Abstract
Watersheds in the Lesser Himalayan region are highly susceptible to natural hazards, particularly those instigated by action and movement of water, such as soil erosion, flood, and mass movements of lands. Hilly watersheds with diversified land use and fragile ecosystems are responsible for accelerating soil erosion. Soil erosion is one of the most implicit hazards as it degrades water and soil quality in a watershed. The study prioritizes the soil erosion-susceptible zones in the Tons river watershed (India) in the Lesser Himalayan region. The interrelationships and role of morphometry, soil quality, slope, and land use together as four components in soil erosion are studied. Remote sensing data and multi-criteria decision method (MCDM) framework has been used to estimate soil erosion susceptibility of sub-watersheds. Results showed that morphometric parameters like elongation ratio and slope of sub-watersheds play a major role in determining the state of erosion.
TopIntroduction
Soil erosion is a threat to humankind as it degrades one of the essential natural resources i.e., soil. Soil erosion depends on combinations of factors such as the steepness of slope, land use & land cover, climate and ecological calamities like forest fires and landslides. On-site and off-site soil erosion have detrimental impacts on natural resources. Soil erodibility, erosivity and land use management practices play a key role in defining the status of the soil. Soil erosion leads to a reduction of protective cover, making the region more vulnerable. In a watershed, soil erosion leads to the degradation of the water quality of the streams as the eroded material is carried down to the lower reaches of the rivers, making it incompatible to carry an excess amount of water and sediment load. Vulnerability assessment towards soil erosion in a watershed plays a key role in identifying the extent of fragility in an area and supports in making appropriate plans for its conservation. Therefore, it is crucial for watershed management's point of view to identify the vulnerable zones towards erosion. Assessing soil erosion vulnerable zones based on various factors responsible for inducing erosion provides a basis for planning different strategies. There are several methods available to assess the region’s susceptibility to soil loss and may be used depending upon the availability of data and other resources for assessment. Several qualitative and quantitative methods are being used worldwide to assess soil erosion and vulnerability zones towards erosion. Studies need to attempt methods based on the availability of accurate input for assessing soil erosion vulnerability. Among various qualitative methods, Multi-criteria decision methods (MCDM) based on different approaches like Više Kriterijumska Optimizacija i Kompromisno Rešenje (VIKOR), Technique for Order of Preference by similarity to Ideal Solution (TOPSIS) and Compound Factors (CF) have been used by researchers worldwide, however, CF approach is the most used method due to its flexibility about the inclusion of different components (Pandey et al., 2021).
The study identifies the most vulnerable sub-watersheds towards soil erosion using MCDM. It highlights the inclusion of various components which play a role in governing soil erosion. The study highlights the importance and application of the MCDM method based on CF value to prioritize zones susceptible to soil erosion. In addition, it suggests that methods like MCDM allow the inclusion of various components due their flexibility and that it may make the study more vigorous. The outcome of the study ranks and provides information on the sub-watersheds that need soil and water conservation. The related objective is to understand the usefulness of methods like MCDM to examine the vulnerability status of watersheds through ranking for strategizing protection and conservation of the watershed.
Key Terms in this Chapter
Soil Erodibility: It is defined as a resistance to two energy sources defines the erodibility of a soil as a material with a greater or lesser degree of coherence: the impact of raindrops on the soil surface, and the shearing action of runoff between clods in grooves or rills.
Watershed: A watershed is the geographical area drained by a watercourse. The concept applies at various scales – from, for example, a farm drained by a creek (a “micro-watershed”) to a large river basin (or a lake basin).
Soil Erosion: Soil erosion is one of the ten major soil threats, identified in the Status of the World's Soil Resources Report. It is defined as the accelerated removal of topsoil from the land surface through water, wind and tillage.
Soil Erosivity: Erosivity is the term used to describe the potential of raindrop impact, runoff from snowmelt, or water applied with an irrigation system rainstorm to detach and erode soil.
Hierarchical Cluster Analysis (HCA): It is a method to build a tree diagram where the groups that are most similar based on characteristics in the study are placed on branches that are close together.
Infiltration Capacity: Infiltration capacity is the maximum rate at which a soil is capable of absorbing water in a given condition. Several factors control infiltration capacity. Antecedent rainfall and soil-moisture conditions.
Morphometry: In geomorphology, morphometry is a quantification of morphology. Indices of watershed morphometry can interpret the shape and hydrological characteristics of a river basin. Morphometric analysis of watershed is the best method to identify the relationship of various aspects in the area. It is a comparative evaluation of different watersheds in various geomorphological and topographical conditions.