Ground Penetrating Radar (GPR) Survey for Structural Design of Imja Lake Lowering for Community Based Flood and Glacial Lake Outburst Risk Reduction Project

The Community Based Flood and Glacial Lake Outburst Risk Reduction Project (CFGORRP) intendeds to reduce human and material losses from probable GLOF at Imja Lake, Solukhumbu District (5010 m) and 27 settlements in downstream in the valley. Based on the previous studies it is proposed that 3m reduction of water level in Imja Lake will reduce GLOF risk through construction of an open channel. To design such a structure, a detailed survey is required and as a part of the project the task of “Detailed Geophysical-GPR Investigation for Structural Design of Imja Lake Lowering” was awarded to the MEH Consultants Pvt. Ltd. Kathmandu.

For the subsurface data collection two geophysical methods were used; i.e. Electric Resistivity Tomography (ERT) and Ground Penetrating Radar (GPR). The later is done in two phases, in October 2014, a field recognisance survey was completed while field data collection was completed in the month of November, 2014. There were four best suitable open channel alignments identified after consultation with other thematic teams during field recognisance survey. Two locations of water seepage were also detected south-eastward of the Imja Khola (on the way to Amalapcha Pass) for the GPR survey in order to get the flow direction.

The GPR data is collected using GSSI SIR-3000 with two antennas of different frequency (100MHz and 200 or 270MHz) for better resolution up to the depth of 13m. A total of 289 longitudinal and transverse GPR profiles were collected during field data collection at pre-recognised five locations. This report provides the geo-environmental interpretation of collected GPR profiles and also correlates the result with available ERT data.