River Health Assessment of the Ganga River via Geomorphic Metrics: The Anthropocene Context

ABSTRACT

Rivers, particularly large river systems, constitute one of the most fundamental life‐support systems that have sustained civilisations and are projected to be a critical determinant for the future sustenance of human civilisations. A river can be termed a healthy ecosystem only when all the flora and fauna are in and along the river, the cultivation in floodplains is healthy, and the river's form is in equilibrium. The Ganga River system in India is a large river system with high geodiversity and biodiversity, where about one‐third of India's population depends on the river directly or indirectly. This study focuses on the development of a Geomorphic River Health Index (gRHI) based on eight geomorphic attributes derived from geospatial data, including sinuosity, braid‐channel ratio, width/depth ratio, occupancy, floodplain development, bar density, bar complexity and stream power. The selected river health parameters were analysed using a multi‐criteria decision‐making technique, the Analytic Hierarchy Process (AHP), in a GIS framework. We adopted a five‐fold river health classification framework (i.e., near‐pristine, good, fair, poor and degraded) for the entire Ganga River system from Gomukh to Farakka. Our results, based on geospatial data and supported by field observations, indicate that most reaches of the Ganga River in the higher mountainous stretch are in ‘near pristine’ condition, while some in the lower reaches fall into the ‘good’ and ‘fair’ classes. In contrast, several reaches in the alluvial part show ‘poor’ river health, primarily associated with flow reduction and sediment accumulation leading to morphological degradation, which is well manifested in geomorphic indicators used for river health assessment in this study. The geomorphic framework presented in this study can serve as a good template to evaluate river health and link this to scenarios of habitat suitability, environmental flows and flood risk associated with large river systems.