Transcript Document

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

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?

This looks like a good spot!

How much water will it yield?

Inflow Hydrograph for Small Watersheds • Need: – Peak Discharge, Q p – Time to Peak Discharge, T p – Shape of the Hydrograph

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)

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, 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 • Blue Pond t c = 5 min = 7 min • Purple Pond t c = 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 Wooded, Sparse Ground Litter, C = 0.20

Commercial, C = 0.85

Wooded, Deep Ground Litter, C = 0.10

Apartments, C = 0.60

Residences, 2 dwellings per acre, C = 0.35

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

Shape of the Hydrograph

• Accepted practice is to assume a step function unit hydrograph to estimate the shape

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

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

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

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

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