Siltation-induced lake deterioration and obligation of lake stewardship: bathymetric survey of Ramgarh Lake in Tarai region, India

Abstract Singh A, Maury C, Shiwani K, Sharma VN, Rana NK. 2026. Siltation-induced lake deterioration and obligation of lake stewardship: bathymetric survey of Ramgarh Lake in Tarai region, India. Lake Reserv Manag. 42:36–51. Lakes fed by surface runoff and altered by human-induced effluents such as sewage from direct or indirect sources can result in substantial deposition of silt into the underlying sediments. This study investigates siltation problems in Ramgarh Lake, which is nurtured by many rivers (Rapti, Ami, Rohini, Ghaghara) and small channels of the Himalayan foothills. The research aims to analyze the problem of siltation in Ramgarh Lake based on the measurements of silt thickness determined from the bathymetric survey. Ramgarh Lake is situated in an urban area with a tray-like bottom for water storage. In 1998, the maximum depth of the lake was 4.5 m. In 2019 the depth was only 2.56 m, a reduction of 2 m recorded across 21 yr. As of 2019, 342 m3 of silt is deposited on the floor of the lake bed with 1–1.5 m thickness. The lake’s total area in 1922 was 1098 ha, which decreased by 390 ha across 97 yr (1922–2019). In total, 12 sewage outfalls have been identified. Concentrations of phosphorus and nitrate in the water column increased by 3 and 2 orders of magnitude across 50 yr (1969–2019), respectively. Both dredging and reduced sewage discharge are required to rejuvenate the health of Ramgarh Lake’s ecosystem.