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Agricultural Pond Private Engineering Resources & Costs

Cavanaugh & Associates offers Agricultural Water Resource Development workshops to help farmers with pond design and engineering. Learn about location, water yield, permits, drainage, and more.

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Agricultural Pond Private Engineering Resources & Costs

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  1. Agricultural PondPrivate Engineering Resources & Costs Agricultural Water Resource Development Workshops Presented by: Cavanaugh & Associates P.A. 530 N. Trade Street, Suite 302 Winston-Salem, NC 336.759.9001

  2. 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?

  3. This looks like a good spot! How much water will it yield?

  4. Inflow Hydrograph for Small Watersheds • Need: • Peak Discharge, Qp • Time to Peak Discharge, Tp • Shape of the Hydrograph

  5. The Rational Method Q = CIA(Calculating peak flood discharge at a given point) • 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)

  6. 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

  7. 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

  8. Determine Rainfall Intensity, I • Depends on • Statistical rainfall for the design location • Designated return period for the design

  9. Determine Composite Runoff Coefficient, C Wooded, Deep Ground Litter, C = 0.10 Wooded, Sparse Ground Litter, C = 0.20 • Depends on land use in the drainage area • Building types • Ground coverings • Soil types • Building densities Commercial, C = 0.85 Apartments, C = 0.60 Residences, 2 dwellings per acre, C = 0.35

  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

  11. Shape of the Hydrograph • Accepted practice is to assume a step function unit hydrograph to estimate the shape

  12. Use the Inflow Hydrograph to determine if the pond is sufficient for your needs.

  13. Excavation Ponds • 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? Source: Dwane Jones/NCSU Co-op Extension

  14. Embankment Ponds • 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? Source: Dwane Jones/NCSU Co-op Extension

  15. 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

  16. 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

  17. 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

  18. 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

  19. 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

  20. Why Hire An Engineer? • Professional recommendation on construction alternatives • Familiar with Dam Safety Rules and other permitting needs • Protect your interest during construction • Reduce your liability and risk • In long run will save money and time

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