Water Surface Ratio Research Articles

Unraveling the Impacts of River Network Connectivity on Ecological Quality Dynamics at a Basin Scale

The ecological quality of river basins is significantly influenced by the complex network of river structures and their connectivity. This study measured the temporal and spatial variability of ecological quality, as reflected by remote sensing ecological indices (RSEI), and examined their responses to river network connectivity (RNC). In total, 8 RNC indices, including river structure of river density (Dr), water surface ratio (Wr), edge-node ratio (β), and network connectivity (γ), and node importance indices of betweenness centrality (BC), PageRank (PG_R), out_degree centrality (Out_D), and in_closeness centrality (In_C), were generated at the subbasin scale. Our results highlighted the significance of RNC in influencing both the values and variability of RSEI, and the extent of this influence varied across different time periods. Specifically, three distinct clusters can be extracted from the temporal variability of RSEI, representing wet, near-normal, and dry years. The river structure index of γ significantly influenced the spatial patterns of subbasin RSEIs, particularly in wet years (R2 = 0.554), whereas β displayed a pronounced U-shape correlation with subbasin RSEIs in dry years (R2 = 0.512). Although node importance indices did not correlate directly with subbasin RSEI levels, as the river structure indices did, they significantly positively affected temporal variability of subbasin RSEIs (EI_SD_t). Higher values of PG_R, Out_D, and In_C were associated with increased subbasin RSEI variability. Based on these correlations, we developed RNC-based RSEI and EI_SD_t models with high adjusted coefficients of determination to facilitate the assessment of ecosystem quality. This study provides essential insights into ecosystem dynamics related to river connectivity within a basin and offers valuable guidance for effective watershed management and conservation efforts aimed at enhancing ecological resilience and sustainability.

Spatial heterogeneity of the effects of river network patterns on water quality in highly urbanized city

River water quality deterioration is a serious problem in urban water environments. River network patterns affect water quality by influencing the flow, mixing, and other processes of water bodies. However, the effects of urban river network patterns on water quality remain poorly understood, thereby hindering the urban planning and management decision-making process. In this study, the geographically weighted regression (GWR) model was used to explore the spatial heterogeneity of the relationship between river network pattern and water quality. The results showed that the river network has a complex structure, high connectivity, and relatively even distribution and morphology. Important river structure indicators affecting water quality included the water surface ratio (Wp) and multifractal features (∆α, ∆f) while important river connectivity indicators included circuitry (α) and network connectivity (γ). River structure has a more complex effect on water quality than connectivity. This study recommends that the Wp should be increased in agricultural areas and appropriately reduced in urban built-up areas, and the number of river segments and nodes should be controlled within a rational configuration. Our study provides key insights for evaluating and optimizing the river network patterns to improve water quality of urban rivers. In the future, the land use intensity, hydrological processes, and human activities should be coupled with the river network pattern to deepen our understanding of urban river environment.

Study on River Protection and Improvement Based on a Comprehensive Statistical Model in a Coastal Plain River Network

When considering the contradictions between river management and protection in a typical plain river network, it is always confirmed that the river area has usually been encroached upon due to the development of human society. Based on the analysis of multiple attributes of the river network, a statistical model has been proposed in this study in order to determine the river network protection indices such as river area ratio, storage capacity and flux. In this study, a numerical method is proposed to improve the structure and connectivity of the river network by calculating the occupation and supplement balance. According to the principle of water area dynamic balance, the river network structure and its connectivity are improved through water area adjustment in a typical coastal city. As the simulation results show, the water surface ratio equals 8.17%, the storage capacity equals 112.6 million m3 and the water flux equals to 656.06 m3/s in the selected study area. The flood drainage capacity is introduced as the priority function, other functions are also improved due to river management and protection. The harmonious and sustainable coexistence between human society and the river network is then promoted. This comprehensive statistical model proved to be a good tool for the coastal area to enhance the comprehensive attributes of the coastal plain river network and the sustainable development of the local area in the future.

