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GRONBERG &ASSOCIATES, INC. <br /> SURVEYING.ENGINEERING AND LAND PLANNING <br /> 445 N.WILLOW DRIVE <br /> LONG LAKE,MINNESOTA 55336 <br /> 952-473-4141 <br /> Fax: 952-473-4435 <br /> PIRATES COVE <br /> DRAINAGE CALCULATIONS <br /> SEPTEMBER 23, 2013 <br /> Drainage area = 0.90±AC. <br /> Time of cont = 10 min. <br /> I 50 = 7.7 in/hr <br /> Runoff"C" factor = 0.5 <br /> Q = CIA = 0.5(7.7)(0.9) = 3.5 CFS <br /> Open channel flow calculations <br /> 2.0 foot berm with 3:1 sideslopes at 0.25' can handle 5.3 CFS which is greater than the <br /> 3.5 CFS for a 50 year storm. Velocity=7.75 Ft/sec. from MNDOT drainage manual, <br /> Chapter 6. Use 12"Class H riprap on filter blanket. <br /> Open-Channel Flow <br /> This calculator uses Chezy and Manning's formula to calculate the wetted perimeter, <br /> hydraulic radius,flow area,Chezy coefficient and flow velocity. <br /> For experimental values of Manning's n factor,click here <br /> Required Information <br /> Enter the Slope: 0.22 Enter the Channel Top 8 <br /> Width(ft): <br /> Enter the Channel Bottom2 Enter the Channel 1 <br /> Width(ft): Height(ft): <br /> Enter the Flow Depth(ft): 0.25 Enter then value: 0.03 <br /> Results <br /> The wetted perimeter is 3.5811 ft The flow is 5.3298,ft3/s <br /> The flow area is 0.6875 ft2 The flow is 2392.046 gal/min <br /> The hydraulic radius is 0.1919 ft The velocity is 7.75251 ftis <br /> The C value is 37.723( <br />