Reappraisal of hydrologic alterations in the Roanoke River basin using extended data and improved RVA method

Hydrologic regime changes of the Roanoke River basin under three different scenarios defined based on different periods of post-impact datasets have been studied. For evaluating the degree of hydrologic alterations, the traditional and improved range of variability approach (RVA) which incorporate periodicity [as an index of periodicity (IP)], trend [as an index of trend (IT)], and symmetry [as an index of symmetry (IS)] of the parameters has been used. Comparative analysis of the results obtained with traditional and improved RVA and that obtained with the histogram matching approach (HMA) has also been performed. The overall degree of hydrologic alteration obtained through traditional RVA for Scenarios-I, II, and III was 0.39, 0.42, and 0.40, respectively. The improved RVA method, when applied to the 32 IHA parameters, indicates that many IHA parameters exhibit a higher IP or IT or IS value compared to the corresponding value of the degree of hydrologic alteration (DR), which underscore the inadequacy of the traditional RVA in assessing the degree of alteration in the flow regime of the Roanoke River. Through principal component analysis, the most ecologically relevant hydrologic indicators for understanding eco-hydrology of Roanoke River have been identified, which include Julian date of maximum flow, monthly flow for July and September, and 90-day maximum flow. Analysis of results further reveals that the combination of improved RVA and HMA can better reveal changes in IHAs and provide a better tool for designing strategies to enhance further the ecosystem services available from a managed river system.

Automated summary

The study examined hydrologic regime changes in the Roanoke River basin under three scenarios and found deficiencies in the traditional RVA in evaluating the degree of hydrologic alterations. The combination of improved RVA and HMA can better design strategies to enhance ecosystem services provided by managed river systems.