Calculation Of Hydrologic Alteration Using RVA-SPA Method Paramater Reduction Using Principal Component Analysis

Anthropogenic activities related to water use have transformed the natural river basins around the world.Last century has seen an unprecedented scale of water related projects in history of earth.These projects have led to significant change in natural flow of the rivers.The need of water for ever-growing world population and economy have created stress on freshwater sources like river to meet the subsequent demand.Diversion and impoundment projects have been built in almost all basins around the world,which regulates a significant portion of natural water flow.It has been estimated that 70% of the world's basin is under the human water regulation.This has caused severe degradation of water environment leading to poor water quality and aquatic habitat loss.Natural flow regime of the river is vital in sustaining biodiversity in river ecosystem and river dependent flood-plain ecosystem.The change in natural flow regime due to regulation projects in river has severely affected the river ecosystem.This decrease in river environment caused massive stir in public leading to concern for improving the water quality in rivers.This forced the policymakers to step onto river restoration programs for physical,chemical and biological restoration.The concept of environmental flow came into existence,whereby the flow required to sustain the biodiversity was deemed to be of importance in preserving river health.This led to the formulation of numerous environmental flow methodologies around the world.Environmental flow is defined as “the quantity,timing and frequency of flow required to sustain river ecosystem and human needs combined”.The methodologies to define environmental flow depends on site specific conditions,the data availability and level of resolution required in maintaining the river health.Rivers with constraints of data,time and cost are best apposite for the use of hydrologic methods,which are less data extensive and easier to formulate.The practice of environmental flow evolved from a single basic minimum flow requirement to a broader concept of variable flow release.The reasoning behind the variable flow is that,river holds variation in biodiversity and these variation requires different level of water flow.Thus,a single flow standard is insufficient,requiring a variable flow setting.The best variation to provide in rivers is variation of that in natural state of rivers when the anthropogenic activities had minimal effects.Quantification of natural flow pattern of the river requires the in-depth knowledge of biodiversity and flow variance relation,thus regarded as a daunting task.Nevertheless,many methodologies have explained these relations in terms of various suites of indicators.Indicators of Hydrologic Alteration(IHA)is a hydrological method with a suite of indicators to quantify the variation of flow in terms of magnitude,duration,timing,rate and frequency.Range of Variability Assessment(RVA)method based on IHA parameters is a popular method to calculate flow alteration in river compared between natural and altered state.RVA method explains the variation of flow parameters over the years and fails to account for the variation of parameters within a single hydrologic year,which too is of prime importance.Set Pair Analysis(SPA)of inner characteristics of one hydrologic year can reveal the variation of IHA parameters within a single year,thus capturing the unexplained variation of RVA method.Moreover,the use of large number of IHA parameters that are statistically redundant within makes computation complex in later stage when environmental flow has to be combined in multi-objective water allocation problem.Principal component analysis(PCA)is a useful statistical tool in removing the data redundancy.The main aim of the thesis is to use hydrological methods for calculation of flow alteration and develop a small suite of parameters which can be taken as a representative indicators of flow alteration in that particular river for future use.A case study on the Trishuli River,Betrawati Station downstream of hydropower is done to assess the flow alteration due to hydropower construction.RVA-SPA method combined to give compressive results on flow alteration calculated the mean alteration of 73.4% classified in high alteration category.Furthermore,the PCA analysis carried out in 32 IHA parameters reduced the overall parameters to five parameters namely;1-day minimum flow;3-day minimum flow;7 day minimum flow;30-day minimum flow and base flow.Reduction of number of parameters involved in IHA using Principal Component Analysis helps in parsimonious study of flow alteration and environmental flow setting for the area in future.