WATER BALANCE OF GLACIAL LAKES IN LANGTANG VALLEY, NEPAL HIMALAYA

It is widely assumed that retreat of glaciers in the Himalaya due to global warming will result in the filling of glacial lakes, which will increase the probability of glacial lake outburst floods (GLOFs). However, glacial lakes will not necessarily fill if they are sites of groundwater recharge. The objective of this study was to carry out the first measurement of the water balance of glacial lakes in the Himalaya in order to determine whether these lakes are sites of groundwater recharge or discharge. The study was carried out in June 2011 in the glacial lakes downstream from Eastern Lirung Glacier, Khyimjung Glacier, and Salbhachum Glacier in the Langtang Valley of Nepal Himalaya, about 8 km from the Tibetan border. For each glacial lake, stream discharge was measured in the outlet stream and multiple inlet streams using the USGS Pygmy Flowmeter or USGS Price Flowmeter, depending upon the stream velocity. The electrical conductivity was measured in each inlet and outlet and at ten locations in each lake as a proxy for total dissolved solids (TDS). The lake levels were monitored for periods ranging from four hours to four days in each lake. The above data are being combined with an empirical relationship between groundwater and inlet stream TDS for granitic and high-grade metamorphic terranes to determine the evaporation rate and the sign and magnitude of groundwater recharge / discharge. Results will be reported at the meeting.