Environmental risk of dissolved oxygen depletion of diverted flood waters in river polder systems - A quasi-2D flood modelling approach

River polders are retention basins contained by levees alongside rivers into which water from the main river channel is diverted during extreme floods in order to cap the peak discharge of the flood hydrograph and to alleviate downstream flood risk by reducing the water levels. The retained water, however, is stagnant and the organic material in the water and the bottom sediments imposes a strong oxygen demand on the water. This paper presents a quasi two-dimensional computer-based methodology to assess the environmental risk exhibited by the operation of polders with which the concentration of dissolved oxygen in river and polder water can be simulated. A Monte-Carlo analysis allows the probability distribution of all the outcomes of the minimum dissolved oxygen levels in the water to be derived. From this analysis, the environmental risk of the dissolved oxygen concentrations in the polder water falling below 2 mg O₂/L (the level considered critical for aquatic ecosystems) can be determined.The August 2002 extreme flood event on the Elbe River, Germany, with a proposed polder system variant was used to calibrate the model. A daily time step was used to for the simulations for a time frame 12-21 August 2008. The results show plausible spatial and temporal variations in the dissolved oxygen concentrations within the polders. The quasi-2D approach was successful in simulating the spatial distribution of water quality constituents in the polder system. There is up to approximately 20% risk that dissolved oxygen levels fall below 2 mg/L in the polders. This risk can potentially increase if sediment oxygen demand increases due to crop residue and water temperatures in polders increase. High nutrient transport in the river during flooding can cause a spurt of phytoplankton growth in the polders.     

Restoring Dynamic Fluvial Processes in Urban Rivers: Learning from the Aire and Isar Rivers

In process-based restoration, the objective is not to create a complex river form directly; instead, interventions are intended to “prompt” the natural processes to restore such forms. The improvements in ecological conditions are actually made over time by flowing water during floods (using the stream’s energy), and by the growth of riparian vegetation (using incoming solar energy). On the Aire River in Geneva, ecological function was restored to a formerly canalized river by providing the river with an espace de liberté. A grid of channels cut into the valley bottom allowed the river to freely flood, erode its bed and banks, and deposit bars, creating complex surfaces on which riparian vegetation established to support the food web of the riverine ecosystem. The diamond-shaped bits of land left between these channels (“lozenges”) gradually erode and evolve as the river migrates, creating complex channel forms. The Isar River in Munich restoration involved adding coarse sediment load, creating erodible bed and banks in place of formerly rigid boundaries, expanding process space for river migration, erosion, and deposition, and increased human access to the river over 8 km. Since restoration, natural transport of sediment has resulted in deposition of gravel bars, whose forms evolve during floods, supporting diverse habitats. The Isar and Aire Rivers provide compelling examples of processbased restoration meeting 4 criteria for process-based restoration: space, energy, materials, and time. They demonstrate the possibilities of urban river restoration to achieve both ecological and social goals through restoration of fluvial process.     

A decision support system for water quality issues in the Manzanares River (Madrid, Spain)

The Manzanares River, located in Madrid (Spain), is the main water supplier of a highly populated region, and it also receives wastewater from the same area. The effluents of eight Waste Water Treatment Plants (WWTPs) downstream of the river, which represent 90% of the flow in the middle and lower parts of the river, are the primary sources of water pollution. Although the situation has improved slightly in the last two years, the water in the river is highly polluted, making it uninhabitable for aquatic life. Water quality modelling is typically used to assess the effect of treatment improvements in water bodies. In this work, the GESCAL module of the Aquatool Decision Support System Shell was used to simulate water quality in the Manzanares River. GESCAL is appropriate for modelling in an integrated way water quality for whole water resources systems, including reservoirs and rivers. A model was built that simulates conductivity, phosphorous, carbonaceous organic matter, dissolved oxygen, organic nitrogen, ammonia, and nitrates. The period from October 2006 to September 2008 was selected for calibration due to the many treatment modifications that occurred during this time. An earlier and longer period, from October 2000 to September 2006, was used for validation. In addition, a daily model was used to analyse the robustness of the GESCAL model. Once the GESCAL model was validated, different scenarios were considered and simulated. First, different combinations of nutrient elimination among the different WWTPs were simulated, leading to the conclusion that investments have to focus on three of the proposed WWTPs. Moreover, these treatments will not be sufficient to maintain fish habitat conditions at all times. Additional measures, such as the increment of the flow in the river or oxygen injection, were simulated. Incrementing the flow of the Manzanares River has been shown to be an efficient means of increasing water quality, but this implies an increment in the risk of water scarcity situations in the Madrid water supply system.     