Influence of river structure and hydrodynamics on water quality in the upper Taihu Basin, China

The Taihu Basin constitutes a complex river network and variable hydrodynamic forces, which contributing to alterations in regional water quality within the Yangtze River Delta. In this study, to explore the underlying mechanism of these dual factors on water quality in the upper Taihu Basin, a combination of graphical analysis, the water quality index (WQI) method, and the partial least square-structural equation model (PLS-SEM) were employed to quantitatively investigate the river structure indices (water surface ratio, WP; river system fractal, Δα; river network connectivity, γ) and hydrodynamic force indices (the flow index, FI), and their influence on water quality. Negative correlations were found between both WP and Δα with FI and a positive correlation between γ and FI. The southern water network had a higher water body area and greater difference in river network density, while the northern river network had enhanced connectivity and stronger water flow, thus exhibiting superior water quality. Regarding the influence of these factors on water quality, the impact of river structure on WQI was statistically insignificant (P > 0.05), while hydrodynamic force was significantly positively correlated with the WQI (P < 0.05). Moreover, in comparison to the path coefficient of 0.657 for the river structure's influence on the WQI, the hydrodynamic force exerted an even more significant impact on water quality with a path coefficient of 0.715. This study suggested that water quality improvements depend on optimizing the structural integrity of river systems and promoting favorable hydrodynamic conditions, with the latter having greater influence. This research provided theoretical underpinning for optimizing river structure and advancing river and lake water environments within the Taihu Basin.

Spatial-temporal evolution of influencing mechanism of urban flooding in the Guangdong Hong Kong Macao greater bay area, China

Extreme weather has been more frequent in recent years. Urban agglomerations, as areas with a high density of human activities, have been plagued by storm flooding. Historically, the main focus of attention on flood control in urban agglomerations has gradually shifted from underground pipe networks to the impervious surface, reflecting profound changes in the influencing mechanism of urban flooding. Exploring the evolution of the mechanisms influencing urban flooding in the Guangdong Hong Kong Macao Greater Bay Area (GBA) urban agglomeration is of great reference significance for formulating flood prevention and control measures and promoting high-quality development of the GBA city cluster. In this paper, we fully use the collected information on urban flooding events from 1980 to 2018 in the GBA city cluster. Correlation analysis and geographically weighted regression (GWR) are used to analyze the influence of impervious surface percentage (ISP), impervious surface aggregation index (AI), impervious surface mean shape index (Shape_MN), vegetation cover (FVC), water surface ratio (WSR), relative elevation (RE) and slope on flooding in urban clusters and their evolution characteristics over time from a global perspective and spatial heterogeneity, respectively. The results show that: 1) ISP, AI, Shape_MN, and WSR are positively correlated with urban flooding, while FVC, RE, and Slope are negatively correlated with urban flooding. The correlations of each factor showed a general trend of gradual strengthening over time, and the increase rate slowed down after 2000, while the correlation of WSR showed a relatively noticeable decrease. 2) The GWR results show that each factor’s influence on urban flooding has pronounced spatial-temporal heterogeneity, and each factor shows different distribution characteristics. This study uses long time series of urban flooding point data to explore the spatial-temporal evolution of the influencing mechanism of urban flooding in the GBA urban agglomeration. We hope to provide a scientific basis for an in-depth understanding of the causes of urban flooding in the GBA, intending to provide auxiliary decision-making support for the formulation of waterlogging prevention and control measures.

