For a series of culverts AMI HydroCAD or Haestad Methods PondPack will work. HydroCAD gives the "most bang for the buck", but has a few limitations.
The "old culverts" may be modeled by increasing the default entrance loss coefficient (Ke) and the contraction coefficient...
In my local area we have 47 years of rainfall data avaiable, yet as engineers we design for the 100 year return period event. The 100 year return period event is a statistical extrapolation of data. The truth of the matter, we are only guessing what a 100 year return period storm is, because...
One approach is to remove any oil and gas from the parking lot prior to release to the pond. Several proprietary oil and grease separator devices are available on the market. StormCeptor is one, CDS Technologies is another. These devices either use detention time or vortex separation to...