2024 03 Drainage Statement

III. Runoff Rate Reduction Performance As noted previously, a majority of stormwater runoff from the project area will be collected by the proposed stormwater conveyance system, detained in an on-site underground detention basin, and released at a controlled rate to the existing onsite stormwater infrastructure. A significant amount of stormwater runoff from the surrounding wooded areas flows through the project area, to be collected and detained in the proposed basin. As these areas remain undisturbed in existing and proposed conditions, peak flows from these areas were accounted for in the basin sizing and outlet control structure design, but were excluded in the peak flow reduction calculations. The undisturbed wooded areas which drain towards the existing headwall within the adjacent Lot 21 were also included in the peak flow calculations, but were excluded in determining the required peak flow reduction. As a result of the improvements associated with the proposed development, the peak flows discharging to each point of analysis decreases for the two (2) and ten (10) year design storms, modeled as 24-hour SCS Type III design storms, as compared to existing conditions. In addition, the proposed basin and outlet control structure have been designed to provide a fifty (50) percent reduction for the two (2) year and a twenty-five (25) percent reduction for the ten (10) year design storms for the project as a whole. Please refer to the appendix of this report for the hydrograph summary reports indicating same. Pre-Development and Post Development Peak Runoff Results Summary Point of Analysis A (Lot 21 Headwall) Pre-Development Design Undisturbed Areas Storm (CFS) 2 Year 0.33 10 Year 0.80 Pre-Development Disturbed Areas (CFS) 0.21 0.52 Point of Analysis B (Concrete Channel) Pre-Development Pre-Development Design Undisturbed Areas Disturbed Areas Storm (CFS) (CFS) 2 Year 1.17 0.36 10 Year 2.84 0.87 Aaron Friedman DEC# 5142-24-00053 Total Allowable Peak Flow Total Proposed Peak Flow (CFS) 0.54 1.32 0.37 0.87 Total Allowable Peak Flow Total Proposed Peak Flow (CFS) 1.53 3.71 1.23 3.48 March 2024 3