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BMP C207: Check Dams <br />Purpose Conswction of small dams across a swalc or ditch reduccs thc ��clocity of <br />concentrated iloµ� and dissipates energy at the check dam. <br />Cnndifions uJU.�e Where temporary channels or pemianent channcls are not yet vegctated, <br />channcl lining is infcasible, and velecity chccks are required. <br />. Check dams may no� be placed in streams unless approeed by the State <br />Department of Fish and \Vildlife. Check danu may not be placed in <br />wctlands without appro��al from a perniitting agency. <br />• Check d�uns shall not be placed below the c�pettcd backwater from <br />any sahnonid bcaring «�aler bchvecn Octobcr I and May 31 to ensure <br />th�t thcre is no loss of high (low refugc habilat for ovenvintering <br />juvenilc salmonids and r,in�rgcnt salmonic' fry. <br />Dcsign und �Vhatcvcr m�tcrial is used, thc dam should forni a triangle whcn viewed <br />/nslal(utinn from the side. This pre��ents imdercuning as �cater flows ocer the (ace of <br />Specifieario�u the dam rather than falling directly onto the ditch bottom. <br />Check dams in associatinn ���ith sumps ���ork morc effceti��ely at slowing <br />flow and retaining sediment than jus� a check dam alone. A deep sump <br />should be provided immcdiately upstream of the check dam. <br />• In some cases, if carcfully located and designcd, check dams can <br />rcmain as pernianent installations with vcry minor rcgrading. They <br />maq bc IcR as cithcr spill�vays, in which casc accumulatcd sediment <br />�could be gr.ided and seeded, or ;;s check danu to prevent (unher <br />scdimcnt from Icavine thc sitc. <br />• Check dams can be constnicted of either rock or pea-gravcl filled bags. <br />Numcrous new producls arc also acailablc for this purpuse. Thcy tcnJ <br />to be rc-usable, quick and easy to install, effective, and cust eflicient. <br />. Chcck dams should bc placcd perpcndicular io thc Oow of watcr. <br />• The marimum spacing bctwcen the dams sh;ill be such that thc toe of <br />thc upslream dam is at thc samc cicvation as thc top of thc do�enstrcam <br />dam. <br />• Kecp the maximum hcigtu at 2 fcel :u the center of the dam. <br />. Kccp Uic ccntcr of thc chcck dam at least 12 inchcs Imvur th:m thc <br />outcr cdgcs at natur.il ground ckvatiun. <br />. Kccp thc sidc slopes of �hc chcek dam at 2: I or Oattcr. <br />• Kcy thc stonc into thc ditch b:+nks and cxtcnd il bcyond thc abutmcnts <br />a mininwm of 18 inches to aeoid washouts Gom ovcrtlow around thc <br />dam. <br />February 2005 Volume ll — Consfn�ction S(om�wafer Pollution P�evenfion 4-75 <br />