South-to-North Water Diversion Project Research Articles

Monitoring artificial canals with multiple SAR satellites: A case study of the Changge Canal of the South-to-North Water Diversion Project in China

Surface monitoring of artificial canals is essential to ensure safe operation. Traditional geodetic tools are commonly employed to monitor the canal of China’s South-to-North Water Diversion Project (SNWDP), which is time-consuming and high-cost. The advanced satellite Synthetic Aperture Radar Interferometry (InSAR) is an effective tool to detect subtle surface deformation, while its application for monitoring canals is short of fine deformation interpretation on a structure scale. In this study, we applied multiple SAR satellites to monitor a typical canal of the Middle Route of the SNWD Project (MRP), the Changge Canal, by extracting the historical deformation, inverting two-dimensional (2D) deformation, and analyzing distortions. The result suggests that the focused canal section is experiencing continuous deformation caused by near coal mining activity. Its vertical and horizontal distortions both reach ±1.5 mm/100 m. The InSAR applicability, including visibility and sensitivity, is applied to the structure-level interpretation of deformation. The InSAR MPs distribution highly depends on canal structures' aspect and surface coverings. The canal structures with high coherence and lower R-Index (i.e., foreshortening) are favorable for detecting InSAR MPs; meanwhile, a few MPs are detected for the structures with high coherence but high R-index. For the sensitivity of the deformation vector along the downslope, its dependency on the aspect opposes InSAR MPs distribution. The structure-level interpretation considering InSAR applicability helps deploy targeted maintenance and analyze deformation mechanisms. The procedure of fine InSAR monitoring applies to similar water diversion projects.

Deformation Evaluation of the South-to-North Water Diversion Project (SNWDP) Central Route over Handan in Hebei, China, Based on Sentinel-1A, Radarsat-2, and TerraSAR-X Datasets

The South-to-North Water Diversion Project (SNWDP) is a megaproject which has been constructed to alleviate imbalanced water resource distribution between northern and southern China. It encompasses three routes distributed in the east, central, and west of China, respectively. The central route (CR) of the SNWDP starts from the Danjiangkou Reservoir and ends in Beijing and Tianjin, running through Hubei, Henan, and Hebei Provinces; it has been in service since December 2014. For this type of megaproject, efficient and effective safety monitoring during its operation is highly challenging to the management department. Multitemporal interferometric synthetic aperture radar (MT-InSAR) has been widely applied in monitoring land deformation, especially in a wide area. However, its ability to show the deformation of one specific facility along the SNWD has not been deeply investigated. This study investigates the capability of MT-InSAR in monitoring the deformation of the canal and ancillary facilities along the SNWD-CR over Handan, Hebei Province, in China, using Sentinel-1, Radarsat-2, and TerraSAR-X datasets. Deformation rates from March 2015 to March 2016 are obtained by applying permanent scatterers (PS)-InSAR to these three SAR datasets. After combining the deformation rates derived by the three datasets, deformation along the SNWDP-CR is evaluated using a method encompassing median absolute deviation (MAD) calculation and heatmap. The evaluation result reveals that one part of the western embankment of the open canal is subsiding at up to 10 mm/year, which may be associated with overirrigation. Besides this location, the most dangerous areas assessed by the proposed method are related to ancillary facilities, mainly aqueducts and crossing-canal bridges.

Length-Weight Relationships of Eight Fish Species in the World’s Largest Water Diversion Project

The study provides the length-weight relationships (LWRs) for eight fish species, viz. Hemiculter bleekeri, H. leucisculus, Opsariichthys bidens (Xenocyprididae), Carassius auratus, Cyprinus carpio (Cyprinidae), Pseudorasbora parva (Gobionidae), Acanthorhodeus chankaensis, and Rhodeus ocellatus (Acheilognathidae), in the world’s largest water diversion project, namely, the middle route of South-to-North Water Diversion Project (SNWDP). Fish specimens were sampled by benthic fyke-nets, gillnets, multimesh gillnets, and electrofishing equipment seasonally from 2015 to 2020. The coefficient of determination (r2) was ranging from 0.964 (R. ocellatus) to 0.986 (H. leucisculus), and the b values for the eight species were within range of 2.5–3.5. Also, our study updates the information on the maximum total length for four species (H. bleekeri, H. leucisculus, A. chankaensis, and O. bidens).

