of material needed for the earthfill 51
  • 7. vi Ponds—Planning, Design, ConstructionAgriculture Handbook 590 Figures Figure 1 Typical embankment and reservoir 1 Figure 2 This pond supplies water to a stockwater trough used by 2 cattle in nearby grazing area Figure 3 Water is pumped out of this pond for irrigation 3 Figure 4 A pond stocked with fish can provide recreation as 4 well as profit Figure 5 A dry hydrant is needed when a pond is close enough 5 to a home or barn to furnish water for fire fighting Figure 6 Details of a dry hydrant installation 5 Figure 7 Ponds are often used for private as well as 6 public recreation Figure 8 Waterfowl use ponds as breeding, feeding, 7 watering places, and as resting places during migration Figure 9 The shoreline of a well-designed pond is protected 7 from erosion by the addition of stone. Such a pond, reflecting nearby trees, increases the value of the surrounding land Figure 10 This pond, which served as a sediment basin while 8 homes in the background were being constructed, now adds variety and value to the community Figure 11 A guide for estimating the approximate size of a 10 drainage area (in acres) required for each acre-foot of storage in an embankment or excavated pond Figure 12 Recommended minimum depth of water for ponds 11 in the United States Figure 13 Land with permanent vegetation makes the 12 most desirable drainage area Figure 14 A preliminary study of two alternative sites for a pond 12 to be used for livestock water, irrigation, and recreation Figure 15 Approximate geographic boundaries for NRCS 19 rainfall distributions
  • 8. vii Ponds—Planning, Design, ConstructionAgriculture Handbook 590 Figure 16 Time of concentration (Tc) nomograph 20 Figure 17a Unit peak discharge (qu) for Type I storm distribution 23 Figure 17b Unit peak discharge (qu) for Type IA storm distribution 23 Figure 17c Unit peak discharge (qu) for Type II storm distribution 23 Figure 17d Unit peak discharge (qu) for Type III storm distribution 23 Figure 18 Borrow material taken from within the reservoir 25 area creates an irregular pond configuration Figure 19 The apparent size of the pond is influenced by 26 surrounding vegetation Figure 20 Plan, profile, and cross section of a natural spillway 29 with vegetation Figure 21 Excavated earth spillway 33 Figure 22 Drop-inlet pipe spillway with antiseep collar 36 Figure 23 Drop-inlet pipe spillways 37 Figure 24 Dam with hooded inlet pipe spillway 39 Figure 25 Pipe inlet spillways that have trash rack and 40 antivortex baffle Figure 26 Water is piped through the dam’s drainpipe to 44 a stockwater trough Figure 27 A core trench is cut on the centerline of a dam 45 Figure 28 Dam side slopes are curved and shaped to blend 46 with surounding topography Figure 29 Finished grading techniques 47 Figure 30 A tree well preserves vegetation 53 Figure 31 Irregular clearing around the pond helps create 54 a natural appearing edge Figure 32 Feathering vegetation at the pond's edge makes 54 a natural transition with existing vegetation
  • 9. viii Ponds—Planning, Design, ConstructionAgriculture Handbook 590 Figure 33 The sod and topsoil in a pond construction area 56 can be stockpiled for later use Figure 34 Geometric excavation graded to create more 58 natural configuration Figure 35 Typical sections of an excavated pond 59 Figure 36 Correct disposal of waste material 60 Figure 37 Waste material and plantings separate the pond 61 from a major highway Figure 38 Disking in chemical additive to seal a pond 62
  • 10. ix Ponds—Planning, Design, ConstructionAgriculture Handbook 590
  • 11. x Ponds—Planning, Design, ConstructionAgriculture Handbook 590 Issued June 1982 Revised November 1997 The United States Department of Agriculture (USDA) prohibits discrimina- tion in its programs on the basis of race, color, national origin, sex, religion, age, disability, political beliefs, and marital or familial status. (Not all prohibited bases apply to all programs.) Persons with disabilities who require alternate means for communication of program information (Braille, large print, audiotape, etc.) should contact the USDA’s TARGET Center at (202) 720-2600 (voice and TDD). To file a complaint, write the Secretary of Agriculture, U.S. Department of Agriculture, Washington, DC, 20250, or call 1-800-245-6340 or (202) 720-1127 (TDD). USDA is an equal opportunity employer.
  • 12. 1 Ponds—Planning, Design, ConstructionAgriculture Handbook 590 Figure 1 Typical embankment and reservoir An embankment pond (fig. 1) is made by building an embankment or dam across a stream or watercourse where the stream valley is depressed enough to permit storing 5 feet or more of water. The land slope may range from gentle to steep. An excavated pond is made by digging a pit or dugout in a nearly level area. Because the water capacity is obtained almost entirely by digging, excavated ponds are used where only a small supply of water is needed. Some ponds are built in gently to moderately sloping areas and the capacity is obtained both by excavating and by building a dam. The criteria and recommendations are for dams that are less than 35 feet high and located where failure of the structure will not result in loss of life; in damage to homes, commercial or industrial buildings, main highways, or railroads; or in interrupted use of public utilities. Local information is essential, and land users are encouraged to consult with specialists experienced in planning and building ponds. Introduction For many years farmers and ranchers have been building ponds for livestock water and for irrigation. By 1980 more than 2.1 million ponds had been built in the United States by land users on privately owned land. More will be needed in the future. The demand for water has increased tremendously in recent years, and ponds are one of the most reliable and economical sources of water. Ponds are now serving a variety of purposes, including water for livestock and for irrigation, fish production, field and orchard spraying, fire protection, energy conservation, wildlife habitat, recreation, erosion control, and land- scape improvement. This handbook describes embankment and excavated ponds and outlines the requirements for building each. The information comes from the field experience and observation of land users, engineers, conservationists, and other specialists. Ponds — Planning, Design, Construction Agriculture Handbook 590 Temporary pool Stage P.S. inlet crest Top of constructed fill Outlet channel Barrel Core trench Frontslope Normal pool Top of settled fill Auxiliary spillway Backslope Outlet section Inlet section Cross section (not to scale)
  • 13. Ponds—Planning, Design, Construction 2 Agriculture Handbook 590 Water needs Livestock Clean water and ample forage are equally essential for livestock to be finished out in a marketable condition. If stockwater provisions in pasture and range areas are inadequate, grazing will be concentrated near the water and other areas will be undergrazed. This can contribute to serious livestock losses and instability in the livestock industry. Watering places must also be properly distributed in relation to the available forage. Areas of abundant forage may be underused if water is not accessible to livestock grazing on any part of that area (fig. 2). Providing enough watering places in pastures encour- ages more uniform grazing, facilitates pasture im- provement practices, retards erosion, and enables farmers to make profitable use of soil-conserving crops and erodible, steep areas unfit for cultivation. An understanding of stockwater requirements helps in planning a pond large enough to meet the needs of the stock using the surrounding grazing area. The average daily consumption of water by different kinds of livestock shown here is a guide for estimating water needs. Kind of livestock Gallons per head per day Beef cattle and horses 12 to 15 Dairy cows (drinking only) 15 Dairy cows (drinking and barn needs) 35 Hogs 4 Sheep 2 The amount of water consumed at one pond depends on the average daily consumption per animal, number of livestock served, and period over which they are served. Figure 2 This pond supplies water to a stockwater trough used by cattle in nearby grazing area
  • 14. 3 Ponds—Planning, Design, ConstructionAgriculture Handbook 590 Irrigation Farm ponds are now an important source of irrigation water (fig. 3), particularly in the East, which does not have the organized irrigation enterprises of the West. Before World War II irrigation was not considered necessary in the humid East. Now many farmers in the East are irrigating their crops. Water requirements for irrigation are greater than those for any other purpose discussed in this hand- book. The area irrigated from a farm pond is limited by the amount of water available throughout the growing season. Pond capacity must be adequate to meet crop requirements and to overcome unavoidable water losses. For example, a 3-inch application of water on l acre requires 81,462 gallons. Consequently, irrigation from farm ponds generally is limited to high-value crops on small acreages, usually less than 50 acres. The required storage capacity of a pond used for irrigation depends on these interrelated factors: water requirements of the crops to be irrigated, effective rainfall expected during the growing season, applica- tion efficiency of the irrigation method, losses due to evaporation and seepage, and the expected inflow to the pond. Your local NRCS conservationist can help you estimate the required capacity of your irrigation pond. Fish production Many land users are finding that fish production is profitable. A properly built and managed pond can yield from l00 to 300 pounds of fish annually for each acre of water surface. A good fish pond can also provide recreation (fig. 4) and can be an added source of income should you wish to open it to people in the community for a fee. Ponds that have a surface area of a quarter acre to several acres can be managed for good fish produc- tion. Ponds of less than 2 acres are popular because they are less difficult to manage than larger ones. A minimum depth of 8 feet over an area of approximately 1,000 square feet is needed for best management. Figure 3 Water is pumped out of this pond for irrigation
  • 15. Ponds—Planning, Design, Construction 4 Agriculture Handbook 590 Field and orchard spraying You may wish to provide water for applying pesticides to your field and orchard crops. Generally, the amount of water needed for spraying is small, but it must be available when needed. About l00 gallons per acre for each application is enough for most field crops. Or- chards, however, may require 1,000 gallons or more per acre for each spraying. Provide a means of conveying water from the pond to the spray tank. In an embankment pond, place a pipe through the dam and a flexible hose at the down- stream end to fill the spray tank by gravity. In an excavated pond, a small pump is needed to fill the tank. Fire protection A dependable water supply is needed for fighting fire. If your pond is located close to your house, barn, or other buildings, provide a centrifugal pump with a power unit and a hose long enough to reach all sides of all the buildings. Also provide for one or more dry hydrants (figs. 5 and 6). Although water-storage requirements for fire protec- tion are not large, the withdrawal rate for fire fighting is high. A satisfactory fire stream should be at least 250 gallons per minute with pressure at the nozzle of at least 50 pounds per square inch. Fire nozzles gener- ally are l inch to 1-1/2 inches in diameter. Use good quality rubber-lined firehoses, 2-1/2 to 3 inches in diameter. Preferably, the hose should be no more than 600 feet long. A typical firehose line consists of 500 feet of 3-inch hose and a 1-1/8 inch smooth nozzle. A centrifugal pump operating at 63 pounds per square inch provides a stream of 265 gallons per minute with a nozzle pres- sure of 50 pounds per square inch. Such a stream running for 5 hours requires 1/4 acre-foot of water. If you live in an area protected by a rural fire fighting organization, provide enough storage to operate sev- eral such streams. One acre-foot of storage is enough for four streams. Your local dealer in pumps, engines, and similar equip- ment can furnish the information you need about pump size, capacity, and engine horsepower. Figure 4 A pond stocked with fish can provide recreation as well as profit
