Plain River Network Research Articles

Removal of Microplastics by Different Treatment Processes in Shanghai Large Municipal Wastewater Treatment Plants

Wastewater treatment plants are important sources of microplastics (MPs) in aquatic environments. The present study was conducted to investigate the number concentration, removal rate, and fate of MPs in two large municipal treatment plants in Shanghai. The MPs number concentration in the influent water of WWTP1 and WWTP2 were (226.27±83.00) piece·L-1 and (171.89±62.98) piece·L-1, respectively. WWTP1 had a MPs removal efficiency of 63.25%, which is slightly higher than that of WWTP2, at 59.84%. The removal efficiency during the primary treatment process of the two sewage treatment plants on MPs accounted for 70%-80% of the whole treatment process. The primary treatment process and secondary treatment process transferred (48.10%±1.62%) and (12.97%±0.05%) of MPs in the sewage to the sludge, respectively. As a whole, (38.82%±1.55%) of MPs in the sewage treatment plants were finally discharged into natural waters, and the remaining (61.18%±1.55%) entered the sludge. This study shows that the removal rate of MPs in Shanghai's municipal treatment plants is low and that after treatment, large amounts still enter the natural waters with the final effluent, which causes significant ecological risks. This study provides basic data of MPs removal and trends of large urban sewage treatment plants in a plain river network area, which can provide reference for further design of MPs removal processes.

Risk Probability Assessment of Sudden Water Pollution in the Plain River Network Based on Random Discharge from Multiple Risk Sources

Starting from the time variance and uncertainty of accidental discharge, this paper describes the probability of the occurrence of the “normal-accident” alternate state for a risk source using the Markov state transfer model, simulates the behaviour of pollutants in rivers using the hydrodynamic and water quality models for non-conservative substances, and tracks the transport path of pollutants in rivers using the water quality model for conservative substances. The above models are coupled with the Sequential Monte Carlo algorithm, and the risk probability analysis model for sudden water pollution in the plain river network is established and applied to the Yixing river network. The results show that (a) the risk probability of exceeding ammonia nitrogen standard (PES of ammonia nitrogen) is lower in the upper reaches and higher in the middle and lower reaches; (b) dynamic changes in pollutant concentration lead to different changes in the PES of ammonia nitrogen in each reach; (c) the differences in the simulated PES values between the sudden scheme and the stable scheme (NPES of ammonia nitrogen) in the upper and middle reaches show a patchy distribution of high and low values, which are related to the risk source location, the water movement direction and the concentration change in the reach after accepting pollutant loads from the risk sources; (d) the NPES of ammonia nitrogen in the lower reaches results from the coupling effect caused by accidental discharges from multiple risk sources; and (e) the different effects of the lower boundary hydrological conditions on the upstream water inflow lead to the different coupling effect on the water quality probability of sections in the downstream area.

Influence of changes in river system structure on hydrological processes in Taihu Basin, China

ABSTRACTWith the rapid economic development and urbanization in Taihu Basin (eastern China), the river system has decayed and the connectivity of rivers and lakes has weakened, resulting in frequent floods. The impact of changes in river system structure on hydrological processes in the plain river network area was analysed against a background of urbanization. An indicator system was built to describe the quantitative, morphological and spatial structure of the river system. Analysis of the change in annual average and extreme water levels revealed the influencing mechanism of the changes in river system structure on the hydrological processes. The results indicate a decreasing tendency in the density of the river system in the study area, with a reduction in water surface ratio by about 20% in the past 50 years. Since the 1960s, the maximum and annual average water levels have increased. The degree of change in the mean monthly, annual lowest and annual highest water levels was great, with that in the non-flood season being higher than in the flood season. The decrease in the number of rivers directly reduced the storage and adjustable capacity of the basin.

