Laserfiche WebLink
Storm Drainage Credits Policy cont. <br />2. Required information by applicant. <br />a. Complete site plan. <br />b. Area of site draining to each outlet paint. <br />c. ~ improved surface draining to each outlet point. <br />d. Specific details about outlet facility{s), <br />e. Calculation of peak outflow rate for 5-year and 100- <br />year design rainfall, using modified rational method <br />with tc of 34 min. or more. <br />3. Calculation Procedure. <br />a. Divide site into areas which drain to each drainage <br />outlet. <br />b. Select design rainfall. <br />c. Route rainfall through pond using modified rational <br />method, choose tc at least 30 min., and use "C" <br />Value from Rossmillers Equation Graph. Determine <br />peak outflow rate by summing all areas. <br />d. Check other rainfall events to determine "worst" <br />case. <br />e. Calculate pre-development rates for parcel using "C" <br />=.20 and assuming no on-site retention. <br />f. Tf peak 5-year outflow less than predevelopment--10~ <br />credit. Tf peak 100-year outflow less than <br />predevelopment--additional 15~ credit. <br />4. Exceptions, Special Cases. <br />a. Off-site water drains to outlet--owner has right to <br />drain this water through his site without detention. <br />Grant credits if he provides sufficient control for <br />his portion of the total flow. {This will require <br />applicant to provide information about watershed <br />beyond his parcel). <br />b. Outlet facility owned by city or others---No Credits. <br />{See Criteria B-1) <br />c. Shared Ponding Situation: A11 ponds have an outlet. <br />Tf outlet is on another's land, no credits {as in b) <br />above, except if the pond level is normally below <br />outlet, regpires historic documentation). Tn this <br />case, if no overflow occurs in a 5-year event, <br />parcel gets 10~ credit. Tf no overflow occurs in <br />100-year event, additional 15$ credit is given. <br />Water Quality Credits <br />1. Criteria: When a parcel provides on-site treatment <br />facilities which function to improve the quality of runoff <br />exiting the site, up to 50~ of the drainage fee may be credited <br />depending of treatment effectiveness. <br />2. Required information by applicant. <br />a. When treatment facility is a "wet" pond. <br />].. Area of site draining to pond and percent <br />impervious. <br />