Exploring the Influences of Stream Network Structure and Connectivity on Water Environment Risk in China

Stream networks are the transportation channels of pollutants that can significantly influence water environment risk (WER). However, the influences of stream network structure and connectivity (SC) on WER at the national scale and its regional variability have been rarely investigated in China. In this study, the WER was assessed from the grey water footprint of nitrogen and phosphorus in 214 catchments in China. The relationship between WER and SC and its regional variability were analyzed using correlation and grey relational analysis. Results showed that the water environment risk index (RI) in some catchments located in the Hai and Liao River Basins was the highest in China (RI &gt; 0.8). On national scale, longitudinal connectivity (Cl) and cyclical connectivity (Cc) had the strongest influences on WER with grey relational degree index (GRAI) of 0.68 and 0.67, respectively. The average slope (Sr) was the most important in humid zones, whereas Cl and water surface ratio (Rw) had a stronger influence in arid zones. In zones with intensive human activities, Cc, river density (Rd), and the node connection ratio (Rnc) mostly affected WER. The main influenced factors varied significantly among nationwide and different zones, which indicated that climate and human activities played an important role in the spatial variation of the relationship between WER and SC. This study highlights the important role of SC on WER and that the relationship between WER and SC varies with climate and human activities.

Evolution of river network due to urbanization in the Southeast Yinzhou Plain of Yongjiang River Basin, China

River networks have important environmental, hydrological, and social functions. However, they have experienced rapid degradation due to urbanization, and the disorder of their flood, water pollution, and river functions has strengthened in many parts of the world. Previous studies have mainly described river networks using traditional indicators and have neglected the spatial non-stationary relationship with urbanization. Thus, in this study, a river network's evolution was revealed not only from the traditional perspectives of quantity and structure but also from the novel perspective of multifractal analysis. Furthermore, a Geographically Weighted Regression model (GWR) was created to detect the relationship with the urbanization in the 1990s–2020s on the Southeast Yinzhou Plain (SYP), China, in order to gain a deeper understanding of the complex irregular and self-similarity spatial components of the river network and reveal the main reasons for its degradation. The results revealed that under rapid urbanization, the river network quantity indicators, such as the drainage density and water surface ratio, decreased dramatically, especially for the low-order rivers. The indicators of the river network's structure, such as the connectivity, circularity, curvature, and box dimension, also exhibited decreasing trends. Even with all of the changes, the dense and relatively uniform spatial distribution of the river network pattern remained stable according to the capacity dimension detection. In general, the rapid urbanization had little effect on the evolution of the first-order tributaries, but as the urban land ratio growth increased, the drainage density of the second-order tributaries decreased at an accelerated rate. The spatial non-stationary relationship detection using the GWR also revealed significant correlations. The results of this study provide a solid guarantee for the recognition, protection, and restoration of the regional river network and the construction of a coordinated human-water society.

Relationship between Eye Blink Frequency and Incremental Exercise among Young Healthy Men.

The aim of the study was to verify the correlation between the frequency of blinking and aerobic physical exercise. The research subjects were 13 healthy man aged 23.3 ± 1 year. Measurements of the blink rate and eye closure times were performed during a progressive aerobic test on a cycle ergometer. During the test, power was gradually increased every minute by 25 W, starting from 50 W. Data acquisition involved using a GoPro camera mounted to the helmet of the research subject. The test continued until the research subject refused to continue. The subjects did not know the goal of the test, in order to ensure objectivity and obtain natural results. The largest number of statistically significant differences was observed between the initial stages and 250 W, as well as between 250 W and 325 W. The analysis showed no significant differences in blink rate, eye closure time, and single blink time in terms of heart rate ranges. Regression models were also determined for eye closure time, blink frequency, and single blink time. The analysis showed that blink frequency and eye closure time were determined by a group of factors (the value of cycle ergometer load power, heart rate, body weight, adipose tissue mass, fat-free mass, and total body water and body surface ratio).

