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DNR METRO REGION TEL:612-772-7977 Apr 12.96 15:36 No.015 P.03 <br />Apdll2.1996 <br />For your ialbnintion, I diMUMod • couple Other poMiUe ttonawtler nuMtenNiit ledniq^ wKA at <br />leeat raeideot of project tree. There eie tedmujiiee which mey not he feasihle for thi« iite» hul <br />which the city iwty went to keep in mind for i\iture prtyecta. <br />Wlwlvn^eerencw ’ the tope of hlufTr or ftcep rlopee, euch m ere often ceen eloog credsa or <br />ravinee, nmofTfixim (uHert or fiom the sttuctuie ita^ can become concentrated and cause <br />eroaionproUflnH. Hb^vever, in onkr to nuninuae these probkma, die gutters on the homes can <br />bedirsetedtotbeflonisofthestiiiMifes (ie., away fkom the steep slopes) and nm over a <br />vegetated area or thfou^ a longer, flatter area befbre entering die area with the steep slopes. <br />With smaller rains, most of the water ibould have an opportunity to infiltrate before leacUitg <br />^ steeper, erosive areas. I know, Ibrexamplei that Riltyr-Purgatoiy-Blufr Creek Waterriied <br />District has succestfliUy required this type of naiofr redirection for doveloprooots along stoqi <br />creek valleys. <br />b.Current development standards usually require ponding to detain the excess runoff produced <br />with a devdoptnent (over pie'pngect conditions), with the intent to keep tho rate of runoff and <br />the flooding elevations no hi^iw than before the devek^mont More recently, ponding for <br />piapaaea of improving the water quality of the water that leaves die site has been a requirement <br />While the impoitanoe of dm cunent design of ponds for water quality UPsatmeot a^ flooding <br />oonbol should not be minimiaod, it diould be lecoghiaed that even if this ponding is ptovidod <br />that the t^vc4umeofitaioffftqm the more impervious siteaii increased. Although the flows <br />nuty not be increased for the peak flood periods, the base flows or more “normal’' flows are <br />increased. This leads to changes in the character of atreamt or ravines, and can cause sorious <br />eroiioti md aedimenlilion probloma as well as loss of vegdatioa and habitat for fish or wikllifit <br />Therefbre, where it is ftatible, we would encourage ponding that is intended to hold dieexoess <br />iunttfflD>8it6 and not overflow to existing flowage systems (except for in extreme events, sudh <br />as the 100-year storm). <br />PlesK contact me at 772-7910 (772-7914 direct/voice mail) should you hava any questions ragarding these <br />comments. <br />Sificarely, <br />Ceil Strauss <br />Area Hydrologist <br />c: <br />• > « ■ <br />1 <br />r' \• • • I