Atmospheric and human‐induced impacts on temporal variability of water level extremes in the Taihu Basin, China

AbstractUnderstanding the variation of water level extremes with their potential drivers can provide insights for flood risk management. In this study, temporal variability of water level extremes is investigated across the plain river network region of the Taihu Basin. The driving force analysis on water level extremes is mainly conducted for atmospheric (rainfall, climatic index, and tide) and anthropogenic forcing. The quantile perturbation method is employed to examine variability of extreme values and the Spearman correlation analysis to identify potential drivers of extreme water level variability. Considering water level extremes in all seasons, the 1990s have statistically significant positive anomalies, while the late 1960s to the 1970s and the 2000s have significant negative anomalies. The oscillation pattern of anomaly in summer has a higher variability than that in the other three seasons. Significant correlations are detected between the anomalies of water level extremes and rainfall (tide level) during summer and winter. Water level extremes in summer and winter have a strong connection to the Pacific Decadal Oscillation and North Atlantic Oscillation/Arctic Oscillation, respectively. Conversely, no consistent significant correlations between water level extremes and climatic indices are found in spring and autumn, which is mainly related to hydraulic structure construction and operation.

Non-stationarity analysis of extreme water level in response to climate change and urbanization in the Taihu Basin, China

Regional climate change as well as urbanization are likely to introduce characteristics of non-stationarity in the extreme water levels (EWL), which in turn will affect the possibility of flooding in the plain river network region. For this study, China’s Taihu Basin as a typical case for analyzing the impacts that climate change and urbanization will have on changes in the EWL. Additionally, changes in the response that EWL will have toward future climate change and urbanization are also studied. A generalized additive model for location, scale and shape (GAMLSS) model with time (t), precipitation (pre) and population (pop) as major predictors was constructed to empirically investigate. Results indicate that the time dependent variables of the GAMLSS clearly describe the temporal variation of the EWL. The GAMLSS with physically-based covariates can capture additional details regarding the changing properties of EWL. According to changes exhibited in the EWL Akaike information criterion values, it is found that the impacts of climate change covariates are larger than that of the urbanization covariates. Additionally, for the study’s sample period of 2015–2099, an increasing trend is found for EWL under the RCP2.6 and RCP4.5 scenarios. It is concluded that flooding risk is likely to increase in China’s Taihu Basin with changing environment conditions, and that some necessary measures should be taken by local water resource management authorities to address the potential risks posed to the region.

Characteristic Analysis and Loss Accounting for Water Pollution in Plain River Network Region - A Case Study of the Yangtze Delta

Because there are many water systems, severe human activities, increasingly serious water pollution problems and great economic loss in the plain river network region, the establishment of scientific and reasonable economic loss function is necessary to guide the protection and management of water resources. Taking the Yangtze Delta as an example, the characteristics of water pollution in the same period are that the flood season is stronger than the non-flood season. The analysis based on the physical mechanism shows that the process of economic loss of water pollution not only accords with S-type curve but also gives a reason for the S-type curve from the aspect of mechanism. The water pollution loss rate function which is constructed on the basis of hyperbolic tangent function divides the development stage into such three stages as non-enrichment, enrichment and saturation of pollutants, gives turning points of each stage as well as the solution and significance of parameters and enriches the physical process of models. The results of living samples show that the comprehensive water grades can be obtained easily and quickly through the river length failure rate. Their good correlation has certain promotion significance. The total water pollution economic loss is bigger. The average economic loss in the flood period from May to July is bigger than that in the flood period from August to September and non-flood period. The living samples prove that there exists pollutant diffusion phenomenon in the flood period.

Risk analysis of sudden water pollution in a plain river network system based on fuzzy-stochastic methods

