Investigation and Treatment of Buried Channels in River Valley Projects in Himalayas

Buried channel is a geomorphic feature often found along river valleys in Himalayas. It is a remnant of an inactive river channel filled or buried by unconsolidated/semi-consolidated sediments which may act as pathways for water transmission. In such condition, if a storage dam or a diversion structure is constructed in the vicinity without properly treating the buried channel at its inlet itself (towards reservoir), the fluctuation in water level and saturation during reservoir filling may cause lot of damages in the downstream. Therefore, it is extremely important to identify the inlet/outlet and the extent of the buried channel at the investigation stage itself so that suitable geotechnical solutions can be suggested at design stage itself. NHPC Limited, India has a lingering legacy of successful negotiation of deep buried channels/fossil valleys at many dam and diversion projects. The paper highlights the methods and techniques used in few projects for prognosis of the buried channel deciphered in the vicinity of dam sites and the extensive treatment carried out to control seepage. It also elaborates how the experience gained from the above projects has been used effectively in finalizing methodology to control seepage through a buried channel in a proposed Hydropower Project.