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K:\01904-610\Admin\Docs\2020 Update\Appendix B - References\Credit Valuation Guide_20200611.docx Value of One Credit: · The average annual rainfall in Hugo (1980-2009) during the growing season is 23.51 inches. Non-Linear Projects · Per Rice Creek Watershed District rules and MPCA performance goals (for non-linear projects), BMPs should be designed to capture 1.1” of runoff from impervious surfaces1. It is assumed that rainfall depths over 1.1” would not be captured and wouldn’t be used for irrigation. Based on rainfall analysis from RCWD approximately 20.38” of rainfall annually could be captured · Assuming one acre of impervious surface, the amount of runoff that will be captured and infiltrated each year is as follows: (1) 1 ∗. ∗ = 1.698 /! · Therefore, 1.698 credits are generated from capturing the runoff of one new acre of impervious surface. · One volume reduction credit is sufficient to cover a non-linear project of 25,650 ft2 of new impervious surface. · One credit is equal to 1 acre-foot of infiltration per year. Equivalence of One Credit: · The BMP size requirements for one acre of new or reconstructed impervious surfaces are as follows: (2) 1 ∗ 1.1 "#ℎ% ∗ = 0.0917 ( )*+ ,(-./ · Capturing runoff from one acre of impervious surface generates 1.698 credits, and 1 acre of new or reconstructed impervious requires 0.0917 acre feet of BMP capacity. Therefore, the number of credits required in terms of impervious area can be determined: (3) .01 234.50 6 = 7 234 6 1 8" = 0.054 )*+ · The amount of impervious surface that requires a 0.0540 acre-foot (2,352 ft3) BMP can be determined using the 1.1” standard for non-linear projects. Linear Projects · The same calculations can be done for public linear projects where RCWD requirements state 1.0” of runoff from new impervious surfaces must be captured. Rainfall analysis from RCWD show 19.87” of rainfall annually could be captured.