Decentralization-based optimization of detention reservoir systems for flood reduction in urban drainage areas

The paper introduces a decentralized approach to optimizing the flood reduction efficiency of multiple detention reservoirs in urban areas. The flood reduction effects of a detention reservoir system were regionally assessed, and a new model was then created using an optimization technique which involved coupling extraordinary particle swarm optimization with a flood simulation engine, Storm Water Management Model, EPA-SWMM, to identify optimal outlet designs for a detention reservoir system. When applied to the To Lich drainage network (Hanoi, Vietnam) the proposed method outperformed the present design, reducing flooding under the design flood event. The performance of the approach was verified by comparing it with the overall objective function of total flooded volume for different design floods. The better performance of the decentralized optimization approach described here, in terms of local and regional flood management, illustrated its effectiveness for urban flooding reduction.     

A Semi-Empirical Investigation of the Influence of Flood-Plain Storage on Flood Flow

A simple model is used to assess the effect of flood-plain storage on flood flows, with a view to developing methods for general use in flood-frequency estimation. Recent floods on the River Severn at Montford are 'unrouted' in order to determine the shape and magnitude of the hydrographs, provided that there had been no overtopping and all flows had been contained within the banks. The model used to unroute the hydrographs has, at its core, a relationship between water depth and flooded area derived from a coarse (50 m) digital terrain model developed from Ordnance Survey 1:50 000 maps. The implications for flood-frequency curves at sites downstream from significant flood-plain storage are discussed.     

Flooding of municipal solid waste landfills — An environmental hazard?

Municipal solid waste (MSW) landfills pose a long-lasting risk for humans and the environment. While landfill emissions under regular operating conditions are well investigated, landfill behaviour and associated emissions in case of flooding are widely unknown, although damages have been documented. This paper aims at developing a methodology for determining the proportion of MSW landfills endangered by flooding, and at evaluating the impact flooded landfills might have on the environment during a flood event.The risk of flooding of MSW landfills is assessed by using information about flood risk zones. Out of 1064 landfills investigated in Austria, 312 sites or about 30% are located in or next to areas flooded on average once in 200 years. Around 5% of these landfills are equipped with flood protection facilities. Material inventories of 147 landfill sites endangered by flooding are established, and potential emissions during a flood event are estimated by assuming the worst case of complete landfill leaching and erosion. The environmental relevance of emissions during flooding is discussed on the basis of a case study in the western part of Austria. Although environmental hazards need to be assessed on a site- and event-specific basis, the results indicate that flooded MSW landfills represent in general small environmental risks for the period of flooding. The longer term consequences of flooding are discussed in a next paper.     

ROOM FOR THE WAAL IN NIJMEGEN,THE NETHERLANDS

The Room for the River project around Nijmegen, The Netherlands is one of the most integrated and most complex cases in the national flood safety strategy. Along the Waal River in Nijmegen, a bypass channel and a new urban river park were created that not only reduce flood risks, but also offer recreational, ecological and aesthetic values.     

The White Cart Water Flood Alleviation Study using Hydrodynamic Mathematical-Modelling Techniques

This paper describes a hydrodynamic mathematical-modelling study to investigate the flooding problem and to recommend various flood-alleviation measures for the White Cart Water on the southern side of Glasgow. The mathematical model covers 36 km of the White Cart to the tidal reaches at the confluence with the River Clyde, and includes 7 km of one of the major tributaries where regular flooding is also a problem. A key aspect of the study was the close proximity of the modelling team which permitted a close scrutiny of the river during high-flow events. From these observations the team obtained a thorough appreciation of river behaviour during potential flood situations, which provided a reliable and comprehensive set of data for model calibration over a wide range of conditions. The proposals for flood alleviation have far-reaching implications and require major capital expenditure. At present they are being examined by Strathclyde Regional Council in consultation with the many interested parties.     