Characterization of elastoplastic behavior and retrieval of active zone depth for expansive soil slopes in the middle-route channel head of the South-to-North Water Diversion Project, China, using InSAR time series

Expansive soil is very destructive for light infrastructures, while the South-to-North Water Diversion Project (SNWDP), one of the most critical projects in China, has a considerable section constructed by it. The significant displacements by the expansive soil slope (ESS) lead to severe damage to the slope prevention in the SNWDP, possibly resulting in slope failure with no timely and appropriate preventive measures. In this study, taking the channel head of the middle route of the SNWDP (Henan, China) as a case, we employed synthetic aperture radar (SAR) data of 134 Sentinel-1 scenes spanning 2017–2021 to characterize the ground displacement on the ESS and, after that, retrieve the active zone depth (AZD) that is a significant parameter to determine the treatment depth. An elastoplastic deformation model under wetting and heating effects (EDWHE) is proposed to accurately interpret ESS's nonlinear deformation, considering the soil lags responding to wetting and heating. The results show that the excavated canal generally has positive LOS displacements, maximum to 18 mm/year, while the filled canal with negative, minimum to −25 mm/year. The InSAR results of our model show a significant improvement compared to traditional models and have a good agreement with GNSS observations. Besides, we find the movement pattern of the ESS sliding toward the slope toe, manifesting the potential risk of progressive landslide. Then, we derive the soil's elastic deformation by the EDWHE and observe that the elastic swelling and shrinkage become frequent and drastic in the monsoon season, which is the principal reason for the expansive soil geohazard. Moreover, we employ a time lag approach to retrieve the AZDs with high spatial resolution and clear distribution patterns. Our works provide a methodology to study ESS's behavior and give the possibility for detecting extensive expansive-soil geohazard and helping subsequent preventive measures.

Land Use and Ecosystem Services Evolution in Danjiangkou Reservoir Area, China: Implications for Sustainable Management of National Projects

The South-to-North Water Diversion Project (SNWDP) is one of the largest cross-basin and cross-region water transfer projects in the world. The Danjiangkou reservoir area, a haven of diverse species, serves as a core water source for the Central Line of the SNWDP. Yet, less research has been conducted on changes in land use and ecosystem services (ESs) in the Danjiangkou reservoir area in the context of the implementation of the SNWDP and other national projects. In this study, we aim to reveal evolutions of land uses and ESs in the Danjiangkou reservoir area and the response of ESs to natural and socio-economic factors. This is essential to enhance the regional sustainable management of the Danjiangkou reservoir area. Based on classified land use maps and the InVEST model, we first analyzed the land use changes and evaluated three typical types of ESs (i.e., water yield (WY), carbon storage (CS) and habitat quality (HQ)) in the Danjiangkou reservoir area during 2000 to 2018. Then, we detected the spatial clustering characteristics and tradeoffs and synergistic relationships of multiple ESs through hot spot analysis and correlation analysis. Finally, we adopt the geographical detector model (GDM) to identify key driving factors of ESs changes. The results show that: (1) During 2000–2018, the area of arable land and woodland decreased by 1.65% and 0.8%, respectively, while the proportion of construction land and water area increased by 1.31% and 1.39%, respectively. (2) The greatest decrease was in WY, decreasing by 59%, while the change in HQ was relatively stable, but showed spatial heterogeneity. (3) The northern, southern and western districts of the reservoir area showed mainly synergies among multiple ESs, while other regions showed mainly trade-offs. (4) Road network density, proportion of construction land and normalized difference vegetation index are the leading factors for ESs variations. These findings can provide reference for formulating more reasonable ecological protection strategies, so as to realize the sustainable management of SNWDP and its headwaters region.

Reducing the Risk of Benthic Algae Outbreaks by Regulating the Flow Velocity in a Simulated South-North Water Diversion Open Channel.

