Assessment of hydrologic alterations caused by Chi‐Chi diversion weir in Chou‐Shui Creek, Taiwan: opportunities for restoring natural flow conditions

Abstract

The Range of Variability Approach (RVA) is used to investigate the hydrologic impacts of a diversion weir on Chou-Shui Creek, Taiwan. Thirty-two hydrologic parameters, called Indicators of Hydrologic Alteration (IHA), are used to evaluate the flow conditions before and after weir construction. One standard deviation from the mean for each of the pre-construction hydrologic parameters is set as the management target range. Under the prevailing diversion rules, large hydrologic alterations are observed, especially for low flows. The means of 19 hydrologic parameters presently fall outside of the targets and the average non-attainment rate for the 32 indicators is 73.2%. Increasing the instream flow release or reducing diversions could mitigate the hydrologic impacts of weir construction. Increasing the instream flow to 40 m 3 /s and reducing monthly water demands by variable percentages significantly improves the altered flow conditions. Under the proposed water release and diversion scheme, 29 hydrologic parameters will fall within the management targets and the average non-attainment rate will be reduced to 35.6%, much closer to the pre-construction value of 25.3%. Restoring the natural flow variability is expected to promote the natural stream biota.

A dual active‐restrictive approach to incorporating environmental flow targets into existing reservoir operation rules

“…There is now a consensus among scientists and river managers that to protect freshwater biodiversity and maintain the ecological services that rivers can provide, managed releases of water from reservoirs, termed environmental flows, are needed to mimic the components of natural flow variability, which include the magnitude, frequency, timing, duration, rate of change, and predictability of extreme events such as floods and droughts [Arthington et al, 2006]. This may explain why, over the past three decades, the scientific field of environmental flows prospered to generate >200 methods for specifying the minimum instream flows or quantifying flow regimes required to sustain the riverine ecosystems and their valued features [Tharme, 2003;Shiau and Wu, 2004a, 2004b, 2007a, 2007b, 2008, 2009. It has also become increasingly clear that failure to meet the environmental flow requirements would lead to adverse consequences for the river users, including the downstream ecosystems and the communities that rely upon them [Arthington and Pusey, 2003].…”

An Ecological Flow Assessment Framework: Building a Bridge to Implementation in Canada

“…The IHA have been recently applied to assess alterations due to dams (Tana River, Kenya (Maingi and Marsh, 2002); Missouri River, USA (Galat and Lipkin, 2000)), diversions (Chou-Shui Creek, Taiwan (Shiau and Wu, 2004)), water extractions (Altamaha River Basin, USA (Shaw, 2001)) and land use changes (Hanlon Creek, Canada (Bradford et al, 2007)). …”

Assessment of Hydrologic Alterations in Elbe and Rhine Rivers, Germany

“…Intensive human activities, such as dam construction, irrigation, and land use change, have strongly modified global hydrologic regimes [16][17][18][19]. Dams built for hydroelectric generation or flood control can alter the downstream hydrologic regime by altering the total streamflow quantity, water quality, and duration of extreme flow [20].…”