Laserfiche WebLink
$~rfoce Water Balance -The surface water balance is stated as <br />a.. <br />where I = infiltration, P = precipitation, M = snowmelt, and Q =overland runoff. The <br />required values for P + M are Those in the right hand column of Table 2.5-20. <br />Accurate estimates of mean monthly overland runoff are difficult to make. A <br />procedure that yields reasonable values is <br />,:.,., <br />.~.Qi = Ri N L rk (Pk - 0.25)2 = Ri N E qk <br />s ' <br />9. k=1 Pk 0.85 k=1 <br />~, <br />~... . <br />where <br />Oi =mean runoff for month i <br />Ri =distribution coefficient based upon the time distribution of available <br />precipitation <br />N =mean number of daily precipitation events <br />rk =relative frequency of precipitation events in the k ih range <br />• Pk = mean of precipitation in k th range <br />S =SCS potential maximum retention <br />Precipitation intervals of 0.5 inches were selected for the computations and <br />the relative frequency of storms with rnagnitvdes falling in each interval wos <br />calculated. This was occomplished by plotting the probability of occurrence for <br />several 24 hour storms and computing, therefrom, the probability of storms falling <br />within the selected intervals. These computations were made only for rainfall events <br />~ and the probabilities were obtained from the recurrence interval of 24 hour storms <br />for Routt County as given in the Rainfall Frequency Atlas of the United States. The <br />~ selected precipitation intervals, the mean precipitation of each interval (Pk) and the <br />~elative frequency (rk) are given in the first three columns of Table 2.5-22. <br />~'' The next step was to estimate o value for the potential maximum retention, <br />S. This was occomplished by calculating S from the soil conservation service (SCS) <br />curve number estimated to be"'fi9W~foF:~{apRie~re„aRt~..~pnge:lent}--irr~fYttr'fiydrofogic <br />condition. The. ntial maximum retention obtained in this manner isb+F9Miv~efl~s. A <br />curve number Qf 5 b beMt~-~a~1s,Ig,~Ayg7pge fof,,J~a, ~JircB•~~a: Mdne~ <br />. 'a,. <br />Existing spoils oi~~~~poriion of the West Ridge which have not been graded or <br />2.5-82 <br />