Fenay Beck Flood-Alleviation Scheme

The paper describes flood detention and channel improvement schemes which have been designed to alleviate the flooding of domestic and industrial properties to a 50-year standard of protection. Landscape architects were incorporated into the design teams to cover environmental aspects.
The flood-detention dam would have been constructed mainly of colliery waste, and the design of the concrete horseshoe spillway and stilling basin was checked using a 1 : 40 physical model. River regulation would be by an automatic vertical gate activated by downstream water levels.
Following planning refusal, a channel-improvement scheme was adopted, which is presently under construction. Reduction in valley storage increased downstream flows, necessitating the enlargement of an old brick and concrete culvert within the ICI works to ensure that there were no detrimental effects within their boundary. An increased benefit/cost ratio of 3.46, as compared with 2.55 obtained for the detention scheme, was partly due to the application of new standards.     

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。     

Causes of seasonal flooding in flood plains: a case of Makurdi,Northern Nigeria

This study assessed several factors and their implication for flooding in Makurdi which is located in the flood plains of the River Benue. The annual rainfall of Makurdi between 1979 and 2008 was analysed for annual totals, intensity, frequency, peak periods and trend to demonstrate propensity to cause flooding while records on relief, water table, urbanisation and the river Benue were examined for their contribution. This study has identified amongst other things that areas of low relief in Makurdi are susceptible to seasonal flooding between June and October annually. The study also identified the causes of floods and factors which intensify floods in Makurdi town. Heavy, intense rainfall and the River Benue spilling its banks are the major causes of floods in Makurdi town. Other factors which intensify flooding in Makurdi town include its low relief, high water table, urbanisation and human activities.     

Post-Implementation Appraisal of a Two-Stage Channel in the River Roding, Essex

T he performance of a two-stage river channel is examined from a combination of collected field data on the River Roding and a hydraulic model study. Particular attention is paid to the vegetation on the upper channel berm, including its seasonal effect on hydraulic resistance and the problem of channel maintenance. Recommendations are made with respect to (a) increasing the present capacity of the River Roding, and (b) the future design of two-stage flood channels intended to meet stringent environmental standards.     

ROBERTSBRIDGE FLOOD ALLEVIATION SCHEME: THE CHALLENGES OF A FAST-TRACK APPROACH

flooding occurred in many locations in the united kingdom in the autumn/winter of 2000. One of the worst affected areas was Robertsbridge, in East Sussex, where over that winter, some properties were flooded up to eight times following those events, the environment agency targeted defences for this high-risk township as one of its high priority projects to'fast-track'to implementation.
studies started in January 2001, which recommended a stand-alone scheme that would project the township against the 1% probability flood. Project development progressed on a'fast-track'basis to allow construction to start in September 2002 with completion planned in the summary of 2003.
project development and implementation is always an obstacle course but the'fast-track'approach magnifies the obstacle and introduces new ones. This paper describes experience from the Robertsbridge flood allevation scheme, with particular reference to some of the problems encountered, both technical and procedural     

SOLVING AN URBAN RIVER EROSION PROBLEM ON THE TILMORE BROOK, HAMPSHIRE (UK)

The Tlimore Brook, In Hampshire, typifies the Impact of new housing development that has taken place In phases over the past 20 years or so, on a river corridor. However, the issue is not one of flooding, because the channel itself had been straightened and deepened in historical times and had been adjusted further by down-cutting; thereby forming an over-large channel sufficient to contain flood flows. Perhaps rarely for lowland Britain, the key problem was that of erosion, threatening adjacent properties. This paper describes the nature of the erosion problem and the subsequent geomorphological design to mitigate it. A key unique feature of this project was the extent of backfilling required, over the entire length, to raise the over-deep channel bed. The project was constructed in 2003.     

Citywide multi-grid urban flood modelling: the July 2012 flood in Beijing

Global flood management is a major issue for most cities which have to deal with worsening factors such as climate change and fast urban growth. Computer models have been used to model and understand urban flooding on a local scale in cities (25–50 km²). It has been practically impossible to model bigger cities in one go in sufficiently high resolution due to the heavy computations involved.

