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

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 pre-monsoon, 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 m3s-1$$ >280\ {m}<^>3{s}<^>{-1} $$ 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.