Learning from the extreme River Tyne flood in January 2005

Extreme floods often demonstrate unanticipated characteristics that pose problems for management and response. The floods on the Tyne and Eden in January 2005 provided numerous examples of such unexpected response. This paper describes characteristics of storm rainfall and runoff generation on the River Tyne catchment, flood effects and damage. Unusual aspects of hydrological behaviour are highlighted as a basis for assessing what lessons can be learned for flood risk management. These include problems associated with coincidence of extreme wind speeds and rainfall, the retarding influence of floodplain storage on flood wave travel time in extreme flows, the influence of critical storm duration on the severity of the resulting flood on headwaters and main river, and the variety of mechanisms of flood occurrence. The occurrence of such an extreme flood provides the opportunity to validate and enhance the review process of the Environment Agency's flood zone maps.     

Logit model for river levee stability evaluation considering the flood return period

Probabilistic models of the binary logit model for both middle/small and large-scale levees are presented for the evaluation of the stability of river levees. Stability can be expressed as the probability of collapse of a levee as estimated by this logit model. The expectation cost (sum of the damage risk potential plus cost of restoring the levee) is adopted for the comprehensive evaluation of river levees where the application is limited to damage done to the levee itself and excludes damage to human life and property. This method, therefore, can be used to determine appropriate types of improvements. The evaluation is statistical and requires a large amount of data including data about non-damaged levees. To circumvent this, we consider the probability of a flood and its return period and show that a practical probability of levee damage actually occuring must be calculated using a combination of the logit model and the return period.     

Sampling frequency and accuracy of SPM flux estimates in two contrasted drainage basins

The present paper is based on discharges and suspended particulate matter concentrations from a 9-years high-resolution database for the Garonne River (large plain river) covering contrasted hydrologic years, and a 12-months high frequency sampling for the Nivelle River (small mountainous river). Annual SPM fluxes in the Garonne River range from 0.6 x 10(6) t year(-1) (1997) to 3.9 x 10(6) t year(-1) (1996). In contrast, the Nivelle River transported 11 x 10(3) t year(-1) from December 1995 to December 1996. From the long-term observation of the Garonne River an empirical relation between SPM* (discharge-weighted mean annual SPM concentrations) and annual discharge was established. This relation allows estimating annual SPM fluxes for the Garonne River with less than 30% deviation from reference values for the whole range of mean annual discharge observed during the past decade. Specific (=area-normalized) annual SPM fluxes (YSPM) range from 11 to 74 t km(-2) year(-1) for the Garonne River. Comparison of these results with YSPM of the Nivelle River (69 t km(-2) year(-1) in 1996) suggests that interannual hydrological variations may have a greater impact on fluvial SPM transport than basin-specific parameters. By extracting individual SPM concentrations and corresponding discharge values from the database, different sampling frequencies were simulated and resulting SPM fluxes were then compared to reference fluxes derived from the complete database. If a deviation of simulated flux estimates from reference fluxes lower than +/-20% is accepted, the Garonne River (large plain river) must be sampled at least every 3 days (10 samples per month) and the Nivelle River every 7 h (approx. 100 samples per month). For the Garonne River this minimum sampling frequency is valid for all contrasted hydrologic years of the observation period. Below these minimum sampling frequencies, annual SPM flux estimates may greatly differ from reference fluxes (up to 200%) and there is high probability of systematic underestimation. Consequently, annual SPM flux estimates for the Garonne River derived from the empirical relation (SPM*-annual discharge) are likely to be more satisfactory (errors <30%) than estimates based on sampling frequencies lower than the minimum frequency. These findings underline the need of adapted sampling strategies for erosion assessment, reliable chemical (e.g. nutrients and pollutants) mass balances and characterisation of fluvial transport mechanisms in the world's contrasted watersheds.     

