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COLORADO LEGACY LAND <br /> ATTACHMENT Z. HYDROLOGY FOR 4.1—ACRE AREA ABOVE ACCESS ROAD <br /> Rational Equation <br /> Qp= CIA <br /> QP= peak runoff rate(cfs) <br /> C= the runoff coefficient(dimensionless) <br /> I= the average intensity of rainfall for a duration equal to the t,(in/hr) <br /> A= the size of the drainage area(acres) <br /> t�= the time of concentration(min) <br /> t�= t;+tt <br /> t;= overland(initial)flow time(min) <br /> tt= channelized flow time(min) <br /> t;= [0.395*1.1-05)(Li)1/21/5o.33 tt= Lt/[60KS"i/z]=Lt/[60Vt] <br /> Cs= runoff coefficient for 5-yr frequency(Table 6-4) LC= waterway length(ft) <br /> L = Length of overland flow So= waterway slope(ft/ft) <br /> S"= average slope along the overland flow path(ft/ft) Vt= travel time velocity(ft/sec) <br /> K= NRCS conveyance factor(Table 6-2) <br /> Imperviousness= 2% (Table 6-3;"Undeveloped Areas,historic flow analysis) <br /> C5= 0.82*i+0.035 4= 108 <br /> = 0.05 So= 0.1 <br /> Li= 1029 K= 15 <br /> S"= 0.45 <br /> t;= 16.0 tt= 0.4 <br /> t,= 16.3 minutes <br /> Return Area Q <br /> C 15-min Intensity <br /> Period (ac) (cfs) <br /> 2-yr 0.01 2.17 4.1 0.09 <br /> 5-yr 0.05 3.03 4.1 0.64 <br /> 10-yr 0.15 3.58 4.1 2.15 <br /> 50-yr 0.40 4.95 4.1 1 8.17 <br /> 100-yr 0.49 5.65 4.1 1 11.40 <br /> PAGE 8 OF 10 <br />