Laserfiche WebLink
Appendix A —Ordinances <br />Updated Storm Water Management Plan (SWMP) <br />City of Ramsey, Minnesota <br />precipitation. <br />Th SCS run ff curve numb r (CN) f r th xicting undev 1 pod ar as and the minimum CN'c f r <br />dev 1 p d c nditi ns shall b limit d t that ch wn in th f 11 wing tabl : <br />Maximum existing CN = 55 <br />Minimum residential devel pment CN = 65 <br />Minimum c mm rcial d v 1 pm nt CN — 90 <br />Minimum industrial devel pment CN = 90 <br />These maxima and minima are general in nature and typically apply t previ usly undevel ped land. <br />There will undoubtedly be cases where the existing land exists as pasture, wetlands, ungrazed meadows, <br />etc. which will require appr priate curve number adjustment in acc rdance with standard SCS TR 20 and <br />TR 55 methodology. <br />The post development runoff rates shall be controlled using infiltration basins, rain gardens or wet <br />retention basins. <br />W t ret nti n basins shall be d signed with dead ct rags v lumec in acs rdancc with the f 11 wing <br />(Wm. Walker Jr., 1987): <br />Given the following definitions: <br />Aw T tal wat rch d area in acr c. <br />Fi Rati f imp rvi us ar a t t tal wat rch d area. <br />CN Ar a w ightcd mean SCS cury number f r the p rvi uu <br />portion of tho watershed. <br />Calculate the maximum c it r tonti n as f 11 ws: <br />S = (1000/CN) - 10 <br />Calculate the run ff f r a 2 year st nn as f 11 ws: <br />(2.5 + 0.8S) <br />Calculate Permanent Pool Volume, V in acre feet as follows: <br />V = R*Aw/12 <br />1. The moan p nd d pth (p nd v lume/curfac area) ch uld be at 1 act 1 feet and n t m ro <br />Appendix A <br />February 20, 2015March 6, 2015 Page 74 <br />