Method to quantify hydrological alterations due to anthropogenic interventions: A case study of Peace River, Canada
Authors: Mohanty Maithili , Tare Vinod 
Published: February 2023

Hydrological alteration refers to any modification to different components of the natural flow regime of a river that human interventions may cause. The interventions are built to store excess water for different purposes, such as hydropower generation, irrigation, and domestic uses. The headwaters of the Peace River in Canada that flows from the Rocky Mountains of British Columbia became regulated by two large dams, the W. A. C. Bennett dam in 1968 and the Peace Canyon dam in 1980. The objective of the paper quantified the hydrological alterations caused by the cascade of dams across the Peace River. We have used a powerful tool 'River Flow Health Index' to quantify the alterations in different flow regime components on a 0-1 scale (0 means unaltered and one means completely altered). Historical hydrological data is obtained from the Water Survey of Canada (http://www.ec.gc.ca/rhc-wsc/) at a gauge station, Peace River near Taylor (coordinates: 56&#176; 8'8.99"N, 120&#176;40'13.01"W) for the years 1945-2015. 1945-1962 is chosen as the reference state because the dams were constructed after 1963. The altered period is referred to the period 1970-2015 after the operation of the dams started. We scrutinized 171 hydrologically relevant parameters grouped into seven components of the flow regime: magnitude, variability, duration, frequency, timing, rate of change, and others. The methodology for estimating the River Flow Health Index (RFHI) consists of four steps: (1) segregation of the flow data based on preimpact and postimpact periods, (2) identification of important hydrological parameters, (3) assessment of the alterations, and (4) development of an index indicating the health of the river flow during the altered period on a 0&#8211;1 scale. The flow health of the river changed significantly due to the dams, with an overall alteration of 0.897. The degree of alterations in different components of the flow regime is magnitude (0.646), variability (0.978), duration (0.941), frequency (1.000), timing (0.978), rate of change (0.801), and others (1.000).Daily flows at the downstream site during 1945&#8211;2015 reveal substantial reductions in flows after the construction of the W. A. C. Bennett and Peace Canyon dams. Homogenization of flows in the post-impact period altered the variability component of the flow regime. The duration and frequency of the extreme events are stunted post-dam regulation. This might result from water storage and release, and these multiple dams can store and attenuate all high-and low-pulse events. Alterations in the timing component resulted in the seasonal shift in streamflow by storing flood flows and releasing or utilizing them during lean seasons. Changes in Group 6, i.e., rate of change after the construction of the dams, indicate dam operations for energy production (i.e., peaking operations). Thus, the results indicate that the large dams across the Peace River can substantially change the natural flow regime. Our results may help upgrade the design and implementation of reservoir operation policies that consider downstream hydrological alterations.