Study on the habitat evolution after dam removal in a habitat-alternative tributary of large hydropower station

Zhenhua Wang; Jingjie Feng; Tao He; Jiuxian Yang; Hang Wan; Yuliang Yuan; Ran Li

doi:10.1016/j.jenvman.2024.121155

Study on the habitat evolution after dam removal in a habitat-alternative tributary of large hydropower station

J Environ Manage. 2024 May 17:360:121155. doi: 10.1016/j.jenvman.2024.121155. Online ahead of print.

Authors

Zhenhua Wang¹, Jingjie Feng², Tao He³, Jiuxian Yang³, Hang Wan⁴, Yuliang Yuan¹, Ran Li¹

Affiliations

¹ State Key Laboratory of Hydraulics and Mountain River Engineering, Sichuan University, Chengdu, Sichuan, 610065, China.
² State Key Laboratory of Hydraulics and Mountain River Engineering, Sichuan University, Chengdu, Sichuan, 610065, China. Electronic address: fengjingjie@scu.edu.cn.
³ Power China Chengdu Engineering Corporation Limited, Chengdu, Sichuan, 611130, China.
⁴ Research Centre of Ecology & Environment for Coastal Area and Deep Sea, Southern Marine Science and Engineering Guangdong Laboratory (Guangzhou), Guangzhou, 511458, China. Electronic address: wanhang@gmlab.ac.cn.

PMID: 38761624
DOI: 10.1016/j.jenvman.2024.121155

Abstract

The establishment of large hydropower stations in the main stream poses a threat to fish habitats. Selecting suitable tributaries as alternative habitats is a practical measure for ecological environment protection during large hydropower station's construction. The small dams constructed on certain tributaries need to be removed in order to restore river connectivity. The removal of dams will activate hydro-sedimentary dynamics and change the original habitat in terms of topography and hydrodynamics. To explore the evolution of fish habitats following the removal of small dams, a dam-removed reach of a habitat-alternative tributary was selected as the research object, and the model of water-sediment transport and riverbed evolution in strongly disturbed dam-removed reaches and the model of fish habitat suitability evaluation were established. The key parameters calibration and model verification were completed by field monitoring results. The simulation results showed dramatic evolution in the reservoir riverbed in the initial stage after dam removal and during the high discharge period. One year after dam removal, there was a noticeable 4.0 m incision in front of the dam, along with a decrease in channel slope at the dam site from about 4.8% to approximately 1.5%. Downstream of the dam, alterations to the riverbed were mainly concentrated near the dam, and sedimentary bodies with a height of around 2.0 m have formed on the left bank following the high discharge period. The fish habitat in most areas of the dam-removed reach was suitable, except for the downstream high-velocity area. To compare the evolution process of fish habitat under two dam removal periods in wet and dry seasons, two dam removal schemes were implemented in March and June. The results showed that the riverbed evolved more gradually in the March scheme, creating a larger and continuous suitable habitat for fish. Therefore, the March scheme was recommended. By revealing the evolutionary pattern of fish habitat after dam removal, this research provides a reliable model for assessing and restoring habitats in dam-removed reaches, and enjoys significant implications for protecting river ecology in hydropower development reaches.

Keywords: Dam removal; Habitat-alternative tributary; Hydrodynamics; River habitat; Riverbed evolution.