Dynamics of CO2 partial pressure and CO2 outgassing in the lower reaches of the Xijiang River, a subtropical monsoon river in China

The partial pressure of carbon dioxide (pCO(2)) in surface water was surveyed monthly at 6 sampling sites along the entire length of the lower reaches of the Xijiang River, a subtropical monsoon river in China, and at the mouths of its major tributaries, over a whole hydrological year from April 2005 to March 2006, to reveal the seasonal and spatial dynamics of pCO(2). Intensive sampling and measurements were also conducted at Wuzhou gauge station in June and July to investigate the impact of floodwater on pCO(2) and to further explore the relationship between river discharge and pCO(2). The pCO(2) levels were well above atmospheric equilibrium (380 microatm) during the entire survey period with obvious seasonal and spatial variations, ranging from 600 microatm to 7200 microatm for the mainstream and from 700 to 11000 microatm for tributaries, respectively. The pattern of pCO(2) seasonal variation across 6 sites was almost consistent with each other with little difference. The pCO(2) levels in the dry season were relatively low, with relatively slight temporal and spatial fluctuations that were predominantly controlled by in situ biogenic activities. While the pCO(2) in the wet season greatly varied with river discharge, both annual maximum and minimum pCO(2) levels occurring in this period. The much higher pCO(2) in the early wet season were mainly induced by increasing baseflow and interflow that flushed significant soil CO(2) into the streams, whereas the lower pCO(2) observed after floods from July to September, some even lower than pCO(2) levels in the dry season, potentially resulted from in situ plankton blooms. The annual minima pCO(2) levels occurring in this period were caused by the dilution effect of floodwater. There was no obvious downstream trend in pCO(2) variation during the whole survey period, probably a consequence of disturbance from tributaries or spatially distinct channel characteristics and water environments. Based on measurements, we estimate that the water-to-air CO(2) flux in the lower reaches of the Xijiang River is about 8.3-15.6 Mg C ha(-1)y(-1). The role of the Xijiang River as a net source of atmospheric CO(2) is undoubted.     

Ecological Planning Practices of the Yellow River National Wetland Park in Jinan Section

Jinan in Shandong Province, China is a city withfavorable location — the Yellow River runs throughthis region from southwest to northeast whilethe notable world heritage Mount Tai is its southbackground. The low reach of the Yellow Riverwhere Jinan is located is a “suspended river,”which is caused by a large amount of sedimentsfrom the upper and middle reaches. Over thepast decades, the levee has ensured the city and villages free from floods. However, it blocks the connection between the north bank area of the Yellow River and the urban town. The problems of ecological imbalance, deterioration of aquatic environment, and fragmented habitats have become more acute. Since 2017, the City Design Practice team of Skidmore, Owings & Merrill LLP (SOM) has collaborated with the Jinan Municipal Government to envision a transformation of the riverfront from ecological, cultural, transportation, and economic aspects and further proposed the idea of building a continuous Yellow River National Wetland Park along the entire Yellow River. The design proposals address the national, watershed, regional, and city scales. From the concept proposed in the plan of the 183 km reach, to the planning strategies of the 30 km core demonstration area, and further to the specific design of the Autumn Colors on the Que and Huabuzhu Mountains Park, SOM has developed step by step from macro-planning to microdesign, to ensure the uniformity and consistency of the entire design at all scales. SOM looks forwards to presenting the Yellow River in Jinan as a proven model for other river cities to follow the construction of the Yellow River National Wetland Park, and providing a practical reference for the planning and design of the Yangtze River Basin and similar watersheds in other countries.     