A comprehensive fuzzy-stochastic risk assessment method is adopted to systematically quantify the stochastic and fuzzy uncertainties related to discharge conditions, environmental standards and health assessment criteria. A sequential Monte Carlo simulation of pollutant behaviour in rivers after the accidental discharge from multiple risk sources is carried out using a risk probability analysis model of sudden water pollution. The fuzzy membership functions based on environmental water quality standards and health impact criteria are established by means of a questionnaire. Then, the simulation results and the membership functions are combined to quantify the stochastic uncertainty of the pollutant concentration and the fuzzy uncertainty of its consequences. Based on the fuzzy logic method, the general risk level is obtained by combining the risk based on the environmental water quality standard and the health risk, and the general risk scores (CS) are obtained via the interpolation method. The risk assessment method is applied to the Yixing area. The results show that (a) the ammonia nitrogen CS values are low in the upper reaches and high in the middle and lower reaches. The ammonia nitrogen CS values under sudden schemes are not less than the corresponding values under the stable scheme. (b) The dynamic concentration changes in the sub-reach affect the probability of exceeding the ammonia nitrogen standard and indirectly affect the changes in the CS values in different reaches. (c) The net variation in the ammonia nitrogen CS values exhibits a concentrated distribution of high and low scores in the upstream areas and a concentrated distribution of high scores in the downstream area. (d) For most of the sections, there is a positive linear correlation between the risk growth rate (GR) and the average duration of the accidental state, and the greater the GR value is, the more sensitive the section is to the accident risk.

Isotopic evidence of nitrate sources and its transformations in a human-impacted watershed.

The considerable spatial and temporal variabilities of nitrogen (N) processing introduce large uncertainties for quantifying N cycles on a large scale, particularly in plain river network regions with complicated hydrographic connections and mixed multiple N sources. In this paper, the dual isotopes δ15N and δ18O and dissolved anions in regularly collected samples (n = 10) from the studied river, which is one of the most seriously polluted rivers in the plain river network regions of the Taihu Lake catchment, were analyzed to ascertain the main nitrate (NO3-) sources and watershed N processing in the context of monsoon climate. The seasonal variations in precipitation, temperature, and hydrology play key roles in the regulation of the river NO3- concentration, NO3- sources, and watershed N processing. Nitrification of N-containing materials in the soil was possibly the major source of NO3- all year round, especially in the rainy season, whereas manure and sewage significantly contributed to the NO3- load in the Taige River in the dry season. Nitrification and denitrification processes within the area were closely related. The significant negative relationship between the water temperature and δ18O-NO3- values indicated the occurrence of nitrification in the soil throughout the year. By contrast, seasonal variations of denitrification were apparent from May to July with the high soil temperature and moisture, thereby indicating the occurrence of denitrification (22.9%) within the watershed. After the assessment of temporal variations of NO3- sources and watershed N processing, improved environmental management practices can be implemented to protect water resources and prevent further water quality deterioration in human-impacted watersheds.

Impacts of anthropogenic activity on the response of water level to rainfall in the urbanized plain river network: A case study in the Hangzhou-Jiaxing-Huzhou region of Taihu Basin