  • 16. 5 Ponds—Planning, Design, ConstructionAgriculture Handbook 590 Figure 5 A dry hydrant is needed when a pond is close enough to a home or barn to furnish water for fire fighting Figure 6 Details of a dry hydrant installation ,,,,,,,,,,,, ,,,,, ,, 24 in 4.5-in bronze cap-steamer hose connection Bronze nipple 4.5-in in steamer to 4 or 6 in pipe 4- or 6-in pipe elbow 4- or 6-in pipe riser Ground lineFrost-free depth Cast iron elbow Gravel covering depth of 12 in Well screen Farm pond water level Suction pipe4- or 6-in galvanized steel or other equally durable pipe Not to scale Pumping lift not over 18 ft
  • 17. Ponds—Planning, Design, Construction 6 Agriculture Handbook 590 Recreation A pond can provide many pleasant hours of swimming, boating, and fishing. The surrounding area can be made into an attractive place for picnics and games (fig. 7). Many land users realize additional income by provid- ing water for public recreation. If the public is invited to use a pond for a fee, the area must be large enough to accommodate several parties engaged in whatever recreation activities are provided. If a pond is to be used for public recreation, supply enough water to overcome evaporation and seepage losses and to maintain a desirable water level. A pond used for swimming must be free of pollution and have an adequate depth of water near a gently sloping shore. Minimum facilities for public use and safety are also needed. These facilities include access roads, parking areas, boat ramps or docks, fireplaces, picnic tables, drinking water, and sanitary facilities. To protect public health, most states have laws and regulations that require water supplies to meet certain prescribed standards if they are to be used for swim- ming and human consumption. Generally, water must be tested and approved before public use is permitted. There are also rules and regulations for building and maintaining public sanitary facilities. The state board of health or a similar agency administers such laws and regulations. Contact your local health agency to become familiar with those regulations before making extensive plans to provide water for public recreation. Waterfowl and other wildlife Ponds attract many kinds of wildlife. Migratory water- fowl often use ponds as resting places in their flights to and from the North. Ducks often use northern ponds as breeding places, particularly where the food supply is ample (fig. 8). Upland game birds use ponds as watering places. Landscape quality Water adds variety to a landscape and further en- hances its quality. Reflections in water attract the eye and help to create a contrast or focal point in the landscape (fig. 9). A pond visible from a home, patio, or entrance road increases the attractiveness of the landscape and often increases land value. Ponds in rural, suburban, and urban areas help to conserve or improve landscape quality. Figure 7 Ponds are often used for private as well as public recreation
  • 18. 7 Ponds—Planning, Design, ConstructionAgriculture Handbook 590 Figure 8 Waterfowl use ponds as breeding, feeding, watering places, and as resting places during migration Figure 9 The shoreline of a well-designed pond is protected from erosion by the addition of stone. Such a pond, reflecting nearby trees, increases the value of the surrounding land
  • 19. Ponds—Planning, Design, Construction 8 Agriculture Handbook 590 Regardless of its purpose, a pond’s appearance can be improved by using appropriate principles and tech- niques of design. Good design includes consideration of size, site visibility, relationship to the surrounding landscape and use patterns, and shoreline configuration. Your local NRCS conservationist can help you apply the basic principles and design techniques. Consult a landscape architect for additional information and special designs. Multiple purposes You may wish to use the water in your pond for more than one purpose; for example, to provide water for livestock, fish production, and spraying field crops. If so, two additional factors must be considered. First, in estimating your water requirements you must total the amounts needed for each purpose and be sure that you provide a supply adequate for all the intended uses. Second, make sure that the purposes for which the water is to be used are compatible. Some combina- tions, such as irrigation and recreation, generally are not compatible. You would probably use most of the water during the irrigation season, making boating and swimming impractical. Ponds used temporarily for grade control or as sedi- ment basins associated with construction sites can be converted later into permanent ponds by cleaning out the sediment, treating the shoreline, and adding land- scape measures (fig. 10). If a sediment basin is to be cleaned and reconstructed as a water element, the standards for dam design should be used. Figure 10 This pond, which served as a sediment basin while homes in the background were being constructed, now adds variety and value to the community
  • 20. 9 Ponds—Planning, Design, ConstructionAgriculture Handbook 590 Preliminary investigations General considerations Selecting a suitable site for your pond is important, and preliminary studies are needed before final design and construction. Analysis and selection of pond sites should be based on landscape structure and associ- ated ecological functions and values. Relationship of the site to other ecological features within the land- scape is critical to achieving planned objectives. If possible, consider more than one location and study each one to select the most ecologically appropriate, esthetic, and practical site. Weighing both onsite and offsite effects of constructing a pond is essential in site selection. Refer to figure 1 and the glossary to become familiar with the components of a pond and associated dam. For economy, locate the pond where the largest stor- age volume can be obtained with the least amount of earthfill. A good site generally is one where a dam can be built across a narrow section of a valley, the side slopes are steep, and the slope of the valley floor permits a large area to be flooded. Such sites also minimize the area of shallow water. Avoid large areas of shallow water because of excessive evaporation and the growth of noxious aquatic plants. If farm ponds are used for watering livestock, make a pond available in or near each pasture or grazing unit. Forcing livestock to travel long distances to water is detrimental to both the livestock and the grazing area. Space watering places so that livestock does not travel more than a quarter mile to reach a pond in rough, broken country or more than a mile in smooth, nearly level areas. Well-spaced watering places encourage uniform grazing and facilitate grassland management. If pond water must be conveyed for use elsewhere, such as for irrigation or fire protection, locate the pond as close to the major water use as practicable. Conveying water is expensive and, if distance is exces- sive, the intended use of the water may not be practical. Ponds for fishing, boating, swimming, or other forms of recreation must be reached easily by automobile, especially if the general public is charged a fee to use the pond. The success of an income-producing recre- ation enterprise often depends on accessibility. Avoid pollution of pond water by selecting a location where drainage from farmsteads, feedlots, corrals, sewage lines, mine dumps, and similar areas does not reach the pond. Use permanent or temporary mea- sures, such as diversions, to redirect runoff from these sources to an appropriate outlet until the areas can be treated. Do not overlook the possibility of failure of the dam and the resulting damage from sudden release of water. Do not locate your pond where failure of the dam could cause loss of life; injury to persons or livestock; damage to homes, industrial buildings, railroads, or highways; or interrupted use of public utilities. If the only suitable pond site presents one or more of these hazards, hire a qualified person to investigate other potential sites to reduce the possibil- ity of failure from improper design or construction. Be sure that no buried pipelines or cables cross a proposed pond site. They could be broken or punc- tured by the excavating equipment, which can result not only in damage to the utility, but also in injury to the operator of the equipment. If a site crossed by pipelines or cable must be used, you must notify the utility company before starting construction and obtain permission to excavate. Avoid sites under powerlines. The wires may be within reach of a fishing rod held by someone fishing from the top of the dam. Area adequacy of the drainage For ponds where surface runoff is the main source of water, the contributing drainage area must be large enough to maintain water in the pond during droughts. However, the drainage area should not be so large that expensive overflow structures are needed to bypass excess runoff during large storms. The amount of runoff that can be expected annually from a given watershed depends on so many interre- lated factors that no set rule can be given for its deter- mination. The physical characteristics that directly affect the yield of water are relief, soil infiltration, plant cover, and surface storage. Storm characteris-
  • 21. Ponds—Planning, Design, Construction 10 Agriculture Handbook 590 tics, such as amount, intensity, and duration of rainfall, also affect water yield. These characteristics vary widely throughout the United States. Each must be considered when evaluating the watershed area condi- tions for a particular pond site. Figure 11 is a general guide for estimating the approxi- mate size of drainage area needed for a desired water- storage capacity. For example, a pond located in west- central Kansas with a capacity of 5 acre-feet requires a drainage area of at least 175 acres under normal condi- tions. If reliable local runoff information is available, use it in preference to the guide. Average physical conditions in the area are assumed to be the normal runoff-producing characteristics for a drainage area, such as moderate slopes, normal soil infiltration, fair to good plant cover, and normal sur- face storage. To apply the information given in figure 11, some adjustments may be necessary to meet local condi- tions. Modify the values in the figure for drainage areas having characteristics other than normal. Re- duce the values by as much as 25 percent for drainage areas having extreme runoff-producing characteristics. Increase them by 50 percent or more for low runoff- producing characteristics. Minimum pond depth To ensure a permanent water supply, the water must be deep enough to meet the intended use requirements and to offset probable seepage and evaporation losses. These vary in different sections of the country and from year to year in any one section. Figure 12 shows the recommended minimum depth of water for ponds if seepage and evaporation losses are normal. Deeper ponds are needed where a permanent or year-round water supply is essential or where seepage losses exceed 3 inches per month. Figure 11 A guide for estimating the approximate size of a drainage area (in acres) required for each acre-foot of storage in an embankment or excavated pond 12033 12087 25001 26083 CT DE FL Note: The numbers in Mountainous areas (green) may not apply because rainfall in them is spotty and varies sharply. 0 200 400 600 Mi 50 35 603088 30 60 12850 1 2 8 50 35 60 60 6030 100 140 140 100 60 60 100 120 100 60 60 50 35 20 12 8 12 20 35 35 20 12 8 5 3 2 1.5 2 3 2 3 2 2 1.5 2 3 3 3 5 5 3 2 2 3 5 3 2 1.522 1.5 2 1 3 5 3 5 3 5 3 3 5 8 1220 60 50 35 20 12 8 5 3 5 35 80 30 35 60 35 12 80 80 60 35 100 80 120 120 120 100 80 80 8 60 30 60 120 140 100 30 60 35 100 35 2 1.5 1 1 5 3 3 3 3
  • 22. 11 Ponds—Planning, Design, ConstructionAgriculture Handbook 590 Drainage area protection To maintain the required depth and capacity of a pond, the inflow must be reasonably free of silt from an eroding watershed. The best protection is adequate application and maintenance of erosion control prac- tices on the contributing drainage area. Land under permanent cover of trees, grass, or forbs is the most desirable drainage area (fig. 13). Cultivated areas protected by conservation practices, such as terraces, conservation tillage, stripcropping, or conservation cropping systems, are the next best watershed conditions. If an eroding or inadequately protected watershed must be used to supply pond water, delay pond con- struction until conservation practices are established. In any event, protection of the drainage area should be started as soon as you decide to build a pond. Figure 12 Recommended minimum depth of water for ponds in the United States Figure 13 Land with permanent vegetation makes the most desirable drainage area Wet Humid Moist subhumid Dry Subhumid Semiarid Arid 5 foot pond depth 6–7 foot pond depth 7–8 foot pond depth 8–10 foot pond depth 10–12 foot pond depth 12–14 foot pond depth Legend 0 200 400 600 Mi
