Option 1: Existing Imperviousness is Less Than 50% The stormwater management plan already in place was created with the existing Winkler Botanical Preserve Pond, which was designed and constructed to treat all runoff from, among other areas, Mark Center Plaza 1A & 1B, which includes the subject site. Based on a review of the design plans for this pond, the post-development peak discharges for the 1- and 2-year storms are reduced below pre-development levels. However, the pond is not designed to achieve this reduction over a 24 hour period, which is required to obtain this credit under this option. Another option for achieving this credit 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. Obviously, short of credit acceptance, please confirm that the subject site meets this criteria for the following reasons, or whether key components are still missing: 1) As shown on the Winkler Botanical Preserve Pond Design Plans that will be provided with the full credit submission, the stormwater management facility that serves this site is designed to: a. Capture and treat 100% of runoff from this site. b. Reduce post-development peak discharge rates below pre-development levels. i. 2-yr pre-development peak discharge = 200 cfs ii. 2-yr post-development peak discharge = 197 cfs iii. 10-yr pre-development peak discharge = 436 cfs iv. 10-yr post-development peak discharge = 396 cfs 2) As shown on the Mark Center Plaza 1A & 1B Preliminary Development Plan and the Winkler Botanical Preserve Pond Plan, the following measures were designed and installed to reduce runoff velocities and prevent erosion in the receiving channels leading to the Winkler Botanical Preserve Pond: a. Rip-rap plunge pools were installed at all pipe outfalls in order to dissipate velocities exiting pipes and entering open channels. See Winkler Botanical Preserve Pond Plan. b. Slope reinforcement was placed downstream of plunge pools for pipe outfalls to further protect stream channels from runoff exiting pipe outfalls and entering stream channels. c. Linear Lakes were installed in the main stream channel which feeds into Winkler Botanical Preserve Pond and conveys most of the runoff from the subject site. Linear Lakes are a series of three weir structures which reduce the velocity of runoff in the open channel and prevent erosion as the stream channel flows into the Winkler Botanical Preserve Pond.
The project team is requesting whether their proposed efforts to protect receiving stream channels are sufficient for credit achievement for Option 1B, Stream Channel Protection, however additional information would need to be provided to determine if the proposed strategies are acceptable. To meet the credit requirements for Stream Channel Protection, the project must implement a stormwater management plan that includes both stream channel protection strategies (such as the ones proposed above) and quantity control strategies that have been implemented on the project site. The project must demonstrate that the post-development rate and quantity values from the project site are below the critical values for the receiving channel. For certification, the project team must provide information on the site\'s pre- and post-development rate and quantity, not the stormwater management facility as provided above, and a narrative describing the strategies that have been implemented to protect the receiving stream channel(s) and control the stormwater quantity so as not to not exceed the critical values for the receiving channel. Please also note that the method of runoff conveyance to downstream or regional facilities is equally important. The project team must demonstrate that unmanaged runoff is conveyed in a safe and non-erosive manner and will not degrade adjacent natural areas and receiving streams. Applicable Internationally.