Case 1 Option 2 Excessive stormwater runoff

One of the most vague options in the LEED rating system.

You need to demonstrate that you are not exceeding the critical capacity of the receiving stream channel, nor are you causing an erosive condition by increasing velocity in the channel.

SSc6.1 Case 1-Option 2 requires the project to 1) include stream channel protections that prevents excessive erosion of the stream bed and banks and 2) pursue stormwater quantity control strategies, so a project must make a concerted effort to reduce both rate and quantity of stormwater runoff from the project site to the receiving water body, similar to the requirements in Option 1, but with obviously less restrictions. The LEED Rating System doesn’t define how a project meets Case 1 - Option 2 because the Rating System can’t define the appropriate level of runoff reduction that is required in order to maintain the in-stream habitat/channel protections for any given water body, which can be defined as the critical capacity value. Oftentimes a municipality can provide this information or the stormwater designer/civil engineer can calculate the critical capacity for a receiving water body.

Honestly, this is/should be a very complex analysis of pre and post development stream morphology and aquatic habitat, but I just don't think GBCI is getting that deep with this analysis. If you have your CE prepare a report that shows some rate and volume reduction, a capacity analysis of the channel, show that it works....you should be good.

In your scenario, if you are causing an increase in runoff rate and volume for the 50 and 100 year storms, you are causing a downstream impact that does not exist today.