1. Agricultural Pond Private 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, Q p –Time to Peak Discharge, T p –Shape of the Hydrograph

5. 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)

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, t c Depends on –Hydraulic Length of the drainage area –Height of the most remote point on the watershed above the outlet point Orange Pond t c = 5 min Blue Pond t c = 7 min Purple Pond t c = 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 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 = 0.60Residences, 2 dwellings per acre, C = 0.35 Wooded, Deep Ground Litter, C = 0.10

10. Time to Peak, T p Based on Q p & 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 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?

14. 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?

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