DEVELOPMENT OF LAKE HYDRODYNAMIC MODEL – CASE STUDIES

Abstract

The lakes and reservoirs serve as a major source of water for irrigation, hydropower generation, domestic and industrial water supply, flood control and draught mitigation, storage place for arresting the sediments, place for recharging the ground water table, in-land navigation, fishing, aquatic agriculture and also serve as place for recreation and tourism to the nearby settlements and dams store water when there is excess flow in river and releases it to downstream as and when the need arises in downstream reaches. In recent years due to rapid urbanization and industrialization, large quantity of domestic waste water, industrial effluents and solid waste generates and Lakes and reservoirs are treated as sink for disposal of domestic waste water and industrial effluents, solid waste disposal. Change in land use and interrupting activities of human beings in the upstream catchment area, larger volume of soil erosion takes place and deposits in lakes and reservoirs and the amount of siltation is increasing every year resulting in reduction of useful life of lakes & reservoirs and decrease in storage capacity resulting in pluvial and riverine flooding. Dams provide many benefits to human beings simultaneously the disaster caused by the dam failure creates damage higher than the damages caused by the other disaster all together. Dam breaks can be described as partial or catastrophic failure leading to uncontrolled release of enormous flood to the downstream. The high floods created by the dam break travel downstream of the dam creates damage to lives and infrastructure like road, bridges, railways and buildings along the reach of flood wave. Additional problems created by these type of extreme flooding includes deposition of sediment in to the flood affect areas. Flood creates many problems such as socio-civil conflicts, environmental problems and economic losses, the losses may be loss to human and animal life and economical loss to rebuild the affected location to its original scenario. Present trend of climatic change is increasing the probability and magnitude of floods. Most recently, Ministry of Environment and Forests, GOI implementing NLCP program for conservation and management of degraded and polluted lakes in urban and Semi-Urban area since lakes are the major source of accessible fresh water, they require sustainable, properly planned and scientific efforts to control the degradation and pollution and focusing more on on preparing emergency action plan by conducting dam breach study for better management of flood caused by the dam break conditions and to reduce the loss of life and property. xii In the present study, two case studies have been considered for development of latest versions of hydraulic model i.e., HEC-RAS ver. 5.0.1, this model is selected because of its freely availability, 2D applicability and requirement of less computation time for the analysis. Two-dimensional models are used since the width of flow is more and flow takes place both in two direction. The first study is to develop hydrodynamic model for of natural Dal lake in Srinagar city of Jammu & Kashmir state having surface area of 21.0 sq.kms. Bathymetry survey is carried out to understand the topography beneath the water surface and DEM and TIN generated from the bathymetry survey is used in developing lake hydrodynamic model and boundary conditions are provided in the model as input and since the study area comes under data scarce region runoff generated based on multi satellite precipitation technique using GPM is also tested for its applicability. Simulation is carried out for existing lake condition with observed inflow, inflow obtained from GPM precipitation data and 3 hypothetical scenarios created considering depositing dredged material of 3.5 m depth in lake as artificial island, adjacent area of lake and completely in dol demb area and fro the simulation hydraulic parameters such as water depth, water surface elevation, bed shear stress and velocity of flow are obtained. The second is developing hydrodynamic model for hypothetical dam break study of Tungabhadra reservoir which is second largest reservoir in Karnataka state and inundation mapping. Hypothetical scenario of dam break is created in the model for the reservoir volume condition and the unsteady dam breach study carried out till Rajolli barrage which is at 130 kms downstream of Tungabhadra reservoir. The results obtained from the simulation provides parameters such as Arrival time of flood, Duration of flood, Depth of flood and Velocity of flood flow, the result shows that about 321.12 sq,kms of agriculture area and 4.98 sq.kms of settlement area may submerge if the dam fails and also the world famous UNESCO recognized world heritage site may submerge partially alarming the severity of condition and shows the necessity of preparing emergency action plan for better management of flood.