  • 23. Ponds—Planning, Design, Construction 12 Agriculture Handbook 590 Landscape evaluation Alternative pond sites should be evaluated for poten- tial visibility and compatibility with surrounding landscape characteristics and use patterns (fig. 14). Identify major viewpoints (points from which the site is viewed) and draw the important sight lines with cross sections, where needed, to determine visibility. If feasible, locate the pond so that the major sight line crosses the longest dimension of water surface. The pond should be placed so that a viewer will see the water first before noticing the dam, pipe inlet, or spillway. Often, minor changes in the dam alignment and spillway location can shift these elements out of view and reduce their prominence. If possible, locate your pond so that some existing trees and shrubs remain along part of the shoreline. Vegetation adds aesthetic value by casting reflections on the water, provides shade on summer days, and helps blend the pond into the surrounding landscape. A pond can often be located and designed so that an island is created for recreation, wildlife habitat, or visual interest. In addition to the more typical farm and residential sites, ponds can be located on poor quality landscapes to rehabilitate abandoned road borrow areas, dumping sites, abandoned rural mines, and other low produc- tion areas. Figure 14 A preliminary study of two alternative sites for a pond to be used for livestock water, irrigation, and recreation Pond capacity Estimate pond capacity to be sure that enough water is stored in the pond to satisfy the intended use re- quirements. A simple method follows: • Establish the normal pond-full water elevation and stake the waterline at this elevation. • Measure the width of the valley at this elevation at regular intervals and use these measurements to compute the pond-full surface area in acres. • Multiply the surface area by 0.4 times the maxi- mum water depth in feet measured at the dam. For example, a pond with a surface area of 3.2 acres and a depth of 12.5 feet at the dam has an approximate capacity of 16 acre-feet (0.4 x 3.2 x 12.5 = 16 acre-feet) [1 acre-foot = 325,651 gallons]. Barn Stockwater trough House Vegetable garden Pond A Pond B Viewpoints Sight lines * * * x x x x x x x x x x x x
  • 24. 13 Ponds—Planning, Design, ConstructionAgriculture Handbook 590 Estimating storm runoff The amount of precipitation, whether it occurs as rain or snow, is the potential source of water that may run off small watersheds. The kind of soil and the type of vegetation affect the amount of water that runs off. Terraces and diversions, along with steepness and shape of a watershed, affect the rate at which water runs off. A spillway is provided to bypass surface runoff after the pond is filled. The tables and charts in the follow- ing sections should be used to estimate the peak discharge rates for the spillway. They provide a quick and reliable estimate of runoff rates and associated volumes for a range of storm rainfall amounts, soil groups, land use, cover conditions, and watershed slopes. Hydrologic groupings of soils Soils are classified in four hydrologic groups accord- ing to infiltration and transmission rates: A—These soils have a high infiltration rate. They are chiefly deep, well-drained sand or gravel. The runoff potential is low. B—These soils have a moderate infiltration rate when thoroughly wet. They are chiefly moderately deep, well-drained soils of moderately fine to moderately coarse texture. C—These soils have a slow infiltration rate when wet. These moderately fine to fine texture soils have a layer that impedes downward movement of water. D—These soils have a very slow infiltration rate. They are chiefly clay soils that have a high swelling poten- tial, soils with a permanent high water table, soils with a claypan at or near the surface, and shallow soils over nearly impervious material. The runoff potential is high. The NRCS district conservationist or your county extension agent can help you classify the soils for a given pond site in one of the four hydrologic groups. Runoff curve numbers Tables 1 through 4 show numerical runoff ratings for a range of soil-use-cover complexes. Because these numbers relate to a set of curves developed from the NRCS runoff equation, they are referred to as curve numbers (CN) in these tables. The watershed upstream from a farm pond often contains areas represented by different curve num- bers. A weighted curve number can be obtained based on the percentage of area for each curve number. For example, assume that the watershed above a pond is mainly (three-fourths) in good pasture and a soil in hydrologic group B. The remainder is cultivated with conservation treatment on a soil in hydrologic group C. A weighted curve number for the total watershed would be: 3/4 x 61 = 46 (approximately) 1/4 x 76 = 20 (approximately) Weighted = 66
  • 25. Ponds—Planning, Design, Construction 14 Agriculture Handbook 590 Table 1 Runoff curve numbers for urban areas 1/ Cover description Average percent Curve numbers for hydrologic soil group impervious area 2/ A B C D Fully developed urban areas (vegetation established) Open space (lawns, parks, golf courses, cemeteries, etc.) 3/ Poor condition (grass cover 50%) 68 79 86 89 Fair condition (grass cover 50 to 75%) 49 69 79 84 Good condition (grass cover 75%) 39 61 74 80 Impervious areas: Paved parking lots, roofs, driveways, etc. 98 98 98 98 (excluding right-of-way) Streets and roads: Paved; curbs and storm sewers (excluding right-of-way) 98 98 98 98 Paved; open ditches (including right-of-way) 83 89 92 93 Gravel (including right-of-way) 76 85 89 91 Dirt (including right-of-way) 72 82 87 89 Western desert urban areas: Natural desert landscaping (pervious areas only) 4/ 63 77 85 88 Artificial desert landscaping (impervious weed barrier, desert shrub with 1- to 2-inch sand or gravel mulch and 96 96 96 96 basin borders) Urban districts: Commercial and business 85 89 92 94 95 Industrial 72 81 88 91 93 Residential districts by average lot size: 1/8 acre or less (town houses) 65 77 85 90 92 1/4 acre 38 61 75 83 87 1/3 acre 30 57 72 81 86 1/2 acre 25 54 70 80 85 1 acre 20 51 68 79 84 2 acres 12 46 65 77 82 Developing urban areas Newly graded areas (pervious areas only, no vegetation) 5/ 77 86 91 94 Idle lands (CN’s are determined using cover types similar to those in table 3) 1/ Average runoff condition, and Ia = 0.2S. 2/ The average percent impervious area shown was used to develop the composite CN’s. Other assumptions are as follows: impervious areas are directly connected to the drainage system, impervious areas have a CN of 98, and pervious areas are considered equivalent to open space in good hydrologic condition. CN’s for other combinations of conditions may be computed using figure 2-3 or 2-4 in NRCS Technical Release 55, Urban Hydrology for Small Watersheds. 3/ CN’s shown are equivalent to those of pasture. Composite CN’s may be computed for other combinations of open space cover type. 4/ Composite CN’s for natural desert landscaping should be computed using figure 2-3 or 2-4 in Technical Release 55, based on the impervious area percentage (CN = 98) and the pervious area CN. The pervious area CN’s are assumed equivalent to desert shrub in poor hydrologic condition. 5/ Composite CN’s to use for the design of temporary measures during grading and construction should be computed using figure 2-3 or 2-4 in Technical Release 55, based on the degree of development (impervious area percentage) and the CN’s for the newly graded pervious areas.
  • 26. 15 Ponds—Planning, Design, ConstructionAgriculture Handbook 590 Table 2 Runoff curve numbers for agricultural lands 1/ Cover description Curve numbers for hydrologic soil group Cover type Treatment 2/ Hydrologic condition 3/ A B C D Fallow Bare soil — 77 86 91 94 Crop residue cover (CR) Poor 76 85 90 93 Good 74 83 88 90 Row crops Straight row (SR) Poor 72 81 88 91 Good 67 78 85 89 SR + CR Poor 71 80 87 90 Good 64 75 82 85 Contoured (C) Poor 70 79 84 88 Good 65 75 82 86 C + CR Poor 69 78 83 87 Good 64 74 81 85 Contoured terraced (CT) Poor 66 74 80 82 Good 62 71 78 81 CT + CR Poor 65 73 79 81 Good 61 70 77 80 Small grain SR Poor 65 76 84 88 Good 63 75 83 87 SR + CR Poor 64 75 83 86 Good 60 72 80 84 C Poor 63 74 82 85 Good 61 73 81 84 C + CR Poor 62 73 81 84 Good 60 72 80 83 CT Poor 61 72 79 82 Good 59 70 78 81 CT + CR Poor 60 71 78 81 Good 58 69 77 80 Closed-seeded SR Poor 66 77 85 89 or broadcast Good 58 72 81 85 legumes or C Poor 64 75 83 85 rotation Good 55 69 78 83 meadow CT Poor 63 73 80 83 Good 51 67 76 80 1/ Average runoff condition, and Ia = 0.2S. 2/ Crop residue cover applies only if residue is on at least 5 percent of the surface throughout the year. 3/ Hydrologic condition is based on combination of factors that affect infiltration and runoff, including (a) density and canopy of vegetative areas, (b) amount of year-round cover, (c) amount of grass or close-seeded legumes in rotations, (d) percentage of residue cover on the land surface (good 20%), and (e) degree of surface roughness. Poor: Factors impair infiltration and tend to increase runoff. Good: Factors encourage average and better than average infiltration and tend to decrease runoff.
  • 27. Ponds—Planning, Design, Construction 16 Agriculture Handbook 590 Table 3 Runoff curve numbers for other agricultural lands 1/ Cover description Curve numbers for hydrologic soil group Cover type Hydrologic condition 3/ A B C D Pasture, grassland, or range—continuous grazing 2/ Poor 68 79 86 89 Fair 49 69 79 84 Good 39 61 74 80 Meadow—continuous grass, protected from — 30 58 71 78 grazing and generally mowed for hay Brush—brush-weed-grass mixture with brush Poor 48 67 77 83 the major element 3/ Fair 35 56 70 77 Good 30 4/ 48 65 73 Woods—grass combination (orchard Poor 57 73 82 86 or tree farm) 5/ Fair 43 65 76 82 Good 32 58 72 79 Woods 6/ Poor 45 66 77 83 Fair 36 60 73 79 Good 30 4/ 55 70 77 Farmsteads—buildings, lanes, driveways, — 59 74 82 86 and surrounding lots. 1/ Average runoff condition, and Ia = 0.2S. 2/ Poor: 50% ground cover or heavily grazed with no mulch. Fair: 50 to 75% ground cover and not heavily grazed. Good: 75% ground cover and lightly or only occasionally grazed. 3/ Poor: 50% ground cover. Fair: 50 to 75% ground cover. Good: 75% ground cover. 4/ Actual curve number is less than 30; use CN = 30 for runoff computations. 5/ CN’s shown were computed for areas with 50% woods and 505 grass (pasture) cover. Other combinations of conditions may be computed from the CN’s for woods and pasture. 6/ Poor: Forest litter, small trees, and brush are destroyed by heavy grazing or regular burning. Fair: Woods are grazed but not burned, and some forest litter covers the soil. Good: Woods are protected from grazing, and litter and brush adequately cover the soil.
  • 28. 17 Ponds—Planning, Design, ConstructionAgriculture Handbook 590 Table 4 Runoff curve numbers for arid and semiarid rangelands 1/ Cover description Curve numbers for hydrologic soil group Cover type Hydrologic condition 2/ A 3/ B C D Herbaceous—mixture of grass, forbs, and Poor — 80 87 93 low-growing brush, with brush the minor element Fair — 71 81 89 Good — 62 74 85 Oak-aspen—mountain brush mixture of oak brush, Poor — 66 74 79 aspen, mountain mahogany, bitter brush, maple, Fair — 48 57 63 and other brush. Good — 30 41 48 Pinyon-juniper—pinyon, juniper, or both Poor — 75 85 89 grass understory Fair — 58 73 80 Good — 41 61 71 Sagebrush with grass understory Poor — 67 80 85 Fair — 51 63 70 Good — 35 47 55 Desert shrub—major plants include saltbush, Poor 63 77 85 88 greasewood, creosotebush, blackbrush, bursage, Fair 55 72 81 86 palo verde, mesquite, and cactus Good 49 68 79 84 1/ Average runoff condition, and Ia = 0.2S. For range in humid regions, use table 3. 2/ Poor: 30% ground cover (litter, grass, and brush overstory). Fair: 30 to 70% ground cover. Good: 70% ground cover. 3/ Curve numbers for group A have been developed only for desert shrub.
