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available, it is ordinarily best to select the most severe snowmelt flood of record and add a factor for deterltining a standard project flood, rather than to cOlRpute one from snowpack. However, it is pos- sible. but highly questionable, to derive snowpack from precipitation and teqlerature records. lhis is not reconnended, because precipita- tion records of snowfall are of poor quality. and losses during the accumulation season are difficult to estimate. Where the standard project flood is a rainflood with snowmelt contribution, a MOderate snowpack is ordinarily most critical. because deeper packs tend to retain or retard runoff from rain and decrease peak runoff rates. Depending on a nUlllber of factors such as rainfall temperatures and stol'lll duration. critical snowpack water equivalent at tlte start of .. standt.rd ~~jKt rai.1\flood ....1' _ ',,"x1.tel, \0 percent of the standard project slo". rainfall. In mountainous regions, deeper snowpack occurs at higher eleva- tions where melt and storlll temperatures are lower. and critical con- ditions are best represented at intenaediate levels where the greatest proportion of the flood runoff originates. Snowpack at the lower levels will then be depleted early in the storM or season, and some snowpack at the higher levels will reMIin after the end of the flood. Section 3.05. Standard project snOWlRelt Temperatures and other 1IN!1t factors during the snowmelt season must be selected with care for standard project use. beca.se, as explained earlier, maxi_ Hlt factors throughout the _It season are not necessarily the most critical. In many cases. it would be best to retain very low temperatures (and other melt factors) during the first quarter of the melt season and then to use maxi_ values during the remainder of the season. but care should be exercised so that proba- bilities of the components are not unreasonably compounded. 3-09