Impact of LULC changes on small watershed morphometry and delineation of sustainable conservation strategies for degraded transboundary rivers

Abstract

Small streams in the large river basins are disappearing, and there is no update on their historical and current morphometric status. Field inventory and visual inspections quantified the impact of land use and land cover (LULC) change on the reference year morphometry (1970-1977) of seven watersheds and fifty-six subwatersheds, using drone imagery and Global Positioning System-based ground control points to refine the reference map and generate the current map (2021-2024). The decreasing stream number (Nu), stream length (Lu), and drainage density (Dd) (1) explained the mechanism of disappearing and shrinking large rivers; (2) classified seven watersheds and fifty-six subwatersheds into near threatened (NT), vulnerable (VU), endangered (EN), critically endangered (CR), and extinct (EX) categories; and (3) emphasized rejuvenation of 9,84,068 km of lost streams to restore Dd ≥ 2 km/km² in the Ganga River basin (GRB). From these empirical estimates, the UN's commitment to restoring 300,000 km of degraded rivers thus needs ~ 150,000 km² of watershed area to delineate ex-situ and in-situ restoration and conservation of disappearing three intrinsic morphometric attributes, i.e., Nu, Lu, and Dd.

Keywords: Drainage density; Morphometry; RRLCC; Stream order; Water policy.

Fig. 1

The location maps of seven watersheds with current year stream networks (2021–2024) in the Ganga River Basin, India (a-b); the seven watersheds are classified into three categories on the basis of dominant livelihood practices i.e. agricultural: (c) Bodla (2022), (d) Danro (2022), and (e) Banki (2021); cultural: (f) Khudar (2024) and (g) Urmil (2024), and industrial: (h) Khudia (2023) and (i) Katri (2023). The shapefile was obtained from open-source website (https://onlinemaps.surveyofindia.gov.in/Home.aspx) to generate map (a). The maps were created using ArcGIS 10.2 software and the website is https://desktop.arcgis.com/.

Fig. 2

Comparative drainage order change map between reference year (1970–1977) and current year (2021–2024) of the seven watersheds: (a) Bodla (i-ii), (b) Banki (i-ii), (c) Danro (i-ii), (d) Katri (i-ii), (e) Khudia (i-ii), (f) Khudar (i-ii), and (g) Urmil (i-ii); the maps show decreasing stream order(s) from the reference year to current year due to the prevalence of anthropogenic alterations of geologic structures and geomorphologies, especially the agricultural diversions resulting in loss of stream number (Nu) and stream length (Lu). The maps were created using ArcGIS 10.2 software and the website is https://desktop.arcgis.com/.

Fig. 3

The land use and land cover (LULC) change analysis between the reference year (1991–1995) and current year (2020–2024) of seven watersheds: (a) Bodla (1995–2020), (b) Khudar (1994–2024), (c) Urmil (1994–2024), (d) Banki (1991–2021), (e) Danro (1992–2022), (f) Katri (1993–2023), and (g) Khudia (1993–2023). The increase in the anthropogenically modified agricultural and built-up areas and decrease in barren land, vegetation, and waterbodies resulting in loss of the stream morphological diversity.