CC PACKET 10131987 - Laserfiche WebLink

Home Browse Search

-2- E. Hydraulic calculations specifying outflow volumes and rates for various rainfall events . C .(2) Adjustments Where Parcel Runoff. Is' Significantly Different • ' From Land Use Standard Where the unit runoff generated by a parcel differs from the assigned amount for that land use catagory by more than 20% , the P•[•d•D. may adjust the oarcels storm water drainage fee in accor- dance with the following procedure : a. Calculation of unit runoff for the parcel shall be deter- mined. by the methods outlined in the Soil Conservation Service Technical Release No . 55 , utilizing a 2 " total rainfall amount and antecedant moisture condition II . b. If calculated unit runoff is shown to differ from the assigned amount for that land use catagory by 200 or more, the number of assigned P.EU ' s for-that parcel shall be adjusted. by multiplying by the ratio of the calculated unit runoff to the standard unit runoff. c. A parcels storm water drainage fee sha11 -be subject to increases as well as decreases by this procedure. d. Because single family. and duplex fees are not based upon actual carcel acreage , no adjustments for unit runoff dif- ferences will be :jade for those land uses . (3) Procedure for Calculltion of Credits for We Ponds A parcel may be credited for up to fifty (50t) percent of theO storm water .drainace fee for onsite measures which are owned and maintained by the applicant which effectively reduce the outflow of sediment/nutrients frcm the site . Credit percentage mall be cased on one-half of the actual percent-age of sediment removal efficiency , as determines ov the follo.aing procedure, rounded to the nearost 5% ; except that no credit will be given for sediment removal efficiencies of less than 20 . A. Calculation of Credits for Wet Ponds a. Determine total site acreage and percent of site that has an ir,;croved or impervious surface . b . Calculate the annual depth of runoff from the following ecuaticn : Dr = P ( . 75 Im+. 15) -5 . 234 ( .25- . 1875 Im) • 397 . fdhere D = annual depth of runof_ r in inches . I = '_=`t of site area, expressed as a 4`ci•-�al. m - p = ann - al uep:.h of pracI _pitation = 29 _. :cues . c. Caic-_ 'Iate annual vol=2 of runoff= _ acre- fee �Jan::ua1 = sito ac:-cage D 12 t d. Determine �• • pone ca_aac_ !ele.a outlet elevatic , ;n acr--=eet. e . Calculate capac_`_ i nflo'.a ratio (C77. ;h CI = e onci eapzc_ �• �• er . annual f . Read sediment removal `ff_cienc CJ 1• .-C,�� ro�lJ�.��1n J _ ra L 1 .