Is water shortage risk decreased at the expense of deteriorating water quality in a large water supply reservoir?

Zhihao Xu; Ximing Cai; Xinan Yin; Meirong Su; Yiping Wu; Zhifeng Yang

doi:10.1016/j.watres.2019.114984

Is water shortage risk decreased at the expense of deteriorating water quality in a large water supply reservoir?

Water Res. 2019 Nov 15:165:114984. doi: 10.1016/j.watres.2019.114984. Epub 2019 Aug 13.

Authors

Zhihao Xu¹, Ximing Cai², Xinan Yin³, Meirong Su⁴, Yiping Wu⁵, Zhifeng Yang⁶

Affiliations

¹ Research Center for Eco-environmental Engineering, Dongguan University of Technology, Songshan Lake, Dongguan, Guangdong, 523808, China; Department of Earth and Environmental Science, School of Human Settlements and Civil Engineering, Xi'an Jiaotong University, Xi'an, Shanxi, 710049, China.
² Department of Civil and Environmental Engineering, University of Illinois at Urbana-Champaign, 1304 W. Springfield, Urbana, IL, USA, 61801.
³ State Key Laboratory of Water Environmental Simulation, School of Environment, Beijing Normal University, Beijing, 100875, China.
⁴ Research Center for Eco-environmental Engineering, Dongguan University of Technology, Songshan Lake, Dongguan, Guangdong, 523808, China.
⁵ Department of Earth and Environmental Science, School of Human Settlements and Civil Engineering, Xi'an Jiaotong University, Xi'an, Shanxi, 710049, China.
⁶ Institute of Environmental and Ecological Engineering, Guangdong University of Technology, Guangzhou, Guangdong, 510006, China; State Key Laboratory of Water Environmental Simulation, School of Environment, Beijing Normal University, Beijing, 100875, China. Electronic address: zfyang@gdut.edu.cn.

PMID: 31465997
DOI: 10.1016/j.watres.2019.114984

Abstract

Reservoir operations affect both the quantity and quality of stored and discharged water. Hedging rules (HRs) are commonly used in water supply reservoir operations to ration water delivery and decrease water shortage risk. However, the increased carryover storage with hedging may aggravate reservoir eutrophication through complex effects on hydrodynamic, temperature, light, nutrient, and sediment conditions. The influencing mechanisms are unclear and require further investigation. This study applies a mathematical modeling approach to comparing the effects of standard operation policy (SOP) and HR, discussing the processes and driving factors, and exploring the relationship between water shortage and water quality indicators. We simulate reservoir operation by SOP and optimize HR to generate water supply schedules, and run a quasi-3D water quality model to simulate reservoir hydrodynamic conditions, nutrient cycles, water-sediment exchanges, and algal dynamics under various water supply schedules. The Danjiangkou Reservoir, the water source for China's South-North Water Transfer Project, is used as a case study. The HR for this reservoir decreases its water shortage risk from 22% under SOP to 8%. Modeling results find that the HR increases sediment phosphorus (P) release by 285.3 tons (5.7%) annually as a consequence of extended reservoir submerged area and aggravated hypolimnetic hypoxia. Increased P release can support algal growth, but this effect is set off by the enhancement of light limiting effect caused by higher storages under HR, consequently decreasing the annual mean chlorophyll a concentration in the deep reservoir by 18%. The HR also improves the horizontal mixing of water by changing the hydraulic retention time and flow velocity field, which mitigates algal bloom risks in the surrounding shallow-water zones but deteriorates water quality of the release to downstream. The water quality analysis offers implications for reservoir managers to coordinate their efforts in mitigating risks of water shortage and water quality degradation.

Keywords: Biogeochemical process; Reservoir eutrophication; Reservoir operation policy; Water quality modeling; Water supply security.

MeSH terms

China
Chlorophyll A
Eutrophication
Phosphorus
Water Quality*
Water Supply
Water*

Substances

Water
Phosphorus
Chlorophyll A