Farm Ponds: Design and Components, Study notes of Agricultural engineering

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AGSM 335 AGSM 335

Water and Soil ManagementWater and Soil Management

SURFACE WATER STORAGESURFACE WATER STORAGE

RESERVOIRS AND DAMSRESERVOIRS AND DAMS

CHAPTER 11 ---CHAPTER 11--- TEXTTEXT

FARM PONDS FARM PONDS

FUNCTIONFUNCTION

ƒ ƒ Water storage for livestock,Water storage for livestock, irrigation, fish production,irrigation, fish production, recreation, etc.recreation, etc.

FARM PONDS FARM PONDS

COMPONENTSCOMPONENTS

ƒ ƒ (^) DamDam -- Note: dams and berms greaterNote: dams and berms greater than 6 feet in height require safetythan 6 feet in height require safety permitting from the Corps ofpermitting from the Corps of Engineers.Engineers.

ƒ ƒ (^) Core trenchCore trench -- Trench located underTrench located under the dam and filled with dam material.the dam and filled with dam material. Used to increase the stability of theUsed to increase the stability of the dam structure and prevent seepage.dam structure and prevent seepage.

FARM PONDSFARM PONDS

COMPONENTSCOMPONENTS

Trickle Spillway (Mechanical Spillway) -Trickle Spillway (Mechanical Spillway)- pipe which passes through the dampipe which passes through the dam to carry low flows.to carry low flows.

OUTLETOUTLET

INLET is SubmergedINLET is Submerged

FARM PONDS FARM PONDS

COMPONENTSCOMPONENTS

Flood Spillway (Emergency Spillway)Flood Spillway (Emergency Spillway) -- waterway which routes heavy floodwaterway which routes heavy flood waters around the side of the dam.waters around the side of the dam. Used to prevent over-Used to prevent over-topping whichtopping which can cause dam failure.can cause dam failure.

Flood SpillwayFlood Spillway

Flood SpillwayFlood Spillway

Flood SpillwayFlood Spillway

Emergency spillwayEmergency spillway conveyanceconveyance

FARM PONDS FARM PONDS

COMPONENTSCOMPONENTS

Invert ElevationInvert Elevation -- the elevation of thethe elevation of the bottom of a trickle spillwaybottom of a trickle spillway ENTRANCE. The lowest elevation atENTRANCE. The lowest elevation at which water will enter the spillway.which water will enter the spillway.

Water below this elevation is the waterWater below this elevation is the water storage needs. Water above this levelstorage needs. Water above this level is foris for ““ FLOODS ..””

FARM PONDSFARM PONDS

SITE SELECTION --SITE SELECTION -- TopographyTopography

NEED a location where the desiredNEED a location where the desired reservoir DEPTH can be obtained overreservoir DEPTH can be obtained over 15 to 20 percent of the surface area (15 to 20 percent of the surface area ( SEESEE FIGURE 11.1).FIGURE 11.1).^ Greater depth needed inGreater depth needed in west due to evaporation rates (want awest due to evaporation rates (want a large depth to surface area ratio).large depth to surface area ratio).

If using a dam, the dam should be locatedIf using a dam, the dam should be located perpendicular to contour linesperpendicular to contour lines (minimizes fill).(minimizes fill).

FIGURE 11.2.FIGURE 11.2. TEXTTEXT

FARM PONDSFARM PONDS

SITE SELECTIONSITE SELECTION ----

Watershed AreaWatershed Area

Should not be soShould not be so large thatlarge that sedimentation orsedimentation or flooding isflooding is problematic.problematic.

FARM PONDSFARM PONDS

SITE SELECTION --SITE SELECTION -- WatershedWatershed AreaArea

If sedimentation is likely (largeIf sedimentation is likely (large cultivated areas in watershed),cultivated areas in watershed), measures should be taken tomeasures should be taken to prevent sediment fromprevent sediment from entering pond.entering pond.

FARM PONDSFARM PONDS

SITE SELECTION --SITE SELECTION -- Watershed AreaWatershed Area

Minimum watershed size required for eachMinimum watershed size required for each acac--ft of stored water provided byft of stored water provided by location in Figure 11.2.location in Figure 11.2.

Maximum watershed size is roughly 2-Maximum watershed size is roughly 2-3 3 times the minimum provided in Figuretimes the minimum provided in Figure 11.2.11.2.

