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• <br />CITY OF EVERETT STORMWATER MANAGEMENT MANUAL <br />Ucsign Crilcria <br />Designeritcriafornarro�vareafiL'crstrips:irethec�rrr��,zss��ecfedjorhasicliltersny�s- Ho���c��cr.tiie <br />sizing o`a narrow area filtcr strip is b.ucd on thc Icngih of Oowpnth draining to thc filtcr strip and thc <br />longi�udinal slope ut the filter strip itself (parallcl to thc flo�vpath). <br />S'rcp ! Detcrmine the Icr,gth of thc (lo��path from thc upstrr.un to Qic do�cnsveam edgc of the imper��io,:s <br />�iea draining sheet flow �o Ihe stnp. Nonnally this is the same .�s the width of tlie paved area, but if the �i!c i: <br />sloped, the flow path m�y br longer ihan the width of lhc impen�ious area. <br />� <br />.Qrp 2 Calculate the longitudinal slope ot ihe filter sirip (:ilong tlu direction of unconcentraied Oow), <br />:+veiagcd over the taal widlh ot �he filtcr strip. 1he minimum sizing slope is 2 percent lf the slope is Ics� <br />ihan 2 percent, use 2 perccnt for sivng purposcs. Thc maximum allu�vzble Gher strip clope is 20 perccnt L' <br />thc slope ercecds 20 pereent, the filter strip must he stepped down ihe slopc so that thc treatment are�u <br />benveen drop sections do not have a longitudinal slope grater than 20 percent. Drop sections must bc <br />� ;�: o� ided �vith erosion protection at the base and (lo�r spreaders to re-sprcad Ilows. Venical drops alone tl;r <br />slop� must not excced 12 inches in hcirJ�t. If �his is r,ot possible, a different treatment faciliry must bc <br />sclected. <br />Stup ? Sclect the appropriatc filtcr strip length for the �lo��path Icngtit and filtcr strip IongiWd;ual sb���e <br />(S!cps 1 e�nd 2 above) from thc graph in I�igurc a.4. Thc filter strip must be designed �o provide thic <br />ininimum lenrth L along the eniire stre;ch of pavement di,�ining into it. <br />� l o ic t rhe groph: Find Ihe lenglh o(�he ilowpath on one o1 the aines (intcrpolate bchrcen cunr� ,i: <br />i;ccess;iq'). f�fove alaig �hc cmve to thc point ��hcre the desi�i longitudinal slope of thc tilicr s� ip /�- <br />.i�is) is directly belo�v. Rcad the filtcr strip lengih on the yazis �chich corresponds to the interscaion <br />,^.:�int <br />U. �,� � 3 4 C. e,� �.� 1� q�e.c�, <br />�: <br />• <br />n <br />.. <br />❑ <br />zo.o <br />I50 <br />t <br />Fi <br />� <br />= ino <br />� <br />�`n <br />W <br />tn <br />Plowpalh <br />= 70 (ccl I ., <br />0 o i—.—: -� <br />o^� 2°�� <br />� <br />- - ----i � <br />_ __ _. ---- — -- <br />� �� I zo rc�� <br />,�-. <br />I� —�' IOfccl I <br />/ <br />S w��A le� Strip c� �otk- <br />c.n� s� t�... I�.� �f - �o �c To A.1 <br />- ---�---,-�, <br />s^o � io^o ise� zm� <br />Pil(cr Slrip tiln�x <br />,A'o�e mir,:n:imiallorc��hlcJ�llrrstrrploir�iri.rJ�i�rf <br />Figure 6.2 Filter Strip Lengths for Narrow Right-of-Way. <br />Volume lll — Flo�;� Conlrol a�;d Trea(ment <br />6-4 <br />