Spatiotemporal change in the river network in rapidly urbanized plain regions of the Yangtze River Delta in China

AbstractRapid urbanization has brought numerous aquatic problems to plain river network regions. We selected three categories (five indicators) of characteristics to describe the physical characteristics of river network systems, including quantitative, structural, and complex characteristics. Using the grid method and hierarchical clustering analysis (HCA), the spatiotemporal change pattern of one plain river network of the Yangtze River Delta was addressed from the 1960s to 2014 based on topographic maps. The results showed that the river density (DR), water surface ratio (WP), and box dimension (D0) in over 82% of the area decreased. The spatial pattern of the water system is divided into four categories by HCA: urban areas, river network areas, mainstream areas, and lake areas. The categories of river network areas and lake areas decreased, while the categories of urban areas and mainstream areas increased from the 1960s to 2014 because of urbanization. There are approximately 12.8% grid cells that change from river network areas to mainstream areas, which is the most important change due to the reduction of tributaries and increase of main streams. These results indicate that river network distribution patterns have the tendency to simplify and remain mainstream. Our study suggests that water systems and river networks should be protected, which would provide support for water resource management in highly urbanized plain regions.

Spatially non-stationary relationships between urbanization and the characteristics and storage-regulation capacities of river systems in the Tai Lake Plain, China

Given environmental or hydrological functions influenced by changing river networks in the development of rapid urbanization, a clear understanding of the relationships between comprehensive urbanization (CUB) and river network characteristics (RNC), storage capacity (RSC), and regulation capacity (RRC) is urgently needed. In the rapidly urbanized Tai Lake Plain (TLP), China, various methods and multisource data were integrated to estimate the dynamics of RNC, RSC, and RRC as well as their interactions with urbanization. The bivariate Moran's I methods were applied to detect and visualize the spatial dependency of RNC, RSC, or RRC on urbanization. Geographically weighted regression (GWR) model was set up to characterize spatial heterogeneity of urbanization influences on RNC, RSC and RRC. Our results indicated that RNC, RSC and RRC variables each showed an overall decreasing trend across space from 1960s to 2010s, particularly in those of tributary rivers. RNC, RSC, or RRC had globally negative correlations with CUB, respectively, but looking at local scale the spatial correlations between each pair were categorized as four types: high-high, high-low, low-low, and low-high. GWR was identified to accurately predict the response of most RNC, RSC, or RRC variables to CUB (R2: 0.6–0.8). The predictive ability of GWR was spatially non-stationary. The obtained relationships presented different directions and strength in space. All variables except for the water surface ratio (Wp) were more positively affected by CUB in the middle eastern parts of TLP. Drainage density, RSC and RRC variables were more negatively influenced by CUB in the northeast compared to other parts. The quantitative results of spatial relationships between urbanization and RNC, RSC or RRC can provide location-specific guidance for river environment protection and regional flood risk management.

Dynamic impacts of changes in river structure and connectivity on water quality under urbanization in the Yangtze River Delta plain

The deterioration of river water quality in urbanized areas is getting more serious, and affects the regional ecology and development of social economy; however, its mechanisms of dynamic variation is still an open question. In this study, we detected the dynamics of water quality and its driven mechanisms in the Yangtze River Delta plain, one of the most developed areas in China. The results showed that the spatial agglomerations of dissolved oxygen (DO), ammonia nitrogen (NH3-N), and total phosphorus (TP) presented seasonal differences, which exhibited a trend of shifting from west to east and then to west from spring to winter. Further, the relative contribution rates of the river network characteristics affecting water quality were quantified on the basis of backpropagation artificial neural networks. We found that the average contribution rates of river structure (more than 60%) were higher than that of river connectivity, and the dominant factors influencing water quality were water surface ratio (WP) and multifractal indices (Δa, Δf). Specifically, the average relative contribution rates of WP, Δa and Δf were 18.72%, 15.03%, and 14.52% during the flood season, respectively, and 15.83%, 16.58%, and 14.54% during the non-flood season. The functional connectivity influenced by obstruction of sluices also influences water quality, which accounting for 11.15% and 12.85% in the flood and non-flood seasons, respectively.

