Preparation of EAP for Ukai Dam using 1D/2D coupled hydrodynamic modelling and Google Earth image

Ukai is the second largest masonry gravity Dam after Sardar Sarovar Dam in Gujarat. Surat, the diamond hub of India and 2nd largest city of Gujarat state is situated 100 km downstream (D/S) of Ukai dam and 19.4 km upstream (U/S) from Arabian Sea. Surat city experienced the catastrophic flood in 1933, 1959, 1968, 1970, 1994, 1998, 2006 and 2013. It is estimated that the single flood event during August 7-14, 2006 in Surat and Hazira twin-city, caused a heavy damage and low lying areas such as Adajan and Rander of Surat were under submergence up to 4-5 m during flood in the year 2006, resulted in the death of 300 people and property damage worth INR 21000/- crores. The peak discharge of 25,768 m³/s recorded was the highest in the history and was responsible for disastrous flood in Surat city. To prevent such type of catastrophic situation in future Surat Irrigation Circle (SIC) has suggested the Levees (structural measures) expansion to increase the discharge carrying capacity near Surat city and reduce the flood inundation in future. To estimate the flood inundation under the levees condition and prepare the Inundation map as per the guideline of Emergency Action Plans (EAP) for Dams, a study has carried out using the 1D/2D coupled HECRAS based hydrodynamic model. 299 surveyed cross sections after 2006 flood have been considered for 1D modelling whereas 30 m SRTM for Lower Tapi Basin and a topographic map at 0.5 m contour interval were used to produce a 5 m grid for Surat city for 2D modelling. The release from the Ukai dam in 2006 was considered as the U/S boundary and Tidal level was considered as the D/S boundary. The model is simulated under the unsteady flow condition and maximum water surface elevation, water depth, velocity and wave arrival time of extreme flooding condition is prepared under the Levees condition. At last, the flood inundation for extreme flooding condition is superimposed over Google Earth image. In future, inundation map contained from the EAP guideline will be available to dam owners to prepare the rescue action plan in case of a dam/ levees failures or extremely large release of dam water during severe weather conditions. It will provide the additional time to the decision making authority to take the appropriate life-saving decisions during flooding.