JMA02P003 262 270 Main Street Development Stormwater Management Report

3.4 Time of Concentration Modifications Decreasing a site’s time of concentration (Tc) can lead directly to increased site runoff rates which, in turn, can create new and/or aggravate existing erosion and flooding problems downstream. This section of the checklist helps identify those nonstructural strategies and LID-BMPs that have been incorporated into the proposed development’s design to effectively minimize such Tc decreases. When reviewing Tc modification strategies, it is important to remember that a drainage area’s Tc should reflect the general conditions throughout the area. As a result, Tc modifications must generally be applied throughout a drainage area, not just along a specific Tc route. A. Specify percentage of site’s total stormwater conveyance system length that will be: Storm sewer: Vegetated swale: Natural channel: Stormwater management facility: Other: Note: the total length of the stormwater conveyance system should be measured from the site’s downstream property line to the downstream limit of sheet flow at the system’s headwaters. B. What design criteria and/or site changes would be required to reduce the storm sewer percentages and increase the vegetated swale and natural channel percentages in A above? C. In conveyance system subareas that have overland or sheet flow over impervious surfaces or turf grass, what practical and effective site changes can be made to: Decrease overland flow slope: Increase overland flow roughness: New Jersey Stormwater BMP Manual • Appendix A: Low Impact Development Checklist • February 2004 • Page A-10