县域城镇空间形态与居住建筑能耗关联性的连续尺度研究——以浙江长兴、福建连江为例

PDF HTML阅读 XML下载 导出引用 引用提醒 县域城镇空间形态与居住建筑能耗关联性的连续尺度研究——以浙江长兴、福建连江为例 DOI: 10.5846/stxb202103280807 作者: 作者单位: 作者简介: 通讯作者: 中图分类号: 基金项目: “十三五”国家重点研发计划课题"（2018YFC0704705）；福建省中青年教师教育科研项目（JAT190034）；福州大学引进人才科研启动项目（511005-GXRC-21024） Correlation between urban spatial form and residential building energy use of towns on a continuous scale: A case of Changxing, Zhejiang and Lianjiang County, Fujian Author: Affiliation: Fund Project: 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:居住建筑能耗受建筑周边空间形态的直接影响，确定空间形态低碳效应及其最佳尺度将有助于实现县域城镇低碳转型。以浙江省长兴县、福建省连江县为例，共计选取49个具有代表性的居住建筑样本，采用GIS分析与数理统计相结合的方式，在居住建筑1800m半径范围内，以200m为间隔建立缓冲区，开展全年、最冷月份能耗期及最热月份能耗期建筑能耗与周边空间形态关联性的连续尺度研究。结果表明：①道路密度、开发密度、容积率均与建筑能耗呈正相关，但各指标对应的能耗时期、尺度范围有较大差异。②水面率、土地利用混合度是与建筑能耗相关的共性指标，但在不同地区的正负效应及尺度范围不同；③影响浙闽地区县域城镇最热月份能耗期能耗的关键形态因子为1000m-道路密度、800m-水面率、1600m-开放空间率；影响连江最冷月份能耗期能耗的关键形态因子为800m-水面率。④就控碳单元设置而言，长兴县可重点关注1000-1200m半径范围，连江县可重点关注800-1000m、1400m半径范围。⑤浙闽地区县域城镇特性指标为开放空间率，与最热月份能耗期建筑能呈负相关；长兴县特性指标为容积率、水岸密度，分别与全年、最冷月份能耗期及最热月份能耗期建筑能耗呈正、负相关。据此提出3个低碳城镇规划建议，为实现我国浙闽地区县域城镇低碳转型、居住建筑节能减排提供理论依据。 Abstract:Since the energy consumption of residential buildings is directly affected by the spatial form surrounding the buildings, determining the low-carbon effect of the spatial shape and its optimal scale contributes to realizing the low-carbon transformation of towns and township.Taking Changxing County of Zhejiang Province and Lianjiang County of Fujian Province for example, 49 representative samples of residential buildings are selected in total and included in this research. Based on both GIS analysis and the method of mathematical statistics, with buffer zones built at the interval of 200m within a radius of 1800m around the residential buildings, a continuous-scale research is conducted on the correlation between building energy consumption and the spatial pattern around throughout the year, in the consumption period of the coldest month and in the consumption period of the hottest month.The results showed that:①road density, development density, and floor area ratio were all positively correlated with building energy consumption, but the energy consumption period and scale range corresponding to each index were quite different. ②Water surface ratio and land use mixing degree were common indicators related to building energy consumption, but their positive and negative effects and scale ranges vary in different regions. ③The key form factors that affect the energy consumption of towns in Zhejiang and Fujian during the monthly energy consumption period with the highest temperature were 1000 m- road density, 800 m- water surface ratio, and 1600 m- open space rate; The key form factor that affects the energy consumption during the energy consumption period of the lowest temperature month in Lianjiang is 800 m-water surface ratio. ④In the selection of carbon control unit, it is necessary for Changxing County to focus on the radius range of 1000 -1200 m, and Lianjiang County to focus on the radius range of 800 -1000 m and 1400 m.⑤ Characteristic indexes of towns in counties in Zhejiang and Fujian were the rate of open space, which was negatively correlated to building energy consumption in the consumption period of the hottest month; characteristic indexes of Changxing County are floor area ratio and waterfront density, which were positively and negatively correlated to building energy consumption throughout the year, in the consumption period of the coldest month and in the consumption period of the hottest month respectively. On such a basis, 3 proposals concerning low carbon urban planning are made herein, which may serve as a theoretical basis for the low carbon transition of county towns and energy saving and emission reduction in residential buildings in Zhejiang Province and Fujian Province. 参考文献 相似文献 引证文献

Spatial Variations and Influencing Factors of River Networks in River Basins of China.

