agricultural pond private engineering resources & costs agricultural water resource development...
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Agricultural PondPrivate Engineering Resources & Costs
Agricultural Water Resource Development Workshops
Presented by:Cavanaugh & Associates P.A.530 N. Trade Street, Suite 302
Winston-Salem, NC336.759.9001
Why Hire An Engineer?• Is the pond in the best location?• How much water do I need?• How much water will it yield?• Will it hold water?• Which will work - Excavated or
embankment? Does it matter?• Are there wetlands?• What about all these permits?
Inflow Hydrograph for Small Watersheds• Need:
– Peak Discharge, Qp
– Time to Peak Discharge, Tp
– Shape of the Hydrograph
The Rational Method
• Q = estimated design discharge (cfs)
• C = Composite Runoff Coefficient for the drainage area
• I = Rainfall intensity for the design storm (inches/hour)
• A = Drainage Area (acres)
Q = CIA(Calculating peak flood discharge at a given point)
Delineating Drainage Area, A• The first step in determining if
your pond is in the “right spot”
• Orange Pond A = 25 acres
• Blue Pond A = 125 acres
• Purple Pond A = 350 acres
Determine Time of Concentration, tc• Depends on
– Hydraulic Length of the drainage area– Height of the most remote point on the
watershed above the outlet point
• Orange Pond tc = 5 min
• Blue Pond tc = 7 min
• Purple Pond tc = 8.3 min
Determine Rainfall Intensity, I
• Depends on– Statistical
rainfall for the design location
– Designated return period for the design
Determine Composite Runoff Coefficient, C• Depends on land
use in the drainage area– Building types– Ground
coverings– Soil types– Building
densities
Commercial, C = 0.85
Wooded, Sparse Ground Litter, C = 0.20
Apartments, C = 0.60 Residences, 2 dwellings per acre, C = 0.35
Wooded, Deep Ground Litter, C = 0.10
Time to Peak, Tp
• Based on Qp & Volume of Water Under the Hydrograph– Qp is estimated by Rational Method– Volume is estimated based on
• duration of the design storm• Soil types• Cover conditions
Shape of the Hydrograph• Accepted practice is to assume a
step function unit hydrograph to estimate the shape
Excavation Ponds
Source: Dwane Jones/NCSU Co-op Extension
• Is there adequate drainage to fill?• What is the level of the water
table?• What is the impact of the water
table?• Will the soil types sustain water
storage?
Embankment Ponds
Source: Dwane Jones/NCSU Co-op Extension
• Is there adequate drainage to fill?
• Will the soil types sustain water storage?
• Is an earthen dam adequate?
• What type of outlets are needed?
• What is the downstream impact?
Embankment Earthen Dams• Built in natural topographic draw• Low flow outlet device • Riser/Barrel Outlet• Emergency spillway• Outlet size calculated using Stage-Storage Function to
control pond level and downstream needs• Dam Construction must meet Dam Safety Requirements
General Steps in Pond Design• Base Topography
– Existing Conditions– Height of Dam Required– Earthwork Required
• Geotechnical Investigation– Dam Core Design– Seepage Control– Compaction & Materials Testing
General Steps in Pond Design• Hydrologic Design
– Rainfall Event Investigation– Peak Discharge– Watershed Yield/Water Supply
• Hydraulic Design– Primary Spillway Design– Riser/Barrel Design– Emergency Spillway Design– Overtopping Control
Construction Considerations• Preparation of Construction
Documents– Plans & specifications to be sealed by
Professional Engineer– Permits required from NC Division
of Land Quality/Dam Safety• Bid Acquisition
– Qualifying construction contractors– Hold bid opening– Ensuring contractor has proper bonds
• Construction Administration– On-site observation of construction to
protect investment and safety– Engineer certification of construction
and as-builts
What’s the Engineering Cost?• Site dependant• Two phases:
– Preliminary Site Evaluation– Design: Engineering Design, Permitting &
Construction Document Preparation• Rough estimate of design cost is 15-20% of
construction cost• Preliminary engineering evaluation
– Preliminary hydraulic & hydrologic calculations– Cost estimate of geotechnical & wetland
investigations– Preliminary design concept – Preliminary cost estimate of engineering costs,
permitting fees and construction costs