A hydro-geomorphologic assessment of flood generation potentiality in ungauged sub-basins and their prioritization based on traditional, statistical, MCDM and Nash-GIUH models of a tropical plateau-fringe River

Abstract

In ungauged sub-basins (SBs), estimation of peak flow (q_p) is inevitable in designing both structural and non-structural flood mitigating measures to control outflow into the Master River. However, the inadequacy of stream flow data is the pivotal challenge in estimating q_p and design flood in ungauged SBs. Therefore, an alternative basin prioritization approach is adopted for flood mitigation and sustainable development of ten tributary SBs of the Shilabati River which is one of the most flood-prone tropical plateau fringe river basins in eastern India. Significant morphometric and hydrologic parameters are used for SB prioritization in terms of five different flood generation potentiality (FGP) models, namely compound factor, hazard degree, principal component analysis, weighted sum analysis and analytical hierarchy process (AHP). Results of the FGP models are compared with the q_p of the Geomorphologic Instantaneous Unit hydrograph (GIUH) model linked with the Nash two-parameter gamma distribution function. Among a total of five Nash-GIUH models, the GIUH_avg model (Nash-GIUH based on average dynamic velocity) is used to evaluate the FGP models. Results imply that AHP-FGP is the most efficient model for SB prioritization. According to AHP scores, the highest priority for flood mitigation is given to SB-6 due to its high FGP value followed by SB-3, and SB-4. Similarly, the highest q_p (0.106 hr^-1) and shortest time to peak (t_p) (4.718 hrs) of GIUH_avg are observed in SB-6, representing the hazardous nature of the SB. Morpho-hydrologic parameters such as time of concentration (T_c), relative relief (R_r) and hypsometric integral (HI) are identified as significant for the AHP-FGP model. In addition, moderate-strong correlations of T_c, R_r and HI with the q_p of GIUH_avg exhibit the association between geomorphologic characteristics and hydrologic behaviour of SBs. Therefore, this study presents an integrated approach of FGP and GIUH-based flood hazard assessment for sub-basin prioritization that will help to develop valuable insights to reduce the formation of quick q_p in ungauged SBs that can trigger flooding in the Master River.