  • 29. Ponds—Planning, Design, Construction 18 Agriculture Handbook 590 Volume of storm runoff Often knowing how much water runs off from a big storm as well as the rate at which it flows is good. The volume is needed to compute needed storage as well as the peak discharge rate. The figures in table 5 are the depth (in inches) at which the storm runoff, if spread evenly, would cover the entire watershed. For example, the volume of runoff from a 3-inch rainfall on a 100-acre watershed with the weighted curve number of 66 would be: 0.55 inch (interpolated between 0.51 and 0.72 inches) 100 acres x 0.55 inch = 55 acre-inches 55 acre-inches ÷12 = 4.55 acre-feet 55 acre-inches x 27,152 gallons per acre-inch = 1.5 million gallons (approximately) Table 5 Runoff depth, in inches Rainfall Curve number (inches) 60 65 70 75 80 85 90 1.0 0 0 0 0.03 0.08 0.17 0.32 1.2 0 0 0.03 0.07 0.15 0.28 0.46 1.4 0 0.02 0.06 0.13 0.24 0.39 0.61 1.6 0.01 0.05 0.11 0.20 0.34 0.52 0.76 1.8 0.03 0.09 0.17 0.29 0.44 0.65 0.93 2.0 0.06 0.14 0.24 0.38 0.56 0.80 1.09 2.5 0.17 0.30 0.46 0.65 0.89 1.18 1.53 3.0 0.33 0.51 0.72 0.96 1.25 1.59 1.98 4.0 0.76 1.03 1.33 1.67 2.04 2.46 2.92 5.0 1.30 1.65 2.04 2.45 2.89 3.37 3.88 6.0 1.92 2.35 2.87 3.28 3.78 4.31 4.85 7.0 2.60 3.10 3.62 4.15 4.69 5.26 5.82 8.0 3.33 3.90 4.47 5.04 5.62 6.22 6.81 9.0 4.10 4.72 5.34 5.95 6.57 7.19 7.79 10.0 4.90 5.57 6.23 6.88 7.52 8.16 8.78 11.0 5.72 6.44 7.13 7.82 8.48 9.14 9.77 12.0 6.56 7.32 8.05 8.76 9.45 10.12 10.76
  • 30. 19 Ponds—Planning, Design, ConstructionAgriculture Handbook 590 Rainfall amounts and expected frequency Maps in U.S. Weather Bureau Technical Paper 40 (USWP-TP-40), Rainfall Frequency Atlas of the United States, show the amount of rainfall expected in a 24- hour period. These maps have also been reprinted in Hydrology for Small Urban Watershed, Technical Release 55. Contact your local NRCS field office for rainfall amounts on maps. Designing an ordinary pond spillway to accommodate the peak rate of runoff from the most intense rain- storm ever known or anticipated is not practical. The spillway for an ordinary farm pond generally is de- signed to pass the runoff from a 25-year frequency storm. This means a storm with only a 4 percent chance of occurring in any year or the size beyond which larger storms would not occur more often than an average of once in 25 years. Designing for a 50-year storm frequency is recommended for spillways for larger dams. A 10-year storm frequency may be ad- equate for sizing the spillway in small ponds. Rainfall distribution The highest peak discharges from small watersheds are usually caused by intense, brief rainfalls that may occur as part of a longer duration storm. Different rainfall distributions with respect to time have been developed for four geographic areas of the United States. For each of these areas, a set of synthetic rainfall distributions having nested rainfall intensities were developed. These distributions maximize the rainfall intensities by incorporating selected storm duration intensities within those needed for longer durations at the same probability level. In figure 15, type I and IA represent the Pacific mari- time climate with wet winters and dry summers. Type III represents Gulf of Mexico and Atlantic coastal areas where tropical storms bring large rainfall amounts. Type II represents the rest of the country. Figure 15 Approximate geographic boundaries for NRCS rainfall distributions Type I Type IA Type II Type III Legend 0 200 400 600 Mi
  • 31. Ponds—Planning, Design, Construction 20 Agriculture Handbook 590 Peak discharge rate The slope of the land above the pond affects the peak discharge rate significantly. The time of concentration along with the runoff curve number, storm rainfall, and rainfall distribution are used to estimate the peak discharge rate. This rate is used to design the auxiliary spillway width and depth of flow. Time of concentration Time of concentration (Tc) is the time it takes for runoff to travel from the hydraulically most distant point of the watershed to the outlet. Tc influences the peak discharge and is a measure of how fast the water runs off the land. For the same size watershed, the shorter the Tc, the larger the peak discharge. This means that the peak discharge has an inverse relation- ship with Tc. Tc can be estimated for small rural water- sheds using equation 1. Figure 16 is a nomograph for solving this equation. T l CN Y c = ( )−        0 8 0 7 0 5 1000 9 1140 . . . [Eq. 1] where: Tc = time of concentration, hr l = flow length, ft CN = runoff curve number Y = average watershed slope, % Figure 16 Time of concentration (Tc) nomograph 0.1 .3 .5 100 1,000 10,000 Flow length (l), feet Time of concentration (Tc), hrs 1.0 2 3 4 5 6 8 10 W atershed slope T= 0.5 1 4 8163264 8070605040 2 9590
  • 32. 21 Ponds—Planning, Design, ConstructionAgriculture Handbook 590 Average watershed slope The average watershed slope (Y) is the slope of the land and not the watercourse. It can be determined from soil survey data or topographic maps. Hillside slopes can be measured with a hand level, lock level, or clinometer in the direction of overland flow. Aver- age watershed slope is an average of individual land slope measurements. The average watershed slope can be determined using equation 2: Y CI A = 100 [Eq. 2] where: Y = average slope, % C = total contour length, ft I = contour interval, ft A = drainage area, ft2 Flow length Flow length (l) is the longest flow path in the water- shed from the watershed divide to the outlet. It is the total path water travels overland and in small channels on the way to the outlet. The flow length can be deter- mined using a map wheel, or it can be marked along the edge of a paper and converted to feet. Ia /P ratio The watershed CN is used to determine the initial abstraction (Ia) from table 6. Ia/P ratio is a parameter that indicates how much of the total rainfall is needed to satisfy the initial abstraction. The larger the Ia/P ratio, the lower the unit peak discharge (qu) for a given Tc. Table 6 Ia values for runoff curve numbers Curve Ia Curve Ia number (in) number (in) 40 3.000 70 0.857 41 2.878 71 0.817 42 2.762 72 0.778 43 2.651 73 0.740 44 2.545 74 0.703 45 2.444 75 0.667 46 2.348 76 0.632 47 2.255 77 0.597 48 2.167 78 0.564 49 2.082 79 0.532 50 2.000 80 0.500 51 1.922 81 0.469 52 1.846 82 0.439 53 1.774 83 0.410 54 1.704 84 0.381 55 1.636 85 0.353 56 1.571 86 0.326 57 1.509 87 0.299 58 1.448 88 0.273 59 1.390 89 0.247 60 1.333 90 0.222 61 1.279 91 0.198 62 1.226 92 0.174 63 1.175 93 0.151 64 1.125 94 0.128 65 1.077 95 0.105 66 1.030 96 0.083 67 0.985 97 0.062 68 0.941 98 0.041 69 0.899
  • 33. Ponds—Planning, Design, Construction 22 Agriculture Handbook 590 Estimating peak discharge rates The unit peak discharge (qu) is obtained from figure 17 depending on the rainfall type. Figure 15 shows the approximate geographic boundaries for the four rainfall distributions. Tc and Ia/P values are needed to obtain a value for qu from the exhibit. The peak dis- charge (qp in ft3/s) is computed as the product of the unit peak discharge (qu in ft3/s/ac-in), the drainage area (A in acres), and the runoff (Q in inches). q q A Qp u= × × [Eq. 3] Example 1 Estimating peak discharge rates Known: Drainage area = 50 acres Cole County, Missouri Flow Path ‘l’ = 1,600 feet Watershed Slope ‘Y’ = 4 percent 25-year, 24-hour rainfall = 6 inches Type II rainfall distribution Runoff Curve Number = 66 (from example in runoff curve number section) Solution: Find Tc Enter figure 16, Tc = 0.60 hours Find Ia /P Enter table 6, use CN = 66, Ia = 1.030 Ia /P = 1.030/6.0 inches = 0.172 Find runoff Enter table 5, at rainfall = 6.0 inches and runoff curve number = 66, Read runoff = 2.44 inches. (Note: It was neces- sary to interpolate between RCN 65 and 70.) Find the peak discharge for spillway design. Enter figure 17(c): qu = 0.7 qp = qu x A x Q qp = 0.7 x 50 x 2.44 = 85 ft3/s
  • 34. 23 Ponds—Planning, Design, ConstructionAgriculture Handbook 590 Figure 17a Unit peak discharge (qu) for Type I storm distribution Figure 17b Unit peak discharge (qu) for Type IA storm distribution Figure 17c Unit peak discharge (qu) for Type II storm distribution Figure 17d Unit peak discharge (qu) for Type III storm distribution 1.0 Time of concentration (Tc), hours Unitpeakdischarge(qu)ft3/sac-in .8 .7 .6 .5 .4 .3 .2 .1 .08 .07 .06 .1 .2 .3 .4 .5 .6 .8 105 Ia /P=.1 .2 .30 .35 .40 .45 .50 .25 1.6 .7 .6 .5 1.0 .4 .3 .2 .1 .07 .1 1.0 10 Time of concentration (Tc), hours Unitpeakdischarge(qu)ft3/sac-in Ia /P=.1.3 .35.40.45.50 1.6 .7 .6 .5 1.0 .4 .3 .2 .1 .07 .1 1.0 10 Time of concentration (Tc), hours Unitpeakdischarge(qu)ft3/sac-in Ia /P=.1.3 .35.40.45.50 .3 .2 .1 .09 .08 .07 .06 .05 .1 1 10 Time of concentration (Tc), hours Unitpeakdischarge(qu)ft3/sac-in Ia /P=.1 .2 .25 .30 .50
  • 35. Ponds—Planning, Design, Construction 24 Agriculture Handbook 590 Embankment ponds Detailed soils investigation Soils in the ponded area—Suitability of a pond site depends on the ability of the soils in the reservoir area to hold water. The soil should contain a layer of mate- rial that is impervious and thick enough to prevent excessive seepage. Clays and silty clays are excellent for this purpose; sandy and gravelly clays are usually satisfactory. Generally, soils with at least 20 percent passing the No. 200 sieve, a Plasticity Index of more than 10 percent, and an undisturbed thickness of at least 3 feet do not have excessive seepage when the water depth is less than 10 feet. Coarse-textured sands and sand-gravel mixtures are highly pervious and therefore usually unsuitable. The absence of a layer of impervious material over part of the ponded area does not necessarily mean that you must abandon the proposed site. You can treat these parts of the area by one of several methods described later in this hand- book. Any of these methods can be expensive. Some limestone areas are especially hazardous as pond sites. Crevices, sinks, or channels that are not visible from the surface may be in the limestone below the soil mantle. They may empty the pond in a short time. In addition, many soils in these areas are granu- lar. Because the granules do not break down readily in water, the soils remain highly permeable. All the factors that may make a limestone site undesirable are not easily recognized without extensive investigations and laboratory tests. The best clue to the suitability of a site in one of these areas is the degree of success others have had with farm ponds in the immediate vicinity. Unless you know that the soils are sufficiently impervi- ous and that leakage will not be a problem, you should make soil borings at intervals over the area to be covered with water. Three or four borings per acre may be enough if the soils are uniform. More may be required if there are significant differences. Foundation conditions—The foundation under a dam must ensure stable support for the structure and provide the necessary resistance to the passage of water. Site surveys Once you determine the probable location of the pond, conduct a site survey to plan and design the dam, spillways, and other features. Those unfamiliar with the use of surveying instruments should employ a licensed surveyor or other qualified professional. Pond surveys generally consist of a profile of the centerline of the dam, a profile of the centerline of the earth spillway, and enough measurements to estimate pond capacity. A simple method of estimating pond capacity is described on page 12. For larger and more complex ponds, particularly those used for water supply or irrigation, you may need a complete topo- graphic survey of the entire pond site. Run a line of profile level surveys along the centerline of the proposed dam and up both sides of the valley well above the expected elevation of the top of the dam and well beyond the probable location of the auxiliary spillway. The profile should show the surface elevation at all significant changes in slope and at intervals of no more than 100 feet. This line of levels establishes the height of the dam and the location and elevation of the earth spillway and the principal spill- way. It is also used to compute the volume of earthfill needed to build the dam. Run a similar line of profile levels along the centerline of the auxiliary spillway. Start from a point on the upstream end that is well below the selected normal water surface elevation and continue to a point on the downstream end where water can be safely discharged without damage to the dam. This line serves as a basis for determining the slope and dimensions of the spill- way. All surveys made at a pond site should be tied to a reference called a bench mark. This may be a large spike driven into a tree, an iron rod driven flush with the ground, a point on the concrete headwall of a culvert, or any object that will remain undisturbed during and after construction of the dam.