太湖流域快速城镇化、水利工程等一系列人类活动对流域水文过程产生了深刻影响.本文以快速城镇化的杭嘉湖地区为例，基于1961-2014年逐日降雨、水位观测资料，构建了水位涨幅（ΔZ）、水位增长速率（k₁）和退水速率（k₂）等指标，旨在揭示变化环境下该地区降雨过程中水位的变化特征及可能的驱动因素.结果表明：1）变化环境下杭嘉湖地区近54年降雨量呈微弱的增加趋势，但降雨过程中的水位涨幅呈下降趋势，尤其是平均水位涨幅呈显著下降趋势，且于2000年左右发生明显变化；突变后水位涨幅下降主要集中在10~50 mm/d的降雨过程中，而大于50 mm/d的降雨过程中突变后水位涨幅较突变前有所升高.2）从空间分布上来看，各站降雨量与水位涨幅存在明显的空间差异，降雨量总体呈增加趋势，增加趋势东强西弱；大部分站点的水位涨幅却呈下降趋势，其中位于区域南部站点的平均水位涨幅下降趋势较东北部更为明显，水位涨幅呈显著下降站点的空间分布与杭嘉湖南排工程等水利工程的分布较为一致.3）通过对杭嘉湖地区降雨过程中水位增长速率和退水速率的变化分析发现，突变后较突变前退水速率有所提高，说明近年来水利工程等设施的完善和有序调度使得杭嘉湖地区的排洪能力有所提高，该变化可能是导致杭嘉湖地区地区突变后一定强度的降雨过程中水位涨幅下降的主要原因.而杭嘉湖地区强降雨过程中水位涨幅依然较高，可能是该地区洪峰水位居高不下的主要原因.此外，由于该地区近年来起涨水位抬升明显，对洪峰水位的抬升也有一定影响.;Rapid urbanization and human activities have a profound impact on the hydrological process in Taihu Basin. This paper constructed three indices include the water level rising (ΔZ), the rate of water level rising (k₁) and the rate of water level recession (k₂). Based on the observation data of daily rainfall and water level during 1961-2014, we try to reveal the variation characteristics of the water level and possible driving factors in the rainfall process in the Hangzhou-Jiaxing-Huzhou region. The results indicate that:(1) The rainfall shows an increasing trend, but the ΔZ shows a decreasing trend during the rainfall process. Especially, the average water level rising shows a significant decreasing trend and the abrupt change occurs in the year 2000 AD. The decreased ΔZ mainly occurs in the rainfall intensity ranged from 10 mm/d to 50 mm/d after 2000 AD. The ΔZ shows an increased trend in heavy rainfall process above 50 mm/d. (2) The rainfall in the east shows a significantly increasing trend than in the west. However, ΔZ in many stations is declining, which is more significant in the south. These changes is inseparable from the flood discharge project in the Hangzhou-Jiaxing-Huzhou region. (3) Through the analysis of the k₁ and k₂ in the rainfall process, k₂ is increased, which indicates that the development of water conservancy facilities and orderly scheduling has improved the flood discharge capacity in recent years. This change may be the main cause for the declined k₂ in a certain intensity of rainfall after 2000 AD. The ΔZ remained high in the heavy rainfall process, which can be related to that the current flood discharge capacity that cannot resist the increase of ΔZ. In addition, the incipient rising water level has increased significantly in recent years, which also makes a certain impact on the flood in the study area.

Evaluation of Plain River Network Hydrologic Connectivity Based on Improved Graph Theory

Based on graph theory, the river network was generalized by a graph model. Considering the influence of water quantity on the hydrologic connectivity of river network, the connectivity factor reflecting water quantity index was taken as the weighted value, the quantitative evaluation model of hydrologic connectivity degree was setted up. By calculating the river network weighted connectivity degree with MATLAB, the quantitative evaluation of river network hydrologic connectivity was realized. Taking the Qinhuai River Basin as an example, the HEC-HMS hydrological model was established for the simulation of short-term and long-term flood. The connectivity level of the river network in the basin under different scale floods was graded by the quantitative evaluation results of connectivity degree. The results showed that the constructed evaluation model has good applicability and reliability.

Effects of anthropogenic activities on long-term changes of nitrogen budget in a plain river network region: A case study in the Taihu Basin

Over recent decades, Taihu Lake, the third largest freshwater lake in China, has borne the brunt of intensive human activities. Non-point source pollutants and discharges of domestic wastewater are now the main cause of eutrophication. To control non-point source pollution, it is useful to have a good understanding of the spatial and temporal distribution of N (nitrogen). In this study, we applied Export Coefficient Model (ECM) and the Net Anthropogenic Nitrogen Inputs (NANI) method to estimate the N loads in the Taihu Basin at county scale since 1980. We found that N inputs and exports had increased from 6432 and 3170 kg N km−2 yr−1 in 1980 to 9722 and 4582 kg N km−2 yr−1 in 2010, respectively. The 151% increase of N inputs, but 144% increase of riverine N outputs suggested the more N was retained within the Taihu Basin. Both the population density and the urban areas were strongly correlated with N inputs and exports. Approximately 38% of the N inputs were exported in 2010, but only 19% were exported in 1980. This ratio illustrated that human activities, especially urbanization and population growth, have upset N budget in the Taihu Basin. This study supported by empirical models provides a case to demonstrate the N cascade in the Taihu Basin and can also be used to support decision making and to facilitate the development of measures to control N in the future.

