Peak Discharge Clause Samples
Peak Discharge. 1. By design, BMPs shall be employed to maintain or reduce the peak runoff discharge rates, to the maximum extent practicable, as compared to pre- development conditions for the 2-year, 10-year, 25-year and 100-year 24-hour design storm applicable to the post-construction site.
2. Separate subcatchments shall be used to model pervious and impervious areas within a watershed areas located in the development site, when calculating runoff volumes and peak discharge rates.
3. Pre-development conditions shall assume “good hydrologic conditions” for appropriate land covers as identified in TR-55 or an equivalent methodology. The meaning of “hydrologic soil group” and “runoff curve number” are as determined in TR-55. However, when pre-development land cover is cropland, rather than using TR-55 values for cropland, the runoff curve numbers in Table 1 shall be used. Hydrologic Soil Group A B C D Runoff Curve Number 56 70 79 83 4. Storm water discharge from a newly developed site must have a stable outlet capable of carrying the design flow at velocities that are non-erosive to the outlet and receiving streams.
Peak Discharge. (Amended 7/26/2021)
1. By design, BMPs shall be employed to maintain or reduce the 1-year, 24- hour; the 2-year, 24-hour; the 10-year, 24-hour; the 25-year, 24-hour; and the 100-year, 24 hour post-construction peak runoff discharge rates to the 1-year, 24-hour; the 2-year, 24-hour; the 10-year, 24-hour; the 25- year, 24-hour; and the 100-year, 24-hour pre-development peak runoff discharge rates respectively, or to the maximum extent practicable. The runoff curve numbers in Table 2. shall be used to represent the actual pre-development conditions. Peak discharges shall be calculated using TR-55 runoff curve number methodology, Atlas 14 precipitation depths, and the appropriate NRCS Wisconsin MSE3 or MSE4 precipitation distribution. On a case-by-case basis, the Village Engineer may allow the use of TP-40 precipitation depths and the Type II distribution. Runoff Curve Number Hydrologic Soil Group A B C D Woodland 30 55 70 77 Grassland 39 61 71 78 Cropland 55 69 78 83 2. This subsection of the Chapter does not apply to any of the following:
a. A post-construction site where the discharge is directly into a lake over 5,000 acres or a stream or river segment draining more than 500 square miles.
b. Except as provided under Section 8.07(3), a redevelopment post- construction site.
c. An in-fill development site less than 5 acres.