Rectangular Desilting Basin as Upstream Physical Barrier for Interception of Turbidity Causing Fine-grained Particles of Mineral Origine Carried Along with Surface Runoff Feeding the Lake: A Case Study of Jait Sagar Lake, Bundi, Rajasthan, India

Abstract

Lakes in hot semi-arid climatic condition are susceptible to turbidity and degraded water quality parameters, due to routine influx of fine-grained mineral particles along with surface runoff contributing to the contained waters in the lakes. Turbidity causing mineral particles originate as a result of fluvial erosion of exposed and often weathered rocky outcrops and unconsolidated sediments within the catchment of the lake; that gets transported to the lake in suspended state along with surface runoff generated after events of torrential rains. These, turbidity causing suspended particles primarily consist of very fine-grained mineral particles comprising of clay, silt, salts, non-metallic and metallic minerals along with some debris of organic origine; together they provided nourishment supporting the growth of autotrophic microorganism (phytoplankton and filamentous algae) in the contained waters of the lake. Fine-grained mineral particles, autotrophic microorganisms and gaseous microbubble collectively cause the actual turbidity in the contained waters of the lake in a state of colloidal equilibrium. This research paper attempts to address the issue of turbidity due to continuous influx of fine-grained mineral particles along with surface runoff entering in the contained waters of the lake, by installation of an upstream physical barrier in the streamlet supplying surface runoff to the lake; as a case study for Jait Sagar Lake, Bundi, Rajasthan, India. The paper presents an easy to construct, customizable design of rectangular desilting basin with baffling structure as an upstream physical barrier, for the envisaged interception of suspended mineral particles flowing along with runoff, prior to their entry into the lake; that is achieved by reducing the flow velocity of runoff. The paper also examines the functional efficiency of rectangular desilting basin by sampling and measurement of post intervention turbidity (in NTU) for two seasons (pre-monsoon and post monsoon) and its comparison with pre-intervention (baseline) turbidity of two seasons at same sampling locations. The outcome of this comparison has provided scientific evidence in favour of functional efficiency of this engineering intervention, that has reduced overall turbidity in contained waters of the lake in excess of 50% for both the seasons (pre-monsoon and post-monsoon season). This design of rectangular desilting basin with baffling structures can be replicated in many other lakes/reservoirs situated in arid and semi-arid regions across the globe for successful interception of suspended mineral particles from the runoff, well-before their entry in the contained waters of the lakes and reservoirs.