The reduction in open-channel flow velocity due to China's South-to-North Water Diversion Project (SNP) increases the risk of benthic algal community blooms resulting in drinking water safety issues. Consequently, it has attracted attention from all walks of life. However, regulatory measures to mitigate the risk of algal blooms and the main risk-causing factors are unclear. This study simulated the river ecosystem of the SNP channel through water diversion. Simulated gradient-increasing river flow velocity affects environmental factors and benthic algal alterations, and can be used to explore the feasibility of regulating the flow velocity to reduce the risk of algal blooms. We found that the algal biomasses in the velocity environments of 0.211 and 0.418 m/s decreased by 30.19% and 39.88%, respectively. Community structure alterations from diatoms to filamentous green algae were 75.56% and 87.53%, respectively. We observed significant differences in biodiversity, especially in terms of richness and evenness. The α diversity index of a species is influenced by physical and chemical environmental factors (especially flow velocity). Our study revealed that flow velocity is the main factor affecting the growth and outbreak of benthic algae. The risk of algal blooms in open channels can be effectively mitigated by regulating the flow velocity. This provides a theoretical basis for ensuring the water safety of large-scale water conservancy projects.

Spatial and Temporal Evolution of Ground Subsidence in the Beijing Plain Area Using Long Time Series Interferometry

Due to the overexploitation of water resources, ground subsidence is becoming increasingly problematic in Beijing, China's political, economic, and cultural capital. This article aims to investigate the relationship between ground subsidence and changes in groundwater depth, and water supply from a long-term point of view. Multisource synthetic aperture radar (SAR) data using the interferometric SAR (InSAR) technique were adopted in this research, combined with a set of leveling and ground subsidence data in the Beijing Plain area from 2003 to 2020. The InSAR results demonstrate that ground subsidence in the plain area increased steadily from 2003 to 2015, expanding from sporadic to continuous laminar dispersion and producing five major subsidence centers. The South-to-North Water Diversion Project (SNWDP) that was completed in 2008 and 2015 considerably reduced the demand for groundwater supply in the Beijing Plain area. Since then, the groundwater level depth has continued to increase. However, since 2016, the ground subsidence rate has dramatically slowed down. The obtained results showed that, thanks to the SNWDP, which resulted in a decline in groundwater exploitation and an increase in renewable water recycling, the ground subsidence in Beijing's plain area has been effectively managed.

Quantitative study on eco-economic compensation for water rights trading along the South-to-North Water Diversion Project in China

Abstract The completion of the South-to-North Water Diversion Project (SNWDP) of China has necessitated water rights trading along the route. However, water rights trading generally results in an externality loss for the seller. The scientific compensation of water rights trading should be considered from the aspects of economy, society and eco-environment. In this study, we quantified the water rights trading compensation along the route from economic, social, and environmental aspects, using a method based on emergy theory. Taking Pingdingshan-Xinmi water rights trading as an example, the eco-economic compensation of Pingdingshan was quantified and analyzed. The results showed that the impact of water rights trading on Pingdingshan was mainly social and ecological in the short term, and the average social and ecological compensation was 0.027 ¥/m3 and 0.32 ¥/m3 respectively. As the economic loss caused by water shortage becomes more prominent in the long term, the social, ecological and economic compensation were shown to be 0.028 ¥/m3, 0.30 ¥/m3 and 4.55 ¥/m3 respectively in 2030. The economic impact of water rights trading on the water seller will become more and more obvious, and reasonable compensation is the key to the sustainable development of the water market.

Characterizing Spatiotemporal Patterns of Land Subsidence after the South-to-North Water Diversion Project Based on Sentinel-1 InSAR Observations in the Eastern Beijing Plain