  • 36. 25 Ponds—Planning, Design, ConstructionAgriculture Handbook 590 Soil borings help to investigate thoroughly the founda- tion conditions under the proposed dam site. The depth of the holes should be at least 1-1/2 times the height of the proposed dam. Ensure there are not any steep dropoffs in the rock surface of the foundation under the dam. Steep dropoffs in the rock surface can result in cracking of the embankment. Study the natural banks (abutments) at the ends of the dam as well as the supporting materials under the dam. If the dam is to be placed on rock, the rock must be exam- ined for thickness and for fissures and seams through which water might pass. Coarse-textured materials, such as gravel, sand, and gravel-sand mixtures, provide good support for a dam, but are highly pervious and do not hold water. Such materials can be used only if they are sealed to prevent seepage under the dam. You can install a cutoff core trench of impervious material under the dam or blan- ket the upstream face of the dam and the pond area with a leak-resistant material. Fine-textured materials, such as silts and clays, are relatively impervious, but have a low degree of stabil- ity. They are not good foundation materials, but gener- ally are satisfactory for the size of dams discussed in this handbook. Flattening the side slopes of some dams may be necessary to reduce the unit load on the foundation. Remove peat, muck, and any soil that has a high organic-matter content from the foundation. Good foundation materials, those that provide both stability and imperviousness, are a mixture of coarse- and fine-textured soils. Some examples are gravel- sand-clay mixtures, gravel-sand-silt mixtures, sand- clay mixtures, and sand-silt mixtures. Less desirable but still acceptable foundation materi- als for ordinary pond dams are gravelly clays, sandy clays, silty clays, silty and clayey fine sands, and clayey silts that have slight plasticity. Fill material—The availability of suitable material for building a dam is a determining factor in selecting a pond site. Enough suitable material should be located close to the site so that placement costs are not exces- sive. If fill material can be taken from the reservoir area, the surrounding landscape will be left undis- turbed and borrow areas will not be visible after the pond has been filled (fig. 18). Materials selected must have enough strength for the dam to remain stable and be tight enough, when prop- erly compacted, to prevent excessive or harmful percolation of water through the dam. Soils described as acceptable for foundation material generally are acceptable for fill material. The exceptions are organic silts and clays. The best material for an earthfill contains particles ranging from small gravel or coarse sand to fine sand and clay in the desired proportions. This material should contain about 20 percent, by weight, clay particles. Though satisfactory earthfills can be built from soils that vary from the ideal, the greater the variance, the more precautions needed. Soils containing a high percentage of gravel or coarse sand are pervious and can allow rapid seepage through the dam. When using these soils, place a core of clay material in the center of the fill and flatten the side slopes to keep the line of seepage from emerging on the downstream slope. Fill material that has a high clay content swells when wet and shrinks when dry. The shrinkage may open dangerous cracks. If these soils are dispersive, they represent a serious hazard to the safety of the embank- ment and should be avoided. Dispersive soils can be identified by how easily they go into suspension in water, by the presence of a gelatinous cloud around a clod of soil in distilled water, and by the indefinite Figure 18 Borrow material taken from within the reservoir area creates an irregular pond configuration ,,,,,,,,,,,,,,,,
  • 37. Ponds—Planning, Design, Construction 26 Agriculture Handbook 590 length of time they stay in suspension in still water. High sodium soils identified in the soil survey for the planned area of the embankment also indicate disper- sive soils. If any of these indicators are found at the proposed site, an engineer should be hired to provide the necessary guidance for sampling, testing, and using these soils for fill. For soils consisting mostly of silt, such as the loess areas of western Iowa and along the Mississippi River in Arkansas, Mississippi, and Tennessee, the right degree of moisture must be main- tained during construction for thorough compaction. To estimate the proportion of sand, silt, and clay in a sample of fill material, first obtain a large bottle with straight sides. Take a representative sample of the fill material and remove any gravel by passing the mate- rial through a 1/4-inch sieve or screen. Fill the bottle to about one-third with the sample material and finish filling with water. Shake the bottle vigorously for several minutes and then allow the soil material to settle for about 24 hours. The coarse material (sand) settles to the bottom first, and finer material (clay) settles last. Estimate the proportion of sand, silt, and clay by measuring the thickness of the different layers with a ruler. Landscape planning—The pond should be located and designed to blend with the existing landform, vegetation, water, and structures with minimum dis- turbance. Landforms can often form the impoundment with minimum excavation. Openings in the vegetation can be used to avoid costly clearing and grubbing. Existing structures, such as stone walls and trails, can be retained to control pedestrian and vehicular traffic and minimize disruption of existing use. In the area where land and water meet, vegetation and landform can provide interesting reflections on the water’s surface, guide attention to or from the water, frame the water to emphasize it, and direct passage around the pond. A pond’s apparent size is not always the same as its actual size. For example, the more sky reflected on the water surface, the larger a pond appears. A pond surrounded by trees will appear smaller than a pond the same size without trees or with some shoreline trees (fig. 19). The shape of a pond should comple- ment its surroundings. Irregular shapes with smooth, flowing shorelines generally are more compatible with the patterns and functions found in most landscapes. Peninsulas, inlets, or islands can be constructed to create diversity in the water’s edge. Spillway requirements A pipe spillway often is used as well as an earth auxil- iary spillway to control runoff from the watershed. The principal spillway is designed to reduce the fre- quency of operation of the auxiliary spillway. Com- monly the principal spillway may be a hooded or canopy inlet with a straight pipe or may be a drop inlet (vertical section) that has a pipe barrel through the dam. The pipe shall be capable of withstanding exter- nal loading with yielding, buckling, or cracking. The pipe joints and all appurtenances need to be water- tight. Pipe materials may be smooth metal, corrugated metal, or plastic. Design limitations exist with all materials. A small principal spillway pipe, formerly called a trickle tube, only handles a small amount of flow. Its purpose is to aid in keeping the auxiliary spillway dry during the passage of small storm events. Hooded or canopy inlets are common. A disadvantage of this type inlet is the larger amount of stage (head over the inlet crest) needed to make the pipe flow at full capacity. Conversely, a drop inlet spillway requires less stage because the size of the inlet may be enlarged to make the barrel flow full. Figure 19 The apparent size of the pond is influenced by surrounding vegetation
  • 38. 27 Ponds—Planning, Design, ConstructionAgriculture Handbook 590 The principal spillway normally is sized to control the runoff from a storm ranging from a 1-year to a 10-year frequency event. This depends on the size of the drain- age area. For pond sites where the drainage area is small (less than 20 acres) and the condition of the vegetated spillway is good, no principal spillway is required except where the pond is spring fed or there are other sources of steady baseflow. In this case, a trickle tube shall be installed. Earth spillways have limitations. Use them only where the soils and topography allow the peak flow to dis- charge safely at a point well downstream and at a velocity that does not cause appreciable erosion either within the spillway or beyond its outlet. Soil borings generally are required for auxiliary spill- ways if a natural site with good plant cover is avail- able. If spillway excavation is required, the investiga- tions should be thorough enough to determine whether the soils can withstand reasonable velocities without serious erosion. Avoid loose sands and other highly erodible soils. No matter how well a dam has been built, it will prob- ably be destroyed during the first severe storm if the capacity of the spillway is inadequate. The function of an auxiliary spillway is to pass excess storm runoff around the dam so that water in the pond does not rise high enough to damage the dam by overtopping. The spillways must also convey the water safely to the outlet channel below without damaging the down- stream slope of the dam. The proper functioning of a pond depends on a correctly designed and installed spillway system. Auxiliary spillways should have the minimum capacity to discharge the peak flow expected from a storm of the frequency and duration shown in table 7 less any reduction creditable to conduit discharge and deten- tion storage. After the spillway capacity requirements are calculated, the permissible velocity must be deter- mined. Table 8 shows the recommended allowable velocity for various cover, degree of erosion resis- tance, and slope of the channel. Table 9 gives the retardance factors for the expected height of the vegetation. Both natural and excavated auxiliary spillways are used. A natural spillway does not require excavation to provide enough capacity to conduct the pond outflow to a safe point of release (fig. 20). The requirements discussed later for excavated spillways do not apply to natural spillways, but the capacity must be adequate. With the required discharge capacity (Q), the end slope of the embankment (Z1), and the slope of the natural ground (Z2) known, the maximum depth of water above the level portion (Hp) can be obtained from table 10. The depth is added to the elevation of the spillway crest to determine the maximum eleva- tion to which water will rise in the reservoir. Table 7 Minimum spillway design storm Drainage Effective Storage Minimum design storm area height Frequency Minimum of dam 1/ duration (acre) (ft) (acre-ft) (yr) (hr) 20 or less 20 or less Less than 50 10 24 20 or less More than 20 Less than 50 25 24 More than 20 20 or less Less than 50 25 24 All others 50 24 1/ The effective height of the dam is the difference in elevation between the auxiliary spillway crest and the lowest point in the cross section taken along the centerline of the dam.
