GIS and AHP-based methods for river risk zone (RRZ) assessment: a case study of the Himalayan rivers in Doon Valley, Uttarakhand, India.

Pollution from both point and non-point sources, over-extraction of freshwater, and significant climatic changes in recent years are some factors that put substantial pressure on worldwide water resources. As the demand for potable water increases globally for human, agricultural, and industrial uses, the need to evaluate the river risk assessment also increases. GIS-based studies in recent years have gained prominence as they are rapid, cheap, and provide insight into the resources for further development of research on the rivers. Therefore, the present study assessed the river risk zone (RRZ) of the Himalayan rivers in the Doon Valley of Uttarakhand in India. A combination of GIS and analytical hierarchical process (AHP) techniques was used in the present study. A total of 15 thematic layers, total dissolved solids (TDS), conductivity, pH, salinity, temperature, depth, drainage density, land use/land cover (LULC), elevation, slope, flow, width, soil type, geology, and aspect, were prepared and studied from primary survey data and open-source digital elevation model (DEM) and satellite imagery for RRZ evaluation. Weights assigned to each class are based on their characteristics and risk towards the river through the AHP method. The RRZ map thus obtained was categorized into five classes: very high, high, medium, low, and very low. The study reveals that about 56.38% of the river area is covered under high and very high-risk zones. The medium, low, and very low-risk zones are observed in 33.71%, 2.93% and 6.98%, respectively. Identifying and monitoring these risk zones give planners and decision-makers opportunities to intervene where it counts most to prevent further degradation or collapse systematically, thus preserving the health and sustainability of river systems over time.