N.H. Admin. Code § Env-Wq 1511.06

Current through Register No. 45, November 7, 2024

Section Env-Wq 1511.06 - Calculations for Stormwater Drainage

(a) Hydrologic analysis shall be performed to demonstrate that the requirements of Env-Wq 1507.05 and Env-Wq 1507.06 are met, unless all of the following criteria are met:

(1) Land slopes are 5% or less;

(2) Conditions for sheet flow, as described by Env-Wq 1511.05, will exist for the full solar array;

(3) The existing ground cover is open space, pasture, grassland, or range, as described by NRCS; and

(4) Gravel or paved access roads and other impervious areas, other than solar panels, account for less than 2% of the area of disturbance.

(b) Land covers to be used for the existing condition shall be woods or meadow, in good condition, as defined in NRCS "National Engineering Handbook", Part 630, Hydrology, or Win TR-20, version 3.20.0000, unless photographic evidence is submitted to support an alternative land cover;

(c) Land cover to be used in the proposed condition shall be "pasture", in good condition, as defined by NRCS per the references in (b) above;

(d) Subject to (a) above, a hydrologic analysis of the proposed condition shall be performed by assigning a curve number of 98 to the area of the panels and the area beneath the panels, except as otherwise allowed below:

(1) For the areas of the solar array where post-development land slopes are equal to or less than 5%:

a. If runoff from panels will discharge as sheet flow pursuant to Env-Wq 1511.05, the impervious area of the panels does not need to be included in the calculation of the curve number; or

b. If runoff from panels will not discharge as sheet flow pursuant to Env-Wq 1511.05, the curve number shall be calculated in accordance with Equation 9-2 of the National Engineering Handbook, Part 630, Hydrology; and

(2) For the areas of the solar array where land slopes are greater than 5% and less than 8% for hydrologic soil group B, C, and D soils, and less than 15% for hydrologic soil group A soils, and runoff from panels will discharge as sheet flow pursuant to Env-Wq 1511.04, the curve number shall be calculated in accordance with Equation 9-2 of the National Engineering Handbook, Part 630, Hydrology.

N.H. Admin. Code § Env-Wq 1511.06

Derived from Number 41, Filed October 12, 2023, Proposed by #13758, Effective 9/28/2023, Expires 9/28/2033 (see Revision Note #4 at chapter heading for Env-Wq 1500).