Current Science

P. V. Timbadiya ¹, P. L. Patel ¹, P. D. Porey ¹

Affiliations
1 Department of Civil Engineering, S.V. National Institute of Technology Surat, Surat 395 007, IN

Abstract

The present study addresses the simulation of floods for the years 2003 and 2006 and the development of stage-discharge relationship along the lower Tapi River in India. The river network and cross-sections, for the present study, were extracted from the fieldsurveyed contours of the Tapi River. Using the aforesaid geometry and hydrological data, supplied by the stakeholders, the MIKE 11 hydrodynamic model was calibrated for the 1998 flood using releases from the Ukai Dam (flood hydrograph) and the tidal water level in the Arabian Sea as the upstream and downstream boundary conditions respectively. The calibrated model was validated using low- and high-flood data of the years 2003 and 2006 respectively. The time series of the simulated flood levels were compared with the corresponding observed values at four intermediate gauging stations: Kakrapar Weir, Mandavi Bridge, Ghala village and the Surat city (Nehru Bridge). The model performance was also evaluated using the standard performance index (i.e. ischolar_main mean square error) and was found to be reasonably satisfactory for such a data-scarce region. The rating curves (i.e. stage-discharge relationship) were also developed from the aforesaid calibrated model which would be useful in flood forecasting and development of flood protection measures along the lower Tapi River.

Keywords

Flood Forecasting, Flood Protection Measures, Hydrodynamic Modelling, Rating Curve, Stage–Discharge Relationship.

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Sadhana Singh ¹, S. Kannan ², P. V. Timbadiya ¹

Affiliations
1 Department of Civil Engineering, S.V. National Institute of Technology-Surat, Surat 395 007, IN
2 Central Water and Power Research Station, Pune 411 024, IN

Abstract

The study presents fine resolution multisite daily precipitation projection for the Tapi basin using the kernel-regression (KR) based statistical downscaling methodology developed by Kannan and Ghosh with and without conditioned on the estimated rainfall state. The models are applied in downscaling of daily monsoon precipitation at a fine resolution of 0.25 comprising 351 grid points in and around the basin. The air temperature, specific humidity, zonal and meridional wind (at surface, 250, 500 and 850 hPa); mean sea level pressure and geopotential height at surface are utilized as predictors from five GCMs under CMIP-5 for two future scenarios, viz. RCP4.5 and RCP8.5. The performance of the downscaling model examined with respect to reproduction of various statistics for training period and indicated the better performance of KR model conditioned on the rainfall state than KR model without conditioned on the rainfall state of the basin. The KR model conditioned on the rainfall state is employed for future projections from GCMs outputs. The statistically downscaled daily precipitation from GCM (MPI-M) and CORDEX (COSMO-CLM) data is compared to quantify uncertainty. The statistically downscaled daily precipitation performs better than corresponding CORDEX data for the present study area. The study also revealed a possibility of decrease in the occurrences of extreme events with an increase in the medium rainfall events in the basin for future.

Keywords

Climate Change, Daily Precipitation, General Circulation Models, Statistical Downscaling.

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