RN-46 : Snowmelt processes

Abstract

The accurate forecasting of the volume of snowmelt runoff likely to occur is of great importance for water resources management, especially to those responsible for operation of multipurpose reservoirs. [he estimation of snowmelt is needed to release the water from reservoirs for hydroelectric power generation, irrigation, municipal use and flood control.

Snowmelt is an overall result of the different heat transfer processes to the snowpack. The sources of heat necessary to melt snow are radiant heat from sun (ii) latent heat of vaporization released by condensation of water and (iii) the heat by conduction from the environment contact with the snow such as from the air, the ground and rainfall. Radiation and turbulent heat transfer processes (sensible and latent heat) are of of primary importance in producing snow-melt. The ground heat flux been observed to be a negligible component in daily totals of energy lance of a snowpack in comparison to the radiation and turbulent heat fluxes. However, the contribution of ground heat flux is found to be significant when melt season as a whole is considered. The heat flux through warm rain on isothermal snowpack at freezing temperatures causes a lot of melt. The Quantity of snowmelt is dependant upon the condition of the snow pack and its environment. It is quite possible for a snowpack to gain heat through one process and loose heat through another.

The determination of snowmelt is quite complex and certain simplifying assumptions are used in practical computation of snowmelt The relative importance of the various heat transfer processes involved in the melting of snowpack varies with time and locale. As a result of this variation, no single method or index for computing snowmelt is found universally applicable to all areas and all times of the year. The temperature index method is mostly used for this purpose. The variations of temperature and humidity could be taken into account by theoretical elevation lapse rate formula. The coefficients of snowmelt by experimental evaluation in terms of appropriate meteorological parameters for each of the several processes of heat transfer to snowpack are yet to be determined in India.