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• <br />Ucsign Critcri;� <br />CITY OF EVERETT STORMWATER MANAGEMENT MANUAL <br />� Design criteria fer nanow arca (ilicr strips are �he smne �s speufred 1or hasic Jilter sn�rrs. Hu�rcvt;, N:r <br />sizing of a narro�r arca filter sirip is based on thc lengih o` (lowpalh draining �o thc (ilter strip and thc <br />loncitudin�l slope of thc fiL•er strip i�sclf (parallel to the flc��p�th). <br />Sr�� 1 Dc tenninc ihe Icngth of Ihe flowpath timn the upstreain to d�c downs[ream edge oflhe impcn ioii. <br />aiea draining shce� ilnw to thc strip Komiallp this is thc �amc u the «idth of the pavcd area, but it thc sit� i; <br />sloped, ihc Oow p:��h ma�� bc lonecr than thc �vidth of Ihc impcn�ious arca. <br />� <br />�:��p 1 Calculatr, ihc longitudinal slope oClhe filter strip (along the direction ofunconcentraied ilow), <br />.3�ciagcd uecr ihe mtal �vidth of the filter sirip. Ihe minimum sizing slopc is 2 percent. If thc slope is !cs. <br />thvi Z perccnl, usc 2 pciccnt for sizing purpn<i�. TLc nuiximum allo�vablc fiLer stnp slopc is 20 perccnt. I; <br />,he slope exceeds 2i) pereent, the filter stnp musi be �tepped do�cn the slope so �hat the treatment areas <br />L•etween drop .�ectinns do net have a longitudinal slope great�r th;m 20 percent Drop sectioas must be <br />� piovidcd �cith crosion protation al thc base and (low sprcadcrs to rc-sprcad Oowc. Vcrtical drops ;�lon: t:i^ <br />>I��pe must not exceed 12 inche� in height. I(this i� not pos�ihle, a ditfierent treatment f,:cilitv must bc <br />ccicued. � <br />S�cp ± Sclect the appropriate filrer strip Icngth for thc ilo��path Icngth and filter slrip lom„iluJinal �!on� <br />i Steps 1 and 2 abo��e) from ihc �sph in Figure a.4. 1'hc filtcr strip must be designed ro procide d;is <br />n•:;nnnum length !, along tl�e cntirc itretth o( pa�cment drainmg into it. <br />i o use the graph Find the Icngth of the flowpalh on onc of thc curves (interpolate bah+cen cun c� .r, <br />necesssrv). hlove ;+long the cune to the point wL-erc the design longrtudinal slope of the filter ,trip is- <br />.:xis) is direcdy below. Rcad the fil�er st� i�? len�th on the yaxis �ehich cortesponds to the inter;ecNr,n <br />��oi,�I <br />vv,;� � 3 Soui�b, 4v.�lf �.;�c�.w_��P��fict.o. <br />'-a o --- -- ---- _ <br />� .s-''� � <br />i � o --- -- --- - ---- '" - <br />; -1----- __ � I � �.. <br />� F io„ �„u, ' " �� <br />. ,.. <br />_� = 30 fret i . �•, i� <br />` i . �- <br />,, " �, <br />- i n u - -x�'- -, ,' - -i '� = - --- �� <br />� � jf �- � �o r��•� <br />VI � � n/�/I �/ —/ <br />� .r _ - <br />� " •''%'' — ' ���`io r��� <br />LL � <br />5�) __..._ '__. .'l_'__"._. . . . <br />I J fl � �1' I ��___f__I � <br />T�-��—� <br />� ���� $';� 10".. 1590 :0".-0 <br />� 4iUrr Slrip tila�� <br />,An�,. minimum. n(lomaA(c fi6crslr�p Irngrh �s .: /ur� <br />I___ — .__—_ — — —_ <br />Figure 6.2 Filter Strip Lengths for Narrow Ri9ht-of•Way. <br />Vnlume lll - I'lor� Confrol and Ticafinent <br />G-J <br />�y <br />