The present paper describes a new modelling approach for urban flooding which allows modelling on large city scale (1000 km²) while keeping sufficient resolution, e.g. 5 m or 10 m grid. The multicell approach is applied for the city of Beijing for July 21st, 2012 flood event. Model results are compared to testimonials from the 2012 event. Comparison to traditional 2D urban flood computations shows that the multicell approach is much faster than standard detailed models while keeping a suitable level of precision.     

山地城市小流域暴雨径流模型的研发及应用

采用ArcEngine二次开发包结合水力学基础算法,建立山地城市暴雨径流模型,以模拟山地城市降雨径流,分析山地城市排水系统的排放能力。应用该模型对重庆市北部新区盘溪河流域排水系统进行了预测和评估,结果表明,模拟结果与实测数据的效率系数Nash-Suttcliffe系数Ens为0.56~0.76,相对误差8.82%~11.8%。模型关键参数率定及敏感性分析表明,最敏感参数为径流宽度、坡度、曼宁系数和不透水面积率。针对排水管道内流量、充满度和溢流检查井个数等方面进行了排水系统排放能力的评估,结果表明,一年一遇暴雨下有0.52%的排水管道长时间处于满流状态,五十年和百年一遇的超载排水管道占排水管道总数5.86%和 8.20%;百年一遇暴雨下有0.72%的检查井发生溢流,一年一遇暴雨下有0.31%的检查井发生溢流。该模型实现了对山地城市暴雨径流的产汇过程模拟以及内涝点位置和数量的识别,为城市雨水管网管理提供决策支持。     

Seasonal variations and annual fluxes of arsenic in the Garonne, Dordogne and Isle Rivers, France

Daily measurements of water discharges and suspended particulate matter (SPM) concentrations and monthly analyses for arsenic were conducted from 1999 to 2005 on the Garonne, Dordogne and Isle Rivers, the three main tributaries of the Gironde Estuary, France. Despite the known historical polymetallic pollution affecting the Lot-Garonne River system, the highest As concentration level was observed in the Isle River. This was explained by the geological context and various Au/As deposits in this watershed. In the three studied rivers, dissolved As concentrations showed important seasonal variations with maximum values in summer. The dissolved As concentrations were closely related to water temperature and their increase in spring/summer appeared to be induced by water temperatures above approximately 15 degrees C, independently from discharge. The reduction of As(V) to more soluble As(III) and/or destruction of solid As carrier phases by micro-organisms could explain this observation, suggesting that temperature-dependent biogeochemical processes play an important role in controlling As partition and speciation in fluvial systems. Water and SPM fluxes in the Garonne River mainly control arsenic inputs into the Gironde Estuary and the downstream coastal zones. Based on the present data, we propose an empirical model to roughly estimate the annual dissolved and particulate As fluxes in the Garonne, Dordogne and Isle Rivers from annual water and SPM fluxes. The comparison of observed As fluxes and those estimated from the empirical model suggests that resuspension of historical, polluted reservoir sediments during a major flood accounted for approximately 50% of the annual As fluxes in 2003.     

Object Oriented Programming and Numerical Methods

Abstract: A generally applicable mathematical model, tailored for use on a Personal Computer, as the design tool to simulate unsteady flood flow in a network of interconnected rivers has been developed and applied to the Sham Chun River along the border between Hong Kong and the People's Republic of China. The effect on the improved Sham Chun River due to the proposed river training in the River Indus, one of its tributaries, is evaluated. The one-dimensional unsteady flow model itself is broadly applicable to a wide range of hydrologic conditions and varying field situations. It incorporates real hydraulic features including branched channels and 'tidal flats' flooding and drying. The time history of water stages and discharges are computed at any desired location throughout the connected essentially one-dimensional channel network subject to initial and boundary conditions. Details are given of techniques adapted in using the computational scheme to quantify the unsteady flow condition and the means to assure an efficient numerical solution as well as to verify the accuracy of the computed outputs by subjection to carefully selected schematic simplified test cases and real prototype cases with numerical solution method is a useful predictive engineering tool in river design.     

