Effects on Water Quality After Water Transfer in the Yinxi Watershed, Ningbo, China
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Desalination and Water Treatment 189 (2020) 179–189 www.deswater.com June doi: 10.5004/dwt.2020.25576 Effects on water quality after water transfer in the Yinxi Watershed, Ningbo, China Hong Zhoua, Jun Liua,*, Ningxia Panb, Zhi Zhangb, Cheng Gaoa, Ruiling Baoa, Xuesong Wanga, Yawen Wua, Weilin Luoa, Jian Xua, Yantan Zhouc aCollege of Hydrology and Water Resources, Hohai University, Nanjing 210098, China, Tel. +86-25-83787603; emails: [email protected] (J. Liu), [email protected] (H. Zhou), [email protected] (C. Gao), [email protected] (R. Bao), [email protected] (X. Wang), [email protected] (Y. Wu), [email protected] (W. Luo), [email protected] (J. Xu) bHaishu District Water Resources Bureau, Ningbo 315100, China, emails: [email protected] (N. Pan), [email protected] (Z. Zhang) cZhejiang Guangchuan Engineering Consultation Co., Ltd., Hangzhou 310020, China, email: [email protected] (Y. Zhou) Received 12 August 2019; Accepted 3 February 2020 abstract With the development of economy and society, water transfer has become an important measure to improve water quality because of its low cost and easy operation. To reduce the negative impacts of sudden water pollution in the Yinxi Watershed, Ningbo, a series of experimental water transfers were conducted. The water quality indicators (chemical oxygen demand, free ammonia nitrogen, and total phosphorus) were analyzed to determine changes in pollutant concentration. The results show that water transfer is an effective measure to improve the water quality but the water quality showed temporal and spatial heterogeneity. To improve the water quality of the Yinxi watershed, the inflow rate of Gaoqiao pumping station and Hongshuiwan check-gate should be 13.44 m3/s and 120,000 m3/d, respectively, and some sluices should be opened to drain water and effectively improve water flow and quality in the whole region. Besides, a 2 d frequency of transfer is needed to improve water quality, and the optimal pattern of transfer is diverting after draining. On the basis, the management of regional water resources to improve water quality is proposed. These experi- mental transfers help to better understand the effects of water transfer on regional water quality, formulate and implement effective water resources management, and provide references for similar watersheds. Keywords: Water transfer; Water resources management; Water quality; Spatial and temporal heterogeneity; Ningbo 1. Introduction specifically to improve water quality in the receiving areas, where water resources may be abundant but polluted. Due to the uneven spatial and temporal distribution of Many different measures have been taken to improve water resources, many water transfer projects have been water quality, including pollution source reduction and built around the world to alleviate shortages of water. For interception strategies [3–6], sediment dredging [7–9], wet- example, China’s south-to-north water transfer project lands construction [10,11], and others. However, there are mainly transfers the abundant water resources of the Yangtze time lags between implementing these projects and seeing River to water-deficient areas in North China through three water quality improvements compared with water trans- routes [1,2]. With the continuous development of the econ- fers. The advantages of water transfer are low cost and easy omy and society, some water transfer projects have emerged operation. When suitable external clean water resources are * Corresponding author. 1944-3994/1944-3986 © 2020 Desalination Publications. All rights reserved. 180 H. Zhou et al. / Desalination and Water Treatment 189 (2020) 179–189 available, the concentration of pollutants in inland rivers can Although some studies have observed the improve- be decreased quickly [12]. ment of water quality by transfer, most of them are aimed at The mechanism of water transfer comes mainly through improving the water quality of lakes or reservoirs and allevi- transferring external clean water resources to dilute pollut- ating eutrophication. Regional water transfer often focuses ants in internal rivers and enhance water flow and water on the improvement of regional water quality by transfer self-purification capacity, thus improving water quality in in a specific situation but fails to make a detailed analysis river networks. At present, the current research on water of the monitored data of transfer measurements to provide transfer projects consists of two types: model simulation baselines and suggestions for the management of water and water transfer measurements. Model simulation mainly resources. Taking the Yinxi watershed of Ningbo City as an uses field measurements of water quality to