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C7 <br />CITY OF EVERETT STORMWATER MANAGEMENT MANUAL <br />Ucsign Critcria <br />� Dcsign criteri� for r�nuw �ice filic; snips aie �hc �omr ;:s _��:, i/i�.�i vi�r l��c�r, _!Iit�•r ur-rps. Ho�ceeir, tne <br />cizing o(a narrow area ;iltcr strip is bascJ on ihc lengtf; of io«p�th draining to Uic filtcr strip and ;Lr <br />longitudin�l slopc of the filter su ip iUclf (par�llel io the (lo��path) <br />Srep 1 netermine d;c Icngth of the flo�tip�th irom the upstream �o the do�+Tistrcam cdge o( the impen ious <br />aiea draining sheM tlow to Ihc qnp. Nonnally Ihis is the samc as ihc wid;h of Ihc pavcd arca, but if ihc �ite !� <br />sloped, ihe flow path may bc longer than the �� iAth of th� impen ious arca. <br />� <br />Srep Z Calculate thc longitudinal slope of the filler slrip (along the direction of unconcentrated (low�, <br />.i�ciaged o�•cr thc tutal width of ihc filtcr ctrip. The minimum sizing slopc is 2 percent Ifthe slope is Ies, <br />�han 2 percen�, ase 2 percent fcir si zing pur�±oses. �I�I:c maximum allowable filter stnp slupe is �0 percr��t. ;. <br />the slope e�ceeds 20 prrceN, the tilter strip musi be }tepped do���i ihe slope so that the treatmem are;s <br />Le��vicen drop sections do not ha�e a Imieitudin�il slope gre,vcr tiian 20 percent. Drop scctiont mu�t he <br />� piovided with crosion protection at the base vid (lo�� sprcaders lo re-spread tlo�s5. Vertical dre��� ;+lo;,e t!., <br />�lope must not excecd 12 inches in height If �his is not possible, a dif(eizm treatment facility mu�i h: <br />,clectcA. <br />.`rcp 3� Select thc appropriate filler s(rip leng�h for �he ilo�epath length and filter urip longitedin,ii zlnp� <br />�Steps i und 2 abovc) from thc graph in Figurc 4.4. Thc filt:r sirip musi hc dcsigncd to providc this <br />minimmn Iength l. along fhe entire suetch of pa�emem draining into it. <br />� fn iae rhz groph Fmd the Ieneth of the flo�cpath on ore of th> curves (interpol:rte bchteen curves .�, <br />necescan�). �1nve alonr the curve to the point ��here the desi�,m Iongitudinal slope of ihe tiher siri� 1 s- <br />.r.i�i is direcily bdo���. Read Il;e f Iter strip lene.lh on ihe y•asis whieh cu�responds to the inieneccion <br />p��ir�t <br />I�'� c. i., 'O �'� v C Ig I S � 2 <br />� <br />u <br />I2nuT-- --� <br />IS.O <br />u <br />Y� <br />� <br />J 100 <br />c <br />� <br />� <br />5p <br />Flowpath <br />3n r��c <br />' ��SP�.,�.4I��� <br />_ � 10 fee� <br />- 1-=-- -- - --- <br />T--•--�� � I I <br />00 � b�a <br />—r-r.�—i <br />Q°.� So�a 10",n �$",o ?0^h <br />Filtcr Sirip 51opc <br />��'nro nnmmum alloH»ble J+/rer str�p /enFth is e J,•� � <br />Figure 6.2 Filter Strip Lengths for Narrow Right�of•Way. <br />Volume fll — Flo�a� Confrol and 1 reatmen� <br />5-a <br />I� <br />