Preferential accumulation of small (

Microplastics are a global concern for their threat to marine ecosystems. Recent studies report a lack of smaller microplastics (<300 μm) in oceans attributed to a “loss in ocean”. Several hypotheses have been proposed to explain the absence of smaller microplastics, but their fate and transport remain an enigma. Our study recovered high concentrations of microplastics (32947 ± 15342 items kg−1 dry sediment) from sediments of a coastal plain river network in eastern China, with the <300 μm fraction accounting for ∼85% of total microplastic particles. Microplastic concentrations were generally higher in sediments from tributary streams and streams surrounded by industrial land use. The high variability of microplastics within the watershed indicates that the distribution of microplastics is regulated by several factors, such as distance to source(s), river flow characteristics, buoyancy behavior, degradation, etc. Fragment and foam forms dominated the small microplastics, while fibers were less prevalent in the <300 μm fraction and more abundant in downstream sites. The dominance of small microplastics in riverine sediments in this study provides a possible mechanism to explain the relative absence of small microplastics in the ocean, and advocates for quantification of the whole size spectrum of microplastics in future studies of riverine microplastic fluxes.

Study on Calculation Method of Water Resources Supply and Demand Balance in Plain River Network Area

After the impoundment of the Three Gorges reservoir, the middle and lower reaches of Yangtze River will have a long distance erosion in a long time, and in the conditions of the same flow, the water level of the three outlets along Jingjiang river reach (Songzi outlet, Taiping outlet, Ouchi outlet) will drop, which leads to the flow diversion reduction of three outlets. Undoubtedly, all these will have an impact on irrigation and water supply of river networks on south bank of Jingjiang river reach. The calculation of water resources supply and demand balance is the foundation of analyzing the influence of the Three Gorges Project on the river networks on south bank of Jingjiang river reach, clearing the key link of water shortage and allocating water resources. The calculation of water resources supply and demand balance in this area, however, has unique complexity of plain river network, which is caused by multi-water sources and multi-water intakes. To handle this problem, the water resources supply and demand balance model in plain water network with multi-water sources and multi-water intakes is established, which is based on the characteristics of plain river network. And this model is utilized to calculate and analyze the water resources supply and demand balance in river networks on south bank of Jingjiang river reach. Relevant research results provide new methods and thoughts for the calculation and analysis of water resources supply and demand balance in plain river network.

Development of a polder module in the SWAT model: SWATpld for simulating polder areas in south‐eastern China

AbstractPolders are one of the most common artificial hydrological entities in the plain river network regions of China. Due to enclosed dikes, manual drainage, and irrigation intake operations, polders have had a significant impact on the hydrological processes of these areas. Distributed hydrological models are effective tools to understand and reproduce the hydrological processes of a watershed. To date, however, few models are able to simulate the drainage and irrigation intake interactions of polders at a watershed scale. This study develops a modified version of the Soil and Water Assessment Tool (SWAT) model, which is designed to better represent polders (SWATpld). The SWATpld model simulates drainage and irrigation intake processes by calculating the excess‐water storage in the inner rivers and irrigation schedule for paddy rice in the polder. Both SWAT and SWATpld models were tested for the Liyang watershed. SWATpld outperformed SWAT in simulating the daily discharge and intake of the experimental polder and predicting the monthly peak flow at the outlet of the Liyang watershed, which suggests that the modified model simulates the hydrological responses of the study watershed with polder operations more realistically than the original SWAT model does. Further evaluation at various locations and in various climate conditions would increase the confidence of this model.

Study on ecological regulation of coastal plain sluice

Coastal plains are densely populated and economically developed, therefore their importance is self-evident. However, there are some problems related with water in coastal plains, such as low flood control capacity and severe water pollution. Due to complicated river network hydrodynamic force, changeable flow direction and uncertain flood concentration and propagation mechanism, it is rather difficult to use sluice scheduling to realize flood control and tackle water pollution. On the base of the measured hydrological data during once-in-a-century Fitow typhoon in 2013 in Yuyao city, by typical analysis, theoretical analysis and process simulation, some key technologies were researched systematically including plain river network sluice ecological scheduling, “one tide” flood control and drainage scheduling and ecological running water scheduling. In the end, single factor health diagnostic evaluation, unit hydrograph of plain water level and evening tide scheduling were put forward.