  • 39. Ponds—Planning, Design, Construction 28 Agriculture Handbook 590 Table 8 Permissible velocity for vegetated spillways 1/ Vegetation - - - - - - - - - - - - - - - - - - - - - - - -Permissible velocity 2/ - - - - - - - - - - - - - - - - - - - - - - Erosion-resistant soils 3/ Easily eroded soils 4/ - - - - - - - - - - - - - - - - - - - - - - - Slope of exit channel (%) - - - - - - - - - - - - - - - - - - - - 0-5 5-10 0-5 5-10 (ft/s) (ft/s) (ft/s) (ft/s) Bermudagrass 8 7 6 5 Bahiagrass 8 7 6 5 Buffalograss 7 6 5 4 Kentucky bluegrass 7 6 5 4 Smooth brome 7 6 5 4 Tall fescue 7 6 5 4 Reed canarygrass 7 6 5 4 Sod-forming grass-legume mixtures 5 4 4 3 Lespedeza sericea 3.5 3.5 2.5 2.5 Weeping lovegrass 3.5 3.5 2.5 2.5 Yellow bluestem 3.5 3.5 2.5 2.5 Native grass mixtures 3.5 3.5 2.5 2.5 1/ SCS TP-61 2/ Increase values 10 percent when the anticipated average use of the spillway is not more frequent than once in 5 years, or 25 percent when the anticipated average use is not more frequent than once in 10 years. 3/ Those with a higher clay content and higher plasticity. Typical soil textures are silty clay, sandy clay, and clay. 4/ Those with a high content of fine sand or silt and lower plasticity, or nonplastic. Typical soil textures are fine sand, silt, sandy loam, and silty loam. Table 9 Guide to selection of vegetal retardance Stand Average height Degree of of vegetation (in) retardance Good Higher than 30 A 11 to 24 B 6 to 10 C 2 to 6 D Less than 2 E Fair Higher than 30 B 11 to 24 C 6 to 10 D 2 to 6 D Less than 2 E
  • 40. 29 Ponds—Planning, Design, ConstructionAgriculture Handbook 590 Figure 20 Plan, profile, and cross section of a natural spillway with vegetation ,,,, ,,,,,,,,,,, ,,,,,,,,, ,,,,,,,,, ,,,,,,,,,,Maximum water elevation End slope protected with rock riprap Natural ground Top of dam HpZ2 Z 1 Typical control section Plan viewProfile L Wing dike used to protect embankment Toe of dam Centerline of dam Embankment to be perpendicular to slope ,,, Spillway crest L Hp Level part
  • 41. Ponds—Planning, Design, Construction 30 Agriculture Handbook 590 Table 10 Hp discharge and velocities for natural vegetated spillways with 3:1 end slope (Z1) Natural Retardance ground - - - - - A - - - - - - - - - - B - - - - - - - - - - C - - - - - - - - - - D - - - - - - - - - - E - - - - - - - - - Slope - - - - slope Z2 Hp Q V Q V Q V Q V Q V Min. Max. (%) (ft) (ft3/s) (ft/s) (ft3/s) (ft/s) (ft3/s) (ft/s) (ft3/s) (ft/s) (ft3/s) (ft/s) (%) (%) 0.5 1.0 19 0.3 28 0.5 47 1.3 68 1.8 130 2.8 0.5 3 1.1 21 .3 35 .5 76 1.5 108 2.1 154 3.0 1.2 29 .4 39 .6 97 1.6 122 2.3 204 3.2 1.3 36 .4 53 .6 125 2.0 189 2.5 250 3.4 1.5 61 .4 87 1.1 210 2.2 291 2.9 393 3.8 1.8 81 .5 187 1.8 384 2.9 454 3.5 651 4.5 2.0 110 .5 286 2.1 524 3.3 749 3.8 860 4.8 1 1.0 10 0.4 16 0.5 31 2.0 45 2.6 64 3.4 1 3 1.1 13 .4 18 .6 50 2.3 63 2.8 90 3.7 1.2 15 .5 21 .8 62 2.5 78 3.1 99 4.0 1.3 22 .6 39 1.0 86 2.7 144 3.4 139 4.3 1.5 40 .7 75 1.8 133 3.1 186 4.0 218 5.1 1.8 56 .8 126 2.3 280 3.8 296 4.5 2.0 98 1.1 184 2.8 328 4.3 389 5.0 2.5 171 2.5 472 4.1 680 5.4 2 1.0 6 0.5 9 0.8 18 2.5 27 3.3 36 4.2 1 3 1.1 7 .7 14 1.0 29 2.8 39 3.6 50 4.5 1.2 9 .8 19 1.1 40 3.1 51 3.9 64 4.9 1.3 13 .9 26 1.6 50 3.4 70 4.3 85 5.3 1.5 21 1.0 39 2.0 70 3.9 109 5.1 127 6.3 1.8 26 1.1 74 2.5 126 4.8 194 5.9 2.0 52 1.3 111 3.2 190 5.4 229 6.4 2.5 88 2.8 238 5.2 339 6.8 3 1.0 4 0.7 7 0.8 15 2.8 21 3.7 28 4.8 1 3 1.1 5 .8 10 .9 24 3.2 31 4.0 38 5.2 1.2 7 .9 14 1.1 33 3.6 41 4.4 49 5.6 1.3 10 1.0 20 1.5 42 3.8 57 4.8 67 6.1 1.5 16 1.2 34 2.8 62 4.4 89 5.7 104 7.2 1.8 23 1.3 57 3.0 112 5.5 143 6.7 2.0 39 1.5 81 3.7 163 6.2 194 7.2 2.5 85 3.1 212 6.0 300 7.8 4 1.2 6 1.0 11 1.4 25 3.9 31 4.8 38 6.1 1 4 1.5 15 1.3 29 3.1 49 4.8 69 5.5 81 7.9 1.8 20 1.4 47 4.1 98 6.1 116 7.3 2.0 30 1.6 65 4.7 139 6.7 161 7.8 2.5 72 3.3 167 6.6 238 8.5 5 1.5 13 1.4 23 3.3 38 5.2 55 6.7 63 8.4 1 5 1.8 17 1.5 37 4.4 76 6.5 95 7.9 2.0 23 1.7 48 5.1 112 7.1 130 8.1 2.5 64 3.7 149 7.1 191 9.2
  • 42. 31 Ponds—Planning, Design, ConstructionAgriculture Handbook 590 The following example shows how to use table 10: Given: Vegetation: good stand of bermudagrass Height: 6 to 10 inches Slope of natural ground: 1.0 percent Solution: From table 9, determine a retardance of C. From table 10, under natural ground slope 1 percent and retardance C column, find Q = 88 ft3/s at Hp = 1.3 ft, and V = 2.7 ft/s. If the freeboard is 1.0 foot, the top of the dam should be constructed 2.3 feet higher than the spillway crest. The velocity is well below the maximum permissible velocity of 6 feet per second given in table 8. Hp can be determined by interpolation when necessary. For a Q greater than that listed in table 10, the spillway should be excavated according to the information in the next section, Excavated auxiliary spillways. Excavated auxiliary spillways—Excavated spill- ways consist of the three elements shown in figure 21. The flow enters the spillway through the inlet channel. The maximum depth of flow (Hp) located upstream from the level part is controlled by the inlet channel, level part, and exit channel. Excavation of the inlet channel or the exit channel, or both, can be omitted where the natural slopes meet the minimum slope requirements. The direction of slope of the exit channel must be such that discharge does not flow against any part of the dam. Wing dikes, sometimes called kicker levees or training levees, can be used to direct the outflow to a safe point of release downstream. The spillway should be excavated into the earth for its full depth. If this is not practical, the end of the dam and any earthfill constructed to confine the flow should be protected by vegetation or riprap. The entrance to the inlet channel should be widened so it is at least 50 percent greater than the bottom width of the level part. The inlet channel should be reasonably short and should be planned with smooth, easy curves for alignment. It should have a slope toward the reser- voir of not less than 2.0 percent to ensure drainage and low water loss at the inlet. With the required discharge capacity, the degree of retardance, permissible velocity, and the natural slope of the exit channel known, the bottom width of the level and exit sections and the depth of the flow (Hp) can be computed using the figures in table 11. This table shows discharge per foot of width. The natural slope of the exit channel should be altered as little as possible. The selection of the degree of retardance for a given auxiliary spillway depends mainly on the height and density of the cover chosen (table 9). Generally, the retardance for uncut grass or vegetation is the one to use for capacity determination. Because protection and retardance are lower during establishment and after mowing, to use a lower degree of retardance when designing for stability may be advisable. The following examples show the use of the informa- tion in table 11: Example 1 where only one retardance is used for capacity and stability: Given: Q = 87 ft3/s (total design capacity) So = 4 percent (slope of exit channel determined from profile, or to be excavated) L = 50 ft Earth spillway is to be excavated in an erosion-resis- tant soil and planted with a sod-forming grass-legume mixture. After establishment, a good stand averaging from 6 to 10 inches in height is expected. Required: Permissible velocity (V) Width of spillway (b) Depth of water in the reservoir above the crest (Hp). Solution: From table 8 for sod-forming grass-legume mixtures, read permissible velocity V = 5 ft/s. From table 9 for average height of vegetation of 6 to 10 inches, determine retardance C.
  • 43. Ponds—Planning, Design, Construction 32 Agriculture Handbook 590 For retardance C, enter table 11 from left at maximum velocity V = 5 ft/s. A 4 percent slope is in the slope range of 1–6 with Q of 3 ft3/s/ft. Hp for L of 50 ft = 1.4 ft. If the freeboard is 1 foot, the spillway should be con- structed 29 feet wide and 2.4 feet deep. For retardance C, enter table 11 from left at maximum velocity V = 5 ft/s. A 4 percent slope is in the slope range of 1–6 with Q of 3 ft3/s/ft. Hp for L of 50 ft = 1.4 ft. If the freeboard is 1 foot, the spillway should be con- structed 29 feet wide and 2.4 feet deep. Example 2 where one retardance is used for stability and another is used for capacity: Given: So = 4 percent (slope of exit channel determined from profile or to be excavated) L = 50 ft Earth spillway is to be excavated in a highly erodible soil and planted with bahiagrass. After establishment a good stand of 11 to 24 inches is expected. Required: Permissible velocity (V) Width of spillway (b) Depth of water in reservoir above the crest (Hp). Solution: From table 8 determine permissible velocity for bahiagrass in a highly erodible soil that has 8 per- cent slope V = 5 ft/s. From table 9, select retardants to be used for stabil- ity during an establishment period that has a good stand of vegetation of 2 to 6 inches (retardance D). Select retardance to be used for capacity for good stand of vegetation that has a length of 11 to 24 inches (retardance B). From table 11, enter from left at maximum velocity V = 5 ft/s. A slope of 6 percent is in the range for Q = 2 ft3/s/ft. Then From table 11, enter q = 2 ft3/s/ft under retardance B and find Hp for L of 25 ft = 1.4 ft. If the freeboard is 1 foot, the spillway should be constructed 50 feet wide and 2.4 feet deep. Protection against erosion—Protect auxiliary spillways against erosion by establishing good plant cover if the soil and climate permit. As soon after construction as practicable, prepare the auxiliary spillway area for seeding or sodding by applying fertilizer or manure. Sow adapted perennial grasses and protect the seedlings to establish a good stand. Mulching is necessary on the slopes. Irrigation is often needed to ensure good germination and growth, par- ticularly if seeding must be done during dry periods. If the added cost is justified, sprigging or sodding suitable grasses, such as bermudagrass, gives quick protection.