FIGURE 11.2.FIGURE 11.2. TEXTTEXT

Watershed area per ac-Watershed area per ac-ft of storageft of storage

FARM PONDS FARM PONDS

SITE SELECTIONSITE SELECTION ----^ StorageStorage RequirementsRequirements

ƒƒ Required storage capacity depends onRequired storage capacity depends on the intended uses, expectedthe intended uses, expected evaporation and seepage rates,evaporation and seepage rates, necessary sediment storage volume,necessary sediment storage volume, and desired volume of carry-and desired volume of carry-over.over.

FARM PONDSFARM PONDS

SITE SELECTIONSITE SELECTION ---- StorageStorage RequirementsRequirements

ƒƒ^ Water needs for several uses areWater needs for several uses are provided in Table 11.1. Select valuesprovided in Table 11.1. Select values from the given range depending onfrom the given range depending on anticipated temperatures.anticipated temperatures.

TABLE 11.1 TEXT

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EARTHEN DAM DESIGN --EARTHEN DAM DESIGN-- Flood StorageFlood Storage DepthDepth

ƒ ƒ Storage provided between bottom ofStorage provided between bottom of the trickle spillway and bottom of thethe trickle spillway and bottom of the flood spillway.flood spillway.

ƒ ƒ Provides storage for smaller flood flowsProvides storage for smaller flood flows so flood spillway does not flow often.so flood spillway does not flow often.

FARM PONDSFARM PONDS

EARTHEN DAM DESIGN --EARTHEN DAM DESIGN-- Flood StorageFlood Storage DepthDepth

ƒ ƒ Excess water is discharged slowly throughExcess water is discharged slowly through the trickle spillway.the trickle spillway.

ƒ ƒ Determine necessary storage depth fromDetermine necessary storage depth from Table 11.2 knowing the peak runoff rate (q,Table 11.2 knowing the peak runoff rate (q, NRCS Method) and the surface area of theNRCS Method) and the surface area of the normal water level (elevation equal to thenormal water level (elevation equal to the trickle spillway invert).trickle spillway invert).

FARM PONDSFARM PONDS

EARTHEN DAM DESIGN --EARTHEN DAM DESIGN-- FreeboardFreeboard

ƒ ƒ Usually 2 feet (0.5 for frost action, 1.0 forUsually 2 feet (0.5 for frost action, 1.0 for flow depth in flood spillway, and 0.5 for waveflow depth in flood spillway, and 0.5 for wave action).action).

ƒ ƒ (^) Should be increased for dam heights greaterShould be increased for dam heights greater than 15 feet (greater safety factor) or waterthan 15 feet (greater safety factor) or water surfaces greater 400 feet long (greater wavesurfaces greater 400 feet long (greater wave action).action).

FARM PONDS FARM PONDS

EARTHEN DAM DESIGN --EARTHEN DAM DESIGN-- Side SlopesSide Slopes

ƒ ƒ Less than 50 feet in height: upstream (wet)Less than 50 feet in height: upstream (wet) sideside -- 3:1, downstream (dry) side3:1, downstream (dry) side -- 2:1 at the2:1 at the steepest.steepest.

ƒ ƒ (^) Flatter side slopes on wet side because wetFlatter side slopes on wet side because wet soil is less stablesoil is less stable

FARM PONDSFARM PONDS

EARTHEN DAM DESIGN --EARTHEN DAM DESIGN-- Side SlopesSide Slopes

ƒ ƒ (^) If downstream surface is mowedIf downstream surface is mowed -- use 2.5:1use 2.5: or flatter.or flatter.

ƒ ƒ (^) Account for dam material in determiningAccount for dam material in determining slopesslopes---- use only what is stable for the soil.use only what is stable for the soil.

FARM PONDSFARM PONDS

EARTHEN DAM DESIGN --EARTHEN DAM DESIGN-- (^) Top WidthTop Width

ƒ ƒ Minimum width = 8 feetMinimum width = 8 feet

ƒ ƒ For all dams >10 feet in height, add 0.5For all dams >10 feet in height, add 0. feet width for every additional foot offeet width for every additional foot of dam height:dam height:

w = 8 + 0.5 (hw = 8 + 0.5 (h -- 10)10)

ƒ ƒ (^) If dam will be crossed by vehicles, use aIf dam will be crossed by vehicles, use a minimum of 12 feet.minimum of 12 feet.

FARM PONDSFARM PONDS

TRICKLE SPILLWAYTRICKLE SPILLWAY

ƒ ƒ Collars should provide a distance of 10 %Collars should provide a distance of 10 % the length of the pipe as it passes throughthe length of the pipe as it passes through the dam (not including the diameter of thethe dam (not including the diameter of the pipe). For example a 4x4 collar around a 1pipe). For example a 4x4 collar around a 1 foot pipe provides 2(2foot pipe provides 2(2--0.5) = 3 feet of0.5) = 3 feet of distance.distance.

