Hydrogeomorphic advancements in river science for water security in India

Abstract

Effective management of rivers and the maintenance of the integrity of linked biophysical systems require multidisciplinary approaches. Thus, River Science is a relatively new arena of scientific inquiry that focuses on problems of sustainable management of river systems and it actively integrates multiple scales and various concepts. This paper presents a review of new developments in hydrogeomorphic processes understanding, which are critical to assess water security for Indian river systems.

Indian rivers are under the influence of a diverse interplay of climatic, geomorphic, tectonic, and anthropogenic forces, and are broadly classified in terms of Himalayan and Peninsular rivers, which can be further subdivided into 6 major types. The Himalayan rivers have received greater attention in comparison to rivers in peninsular India. Within the backdrop of changing climate, an improved understanding of the interrelationships between hydrological, morphological and ecological processes is the key to quantifying water security for Indian rivers in the near future. Geomorphic threshold, hydrological and sediment connectivity, Groundwater-Surfacewater (GW-SW) interaction and Environmental-flow (E-flow) assessment are the essential elements to understand the hydrology-morphological-ecological processes. Such studies have been initiated in Indian river systems, however, these are still limited in number. Stream power distribution based approaches are frequently employed to understand hydrological controls on morphological processes and form in regulated and unregulated rivers. As a majority of the Himalayan rivers are hydrologically and morphologically disconnected due to large dams or barrages, the result is a discontinuum of channel processes. Peninsular rivers are dominantly bedrock and highly regulated river systems, which show significant short- to long-term flow variability and have tributaries which are not perennial. Disconnectivity due to extensive flow regulation and water withdrawals impose great stress on the flow processes and sediment transport, and result in the progressive decline in channel morphology, habitat, and ecosystem flow needs. A critical research question in highly regulated river systems is regarding how the flow regime at the reach scale and the associated hydrogeomorphic variability can be systematically characterized. Identification of geomorphic thresholds at different scales and quantification of (a) hydrological and sediment connectivity in river systems, (b) surface–groundwater interaction, and (c) E-flow assessment for different reaches in each river basin are the major gaps in River Science studies specific to Indian river systems. Especially, E-flow assessment for different river basins using a holistic approach must be the leading area of River Science research to aid management and policy making with the goal of enhancing water security. Relatively less studied peninsular rivers need more quantitative process-based hydrogeomorphic studies and their application for E-flow assessment.