Calculation of the mercury accumulation in the Idrijca River alluvial plain sediments

From the historic literature on the Idrija mercury mine, it is evident that part of the smelting and mining waste was dumped into the Idrijca River. This waste was transported downstream during floods. The amount of mercury which has accumulated in the alluvial sediments of the Idrijca River until the present was studied. Mapping of Holocene river terraces of the Idrijca River was performed in order to estimate the volume of the alluvial sediment. For the purpose of the assessment of the mercury concentration, we sampled the alluvial sediments on different levels and performed an analysis of variance. The greatest variability is between the floodplain and terraces inside the same alluvial plain. Considering this fact, which determined the methodology employed for calculation, we estimated that about 2029 tons of mercury is stored in the Idrijca River alluvial sediments.     

Forecasting risk along a river basin using a probabilistic and deterministic model for environmental risk assessment of effluents through ecotoxicological evaluation and GIS

This work presents a computer model for Risk Assessment of Basins by Ecotoxicological Evaluation (RABETOX). The model is based on whole effluent toxicity testing and water flows along a specific river basin. It is capable of estimating the risk along a river segment using deterministic and probabilistic approaches. The Henares River Basin was selected as a case study to demonstrate the importance of seasonal hydrological variations in Mediterranean regions.As model inputs, two different ecotoxicity tests (the miniaturized Daphnia magna acute test and the D.magna feeding test) were performed on grab samples from 5 waste water treatment plant effluents. Also used as model inputs were flow data from the past 25 years, water velocity measurements and precise distance measurements using Geographical Information Systems (GIS). The model was implemented into a spreadsheet and the results were interpreted and represented using GIS in order to facilitate risk communication. To better understand the bioassays results, the effluents were screened through SPME-GC/MS analysis.The deterministic model, performed each month during one calendar year, showed a significant seasonal variation of risk while revealing that September represents the worst-case scenario with values up to 950 Risk Units. This classifies the entire area of study for the month of September as “sublethal significant risk for standard species”.The probabilistic approach using Monte Carlo analysis was performed on 7 different forecast points distributed along the Henares River. A 0% probability of finding “low risk” was found at all forecast points with a more than 50% probability of finding “potential risk for sensitive species”.The values obtained through both the deterministic and probabilistic approximations reveal the presence of certain substances, which might be causing sublethal effects in the aquatic species present in the Henares River.     

From Flood Land to New Urban Area: Water Adaptation History and Visions for Daodi Flood Land in the West of Beijing

Daodi Flood Land, located in Mentougou District of Beijing, is a relatively separate flood land in the lower reaches and on the east of Yonding River. This largest landscape character area in the west of Beijing along the river illustrates the history of human–water interaction and discloses the trends and problems of rural urbanization. Focusing on Daodi Flood Land, this paper expands the research on adaptation by introducing basic concepts and research framework, and reviews the research trends from spatial, temporal, and participant aspects. Considering the typical characters of the study area, this research employed participatory approaches, such as mapping and problem and solution trees, due to the lack of continuous and accurate data. Basing on literature review and field investigation on issues of floods, agricultural irrigation, and water resource utilization, water adaptive development visions for the study area were proposed from perspectives of landscape and culture. Finally, the paper further analyzes the structural relations between adaptation problems, natural and social systems, passive and active adaptations, and planned and unplanned adaptations, with the aim to provide reference for relevant studies and applications of adaptation approaches in other cases.     

