Stream Channel Protection? (case 1, option 2)

Josh - can you get around the CO cistern issue if you don't reuse the water, but just detain it in a cistern and percolate it to landscape over a longer period of time? Seems like that wouldn't be an appropriation, and actually, you'd be adding water to the system.

But you raise another point that I've wondered about with the intent of the credit. If the stormwater flows through all man-made structures, where is the real benefit from this credit? Here in tiny Santa Monica, just one of the stormdrain outflow points can release 50 MGD during a storm event. It releases 500,000 gal/day in DRY weather. While infiltration to the aquifer is still preferable, and one might make an argument about reducing storm volumes overall, I'm not sure I see how rate reductions have any impact to an enormous storm river flowing through a concrete channel and into the ocean...

Perhaps another relevant distinction to this credit would involve the nature of the local stormwater system infrastructure?

I suppose it would if there were any rivers or if there were a treatment plant. Stormwater from buildings (and building sites) only ever flows through concrete structures and then goes into the ocean untreated. The rate at outfall is influenced far more by the gradient of the concrete channel than by any additional flows from any individual building (no matter the rate). There could be no erosion throughout the system except at the beach between the storm drain outfall and the ocean, and that area is hardly a natural system, as public works moves the sand around there all the time, wet or dry.

Beyond that, the mitigation provided by any new building is negligible (and probably will always be negligible) since the vast majority of stormwater is coming from existing buildings and infrastructure. Obviously buildings should still pursue best practices, but it seems that for this credit, rate reductions have been tougher to achieve around here even though volume reductions and infiltration are probably more important.

Looking forward to hearing if Option 2 works for you, as I don't know of anyone who has pursued that yet...

the intent of Option 2 for Case #1 has never been clear to me. I think the simple response is that you don't have to do anything about peak and volume if you can show that there is no downstream erosion. If there is a pipe all the way to the receiving waters and there is erosion protection at the outfall of the pipe, then it seems that you have met the criteria. That does not seem to meet the intent of the credit. I think the key to this option is the second sentence that states: The stormwater management plan must include a stream channel protection AND (my capital letters) quantity control strategies. The first unstated assumption is that the channel must be protected, but how far? I have used the EPA definition that the channel must be protected to the point where the flow enters The Waters of the U.S. This may be along ways or a short distance.

Second, I have put importance on the word AND in the second sentence in Option 2 to suggest that an acceptable strategy may not have to limit volume, but does limit flow rate. Of course, increased volume as well as increased flow rate will cause greater erosion in a natural stream channel, but I would expect to see documentation that can demonstrate that the channel protection will protect against the flow rate and volume entering the stream and that the flow rate has been reduced to predevelopment conditions.

This is really the only reasonable strategy that works in places where there is little opportunity for infiltration (clay soils). This is also consistent with water law in Colorado