Question

At the time of the construction, the developer planned on maintaining the stormwater pond as an ornamental, wet bottom pond. Fear of the West Nile virus from the potential home owners has caused a change in plan. Unfortunately, the outlet structure has already been delivered. Your builder has informed you that he has the ability to core drill a 12-inch diameter hole in the structure that will allow the basin to drain. It won’t be pretty, but it will do the job. You know that the local ordinance limits the flow that can be released from up to a 100-year storm to the equivalent flow from a 10-year storm if the site were not developed. The builder needs you to tell him the centerline elevation he should drill the hole if you know that the overflow weir has been set at an elevation of 780.0 ft above MSL.(30 points).

Center Line Elevation = ____________ ft above MSL

Answer 1

The Centre line elevation may be above or below 780 feet (msl of weir) and the discharge may be carried through a pipe by lift or gravity. In case of lift, the pump capacity (discharge/ power) must be determined depending on height of lift (weir to site) and in case of gravity flow (as open channel uniform flow in pipe to ensure virus issues) before discharging into the weir that can handle at least 100 year return period flood. The pipe discharge should not exceed flow of 10 year return period for current/ existing conditions. The length of pipe shall be determined based on location of weir w.r.t building site. Due consideration must be given to friction losses, manning n and pipe material. Appropriate gate valves, air valves and scour valves must be put in place.