基于 CAESAR-Lisflood 的弯曲型河流景观演化与洪泛区治理——以英国塞文河为例

在风景园林学科中,河流沿岸规划设计常较少考虑河道景观长时空维度下的演化过程,而对演化规律的认知能够使设计方案更具科学性。以英国塞文河凯尔苏斯河段流域为例,以综合元胞自动机模型及流体动力学模型的CAESAR-Lisflood平台为依托,进行弯曲型河流河道景观长时空维度上的演化预测、洪泛区洪水多情境变化分析及生态防洪措施治理数值模拟。研究发现凯尔苏斯村庄流域汇水量大,河流搬运能力强,河床随时间变化逐步抬高,易发生洪水灾害及河流改道现象,村庄处于高洪水风险中,设置丁坝的防洪综合效益最好。首次将CAESAR-Lisflood模型运用到风景园林学科,对于河道景观演化的模拟研究,创新性地提出能够使防洪措施更精确可控的设置,为规划方案的设置与比选提供新思路,以此指导河流沿岸绿地空间景观规划。     

十九世纪珠江流域文化景观特征 ——基于西方文献的分析

自古以来，河流及其流域构成了一些最 具活力和最复杂的景观。河流维系着人类社会， 人类社会则以多种方式利用河流，从而产生璀璨 的流域文明。广州作为西方人眼中的一座 “神 奇”城市，两千年来一直是中国最重要的海上门 户，现如今，我们可以从外国商人、船长、旅行 者、传教士等游记、报告或图像记录中获得大量 关于珠江流域文化景观的详细描述。本文尝试 将珠江流域的河流系统及其相关的文化景观作 为人类经验的重要组成部分进行研究，透过西 方人的视野，去分析其对珠江流域及其文化景 观的所见所闻，并深入挖掘珠江流域文化景观 的构成与特征，从而归纳出珠江流域文化景观 中的人水共生关系，为珠江流域文化遗产保护 研究提供了全新的视角与思路。     

Neural network modeling of salinity variation in Apalachicola River.

Salinity is an important indicator for water quality and aquatic ecosystem in tidal rivers. The increase of salinity intrusion in a river may have an adverse effect on the aquatic environment system. This study presents an application of the artificial neural network (ANN) to assess salinity variation responding to the multiple forcing functions of freshwater input, tide, and wind in Apalachicola River, Florida. Parameters in the neural network model were trained until the model predictions of salinity matched well with the observations. Then, the trained model was validated by applying the model to another independent data set. The results indicate that the ANN model is capable of correlating the non-linear time series of salinity to the multiple forcing signals of wind, tides. and freshwater input in the Apalachicola River. This study suggests that the ANN model is an easy-to-use modeling tool for engineers and water resource managers to obtain a quick preliminary assessment of salinity variation in response to the engineering modifications to the river system.     

Flood Forecasting and Warning on the River Rhine

The River Rhine has its source in the glaciers of the Swiss mountains and eventually flows to the flat-lands of The Netherlands. The course of the river can be split into six major morphological sections within different climatological regions. This heterogeneity (in the hydrological sense) is reflected in twenty-five flood-warning centres along the Rhine and its tributaries. There is one flood-warning centre in Switzerland, one in France, three in Germany and one in The Netherlands. This paper describes the organisation and responsibilities of the German flood-warning centres.
The Federal Institute of Hydrology provides the German centres at Mainz and Duisburg with forecast results. These results were obtained by a statistical multichannel filtering model between 1980 and 1997. Commencing in 1998, a new forecasting system has been in use, which is built up by hydrodynamic models for the most important river reaches, coupled with statistical approaches for some input gauges. The implementation and data usage of this new system is discussed and forecast results for the 1993, 1995 and the 1998 floods are presented. Finally, the paper provides an outlook on the linking with precipitation-runoff models.     