Analysis of the spatial variations in river networks and the related influencing factors is crucial for the management and protection of basins. To gain insight into the spatial variations and influencing factors of river networks between large basins, in this study, three river basins from north to south in China (Songhua River Basin, Yellow River Basin and Pearl River Basin) were selected for investigation. First, based on a digital elevation model, different river networks with six drainage accumulation thresholds of three basins were extracted using ArcGIS. The optimal networks were determined through fitting the relationship between the accumulation threshold and related drainage density. Then, we used two indicators, drainage density and water surface ratio, to characterize the spatial variations of three basins. Finally, Pearson’s correlation coefficients were calculated between those two indicators and natural/human influencing factors. The results showed that drainage density and water surface ratio decreased from north to south in China and were negatively correlated with natural/human influencing factors. Drainage density was more influenced by natural factors than by human factors, while the opposite was true for water surface ratio. These findings may provide some basis for the management and protection of the river network.

Interaction between the characteristics of urban three-dimensional landscape pattern and social-environmental factors based on boosted regression tree

Vertical expansion makes the structure and pattern of the city more complicated. Traditional two-dimensional landscape pattern cannot completely reflect the ecological structure and functional characteristics of urban landscape. In this study, we used the three-dimensional landscape pattern metrics to quantify the regional three-dimensional landscape pattern, and used boosted regression tree (BRT) machine learning algorithms to comprehensively analyze the interaction between social-environmental factors and urban landscape patterns in the central part of Shanghai. Results showed that high building ratio, mean architecture height, and architecture height standard deviation had higher values in the surrounding area of the inner ring. The number of buildings and landscape shape index were higher in the outer ring than those in other area. Building coverage ratio, floor area ratio and Shannon's diversity index had higher values in the central part, with the metrics of Puxi being generally higher than those of Pudong. Population density and normalized vegetation index (NDVI) interacted most significantly with the three-dimensional landscape pattern, with GDP as the least influential factor. Within a certain range, the three-dimensional landscape pattern metrics increased with larger population density in the social factors, and decreased with lower rate of NDVI and water surface ratio in the environmental factors. Our results demonstrated that the BRT method was effective in quantifying the interaction between landscape pattern and social-environmental factors. Our results help improve the understanding of the relationship between ecological environment and human well-being in the central part of Shanghai and provide a scientific basis for the urban three-dimensional expansion planning.

Sea-land hydrological connectivity of coastal wetlands based on water salinity and hydrological structure.

In this study, with water salinity as the core index, sea-land hydrological connectivity index was constructed by integrating the hydrological structure connectivity index (water surface ratio, intake and outtake density, sea-land distance, and ditch distance). Based on multi-scale spatial analysis, we carried out the spatial quantitative analysis and classification of sea-land hydrological connectivity in the study area under an evaluation unit of 150 m×150 m grid. The results showed that sea-land hydrological connectivity gradually decreased from sea to land, with different decreasing rates. The spatial differentiation of water salinity in the study area was substantial, with certain impacts on the change rate of hydrological connectivity. The sea-land hydrological connectivity was divided into four grades, which was excellent, good, medium, and poor. The areas under excellent and good grades were mainly distributed in offshore areas, with saltwater aquaculture ponds and farmland as the main land use types. The regions with moderate and poor land use were mainly distributed in inland areas, with freshwater aquaculture ponds and farmland as the land use types. The hydrological process of coastal wetlands was complex. Quantitative coastal wetland hydrological connectivity could provide reference for coastal wetland status assessment and wetland restoration.