ƒ ƒ Distance Needed = 0.1 * length of trickleDistance Needed = 0.1 * length of trickle spillway.spillway.

FARM PONDS FARM PONDS

TRICKLE SPILLWAYTRICKLE SPILLWAY

ƒ ƒ Distance Provided by each collar = width ofDistance Provided by each collar = width of collarcollar -- diameter of pipe.diameter of pipe.

ƒ ƒ May need to provide a trash (critter) gate atMay need to provide a trash (critter) gate at either end of the spillway.either end of the spillway.

FARM PONDS FARM PONDS

FLOOD SPILLWAY --FLOOD SPILLWAY-- LocationLocation

ƒ ƒ Usually a vegetated waterway (leastUsually a vegetated waterway (least expensive).expensive).

ƒ ƒ Should not pass over any filled materialShould not pass over any filled material associated with the dam.associated with the dam.

ƒ ƒ May take advantage of natural low spotsMay take advantage of natural low spots---- broad shallow flow over a large area is ok ifbroad shallow flow over a large area is ok if it does not endanger the dam or lead toit does not endanger the dam or lead to heavy erosion.heavy erosion.

FARM PONDSFARM PONDS

FLOOD SPILLWAY –FLOOD SPILLWAY– DesignDesign

ƒ ƒ Usually designed for the 25Usually designed for the 25--year peak runoffyear peak runoff rate (q, NRCS Method). Use a more severerate (q, NRCS Method). Use a more severe storm if damage risks are high. (storm if damage risks are high. (SEESEE FOLLOWING TABLE).FOLLOWING TABLE).

ƒ ƒ Flow controlled where flow passes over aFlow controlled where flow passes over a level section beside the top of the damlevel section beside the top of the dam (called the control section). Use a(called the control section). Use a 1 foot flow1 foot flow depthdepth. Determine the channel width using:. Determine the channel width using: W = q/3.2W = q/3.

From Handout NOTESFrom Handout NOTES

FARM PONDSFARM PONDS

FLOOD SPILLWAY --FLOOD SPILLWAY-- DesignDesign

ƒ ƒ Slope on the lower end of the spillway isSlope on the lower end of the spillway is steeper. Here design the spillway as yousteeper. Here design the spillway as you would any vegetated waterway (use designwould any vegetated waterway (use design procedures given in class and nomographsprocedures given in class and nomographs in Chapter 8).in Chapter 8).

FARM PONDS FARM PONDS

SEEPAGE CONTROLSEEPAGE CONTROL

ƒ ƒ May occur through dam or throughMay occur through dam or through underlying soil strata.underlying soil strata.

ƒ ƒ If good construction material use it in theIf good construction material use it in the core trench and in the middle of the damcore trench and in the middle of the dam (make a core or key as described earlier).(make a core or key as described earlier).

ƒ ƒ Core trench should have a minimum width ofCore trench should have a minimum width of 8 feet and have 1:1 side slopes. It should8 feet and have 1:1 side slopes. It should extend to an impermeable soil layer.extend to an impermeable soil layer.

FARM PONDSFARM PONDS

SEEPAGE CONTROLSEEPAGE CONTROL

ƒ ƒ Fill should be thoroughly compacted duringFill should be thoroughly compacted during construction.construction.

ƒ ƒ May take alternative measures to limitMay take alternative measures to limit seepage including: compaction of inundatedseepage including: compaction of inundated areas using local clays, dispersement of clayareas using local clays, dispersement of clay soil with chemicals, lining with swellingsoil with chemicals, lining with swelling clays (bentonite), lining with a geofabric.clays (bentonite), lining with a geofabric.

FARM PONDS FARM PONDS

DESIGN PROCEDUREDESIGN PROCEDURE

ƒ ƒ Determine the annual volume of waterDetermine the annual volume of water needed onneeded on--site (Table 11.1).site (Table 11.1).

ƒ ƒ Determine minimum storage in the pondDetermine minimum storage in the pond allowing for seepage, evaporation, andallowing for seepage, evaporation, and sedimentation (~ 50%).sedimentation (~ 50%).

ƒ ƒ (^) Determine minimum drainage area needed toDetermine minimum drainage area needed to supply required volume (Figure 11.2)supply required volume (Figure 11.2)

FIGURE 11.2.FIGURE 11.2. TEXTTEXT