深圳市茅洲河流域(宝安片区)黑臭水体治理研究

从目标层、子目标层、方案层3个层面建立了深圳市茅洲河流域(宝安片区)黑臭水体治理系统构架,以2020年底茅洲河流域基本做到水清岸绿、鱼翔浅底为最终目标导向,过程中实现污水不入河、河水不入厂、污染清出河、清水补入河四项子目标,具体采取源头分离、迁移隔离、终端处理、闸门改造、管网改造、泵站改造、漂浮物清理、淤泥清理与处置及清水补给九项措施,从全局着手,做到流域统筹、系统治理。     

Thoughts on Synergetic Development of Watershed Management and Regional Economy

Zhu Qingping, the interviewee, is a prominent expert in China’s watershed management. Starting with the modes of China’s watershed management and the changes of water management philosophy, Zhu emphasizes that watershed management often involves various factors, including public resources, infrastructure construction, ecosystems, historical and cultural traditions, and population, all of which shall be taken into consideration as a whole. The interview then goes to the management of the Yellow River Basin, where Zhu explains the impacts between river flows and urban development, suggests a great opportunity for development the cities in the lower reaches of Yellow River Basin have, and proposes an idea of building a national ecological and cultural belt along the river. He further argues that watershed management requires collaborations across industries, disciplines, and administrative regions and divisions. He also believes that public engagement and maintenance plays an important role in watershed management and an intelligent water / watershed management system needs to be established by networking integrated big-data platforms to facilitate a more intelligent and coordinated water resource management while better ensuring water security at varied scales.     

Can sediment data be used to predict alkalinity and base cation chemistry of surface waters?

We hypothesise that stream sediment elemental composition can predict mean and minimum concentrations of alkalinity, Ca and Mg in the river water throughout a river network. We tested this hypothesis for the River Derwent catchment in North Yorkshire, England, by using 6 years of water chemistry data from the Environment Agency and a digital elevation model to flow path-weight British Geological Survey (BGS) sediment element concentration data. The predictive models for mean concentrations were excellent for Ca and alkalinity, but less good for Mg, and did not require land use data inputs as stream water sediment composition seems to reflect all aspects of the riparian zone soil system. Predictive model forms were linear. Attempts to predict minimum values for Ca and alkalinity also were less satisfactory. This probably is due to variations in hydrological response times to individual precipitation events across the catchment.     

Integrated Catchment Modelling as a Water Resources Management Tool

Groundwater models are becoming increasingly important in water resources management. Most aquifers in the UK are closely linked with river systems, to which they contribute baseflow from seepages and springs. As a result, major groundwater abstractions almost inevitably affect river flows. To assess with confidence the effect of utilizing ground-water resources, an aquifer and river system has to be linked within an integrated model which can simulate varying hydrogeological conditions throughout the catchment.
The main features of an integrated catchment management model, which links aquifer and river systems, are described in this paper. The model has been applied to a number of catchments in southern England including the River Darent in Kent, which is probably the most well-known and worst-affected of all rivers identified nationally as suffering from over-abstraction.
The process of model preparation and calibration is illustrated with reference to the River Darent. Twenty years of river flow and groundwater hydrograph records were used in producing a close simulation of modelled and actual hydrological conditions. The model was then operated to assess a large number of possible options for restoring flows to the river. Examples of various management strategy simulations are given, leading to formulation of a water resources management plan for the Darent. This involved (a) reductions in selected abstractions, (b) flow augmentation using river support boreholes, and (c) meeting peak groundwater supply demands in drought periods.     

Water balance estimation via SESOIL: Pinios River Basin, Greece

The mathematical modelling of a river basin water balance is a complex process which requires extensive calibration and the use of data that are frequently not available. The seasonal soil compartment model, SESOIL, of the USEPA, is an international tool well suited for this purpose. Knowledge of the water balance on an annual or a monthly basis is particularly important in regions with increased water demand and limited resources. SESOIL has been applied to the Pinios River Basin in Central Greece. Observed input and simulated output are discussed. The model behaved well. The study extends the use of SESOIL which can be run with limited calibration compared to other models in the literature and with data readily available in Europe such as the Corine land cover. Simulations can be used for water allocation practices, water related impacts due to climatic changes and other human activities indicated in the new EC Water Framework Directive EC/2000/60.