A hydrodynamic model coupled multiple scenarios for plain river network and its application

The plain river network is not only complex in shape but also contains many complex scenarios, such as interval inflow and outflow, hydraulic structures and water storage area, etc., which increases the difficulty of runoff simulation in plain river network. To address this problem, a hydrodynamic (HD) model coupled multiple scenarios that may occur in plain river network was proposed, which was used to simulate the runoff process of the plain river network. To illustrate the proposed model, Xi River was chosen as a study area. We designed some experiments for each scenario, and the experimental results show that simulation results have good consistency with the observation. It is worth noting that the simulation accuracy of the water level is always higher than the simulation accuracy of the flow. Moreover, the runoff simulation accuracy of runoff events with large runoff is relatively high. It turns out that HD model is suitable for runoff simulation of plain river network. In addition, we compared the flood diversion effects of water storage area and sluice, and the results show that the effect of water storage area is more obvious than sluice, and the flood diversion method combined with sluice and water storage area has better flood diversion effect. In conclusion, HD model is good at simulating floodplain storage effects, backwater and the change of water level and flow under the condition of engineering dispatching, which has important guiding significance for flood control in plain river network.

Effect of urbanization on the river network structure and functions-A case study in Suzhou City

针对城市化对平原河网水系结构的影响所引起的洪涝灾害频发等一系列水文问题，以我国典型平原河网地区苏州市为例，根据不同城市化程度分为主城区、市辖区、其他市县区，基于1991、2001和2015年三期遥感影像与1960s、1980s和2010s三个时期的水系数据，应用RS/GIS等技术，构建水系结构参数指标，重点探讨了城市化对河网水系结构及功能的影响.结果表明：城镇用地迅速增长，主要以牺牲水田、水域等土地利用方式为代价，到2015年全区城镇用地面积所占比重已达到41.35%，土地利用类型的变化规律与城市化进程的差异性保持一致；水系结构变化主要受城市化影响，且基本与城市化进程呈现同步性.近50年来，全区的水面率、河网密度、支流发育系数、主干河流面积长度比、河网复杂度和河网结构稳定度分别减少了19.63%、6.91%、7.34%、1.06%、5.49%和7.87%，城市化水平与各指数均呈负相关关系；人类活动不仅直接影响河流功能，也间接地通过改变平原河网的水系结构导致其功能发生改变，如河网调蓄能力下降、河流生态功能受损等.该研究为城市化地区河流水系保护及防洪减灾提供参考与理论支撑.;This paper centers on a series of urban hydrological problems like flood and waterlogging disasters resulting from the impacts of urbanization on river network structure. In this paper, Suzhou City, one of the typical plain river network areas in China, is taken as an object of the study. Based on different stages of urbanization, Suzhou City is divided into main urban district, municipal district and other county-level district. This research conducts both qualitative and quantitative analysis with the help of the remote sensing images in 1991, 2001 and 2015, as well as the stream data in 1960s, 1980s and 2010s, focusing on the influence of urbanization on the river network structure and functions. The study shows that:With the rapid development of urbanization, urban space continues to expand at the expense of farmland and water area primarily. The proportion of urban land in Suzhou City has reached 41.35% by 2015. The change rules of land-use type are basically consistent with different stages of urbanization. The change of river system structure is mainly affected by urbanization, which remains synchronized with such process. In the past 50 years, water rate, drainage density, tributary development coefficient, river area length ratio, drainage complexity, and drainage network structure stability have decreased by 19.63%, 6.91%, 7.34%, 1.06%, 5.49% and 7.87%, respectively in Suzhou City. Also, there exists negative correlations between urbanization level and each index. Human activities not only directly affect the functions of rivers, but also change the functions of rivers indirectly by changing the river system structure of the plain river network. The study serves as reference and theoretical support for the protection of river system and the flood control in urban areas.

