Integrating satellite altimeter data and geomorphic in‐stream flow tool to assess reach average hydraulic habitat of the Ganga River dolphin

Abstract

The Ganga River ecosystem is under severe anthropogenic stress. Flow regulations through structural barriers alter the geomorphic and hydraulic geometry of riverine habitats. Determining the ecological health of river habitats under the contemporary modification is detrimental to its restoration and management. This study evaluates reach averaged hydraulic habitat of the endangered Ganga River dolphin (Platanista gangetica) in a stretch between Bijnor and Narora barrages. We consider an optimal minimum flow depth as the determining factor of habitat suitability. Field measurement of the hydraulic geometry and flow characteristics show that the optimal flow depth is available in the study reach during the monsoon period, while in the premonsoon, the minimum depth is present only in the reach upstream to Narora barrage. We use a geomorphic instream flow tool (GIFT) and satellite altimeter water level data to simulate reach averaged hydraulic habitat in varying flow conditions in area upstream of Narora barrage. We observe that to maintain the minimum flow depth which supports the dolphin habitat in the study reach, an optimal discharge of about > 280 m 3 s À1 is essential. Furthermore, we develop a water-level (altimeter) and discharge (simulated from GIFT) rating curve for the study reach. It can be used to get a first-order estimate of discharge for a given water level or vice versa. This study indicates that the altimetry datasets are good precursors for estimating averaged hydraulic habitat of rivers in the data-scarce regions. The application of altimeter data can be a boon in the effective management of river habitat health over a reach scale.

Hydrodynamic modelling to assess habitat suitability of the Ganga River dolphins

“…Studies such as Bashir et al (2010), Choudhary et al (2012), Paudel et al (2020), Sonkar et al (2023) and Wakid (2009) show that the GRD prefers reaches that have minimum flow depth of and velocity above . Spatial variability of the simulated hydraulics shows that at the lowest , the relative frequency of low flow depth is more (0.08–0.17) in the study reach.…”

“…The Courant-Friedrichs-Lewy (CFL) condition criteria checks the model stability (Boffi et al, 2007). The construction of large dams and barrages on the Ganga River have significantly altered the flow regime and eventually have degraded the habitat suitability of different aquatic species (Dey et al, 2019;Sonkar & Gaurav, 2020;Sonkar et al, 2019Sonkar et al, , 2023. This study simulates the hydraulic habitat suitability of GRD under the varying flow conditions.…”