We wish to pursue credit in both SSc5.1 and SSc6.1. We are limiting site disturbance within the prescribed distances listed in credit SSc5.1. The site is suburban, and the stormwater detention/retention facility feeds into an existing seasonal stream. The stream is otherwise outside the boundary of the development footprint. For SSc6.1 the slope of the stream base is relatively steep (approximately 7 percent) and the base is narrow with a steep bank (approximately 2:1) that varies from 6 to 60-feet deep. Consequently, we would like to implement a strategy of placing rock-check dams or log dams to prevent excessive stream channel erosion in addition to limiting the post-development runoff rate and quantity to pre-development values for the 1 and 2-year design storms. There are two questions. 1. Do the stream protection measures fall into the same category as constructed areas with permeable surfaces (like stormwater detention facilities)? If so, we will include those areas (and any necessary construction access) within the Development Footprint. 2. If the stream protection measures are not classified as constructed areas, can permanent stream protection measures be installed outside of the development footprint? The intent will be to place the stream protection measures, and then restore the landscape where site disturbance is required to install the stream protection measures.
The applicant would like to incorporate stream stabilization into their stormwater management plan. The applicant is asking if the stream stabilization would be included in their development area, and if not could the stream protection measures be installed outside of the development footprint. Stormwater and retention facilities are normally upstream from the existing seasonal stream to demonstrate that the post-development increase in site generated runoff from the 2-yr 24 hour storm is accounted for on-site. As the project team is pursuing this strategy in addition to limiting the post-development runoff rate and quantity to pre-development values for the 1 and 2-year design storms, the requirements of SSc6.1 have been satisfied, without the stream protection measures. If the project team demonstrates proof of ownership for this area and expands the project boundary to include the seasonal stream then the protection of this area with rock-check dams, etc. into the project submittal is acceptable. Though it is not necessary for SSc6.1, restoring habitat in this area may help with SSc5.1. 1) Once included in the LEED Project Boundary, stream restoration and construction access must be included in permeable area calculations. The intent of SSc6.1 is to "Implement a stormwater management plan that protects receiving stream channels from excessive erosion by implementing a stream channel protection strategy and quantity control strategies" which may already be accomplished as mentioned above by "limiting the post-development runoff rate and quantity to pre-development values for the 1 and 2-year design storms". Since expanding the LEED project boundary is proposed, and protecting what is now considered an on-site section of the stream, the downstream section of this channel must also be protected from excessive erosion. Rehabilitating a heavily impacted section of this channel effectively moves the area that we need to be protecting (to satisfy SSc6.1) downstream of the new project boundary. The downstream channel section adjacent to the LEED Project Boundary becomes the receiving stream channel and the project team must demonstrate that the stormwater management plan will protect that section from excessive erosion. 2) Stream protection measures could be conducted outside the project as a part of the project\'s stormwater projection plan (please note that Corps of Engineers, Fish & Game, and relevant local agency approval is necessary). This approach would protect the on-site receiving waters from excessive erosion. The applicant must demonstrate that check dams are the best erosion control measure and that they meet SSc5.1 intent of providing habitat and promoting biodiversity. Generally, it is more effective to deal with runoff on the project site rather than to attempt to stabilize sections of river downstream. If this option is pursued, then the receiving waters keep moving further downstream while project expenses and overall impact tend to increase. Retaining or infiltrating increased runoff on-site is likely a more cost effective option,and will satisfy SSc6.1, while limiting impact to the steep channel section. Applicable Internationally.