Characteristics of shallow groundwater and its influences in plain river network region of Taihu Basin

鉴于浅层地下水在维持区域生态功能方面的重要作用，基于2005-2015年太湖平原水网地区苏州市的14个浅层地下水监测井水位及2005-2014年降水、河道水位和蒸发等日尺度数据，开展浅层地下水埋深动态特征及影响因素研究.结果显示：苏州市浅层地下水总体呈由北往南、自西向东的流场方向，主要受地形因素的影响；年际及丰水期埋深有所减小，枯水期反之，各区域变化过程不一致；枯水期浅层地下水动态特征受不同量级降水总量和次数的显著影响，且与地表水过程关系密切，汛期反之.此外均受到引排水和下垫面变化等因素的影响；浅层地下水埋深对降水具有滞后性，多滞后1~2 d；通过对地形地貌条件、土地利用类型、河湖密度以及浅层地下水埋深状况等因素的综合分析，浅层地下水动态特征可表达为耕地区、水网密布区、高度城镇化区及低山林区4种特征类型.;In view of the important role in the maintenance of regional ecologic function, the spatio-temporal characteristics of shallow groundwater burial depth (SGBD) and its influential factors were studied based on the daily SGBD data (from 2005 to 2015) and regional precipitation, water level and evaporation data (from 2005 to 2014) in Taihu Basin. The results indicated that:The shallow groundwater in Suzhou showed a flow direction from north to south, and from west to east, which is mainly affected by regional topographic conditions. The regional SGBD showed a slightly reduction in annual and flood season scale, while increase in non-flood seasons. The change processes varied among regions. The variation of SGBD is significantly related to the amount and frequency of different precipitation ranks in non-flood seasons, and affected by surface water. Moreover, the diversion and drainage, and underlying surface change were also the influential variables. While these features were opposite in flood seasons. The variation of SGBD often lags 1 to 2 days to precipitation. The characterization of shallow groundwater could be divided to four types, such as the agricultural, watery, urbanized and low mountainous regions, through the overlay of the influential variables, such as geomorphologic conditions, land use types, densities of rivers and lakes, and shallow groundwater burial depth.

Prediction of the future flood severity in plain river network region based on numerical model: A case study

Suzhou is one of China's most developed regions, located in the eastern part of the Yangtze Delta. Due to its location and river features, it may at a high risk of flood under the climate change background in the future. In order to investigate the flood response to the extreme scenario in this region, 1-D hydrodynamic model with real-time operations of sluices and pumps is established. The rain-runoff processes of the urban and rural areas are simulated by two lumped hydrologic models, respectively. Indicators for a quantitative assessment of the flood severity in this region are proposed. The results indicate that the existing flood control system could prevent the Suzhou Downtown from inundation in the future. The difficulty of draining the Taihu Lake floods should be given attention to avoid the flood hazard. The modelling approach based on the in-bank model and the evaluation parameters could be effective for the flood severity estimation in the plain river network catchment. The insights from this study of the possible future extreme flood events may assist the policy making and the flood control planning.

Study of Water Environmental Cumulative Risk Assessment Based on Control Unit and Management Platform Application in Plain River Network

As the gradual deterioration of the environment, the method of environmental risk assessment has been developed from basing only on a single source to basing on a cumulative risk source. In accordance with the water environment features of the plain river network area, a cumulative risk assessment system of water environment in the plain river network area was established in this paper, the design process for which could be divided into three step: (1) Control unit divided reasonably was chosen as the basic unit for water quality management. (2) On that basis, according to the characteristics of the plain river network area, the cumulative risk indexes were selected. The index weight is calculated using entropy method and analytic hierarchy process (AHP), which could determine the risk grade of each control unit. (3) The cumulative risk assessment method is coupled to the existing water environment management platform. The platform with a dynamic database can realize the dynamic calculation and visualization of the cumulative risk grade. In this paper, the Zhejiang area of Taihu Basin was selected to be the research target as the typical plain river network area. Thirty-five control units were divided with regional water environment and control section. Taking the data in the year 2011 as example, the proposed cumulative risk assessment method was used to identify the control units in different grades and the results demonstrated that the numbers of high-, medium-, low- and extremely low-risk control units are 13, 12, 5 and 5, respectively. It is necessary to give priority to the high-risk control unit. Therefore, the cumulative risk assessment method based on the control unit provides an essential theoretical basis for reducing the probability of water pollution and reducing the degree of water pollution damage.