Some hydrologic aspects of snowmelt runoff under summer conditions, in the Barpu glacier basin, Central Karakoram, Himalaya, northern Pakistan

Snow and ice in high mountains represent and important water resource in many parts of the world, especially the dry continental interior of Central Asia. In the Northern Areas of Pakistan, mountain ranges are the primary sources of annually renewed water supplies. They give rise to rivers which are the only significant, sustainable source of fresh water. The Indus basin is drained by the river Indus and its major tributaries, the Kabul, Jhelum, Chanab, Ravi and Sutlej. Snowmelt contributes about 70 percent to the annual flow of these rivers, but is not timed to meet the requirements for crop production, hydroelectric power generation, and other multi-purpose objectives. This situation has led to the development of an irrigation economy that requires effective management of the water resources in these drainage basins. A basic understanding of snow distribution and its contribution to streamflow is needed for effective prediction of flow events. Snowfields between elevation of 2,500 m and 5,500 m constitute a small percentage of the area contributing to runoff in the Central Karakoram, Northern Pakistan. However, they are considered to have a higher water content, and to produce runoff for longer periods than snowpacks at lower elevations. The melt regime of a basin may be better understood by examining snowpack recession and runoff hydrograph. Identifying the time of daily peak flow, snow cover/runoff relation and its variation through the season may prove helpful to flow modelling. This study involved taking hydrological and meteorological observations in two small snow-fed basins having different aspects in the basin of Barpu Glacier in the Central Karakoram range of the Himalaya in Pakistan. The conservational network was designed to cover a range of elevations within the experimental basins. This type of network is essential to account for the effects of typography and microclimate on snow hydrology. Patterns of snowmelt runoff examined in two contrasting environments within the Barpu Glacier Basin suggest that topography influences the rate of spring snowmelt in several ways. Aspect and degree of slope modify the winter and spring snowpack by causing unequal rates of ablation. Relief creates an unequal distribution of snow which in turn causes areal variation in the volume of spring melt. Normal linear and curvilinear multiple regression anaylsis is an appropriate method for studying of hydrologic relationships. Snow cover area and subsequent snowmelt runoff can be correlated to estimate streamflow. For a particular catchment, the relationship between area of snow-cover and snowmelt runoff appears to depend on morphometrical factors such as elevation, aspect, slope, and drainage density. However, for each basin a different empirical relation exists between snow cover and snow-melt runoff. The logarithmic relationships between snow-cover and snowmelt runoff indicates a substantial increase in snowdepth with increasing elevation. The results also suggest that mean temperature is the best single indicator of runoff variation. Meteorological observations over a range of elevations provide valuable information concerning the altitudinal gradient. The concluding chapter reviews some of the practical and technical implications of the work for hydrological investigations in the Upper Indus Basin. It suggests what can (and cannot) be learned from this type of study in relation to macroscale water resource assessment and forecasting