Offline Optimization of Sluice Control Rules in the Urban Water System for Flooding Mitigation

A real-time control (RTC) system can substantially improve the efficiency in urban flooding mitigation by optimizing the capacity of drainage and storage in existing drainage systems. However, few studies have investigated the RTC for an Urban Water System (UWS) in cities with a high water surface ratio for flooding mitigation. In this study, control rules of the actuators in an UWS were developed by an offline optimization system that combines a hydraulic model, the stormwater management model (SWMM) with an optimization model solved by the differential evolution (DE) algorithm. Iteratively simulating only the downstream UWS hydraulic model, the objectives of this study were to (i) minimize the flooding volume from the UWS and (ii) minimize the cumulative water depths above the control lines in real-time. Results showed that the optimal control rules outperformed the current fully open and closed rules, indicating the UWS’s retaining and draining capacity was effectively utilized through the offline optimization. This study also found that the robust control rules might be biased and have little effect under most rainfalls, especially mild storms, as they are derived from the system’s average performance under various rainfall conditions.

城市化下平原河流水系变化及空间响应

针对平原河网地区水系形态难以刻画并且受城市化的空间影响难以定量等问题，以太湖平原杭嘉湖地区为例，基于地形图获取的1980s与2010s水系数据和遥感影像等资料，运用多重分形理论及地理加权回归模型，定量揭示了20世纪80年代以来城市发展对河网水系演变的影响。结果表明：（1）杭嘉湖地区河网密度和水面率均呈减小趋势，衰减率分别为10%、13%；区内水系分布集中，均匀性下降；河流曲度降幅为0.5%，干流面积长度比在中、高城市化区域增幅较大。（2）水系变化对城市化的响应在空间上存在较为明显的异质性。城市化水平越低，水系形态演变越剧烈，空间分布不规则性越明显。（3）杭嘉湖地区存在"低-低"、"低-中"、"低-高"、"中-高"4种不同的城市化水平转变类型。城市化水平未发生转变时，水面率衰减更为剧烈，且水系空间分布均匀性下降，水系形态变化较大；城市化水平转变幅度越大，水系均匀化分布趋势越明显；受政策影响"中-高"发展区域仅河网密度变化较为明显。本研究将为城市河网水系保护和生态环境可持续发展提供科学参考。;With the rapid development of urbanization, the river network morphology in the plain area is harder to describe, not to mention the difficulty in quantifying the spatial influence of urbanization. Based on the data of river network in the 1980s and 2010s obtained by topographic map and the data of LUCC from remote sensing images, this paper quantitatively reveals the impact of urbanization on the river network since 1980s in the Hangzhou-Jiaxing-Huzhou area of Taihu Lake Plain with the application of multifractal theory and geographically weighted regression model. The results show that: (1) both the density and water surface ratio of river network present a decreasing trend, and their attenuation rates are 10% and 13%, respectively. From the multifractal perspective, the distribution of the river network was concentrated and the uniformity was decreased. Besides, the river sinuosity decreased by 0.5%, and the main river area length ratio increased significantly in the moderately and highly urbanized areas. (2) The response of river network evolution to urbanization has obvious heterogeneity in space. The lower the urbanization level is, the greater the evolution of river network morphology is, and the more obvious the irregularity of spatial distribution is. (3) There are four different types of urbanization level transformation in Hangzhou-Jiaxing-Huzhou region: low-low, low-moderate, low-high, and moderate-high. When the urbanization level does not change, the spatial distribution uniformity decreases, the river network morphology changes greatly and the attenuation of water surface ratio is greater. Furthermore, the greater the transformation is, the more obvious the homogenization trend of river network distribution is. Due to the effects of policy, only river network density changes significantly in the moderate-high development area. This study will provide scientific support for the sustainable development of ecological environment, so as to protect the river network.