The eastern Beijing plain has been suffering severe subsidence for the last decades, mainly associated with the long-term excessive extraction of groundwater resource. Since the end of 2014, the annual water supply in Beijing plain has reached several hundred million cubic meters because of the South-to-North Water Diversion (SNWD) Project, which has reduced the groundwater exploitation and changed the status of land subsidence. In this work, we first obtain the current spatiotemporal variations of land subsidence in the eastern Beijing plain by using progressive small baseline subsets (SBAS) InSAR time series analysis method with Sentinel-1 SAR data acquired from July 2015 to December 2021. Then, we analyze the correlations between InSAR-derived subsidence and groundwater level change by applying the cross wavelet method. The results show that two major subsidence zones are successfully detected with the maximum deformation rate of −150 mm/yr and maximum cumulative deformation of −950 mm. Besides, the ground deformation at different stages from 2016 to 2021 reveal that the area and magnitude of major deformation significantly slow down, even in the regions with severe subsidence, especially in the year of 2017, which is about two years later than the start time of SNWD Project in Beijing. Further, we find the InSAR-derived subsidence lags groundwater level change with about 1–2-month lagging time, indicating that the dynamic variation of groundwater level fluctuation may be the main factor affecting the uneven subsidence in the severe subsiding zones. Last, differential subsidence rates are identified at both sides of geological faults, such as Nankou-Sunhe fault and Nanyuan-Tongxian fault, from the observed deformation map, which could be explained that the groundwater flow is blocked when a fault is encountered. These findings can provide significant information to reveal the deformation mechanisms of land subsidence, establish the hydrogeological models and assist decision-making, early warning and hazard relief in Beijing, China.

Evolution of groundwater salinity and fluoride in the deep confined aquifers of Cangzhou in the North China plain after the South-to-North Water Diversion Project

The South-to-North Water Diversion Project (SNWDP) has greatly improved the water shortage in the North China Plain. However, the impact of the SNWDP on the evolution of groundwater chemistry, especially fluoride and salinity, was still unknown. Cangzhou, one of the recipient cities of SNWDP and suffered from severe land subsidence, was selected to collect the deep confined groundwater samples before and after the SNWDP. The results showed that groundwater fluoride concentration decreased after the SNWDP, with a median value of 4.39 mg/L in 2017 and 3.00 mg/L in 2021, respectively. This trend was more clearly observed in the land subsidence area, which could be related to the reduction of land subsidence, due to the stopping pumping of deep groundwater. The pore water in clayey sediments contains fluoride up to 7.02 mg/L, which can be released into groundwater due to the sediment compaction before the SNWDP. The extensive exploitation during last decades changed the groundwater recharge patterns, resulting in over 60% deep groundwater being recharged by the pore water released from clayey sediment. The results of the Small Baseline Subset Interferometric Synthetic Aperture Radar (SBAS-InSAR) suggested that land subsidence has slowed down after the SNWDP, especially in the central area of land subsidence, thereby restricting the release of fluoride-rich pore water. However, groundwater salinity increased after the SNWDP, and the number of samples exceeding the drinking standard (TDS <1000 mg/L) increased by 26.4%. The rising groundwater level favors the water-rock interaction, promoting the dissolution of soluble minerals, for instance, halite, which was reflected by the results of inverse and forward modeling using the PHREEQC. Groundwater salinization after the SNWDP potentially induces the fluorite dissolution and causes the elevation of groundwater fluoride concentration. However, the calculated results indicate that the amount of F elevation related to groundwater salinization is significantly lower than the contribution of fluoride-rich pore water from clay sediment compaction. The findings of this study provide a comprehensive assessment of the influence of the SNWDP on the groundwater quality and some new insights for the management of groundwater resources.

Proper Pricing Approach to the Water Supply Cost Sharing: A Case Study of the Eastern Route of the South to North Water Diversion Project in China

Conflict in cost sharing is normal in complex water distribution system projects, such as the inter-basin water diversion project (IWDP). China’s South to North Water Diversion Project (SNWDP) is the largest IWDP in the world, with a complex relationship between upstream and downstream users of the water supply. Therefore, it is necessary to propose an applicable and unsophisticated cost-sharing method to deal with the complex relationship between upstream and downstream users. This paper proposes an improved cost-sharing method based on the continuity equation of water quantity and the balance equation of the project cost between upstream and downstream users. The fairness of sharing the joint cost between parties involved in the eastern route of SNWDP (ER-SNWDP) obtained using the proposed improved cost-sharing method is investigated by comparing its results with the existing cost-sharing method. The results demonstrate that the proposed method can overcome the non-convergence issue of the existing sharing formula and reduce the differences between upstream and downstream users’ sharing costs. The improved method provides a cost-sharing strategy that is more easily accepted by both the upstream and downstream users than the existing estimation approach. Therefore, the proposed pricing approach can provide technical guidance for decision makers in the effective operation of large-scale IWDPs in areas with quasi water markets.

