The way that we have calculated run-off volume is to calculate a weighted average run-off coefficient, as you would for the Rational Method. You do this for pre and post development conditions, and essentially, the Run-off Coefficient needs to be the same. For instance, if the Run-off Coefficient is 0.35 for an undeveloped site, and the Run-off Coefficent for the developed site is 0.70, then the volume that must be mitigated is the difference in Run-off Coefficient times the rainfall for the one-and two-year 24 hour design storms. The approach to meeting the volume requirement can be with green-roofs, porous pavment, cisterns and reuse, infiltration basins, bioswales, etc.
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John Covello
Senior Sustainability ManagerUL Solutions
9 thumbs up
October 11, 2013 - 4:25 am
Hello,
I have a question regarding silt and run off. Our project is located in Phuket Thailand. Our project is planning to have a series of retention ponds and bioswales to collect rain water runoff.
The storms though have occasionally hit with great intensity in the last few years. What happens if a storm comes that exceeds the 2 year 24 hour limit, which is quite possible here and overwhelms the system resulting in some erosion. There would be silt that would enter the ocean the project is located on. Does that effect the credit standing in any way?