Disappearing streams and morphometric degradation in small watersheds of the Ganga River basin

The assessment of irreversibly disappearing intrinsic morphometric parameters, mainly the number of streams (Nu), length of streams (Lu), and drainage density (Dd) of small watersheds in large river basins, are essential to (i) restore and conserve existing spatial organization of stream networks and (ii) underscore historical, present, and future watershed management in changing land use pattern. We carried out the field inventory of the Danro watershed in 2022 to depict extreme morphometric changes in the small watershed and subwatersheds. The reference year (1977) and current year (2022) morphometric comparison showed a 69% loss in the Nu, Lu, and Dd, resulting in the shifting of the 6th-order dendritic Danro into a 4th-order river. The River Red List Categories and Criteria (RRLCC) revealed the Endangered (EN) status of the Danro watershed, while two, five, and four subwatersheds were classified as Vulnerable (VU), Endangered (EN), and Critically Endangered (CR), respectively. The width of the administrative boundaries (WAB) on both the right and left stream banks was determined using the drainage density ratio (DdR) and the mean stream width (MSW). The morphometric attributes integrated with the RRLCC framework serve as diagnostic tools to quantify stream network degradation, delineate WAB, and inform site-specific restoration and conservation planning, including statutory in-situ and ex-situ land allocation to protect natural river boundaries, stream buffer zone design, sustainable land-use transitions, aquifer and flood management, etc. Our findings thus underscore the urgent need to rejuvenate and conserve small watersheds to impart ecohydrological resilience to the shrinking large river basins.