Influence of flooding, salinity and inundation time on the bioavailability of metals in wetlands

Controlled flooding of lowlands is considered as a potential water management strategy to minimize the risk of flooding of inhabited areas during high water periods. However, due to industrial activities, river water, sediments and soils are often contaminated with metals which may have adverse effects on the ecosystem's structure and functioning. Additionally, salinity may greatly affect the bioavailability and toxicity of metals present or imported into these systems. The effect of contaminated soils under different flooding and salinity exposure scenarios on the growth, reproduction and metal accumulation in the oligochaete Tubifex tubifex (Müller, 1774) were examined. In these bioassays metal contaminated soils were flooded with water of different salinities (0 and 3 psu), and tested after 0, 6 and 12 months of permanent inundation. We indeed found that inundation time had significant decreasing effects on Cu and Zn accumulation; although initial accumulation of Cu and Zn was higher in the previously unflooded soil at the start of the flooding treatment, these differences seem to disappear after 6 months of permanent inundation. Moreover, the complex interaction between substrate type and salinity suggests that redox potential is probably of major importance.     

A Microcomputer Model for Flood Prediction with Applications

Abstract: A generally applicable mathematical model, tailored for use on a Personal Computer, as the design tool to simulate unsteady flood flow in a network of interconnected rivers has been developed and applied to the Sham Chun River along the border between Hong Kong and the People's Republic of China. The effect on the improved Sham Chun River due to the proposed river training in the River Indus, one of its tributaries, is evaluated. The one-dimensional unsteady flow model itself is broadly applicable to a wide range of hydrologic conditions and varying field situations. It incorporates real hydraulic features including branched channels and 'tidal flats' flooding and drying. The time history of water stages and discharges are computed at any desired location throughout the connected essentially one-dimensional channel network subject to initial and boundary conditions. Details are given of techniques adapted in using the computational scheme to quantify the unsteady flow condition and the means to assure an efficient numerical solution as well as to verify the accuracy of the computed outputs by subjection to carefully selected schematic simplified test cases and real prototype cases with numerical solution method is a useful predictive engineering tool in river design.     

Environmental Effects of Hydro-Electric Power Generation in Africa and the Potential for Artificial Floods

Electricity is a fundamental requirement for economic growth, and hydro-electric power is often thought to be environmentally benign. However, the construction and operation of many hydro-power dams in Africa have had significant negative impacts on the environment and rural economies. Reduced downstream flooding has destroyed fisheries and starved the floodplain soils of moisture and nutrients. Often the worst-affected areas have no electrification and therefore do not benefit from power generation. New dams which are planned in Kenya and Tanzania have been specifically designed to make flood releases. This will allow electricity to be generated whilst maintaining a dynamic flooding pattern for the short-term economic importance of fisheries and agriculture and the longer-term importance of soil fertility and biodiversity. Involvement of local community representatives in deciding when flood waters should be released on the Phongolo River in South Africa has resulted in substantial benefits to floodplain users.     

Modelling instream nitrogen variability in the Dee catchment, NE Scotland

The Integrated Nitrogen in CAtchments model (INCA) was applied to the River Dee, Aberdeenshire, NE Scotland. To a first approximation the model was able to simulate the annual mean streamwater NO3-N concentrations observed along the length of the main channel. This provided the basis for using INCA to subsequently explore the effects of N deposition and land use management on streamwater NO3-N concentrations and loads. On an annual timescale, the model predictions suggest that NO3-N concentrations will decrease by 5% following a 20% reduction in fertiliser application. Furthermore, model results also suggest that a 50% increase in N deposition will cause a 15% increase in the streamwater NO3-N concentrations. The utility of INCA as a tool for catchment management is discussed, current limitations are highlighted and possible improvements are suggested.