Impact of local environmental standards on water environmental carrying capacity in large water diversion project: A system dynamics analysis in Shandong, China

Large water diversion projects have extensive impact on the water systems in the receiving areas, where inevitable regional responses are aroused and alert to local environmental carrying capacity. To ensure the water quality of China's eastern South-to-North Water Diversion Project (SNWDP), Shandong Province had issued strict local wastewater discharge standards since 2006. However, some flexibility exists in the enforcement of local standards, which created uncertainty to the outcomes. A system dynamic (SD) model and Water Environmental Carrying Capacity (WECC) method were integrated to dynamically illustrate the interaction between the enforcement of the local standards and the performance of the regional water system. The WECC was calculated based on an indicator system representing the multi-dimensional impact of the local standards on the regional water system. The SD model was constructed to simulate and forecast the variations of those indicators of WECC. The SD-WECC model was trained and validated with yearly data from 2000 to 2020, then four scenarios with different levels of enforcement of local standards were illustrated. The results showed that overall WECC improves during period from 2000 to 2025, and that the SNWDP improves the balance of water supply and demand in Shandong in the long run in the three scenarios that have introduced the local standards. The adoption of the local standard helps the concentration of industrial Chemical Oxygen Demand (COD) discharge to meet the discharging standards earlier by stimulating the investment in pollution control. Therefore, the flexibility in local water environment management enabled the local actors to pursue a balance between environmental protection and economic growth in a dynamic context with multi-objects for local development.

Characterization of Aquifer System and Groundwater Storage Change Due to South-to-North Water Diversion Project at Huairou Groundwater Reserve Site, Beijing, China, Using Geodetic and Hydrological Data

Groundwater overexploitation is a critical issue in the North China Plain (NCP), resulting in groundwater level decline and surface subsidence for the last half-century. This problem, however, has been greatly alleviated by the South-to-North Water Diversion (SNWD) Project since 2015. Monitoring of this process has been steadily improved in recent years using water level and geodetic observations. Here, we characterize the water storage change at the Huairou groundwater reserve site (HGRS) in Beijing due to the SNWD by combining Interferometric Synthetic Aperture Radar (InSAR) data of the Sentinel-1 satellites, continuous Global Positioning System (GPS) data, and well water level data observed during the same time. InSAR observations revealed subsidence up to ~400 mm in the Beijing plain but uplift at ~40 mm in the HGRS during 2015–2019, and more than 70% of the uplift occurred from October 2018 to January 2019. By integrating the most significant uplift deformation during October 2018 to January 2019 with water level observations at the same time, we estimated the storativity of the confined aquifer system at HGRS as 1.68–7.82×10−3, weighing in the correction for effective stress and surface deformation for various situations. Based on the estimated aquifer storativity and the observed water level change in the unconfined and confined aquifer, the recharged water storage for the confined and unconfined aquifers was estimated as 1.20–1.39×107 m3 and ~2.86×108 m3 from 6 October 2018 to 22 January 2019, respectively, which is about 4% and 91% of the surface water recharge through river channels in the same period due to the SNWD Project. Our study demonstrates that integration of geodetic and hydrological data can provide crucial information for the assessment of groundwater circulation and assistance of groundwater management.

Beijing Land Subsidence Revealed Using PS-InSAR with Long Time Series TerraSAR-X SAR Data

Beijing is a major city suffering from land subsidence due to long-term over-exploitation of groundwater. The South-to-North Water Diversion Project (SNWDP), however, has had a significant impact on the structure of water consumption since the end of 2014, and it is changing the status of land subsidence in Beijing. In this study, we employed Persistent Scatterers Synthetic Aperture Radar Interferometric (PS-InSAR) to investigate the decadal evolution of land subsidence in Beijing with 100 TerraSAR-X stripmap images collected from April 2010 to December 2019. The water resources, historic climate and urban construction data were compiled for the years of 2010 to 2019 to analyze changes in groundwater level, human activity, surface geology, active faults and land subsidence patterns. The results show that the changes in the water supply structure are correlated to a rise in groundwater level after 2015. These changes include an increase in the water supply from the SNWDP, a reduction in groundwater exploitation, the optimization of water consumption, replacing recycled water for environmental water and a reduction in the use of water for agriculture. Land subsidence in the study area was concentrated in the eastern regions, trending towards a decreasing velocity starting about two years after the commencement of SNWDP in 2015. Uneven subsidence in the land subsidence area was related to excavations of underground soil, and the construction of Line 6 and Line 7 led to rapid nonlinear subsidence. Our results have scientific significance for reducing subsidence hazards in the context of SNWDP and urban expansion.