  • 44. 33 Ponds—Planning, Design, ConstructionAgriculture Handbook 590 Figure 21 Excavated earth spillway ,,,,,, ,, ,,,Exit channel CL CL CL CL Exit channel Embankment Inlet channel Wing dike Level portion (Note: Use care to keep all machinery and traffic out of the spillway discharge area to protect sod.) (Note: Neither the location nor the alignment of the level portion has to coincide with the center line of the dam.) Embankment Berm Excavated earth spillway Optional with sod or riprap on wing dike Plan view of earth spillways Profile along centerline Cross section of level portion Level portion Inlet channel ,,,,,,, ,,,,,,, Exit channel Level portion Water surface Inlet channel Se Hp So Definition of terms: Hp = depth of water in reservoir above crest L = length of level portion min. 25 ft b = bottom width of spillway So = slope for exit channel Se = slope of inlet channel L b 1 3
  • 45. Ponds—Planning, Design, Construction 34 Agriculture Handbook 590 Table 11 Depth of flow (Hp) and slope range at retardance values for various discharges, velocities, and crest lengths Maximum Discharge - - - - - - - - - - - - - - - - - - - - - - - - Hp - - - - - - - - - - - - - - - -- - - - - - - - Slope- - - - - velocity - - - - - - - - - - - - - - - - - - - - - - - - L - - - - - - - - - - - - - - - -- - - - Min. Max. 25 50 100 200 (ft/s) (ft3/s/ft) (ft) (ft) (ft) (ft) (%) (%) Retardance A 3 3 2.3 2.5 2.7 3.1 1 11 4 4 2.3 2.5 2.8 3.1 1 12 4 5 2.5 2.6 2.9 3.2 1 7 5 6 2.6 2.7 3.0 3.3 1 9 6 7 2.7 2.8 3.1 3.5 1 12 7 10 3.0 3.2 3.4 3.8 1 9 8 12.5 3.3 3.5 3.7 4.1 1 10 Retardance B 2 1 1.2 1.4 1.5 1.8 1 12 2 1.25 1.3 1.4 1.6 1.9 1 7 3 1.5 1.3 1.5 1.7 1.9 1 12 3 2 1.4 1.5 1.7 1.9 1 8 4 3 1.6 1.7 1.9 2.2 1 9 5 4 1.8 1.9 2.1 2.4 1 8 6 5 1.9 2.1 2.3 2.5 1 10 7 6 2.1 2.2 2.4 2.7 1 11 8 7 2.2 2.4 2.6 2.9 1 12 Retardance C 2 0.5 0.7 0.8 0.9 1.1 1 6 2 1 0.9 1.0 1.2 1.3 1 3 3 1.25 0.9 1.0 1.2 1.3 1 6 4 1.5 1.0 1.1 1.2 1.4 1 12 4 2 1.1 1.2 1.4 1.6 1 7 5 3 1.3 1.4 1.6 1.8 1 6 6 4 1.5 1.6 1.8 2.0 1 12 8 5 1.7 1.8 2.0 2.2 1 12 9 6 1.8 2.0 2.1 2.4 1 12 9 7 2.0 2.1 2.3 2.5 1 10 10 7.5 2.1 2.2 2.4 2.6 1 12 Retardance D 2 0.5 0.6 0.7 0.8 0.9 1 6 3 1 0.8 0.9 1.0 1.1 1 6 3 1.25 0.8 0.9 1.0 1.2 1 4 4 1.25 0.8 0.9 1.0 1.2 1 10 4 2 1.0 1.1 1.3 1.4 1 4 5 1.5 0.9 1.0 1.2 1.3 1 12 5 2 1.0 1.2 1.3 1.4 1 9 5 3 1.2 1.3 1.5 1.7 1 4 6 2.5 1.1 1.2 1.4 1.5 1 11 6 3 1.2 1.3 1.5 1.7 1 7 7 3 1.2 1.3 1.5 1.7 1 12 7 4 1.4 1.5 1.7 1.9 1 7 8 4 1.4 1.5 1.7 1.9 1 12 8 5 1.6 1.7 1.9 2.0 1 8 10 6 1.8 1.9 2.0 2.2 1 12
  • 46. 35 Ponds—Planning, Design, ConstructionAgriculture Handbook 590 Table 11 Depth of flow (Hp) and slope range at retardance values for various discharges, velocities, and crest lengths— Continued. Maximum Discharge - - - - - - - - - - - - - - - - - - - - - - - - Hp - - - - - - - - - - - - - - - -- - - - - - - - Slope- - - - - velocity - - - - - - - - - - - - - - - - - - - - - - - - L - - - - - - - - - - - - - - - -- - - - Min. Max. 25 50 100 200 (ft/s) (ft3/s/ft) (ft) (ft) (ft) (ft) (%) (%) Retardance E 2 0.5 0.5 0.5 0.6 0.7 1 2 3 0.5 0.5 0.5 0.6 0.7 1 9 3 1 0.7 0.7 0.8 0.9 1 3 4 1 0.7 0.7 0.8 0.9 1 6 4 1.25 0.7 0.8 0.9 1.0 1 5 5 1 0.7 0.7 0.8 0.9 1 12 5 2 0.9 1.0 1.1 1.2 1 4 6 1.5 0.8 0.9 1.0 1.1 1 12 6 2 0.9 1.0 1.1 1.2 1 7 6 3 1.2 1.2 1.3 1.5 1 4 7 2 0.9 1.0 1.1 1.2 1 12 7 3 1.2 1.2 1.3 1.5 1 7 8 3 1.2 1.2 1.3 1.5 1 10 8 4 1.4 1.4 1.5 1.7 1 6 10 4 1.4 1.4 1.5 1.7 1 12
  • 47. Ponds—Planning, Design, Construction 36 Agriculture Handbook 590 Pipes through the dam Pipe spillways—Protect the vegetation in earth spillway channels against saturation from spring flow or low flows that may continue for several days after a storm. A pipe placed under or through the dam pro- vides this protection. The crest elevation of the en- trance should be 12 inches or more below the top of the control section of the auxiliary spillway. The pipe should be large enough to discharge flow from springs, snowmelt, or seepage. It should also have enough capacity to discharge prolonged surface flow following an intense storm. This rate of flow generally is estimated. If both spring flow and pro- longed surface flow can be expected, the pipe should be large enough to discharge both. Drop inlet and hood inlet pipe spillways are commonly used for ponds. Figure 22 Drop-inlet pipe spillway with antiseep collar Drop-inlet pipe spillway—A drop-inlet consists of a pipe barrel (fig. 22) located under the dam and a riser connected to the upstream end of the barrel. This riser can also be used to drain the pond if a suitable valve or gate is attached at its upstream end (fig. 23). With the required discharge capacity determined, use table 12 or 13 to select an adequate pipe size for the barrel and riser. Table 12 is for barrels of smooth pipe, and table 13 is for barrels of corrugated metal pipe. The diameter of the riser must be somewhat larger than the diameter of the barrel if the tube is to flow full. Recommended combinations of barrel and riser diameters are shown in the tables. In these tables the total head is the vertical distance between a point 1 foot above the riser crest and the centerline of the barrel at its outlet end. Because pipes of small diam- eter are easily clogged by trash and rodents, no pipe smaller than 6 inches in diameter should be used for the barrel.
  • 48. 37 Ponds—Planning, Design, ConstructionAgriculture Handbook 590 Figure 23 Drop-inlet pipe spillways (a) With sand-gravel filter (b) With antiseep collar ,,,,,,,,,, ,,,,,,,,,,,,, , ,, ,, , ,,,,,,,, Trash rack Coupling Concrete base Filter diaphragm Sand-gravel filter Rock cover Core fill Berm Pipe Ground surface Valve well Pond Trash guard Ground surface ,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,, ,,,, ,,, ,,,,,, , , Trash rack Coupling Concrete base Antiseep collar Core fill Pipe Berm Valve well Pond Trash guard
  • 49. Ponds—Planning, Design, Construction 38 Agriculture Handbook 590 Table 12 Discharge values for smooth pipe drop inlets 1/ Total head Ratio of barrel diameter to riser diameter (in) 6:8 8:10 10:12 12:15 15:24 18:36 (ft) (ft3/s) (ft3/s) (ft3/s) (ft3/s) (ft3/s) (ft3/s) 6 1.54 3.1 5.3 8.1 13.6 20.6 8 1.66 3.3 5.7 8.9 14.8 22.5 10 1.76 3.5 6.1 9.6 15.8 24.3 12 1.86 3.7 6.5 10.2 16.8 26.1 14 1.94 3.9 6.8 10.7 17.8 27.8 16 2.00 4.0 7.0 11.1 18.6 29.2 18 2.06 4.1 7.2 11.5 19.3 30.4 20 2.10 4.2 7.4 11.8 19.9 31.3 22 2.14 4.3 7.6 12.1 20.5 32.2 24 2.18 4.4 7.8 12.4 21.0 33.0 26 2.21 4.5 8.0 12.6 21.5 33.8 1/ Length of pipe barrel used in calculations is based on a dam with a 12-foot top width and 2.5:1 side slopes. Discharge values are based on a minimum head on the riser crest of 12 inches. Pipe flow based on Manning’s n = 0.012. Table 13 Discharge values for corrugated metal pipe drop inlets 1/ Total head Ratio of barrel diameter to riser diameter (in) 6:8 8:10 10:12 12:15 15:21 18:24 (ft) (ft3/s) (ft3/s) (ft3/s) (ft3/s) (ft3/s) (ft3/s) 6 0.85 1.73 3.1 5.1 8.8 14.1 8 0.90 1.85 3.3 5.4 9.4 15.0 10 0.94 1.96 3.5 5.7 9.9 15.9 12 0.98 2.07 3.7 6.0 10.4 16.7 14 1.02 2.15 3.8 6.2 10.8 17.5 16 1.05 2.21 3.9 6.4 11.1 18.1 18 1.07 2.26 4.0 6.6 11.4 18.6 20 1.09 2.30 4.1 6.7 11.7 18.9 22 1.11 2.34 4.2 6.8 11.9 19.3 24 1.12 2.37 4.2 6.9 12.1 19.6 26 1.13 2.40 4.3 7.0 12.3 19.9 1/ Length of pipe barrel used in calculations is based on a dam with a 12-foot top width and 2.5:1 side slopes. Discharge values are based on a minimum head on the riser crest of 12 inches. Pipe flow based on Manning’s n = 0.012.
