DAM SAFETY ANALYSIS OF MATATILA DAM FROM HYDROLOGIC AND HYDRAULIC CONSIDERATIONS

Abstract

Matatila Dam which is located on Betwa river of Ganga basin has faced the problem of flood passing through the spillway safely in the recent past. The hydrology of the Matatila dam was studied during the 1950’s. It has been observed that the design flood calculations were first made based on empirical formula and later on frequency analysis. The decision on spillway capacity of a dam, including the decision of its surcharge storage, freeboard etc., constitutes an important hydrologic and engineering decision affecting safety of the dams. BIS published the guidelines for fixing of spillway capacity, BIS 11223-1985, which defines the Design Flood, by classifying the safety of dams as small, intermediate and large. As per the guidelines the Design flood for Matatila dams falls in the category of PMF, which necessitates the review of hydrology of the dam. The hydrology of a particular basin or project undergoes tremendous changes due to certain factors such as climate change, urbanization, deforestation, soil erosion, heavy spell of short duration rainfall etc. Nearly after 20 years of Matatila dam, Rajghat dam was planned and constructed which is 50 km upstream of the Matatila dam. Thus, it may be necessary to assess the revised design flood and to analyse various scenarios for regulation of the reservoir for the safety of dam. Considering the state-of-the-art technology or methods of analysis and the data availability for rainfall and discharge in recent years, hydrologic modelling in large scale is possible. Modern methods of flood estimation like meteorological-physical methods and availability of mathematical modelling software like ARC-GIS, HEC-HMS may be used for quite accurate estimation of the design flood. In this study the design floods for both dams have been assessed using the latest techniques available viz. quasi distributed modelling using hydro-meteorological approach. The flood estimation reports and PMP atlas for Ganga basin published by CWC, which provide the Synthetic Unit Hydrographs of the subzone, are based on the record of the past storms and isohyets occurred over the catchment, Moisture Adjustment Factors etc. These have been used in this study. ARC-GIS have been used for catchment delineation using the Digital Elevation Model. HEC-HMS model has been used for convolution of lumped response at the outlet of Page xiii of 103 each sub-basin and the reservoir routing and channel routing the lumped responses through the reservoirs and a network of channels/rivers. The results of the model have shown that, compared to the original design flood, the revised design flood at Matatila dam has been exceeded by 46 percent. In this context, the upstream Rajghat reservoir, which is of higher capacity, may be regulated to improve the safety of downstream Matatila dam and it has been studied by generating various scenarios. Five scenarios have been generated by utilising the available freeboard and reducing the spillway capacity. A final design flood has been arrived at 29068 cumec in this study which exceeds the original flood by 24 percent only. It has been recommended that along with the specified rule curve for reservoir operation at Rajghat dam, further suitable structural and/or non-structural measures be adopted to enhance the safety of Matatila Dam.