Assessment of the anthropogenic interventions and related responses of Karala River, Jalpaiguri, India: a multiple indicator-based analysis

The sub-Himalayan foothill region is experiencing rapid land-use transformation over the last few decades resulting in the decay of several rivers such as Mahananda, Balason, Sahu, Rakti, Panchanai, Dharala, and Karala. A small rain-fed tributary of Teesta, Karala, has almost decayed in recent years but no notable assessment of its condition has been done to date. This study mainly aims to measure the intensity of human interventions and related responses of Karala through reach-wise, multiple indicator-based assessments. Initially, the reaches have been delineated by segmenting the river into 10 equidistant segments. Characterization of land-use and land-cover has been done for all such reaches. To determine the nature of hydro-geomorphology and water quality of the river 14 indicators are selected and categorized into 3 indices. According to the measured reach-wise mean (R-m), with the highest 4.70 (Reach 1) and lowest 2.21 (R9), it is clear that the need for restoration increases downstream since those areas portray massive deviation from least disturbed conditions (LDC). It is also revealed that the change in the bar area (ID7), vegetation condition (ID3), non-point sources of pollution (NPSP), and channel width (ID8) indicate also an alarming condition within the lower part of the river channel. It is evident that as the river approaches downstream, the natural state of landcover is lost due to intensive human intervention, mostly due to massive land-use transformation reflected in a 600% increase in built-up area in and around the Jalpaiguri region from 1990 to 2020. Hydrologically as well as ecologically sensitive rivers like Karala are the inseparable parts of the sub-Himalayan foothills. Degradation of such, due to, the human alteration would eventually disarrange the entire ecosystem. This easy-to-use, rapid, and coast effective methodology was found useful in distinguishing the extent of alterations by human intervention and the responses of such river systems.