are two approaches for defining a computer model of a watershed; a lumped model, which does not take into account spatial variability of processes, and a model, which consider these. A lumped model is a simple approach and can be applied for basins that have a wide variety of physical features. However, the major limitation with these models is that it does not run beyond a single event (USACE, 1998). Distributed model on the other hand can be run for continuous simulation. In such models, the watershed is divided into subunits with variables being computed separately for each. This method of subdividing the basin is logical one, since in mountainous areas hydrological and meteorological conditions are typically related to elevation. SNOWMOD is a semi distributed hydrological model, which allows the basin to be divided into number of bands. The number depends upon the topographic relief of the basin. There is no specified criteria for slicing the basin in different altitudinal, but an altitude difference of about 500 to 600 m is considered appropriate for dividing the basin into different elevation bands. Precipitation input for each band is the sum of snowmelt and rainfall. Runoff for each band is computed from watershed runoff characteristics developed for that particular band. Stream flow for the whole basin is obtained by summing the runoff synthesized for all elevation bands. The program stores a value for each component of flow and each routing increment for every elevation band. It maintains an inventory of snow cover area, soil moisture, snow accumulation, and all other values required for making the computation for the next period. 5.3.2 Precipitation data and distribution The most challenging object of hydrological simulation of a mountain basin is the measurement of meteorological variables. The major problems posed in high mountain areas are the accessibility to the mountains on a continuous basis, the accuracy of measured meteorological variables, and the areal representativeness of measurements (Panagoulia, 1992). It has been observed that the most important factor in accurate estimation of snowmelt runoff is the assumptions of the spatial distribution and form of precipitation. In a distributed model, it is very essential to distinguish between rain and snow in each elevation band because these two form of precipitation behaves very differently in terms of contribution to the stream flow. Rainfall contributes faster to the stream flow whereas snowfall is stored in the basin until it melts. The form of precipitation is influenced by two factors; meteorological and topographical. Meteorological factors includes air temperature, lapse rate, wind etc and
are two approaches for defining a computer model of a watershed; a lumped model, which does not take into account spatial variability of processes, and a model, which consider these. A lumped model is a simple approach and can be applied for basins that have a wide variety of physical features. However, the major limitation with these models is that it does not run beyond a single event (USACE, 1998). Distributed model on the other hand can be run for continuous simulation. In such models, the watershed is divided into subunits with variables being computed separately for each. This method of subdividing the basin is logical one, since in mountainous areas hydrological and meteorological conditions are typically related to elevation. SNOWMOD is a semi distributed hydrological model, which allows the basin to be divided into number of bands. The number depends upon the topographic relief of the basin. There is no specified criteria for slicing the basin in different altitudinal, but an altitude difference of about 500 to 600 m is considered appropriate for dividing the basin into different elevation bands. Precipitation input for each band is the sum of snowmelt and rainfall. Runoff for each band is computed from watershed runoff characteristics developed for that particular band. Stream flow for the whole basin is obtained by summing the runoff synthesized for all elevation bands. The program stores a value for each component of flow and each routing increment for every elevation band. It maintains an inventory of snow cover area, soil moisture, snow accumulation, and all other values required for making the computation for the next period. 5.3.2 Precipitation data and distribution The most challenging object of hydrological simulation of a mountain basin is the measurement of meteorological variables. The major problems posed in high mountain areas are the accessibility to the mountains on a continuous basis, the accuracy of measured meteorological variables, and the areal representativeness of measurements (Panagoulia, 1992). It has been observed that the most important factor in accurate estimation of snowmelt runoff is the assumptions of the spatial distribution and form of precipitation. In a distributed model, it is very essential to distinguish between rain and snow in each elevation band because these two form of precipitation behaves very differently in terms of contribution to the stream flow. Rainfall contributes faster to the stream flow whereas snowfall is stored in the basin until it melts. The form of precipitation is influenced by two factors; meteorological and topographical. Meteorological factors includes air temperature, lapse rate, wind etc and
SKJ1_PDS_Report_Contents.docx