  • 50. 39 Ponds—Planning, Design, ConstructionAgriculture Handbook 590 Hood-inlet pipe spillway—A hood-inlet consists of a pipe laid in the earthfill (fig. 24). The inlet end of the pipe is cut at an angle to form a hood. An antivortex device, usually metal, is attached to the entrance of the pipe to increase the hydraulic efficiency of the tube. Typical installations of hood inlets and details of the antivortex device are shown in figure 25. Often a hood-inlet can be built at less cost than a drop-inlet because no riser is needed. The major disadvantage of this kind of pipe spillway is that it cannot be used as a drain. Figure 24 Dam with hooded inlet pipe spillway (b) With antiseep collar (a) With sand-gravel filter ,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,, Dam Hooded inlet Pond Pipe Support for cantilever outlet (optional) Core fill Antiseep collar ,,,, ,,,, ,,,, ,,,, ,,,, ,,,, ,,,, ,,,, ,,,, ,,,, ,,,, ,,,, ,,,, ,,,, ,,,, ,, ,,, ,,,, ,, Dam Hooded inlet Core fill Pond Pipe Support for cantilever outlet (optional) Rock cover Filter diaphragm Sand-gravel filter
  • 51. Ponds—Planning, Design, Construction 40 Agriculture Handbook 590 Figure 25 Pipe inlet spillways that have trash rack and antivortex baffle C.M. pipe riser with tee section welded to it Reinforced concrete base Steel rod trash rack Antivortex baffle plate , , C.M. pipe riser 1-in diameter pipe Locknut and washer on each side 4-in by 4-in post 2-in by 12-in plank , Steel rods ,,,,, ,,, ,,,, Pipe Angle iron Antivortex baffle Reinforced concrete apron Flat iron Steel rod Brace Flat iron
  • 52. 41 Ponds—Planning, Design, ConstructionAgriculture Handbook 590 The required diameter for a hood-inlet pipe can be selected from table 14 or 15 after estimating the dis- charge capacity, Q, and determining the total head, H. The tables also show the minimum head, h, required above the invert or crest elevation of the pipe en- trance. Unless you provide this minimum head, the pipe will not flow full. Pipe made of cast iron, smooth steel, concrete, plastic, or corrugated metal is suitable for either kind of pipe spillway. All joints must be watertight. A concrete cradle or bedding is needed for concrete pipe to en- sure a firm foundation and good alignment of the conduit. Seal the joints of concrete pipe with an ap- proved type of rubber gasket to give them the desired amount of flexibility. For all pipe spillways, use new pipe or pipe so slightly used that it may be considered equivalent to new pipe. To retard seepage through the embankment along the outside surface of the pipe, compact the fill around the pipe and use a filter and drainage diaphragm around the pipe like that shown in figure 24. One filter and drainage diaphragm should be used around any structure that extends through the em- bankment to the downstream slope. The diaphragm should be located downstream of the centerline of a homogeneous embankment or downstream of the cutoff trench. The diaphragm should be a minimum of 3 feet thick and extend around the pipe surface a minimum of 2 times the outside diameter of the pipe (2Do). When a cradle or bedding is used under the pipe, the vertical downward 2Do is measured from the bottom of the cradle or bedding. If bedrock is encoun- tered within the 2Do measurement, the diaphragm should terminate at the bedrock surface. The location Table 14 Minimum head, h (ft), required above the invert of hood inlets to provide full flow, Q (ft3/s), for various sizes of smooth pipe and values of total head, H 1/ Total head Diameter of pipe in inches (ft) 6 8 10 12 15 18 6 h = 0.63 h = 0.85 h = 1.04 h = 1.23 h = 1.54 h = 1.82 Q = 1.63 Q = 3.0 Q = 5.3 Q = 8.5 Q = 14.0 Q = 21.2 8 h = 0.65 h = 0.86 h = 1.06 h = 1.27 h = 1.57 h = 1.87 Q = 1.78 Q = 3.5 Q = 6.0 Q = 9.3 Q = 15.5 Q = 23.3 10 h = 0.66 h = 0.87 h = 1.08 h = 1.30 h = 1.60 h = 1.91 Q = 1.93 Q = 3.8 Q = 6.6 Q = 10.2 Q = 17.0 Q = 25.4 12 h = 0.67 h = 0.88 h = 1.09 h = 1.32 h = 1.63 h = 1.94 Q = 2.06 Q = 4.1 Q = 7.1 Q = 10.9 Q = 18.3 Q = 27.5 14 h = 0.67 h = 0.89 h = 1.11 h = 1.33 h = 1.65 h = 1.96 Q = 2.18 Q = 4.3 Q = 7.5 Q = 11.6 Q = 19.5 Q = 29.4 16 h = 0.68 h = 0.90 h = 1.13 h = 1.35 h = 1.67 h = 1.98 Q = 2.28 Q = 4.5 Q = 7.8 Q = 12.2 Q = 20.5 Q = 31.0 18 h = 0.69 h = 0.91 h = 1.14 h = 1.36 h = 1.69 h = 2.00 Q = 2.36 Q = 4.7 Q = 8.1 Q = 12.7 Q = 21.4 Q = 32.5 20 h = 0.69 h = 0.92 h = 1.15 h = 1.37 h = 1.70 h = 2.02 Q = 2.43 Q = 4.9 Q = 8.4 Q = 13.2 Q = 22.2 Q = 33.9 22 h = 0.70 h = 0.93 h = 1.16 h = 1.38 h = 1.71 h = 2.04 Q = 2.50 Q = 5.0 Q = 8.7 Q = 13.6 Q = 23.0 Q = 35.1 24 h = 0.70 h = 0.93 h = 1.16 h = 1.39 h = 1.72 h = 2.05 Q = 2.56 Q = 5.1 Q = 9.0 Q = 14.0 Q = 23.7 Q = 36.3 26 h = 0.71 h = 0.94 h = 1.17 h = 1.40 h = 1.73 h = 2.07 Q = 2.60 Q = 5.2 Q = 9.3 Q = 14.4 Q = 24.4 Q = 37.5 1/ Length of pipe used in calculations is based on a dam with a 12-foot top width and 2.5:1 side slopes. Pipe flow based on Manning’s n = 0.012.
  • 53. Ponds—Planning, Design, Construction 42 Agriculture Handbook 590 Table 15 Minimum head, h (ft), required above the invert of hood inlets to provide full flow, Q (ft3/s), for various sizes of corrugated pipe and values of total head, H 1/ Total head Diameter of pipe in inches (ft) 6 8 10 12 15 18 6 h = 0.59 h = 0.78 h = 0.97 h = 1.17 h = 1.46 h = 1.75 Q = 0.92 Q = 1.9 Q = 3.3 Q = 5.3 Q = 9.1 Q = 14.5 8 h = 0.59 h = 0.79 h = 0.98 h = 1.18 h = 1.48 h = 1.77 Q = 1.00 Q = 2.1 Q = 3.6 Q = 5.8 Q = 10.0 Q = 16.0 10 h = 0.60 h = 0.79 h = 0.99 h = 1.19 h = 1.49 h = 1.79 Q = 1.06 Q = 2.2 Q = 3.9 Q = 6.3 Q = 10.9 Q = 17.3 12 h = 0.60 h = 0.80 h = 1.00 h = 1.20 h = 1.50 h = 1.80 Q = 1.12 Q = 2.3 Q = 4.2 Q = 6.7 Q = 11.6 Q = 18.5 14 h = 0.61 h = 0.81 h = 1.01 h = 1.21 h = 1.51 h = 1.82 Q = 1.18 Q = 2.4 Q = 4.4 Q = 7.1 Q = 12.2 Q = 19.6 16 h = 0.61 h = 0.81 h = 1.01 h = 1.21 h = 1.52 h = 1.82 Q = 1.22 Q = 2.5 Q = 4.6 Q = 7.4 Q = 12.7 Q = 20.5 18 h = 0.61 h = 0.81 h = 1.02 h = 1.22 h = 1.53 h = 1.83 Q = 1.26 Q = 2.6 Q = 4.8 Q = 7.6 Q = 13.2 Q = 21.3 20 h = 0.62 h = 0.82 h = 1.03 h = 1.23 h = 1.54 h = 1.85 Q = 1.30 Q = 2.7 Q = 4.9 Q = 7.8 Q = 13.7 Q = 21.9 22 h = 0.62 h = 0.83 h = 1.03 h = 1.24 h = 1.55 h = 1.86 Q = 1.33 Q = 2.8 Q = 5.0 Q = 8.0 Q = 14.1 Q = 22.5 24 h = 0.63 h = 0.83 h = 1.04 h = 1.25 h = 1.56 h = 1.88 Q = 1.35 Q = 2.8 Q = 5.1 Q = 8.2 Q = 14.5 Q = 23.0 26 h = 0.63 h = 0.84 h = 1.05 h = 1.26 h = 1.58 h = 1.89 Q = 1.37 Q = 2.9 Q = 5.2 Q = 8.3 Q = 14.7 Q = 23.4 1/ Length of pipe used in calculations is based on a dam with a 12-foot top width and 2.5:1 side slopes. Pipe flow based on Manning’s n = 0.025. of the diaphragm should never result in a minimum soil cover over a portion of the diaphragm measured normal to the nearest embankment surface of less than 2 feet. If this requirement is exceeded, the filter and drainage diaphragm should be moved upstream until the 2-foot minimum is reached. The outlet for the filter and drainage diaphragm should extend around the pipe surface a minimum of 1.5 times the outside diameter of the pipe (1.5Do) that has 1 foot around the pipe being a minimum. In most cases where the embankment core consists of fine-grained materials, such as sandy or gravely silts and sandy or gravely clay (15 to 85 percent passing the No. 200 sieve), an aggregate conforming to ASTM C-33 fine concrete aggregate is suitable for the filter and drainage diaphragm material. A fat clay or elastic silt (more than 85 percent passing No. 200 sieve) core requires special design considerations, and an engi- neer experienced in filter design should be consulted. Using a filter and drainage diaphragm has many advan- tages. Some are as follows: • They provide positive seepage control along structures that extend through the fill. • Unlike concrete antiseep collars, they do not require curing time. • Installation is easy with little opportunity for constructed failure. The construction can consist mostly of excavation and backfilling with the filter material at appropriate locations. Antiseep collars can be used instead of the filter and drainage diaphragm. Antiseep collars have been used
  • 54. 43 Ponds—Planning, Design, ConstructionAgriculture Handbook 590 with pipe spillways for many years. More fabricated materials are required for this type of installation. Both types of seepage control are acceptable; in either case, proper installation is imperative. If an antiseep collar is used, it should extend into the fill a minimum of 24 inches perpendicular to the pipe. If the dam is less than 15 feet high, one antiseep collar at the centerline of the fill is enough. For higher dams, use two or more collars equally spaced between the fill centerline and the upstream end of the conduit when a hood-inlet pipe is used. If a drop-inlet pipe is used, the antiseep collars should be equally spaced between the riser and centerline of the fill. Use trash racks to keep pipes from clogging with trash and debris. Of the many kinds of racks that have been used, the three shown in figure 25 have proved the most successful. Extend the pipe 6 to 10 feet beyond the downstream toe of the dam to prevent damage by the flow of water from the pipe. For larger pipes, support the extension with a timber brace. Drainpipes—Some state regulatory agencies require that provision be made for draining ponds completely or for fluctuating the water level to eliminate breeding places for mosquitoes. Whether compulsory or not, provision for draining a pond is desirable and recom- mended. It permits good pond management for fish production and allows maintenance and repair with- out cutting the fill or using siphons, pumps, or other devices to remove the water. Install a suitable gate or other control device and extend the drainpipe to the upstream toe of the dam to drain the pond. Water-supply pipes—Provide a water-supply pipe that runs through the dam if water is to be used at some point below the dam for supplying a stockwater trough, for irrigation, or for filling an orchard spray tank (fig. 26). This pipe is in addition to the principal spillway. A water-supply pipe should be rigid and have watertight joints, a strainer at its upper end, and a valve at its outlet end. For a small rate of flow, such as that needed to fill stockwater troughs, use steel or plastic pipe that is l-l/2 inches in diameter. For a larger rate of flow, such as that needed for irrigation, use steel, plastic, or concrete pipe of larger diameter. Water-supply pipes also should have watertight joints and antiseep collars or a filter and drainage diaphragm.
  • 55. Ponds—Planning, Design, Construction 44 Agriculture Handbook 590 Figure 26 Water is piped through the dam’s drainpipe to a stockwater trough (a) Pipe with sand-gravel filter ,,,,,,,,,,,, ,,,,,,,,,,,, ,,,,,,,, , , , Pond 6-inch concrete base Extended pipe above water level to show location of intake Riser with 1/4-inch holes Corrugated metal pipe with 1-inch holes. Pipe filled with coarse gravel Valve Trough Bell tile around valve and pipe for suitable housing Union Core fill Ground surface Filter diaphragm Sand-gravel filter Rock cover Cap connection may be used for other purposes Control valve (b) Pipe with antiseep collars ,,,,,,,,,,,,,,,,,,,,,,,,,, ,Pond Extended pipe above water level to show location of intake Riser with 1/4-inch holes Corrugated metal pipe with 1-inch holes. Pipe filled with coarse gravel Valve Trough Bell tile around valve and pipe for suitable housing Union Control valve Core fill Antiseep collar 6-inch concrete base Cap connection may be used for other purposes