Impact of Climate Change on Water Resources in the Western Route Areas of the South-to-North Water Diversion Project

The South-to-North Water Diversion Project (SNWDP) is a national strategic project for water shortages in northern China. Climate change will affect the availability of water resources in both source and receiving areas. A grid-based RCCC-WBM model based on climate projections from nine Global Climate Models under SSP2-4.5 was used for analyzing the changes in temperature, precipitation, and streamflow in the near future (2025–2045, NF) and far future (2040–2060, FF) relative to the baseline (1956–2000). The results showed that: (1) the temperature of the western route will increase significantly in the NF and FF with an extent of 1.6 °C and 2.0 °C, respectively, (2) precipitation will very likely increase even though Global Climate Model (GCM) projections are quite dispersed and uncertain, and (3) over half of the GCMs projected that streamflow of receiving area will slightly increase with a rate of 1.68% [−8.67%, 12.3%] and 2.78% [−3.30%, 11.0%] in the NF and FF, respectively. Climate change will support the planning of the western route to a certain extent. However, water supply risk induced by the extreme situation of climate change should be paid adequate consideration when the project operates in practice due to the large dispersion and uncertainty of GCM projections.

Study on ecological environment change of water source area of the middle route of South-to-North Water Diversion Project in the past 20 years

The South-to-North Water Diversion Project (SNWDP), which began operation in 2013, is an important step in China’s water resources development, and the middle route of SNWDP is one of the most important parts. However, this project has caused a certain negative impact on the ecological environment of Danjiangkou reservoir, the water source area of this project. This study uses DEM data and Landsat data for different years to analyze land-use changes in QGIS software and discusses the causes and impacts of the middle route of SNWDP. The results show that the present area of water and vegetation increased significantly, while the cultivated land and human area (including urban, rural and other areas of human activity) decreased obviously compared with 1999. The reasons for this change include natural conditions, engineering construction and policies, but policies such as raising the Danjiangkou dam and returning farmland to forests have played a bigger role. The impacts of SNWDP include water quality deterioration, soil erosion, changes in vegetation area, changes in biodiversity and changes in the lives of residents in the area. These impacts have positive reference significance for the construction of water conservancy undertakings in China in the future.

Modeling the effects of water diversion projects on surface water and groundwater interactions in the central Yangtze River basin

Due to the lack of the quantification of surface water (SW) and groundwater (GW) interaction, the chemicals transport and fate and wetland evolution are hard to predict under impact of both the natural condition and water diversion projects. To address this issue, a 3D regional numerical model is proposed in this study to analyze the effects of the South-to-North Water Diversion (SNWD) and Yangtze-Hanjiang Water Diversion (YHWD) projects on groundwater flow regimes and SW-GW interactions of Jianghan Plain in the central Yangtze River basin. The model results show that the Yangtze River and groundwater interactive pattern varied little, whereas the exchange capacity has been significantly affected by the SNWD but little affected by the YHWD. If only implemented SNWD project, the Hanjiang River and groundwater interactive pattern varied and the net exchange rate between the Hanjiang River and groundwater decreased by 69.3% compared to natural condition. Since YHWD was introduced to complement SNWD, the net exchange rate has been reduced by 25.3% compared with that under the only SNWD. SNWD and YHWD projects implementation caused the decrease of the groundwater level along the Yangtze River with the maximum value of 0.19 m but the increase of groundwater level along the Hanjiang River with the maximum rise reaching up to 0.78 m. This study provides the insights for quantification of GW-SW interaction at regional scale, which will benefiting for integrated water resource management and understanding contaminant reactive transport and wetland evolution in the central Yangtze River basin.