calibrate the example, this study conducts an in-depth assessment of the model or directly takes empirical values of parameters in the improvement of water quality and puts forward recommen- model for simulation. For example, Shang et al. [13] chose dations for regional water resources management. the city of Kunshan as their study area. Their water trans- fer scheme was designed using reasonable determinations of quality improvement targets and existing engineering 2. Materials and methods conditions. The simulation and decision analyses were con- 2.1. Study area ducted with the MIKE 11 model. Li et al. [14] used the con- cept of water age and Lagrangian particle tracking, based on Located in northeast Zhejiang Province, Ningbo is situ- a three-dimensional environmental fluid dynamics model ated on the coast of the East China Sea, at the middle of the (EFDC) to evaluate water transferred from the Yangtze River continental coastal zone and the south wing of the Yangtze along several transfer routes and its impact on the environ- River Delta, with the Zhoushan Islands to the east, Shaoxing ment of Lake Taihu. Cui et al. [15] selected the urban area to the west, Sanmen Bay in the south, and Hangzhou Bay to of Changshu to construct a regional water quantity and the north. Ningbo’s water system is comprised of the Yong quality model, calibrate the model with monitoring data, River basin, Xiangshan Port, and Sanmen Bay. The Yong and propose the scheme of water transfer to improve water River basin is separated into six watersheds: Yuyao, Cixi, quality. Taking the Qinhuai River basin as an example, Song Zhenhai, Jiangkou, Yindongnan, and Yinxi, according to the and Pang [16] put forward several schemes using combined river system and administrative divisions. measures of source reduction, pollution interception, and The study area is the Yinxi watershed, covering an area water transfer, and they calculated water quality improve- of 225 km2, where the water system is well developed. After ment with a mathematical model. years of excavation, five horizontal and five vertical main At present, the mixture of rainwater and sewage pipes, rivers have formed. The upper reaches of the region are along with the leakage of sewage, are serious problems in hilly rivers, some of which have reservoirs. In flood season, China, making it difficult to investigate and accurately sim- river floods in hilly areas are partly impounded by reser- ulate point source and non-point source pollution. As for voirs and partly drained to the Fenghua River or Yao River water quality simulations, whether the model is calibrated through the Hupo, Meiliangqiao, and Xiaoxigang Rivers or not, the simulation results are uncertain, because mod- in the interior plains. During the non-flood season, large els usually overestimate the improvements in water quality upstream reservoirs also discharge water to supplement observed in practice [17]. Therefore, it is necessary to carry the ecological water demand of the river. Most floods in the out water transfer measurements to obtain accurate data for plain areas are discharged eastward through sluices along water quality improvement. the Fenghua River and partly northward to the Yao River. Water transfer measurements are mainly to observe the The main sluices are Baofeng, Chenglangqi, Duantangqi, water flow (speed, volume) or water quality improvement Xiachen, Shillongchiqi, and Fengpengqi sluices, which dis- in the receiving area. To improve the water quality of Lake charge into the East China Sea through the Yao, Fenghua, Taihu, two experimental transfers were carried out in winter and Yong Rivers. The Yao River sluice gate is built about and spring of 2002 and summer and autumn of 2003, Hu et 3 km upstream from the confluence of the Yao and Yong al. [17] pointed out that, during the transfer period in 2002, Rivers; its main purposes are to block saltwater and store total phosphorus (TP) concentration in the southwest, cen- freshwater to meet the needs of production and living in the tral, and east Taihu Bay decreased significantly by 62%, 46%, upstream region. Neither Yong River nor Fenghua River is and 31%, respectively. In 2003, TP concentration in Meiliang equipped with tide gates, even though both are tidal chan- Bay and southwest areas decreased even more significantly. nels. All sluice gates can drain water when tidal levels are Fornarelli and Antenucci [18] investigated the effect of trans- lower than inland river water levels. The location of the fer between two reservoirs on the quality of the receiving res- Yinxi watershed in Ningbo is shown in Fig. 1. ervoir, and they implemented different management strate- The main sources of water transfer are Jiaokou Reservoir gies according to the water volume and frequency of water in the upper reaches and the Yao River, for which