Abstract
Anthropogenic activities have led to the transformation of river basins and natural flow alteration around the world. Alteration in flow regimes have adverse effects on river ecosystems. Flow value changes signify the alteration extent and a number of flow related indices can be used to assess the extent of alteration in a river ecosystem. Selection of a few and ecologically relevant indices from a large set of available indices is a daunting task. Principal Component Analysis helps to reduce these large indices to a few ecologically significant indices and removes statistical redundancy of data to give uncorrelated data sets. These representative indices are useful in the primary investigation of a less studied area like the Kaligandaki River basin, Nepal. This paper uses reduced indices from the Kaligandaki River to calculate the alteration on the river section downstream of a hydropower facility using the Histogram Comparison Approach (HCA) combined with Hydrologic Year Types (HYT). The combined approach eliminates the potential underestimation of alteration values which may occur due to the exemption of hydrologic year types from the analysis, a feature equally relevant in river ecology. A new metric is used for the calculation of combined alteration using HCA-HYT in this paper. The analysis showed 60.71 percent alteration in the natural flow regime in the area past a hydropower construction, which is classified in the high alteration category. The study can be a guide for further analysis of the ecological flow management of a river section and a parsimonious approach to other areas where hydrological data is limited to historical flow records only.
Highlights
Rivers are integral parts of human civilization and ecosystems in their own right, with their health depending on the flow regime characteristics [1,2,3]
Matching Approach (HMA) and its subsequent extension Histogram Comparison Approach (HCA), we considered the alteration on whole flow regime, unlike the RVA approach which only considered alteration within a predefined target range [22,23]
The 32 principal component axis associated with the original data are represented by F1, F2, . . . , The 32 principal component axis associated to with the original data are represented
Summary
Rivers are integral parts of human civilization and ecosystems in their own right, with their health depending on the flow regime characteristics [1,2,3]. The direct link of flow regime characteristics with the ecological attributes are of prime concern for the solid foundation of eco-hydrology [9,10]. While this direct link establishment is a mammoth task, various ecological linkages of flow parameters have been intensively studied while considering broader ecological consequences [1,11,12,13,14] Quantifying the flow regime for proper flow management considering ecological consequences has promoted the development of various hydrologic indicators [15]. The main challenge here is to quantify the level of flow variations after the natural period
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