Laserfiche WebLink
11-2 <br />• <br />• <br />Methods of Eatlmation <br />Reeional analysis <br />This method ie one of the moat useflil. for enowmelt floods. See Chapter ; <br />for details of the method. <br />Deeree~lav method, uneased watersheds <br />This method is widely used because of its adaptability to usual data <br />conditions. Similar methods going into more detail are available but <br />seldom applicable because of lack of required data. <br />The degree-day method uses the equation: <br />M=KD (l <br />where M = the watershed snowmelt in inches per day. <br />K = a constant that varies with watershed and climatic condition: <br />D = the number of degree-days for a given day. <br />A degree-day is a day with an average temperature one degree above 32o F. <br />Maximum and mininnim temperatures, ae found in "Climatological Data," are <br />averaged to get the daily average temperature. A day with an average of <br />40° F. gives eight degree-days; with an average of 51° F., nineteen <br />degree days. The general form of the method is given below. A corking <br />arrangement of the data is shown on table 11-1. In most cases the table <br />can be condensed. The steps in the method are: <br />1. Using precipitation stations or snow survey data, show either <br />(s) the total available eater equivalent at the beginning of <br />the melt season (table 11-1) or (b) the precipitation and the <br />eater equivalent by days (table 11-2). The first procedure ie <br />used where there is generally only one melt period per year; the <br />second, where melt periods occur intermittently through the <br />winter and spring. Water equivalent is the depth of water, in <br />inches, that results from melting a given depth of snow, and <br />it is dependent on both depth and density of snow. Snow <br />surveys give field determinations of water equivalents. Where <br />such surveys are not made, it is customary to use one-tenth of <br />the snow 3epth as the depth of eater equivalent. <br />For temperature stations in tie watershed, tabulate average <br />temperatures for the melt periods. (Note: ma,rim++m and <br />minimum values as given in "Climatological Data^ can be <br />averaged mentally to avoid tabulation of averages below <br />33° F.) <br />