Inversion of Groundwater Storage Variations Considering Lag Effect in Beijing Plain, from RadarSat-2 with SBAS-InSAR Technology

The long-term over-exploitation of groundwater has not only caused the compaction of aquifer thickness and surface deformation but has also further aggravated the loss of groundwater storage (GWS) in Beijing plain. The South-to-North Water Diversion Project (SNWDP) furnishes a new source of water for Beijing. By reviewing related studies, it was found that there are few studies on the realization of GWS estimation based on InSAR technology considering the lag effect. Therefore, in this study, firstly, the long-time series deformation characteristics of Beijing plain were obtained from 46 RadarSat-2 images using small baseline subset interferometric synthetic aperture radar (SBAS-InSAR) technology. Secondly, the seasonal components of surface deformation and hydraulic head change were extracted by means of multichannel singular spectrum analysis (MSSA), verifying the separation accuracy by means of Monto Carlo-SSA (MC-SSA). Finally, for the hydrodynamic delay (aquifer water supply/drainage) of the complex aquifer system, we introduced the time lag cross-correlation (TLCC) approach to correct the hysteresis response of seasonal deformation relative to the variation of the aquifer system head, so as to realize the estimation of aquifer storage properties and GWS loss, even unrecoverable GWS (UGWS). The results showed that the average annual variation of total GWS (TGWS) in Beijing plain was −6.702 × 107 m3, of which the depletion volume of UGWS was −6.168 × 107 m3, accounting for 92.03% of the TGWS. On a temporal scale, the depletion of UGWS lagged behind the total head change, with about one year of lag time. On a spatial scale, in contrast to the north of Beijing plain, the depletion of UGWS in the south only recovered briefly after 2015 and then continued to decline. This further indicated that the process of the decline of middle-deep confined head and long-term GWS loss caused by over-exploitation of groundwater was irreversible. These findings are of great significance to optimize the allocation of groundwater resources, reduce the harm of land subsidence and protect groundwater resources.

Water Pricing Mechanism for China's South‐to‐North Water Diversion Project: Design, Evaluation, and Suggestions

AbstractSince the completion of first‐phase projects on the eastern and middle routes of the South‐to‐North Water Diversion (SNWD), the design and implementation of water pricing mechanism have become the key factors that affect the project operation. This paper launches the evaluation of implementation effect on the water price policy of the SNWD built projects in 2018 by coordinating the consumption of transfer water, allocation of receiving‐areas’ water resources, collection of water fee for transfer water, as well as the implementation of local water price policies, which mainly exerted a comprehensive and interactive influence on the water price policy. Based on a series of data statistics and analysis, the usage of water transferred from the Yangtze River, improvement of regional water resources allocation, collection of water fee, and the implementation results of local water price policies were systematically analyzed. The main conclusions and corresponding suggestions were put forward to provide useful references on the formulation of water price policies for the design, optimization, and adjustment of the subsequent water pricing mechanism in the SNWD project.

Time-Lag Effect: River Algal Blooms on Multiple Driving Factors

Compared to the eutrophication of lakes and reservoirs, the mechanism of river algal blooms in a flowing water body are more complicated, and often lead to serious consequence in catchment scale. Due to the simultaneous impact of a variety of environmental pressures, the water ecosystem integrity state often shows a response characteristic of accumulation, complexity and time lag, therefore it is difficult to use conventional hydrodynamic and water quality models to scientifically characterize and analyze. The lower Hanjiang River (HR) is an important influence area of the middle route of the South-to-North Water Diversion Project (SNWDP) in China, continuous river blooms issue has become a major national concern. In this study, a time-lag analysis approach was developed to identify the causes of algal blooms formation and the time-lag response law in the lower HR, including principal component analysis (PCA), grey relation analysis (GRA), and Almon Distributed Lag Model. Results found that, the hydrological regime (ΔH) contributes the most to the river bloom, especially due to the flow hindrance of the Yangtze River (YR) and the water project upstream. It is also found that the algal bloom outbreak in the lower HR is not an immediate response to the driving factors. It has a time lag of about 1 period (10 days) in the response with antecedent driving factors. Finally, we discussed the influence and its responding mechanism of ΔH on the growth of phytoplankton. The research can provide early warning for the prevention and control of algal blooms in the large river system.