Multiphase distribution and spatial patterns of perfluoroalkyl acids (PFAAs) associated with catchment characteristics in a plain river network

Perfluoroalkyl acids (PFAAs) have emerged as global concerning contaminants because of their persistence, bioaccumulation, and toxicological effects. The transport and fate of PFAAs on dimension of plain river networks (PRNs) are difficult to model due to the unique regional characteristics (i.e., undirectional flows, low slope, complicated structure and connectivity) and the lack of data on PFAAs concentrations and compositions. A typical PRN (Taihu Basin, China) was selected to elucidate the spatial patterns of PFAAs in multi-matrices, including colloidal phase, soluble phase, suspended particles, and sediment. PFAAs were ubiquitously detected in plain rivers with total concentrations of 18.48–1220 ng/L in colloids, 139.07–721.37 ng/L in soluble phase, 97.69–2247 ng/g dw in suspended particles, and <72.04–178.12 ng/g dw in sediment. PFAAs were more likely to transport via dissolved phase and accumulate into sediment. Colloids carried 45.46–62.59% of ∑PFAAs in overlying water, while suspended particles contained <36.63% of ∑PFAAs, suggesting the important role of colloids in preloading PFAAs. Moreover, PFAAs variability was correlated with indicators of the structure and connectivity of river network by gray relational analysis. The mean gray relational degrees can be sorted as edge-node ratio (0.7609) > network connectivity (0.7191) > river density (0.7012) > water surface ratio (0.6887) > river development coefficient (0.6504) > functional connectivity (0.4780). These results suggested that the effects of catchment characteristics should be taken into account in understanding PFAAs fate in the PRNs.

Selection of treatment methods for soft foundation of river in a reclamation area

Several drainage channels are usually planned in the reclamation area in order to ensure the basic water surface ratio. It is necessary to conduct deep foundation treatment before the excavation of the river due to the high water content of hydraulic fill in reclamation area. Cement mixing pile method has been widely used in the treatment of river soft foundation as a method with mature construction technology, moderate overall cost and obvious treatment effect. Taking a river in a reclamation area as an example, it is recommended to adopt the cement mixing pile method to treat the soft foundation of the river after comparing the vacuum preloading method and cement mixing pile method.

An indicator system for assessing the impact of human activities on river structure

The impact of human activities on river systems has reached a state in which they can no longer be considered to be controlled only by natural processes of the Earth but also by anthropogenic forces in many regions of world. However, most approaches for assessing the impact still consider human activities to be an external influence in the study of feedback mechanisms between human activities and river systems, and they are usually complicated and specialized. This paper aims to develop an indicator system that includes the artificial water surface ratio (AWSR), artificial water surface density ratio (AWSDR), disruption of longitudinal connectivity ratio (DLCR), artificial river ratio (ARR), sinuosity of artificial cutoff (SAC), channelization ratio (CR), artificial levee ratio (ALR), road along river ratio (RARR), artificial sediment transport ratio (ASTR) and the integrated river structure impact index (IRSII) to quantitatively assess the impact of human activities on river structure by comparing natural and anthropogenic forces in a river system. The Nanliu River basin under the dramatic impact of human activities was selected to validate the indicator system. The case results showed the Nanliu River has become an anthropogenic river according to its high IRSII value (greater than 0.49). The artificialwater surface area and artificialsediment discharge were 2.96 (AWSR = 2.96) and 2.51 (ASTR = 2.51) times of the outcome of natural process. The river was dramatically blocked by human-made buildings (DLCR = 68.63) and artificialchannel accounts for 54.23% of total length of natural river (ARR = 0.54). Within the river basin, upper and lower sub-basins in areas with a higher economic level were more affected by human activities. Future management of the Nanliu River basin should focus on restoration of river connectivity, sand mining and irrigation issues. Unlike most previous assessment methods, the approach developed in this study is simple and readily comprehensible by the public and decision makers, cost-effective for long-term monitoring and not subject to the reference condition.