Possibilities of urban flood reduction through distributed-scale rainwater harvesting

Urban flooding in Chittagong City usually occurs during the monsoon season and a rainwater harvesting(RWH) system can be used as a remedial measure. This study examines the feasibility of rain barrel RWH system at a distributed scale within an urbanized area located in the northwestern part of Chittagong City that experiences flash flooding on a regular basis. For flood modeling, the storm water management model(SWMM) was employed with rain barrel low-impact development(LID) as a flood reduction measure. The Hydrologic Engineering Center's River Analysis System(HEC-RAS) inundation model was coupled with SWMM to observe the detailed and spatial extent of flood reduction.Compared to SWMM simulated floods, the simulated inundation depth using remote sensing data and the HEC-RAS showed a reasonable match,i.e., the correlation coefficients were found to be 0.70 and 0.98, respectively. Finally, using LID, i.e., RWH, a reduction of 28.66% could be achieved for reducing flood extent. Moreover, the study showed that 10%e60% imperviousness of the subcatchment area can yield a monthly RWH potential of 0.04 e0.45 m~3 from a square meter of rooftop area. The model can be used for necessary decision making for flood reduction and to establish a distributed RWH system in the study area.     

Rainwater harvesting systems: An urban flood risk mitigation measure in arid areas

Rainwater harvesting (RWH) systems have been developed to compensate for shortage in the water supply worldwide. Such systems are not very common in arid areas, particularly in the Gulf Region, due to the scarcity of rainfall and their reduced efficiency in covering water demand and reducing water consumption rates. In spite of this, RWH systems have the potential to reduce urban flood risks, particularly in densely populated areas. This study aimed to assess the potential use of RWH systems as urban flood mitigation measures in arid areas. Their utility in the retention of stormwater runoff and the reduction of water depth and extent were evaluated. The study was conducted in a residential area in Bahrain that experienced waterlogging after heavy rainfall events. The water demand patterns of housing units were analyzed, and the daily water balance for RWH tanks was evaluated. The effect of the implementation of RWH systems on the flood volume was evaluated with a twodimensional hydrodynamic model. Flood simulations were conducted in several rainfall scenarios with different probabilities of occurrence. The results showed significant reductions in the flood depth and flood extent, but these effects were highly dependent on the rainfall intensity of the event. RWH systems are effective flood mitigation measures, particularly in urban arid regions short of proper stormwater control infrastructure, and they enhance the resilience of the built environment to urban floods.     

Planning flood control projects in urban areas

Planning and design of flood control projects invariably involves a consideration of sociological, economic, political and ecological factors in order to derive maximum benefits from the project. In urbanizing areas, this is often a rule rather than an exception where a project tends to have a variety of interrelated impacts on the environment. This paper presents the details of the planning efforts by the City of Louisville in Kentucky to implement a major flood control project with an overall goal to evaluate and rectify serious environmental problems brought upon by rapid urbanization in the area. This project was carried out by the U.S. Army Corps of Engineers, Louisville, District, to provide flood mitigation measures in the Beargrass Creek basin, which incorporates a major portion of the City of Louisville. The procedures and considerations used in the formulation, evaluation and the final selection of suitable flood control measures as devloped by the U.S. Army Corps of Engineers, are critically examined.     

城市排渍规模的确定

城市排渍规模问题，一直在不同的设计部门及政府主管部门之间争论，同一城市同一地点的排渍流量，由不同部门，不同的设计理论，设计结果相差悬殊，而城市排渍规模定的过大，会造成建设、管理、维护、运行资金的巨大浪费，定的过小又会因内渍造成巨大灾害损失。本文就这个问题结合株洲市近二十年来在这方面的一些经验教训做点初步的探讨，以期找出一些共性的东西，供规范制定者及设计同行参考。     

Impacts of urban areas and urban growth on groundwater in the Great Lakes Basin of North America

The Great Lakes Basin (GLB) holds vast reserves of groundwater, the great majority of which eventually drains to the lakes. Urban growth significantly affects both the quality and quantity of this groundwater and thereby represents a potential threat to the long-term viability of the Great Lakes hydrologic system. Urban areas import, manufacture, store, transport, and utilise large volumes of chemicals, a proportion of which inevitably finds its way to the shallow sub-surface. In many cases, potentially polluting chemicals are applied directly to urban surfaces (e.g. as road salts, fertilizers and pesticides), are stored in the subsurface (e.g. gasoline tanks) or are released to the subsurface (e.g. septic systems). Because most of the basin's larger urban areas rely almost exclusively on lake-based supplies, very little attention is given to the accumulation of contaminants in shallow urban groundwaters and the serious risks they pose. Assessment of the problem is complicated by the widespread use of urban fill and a complex network of drains, pipes and tunnels that create “urban karst”, a shallow artificial aquifer, unique to urban settings, that exerts a major, yet often unpredictable influence on groundwater flow and contaminant transport. Management of ground water pollution, and its impact on the receiving Great Lakes, will require rigorous audits of all urban sources of contamination together with the development and calibration of groundwater flow and transport models that will enable the fate of urban pollutants to be reliably predicted even when groundwater is not used for supply.     

城市防洪规划中的控制要素

城市防洪规划是城市总体规划的组成部分,目前一些防洪规划对城市防洪设施建设缺乏明确的指导意见,难以成为城市防洪工程建设的依据.编制城市防洪规划要确定合适的防洪标准,制定科学的城市防洪方案.防洪方案应结合排洪、调洪、分洪、滞洪和避洪五方面综合作用,以争取最大的安全效益.制定城市防洪方案应该明确提出对排洪河道、防洪水库、分洪区、山地植被和避洪高程共5个方面的若干规划控制要素.     

Urban and river flooding:Comparison of flood risk management approaches in the UK and China and an assessment of future knowledge needs

Increased urbanisation,economic growth,and long-term climate variability have made both the UK and China more susceptible to urban and river flooding,putting people and property at increased risk.This paper presents a review of the current flooding challenges that are affecting the UK and China and the actions that each country is undertaking to tackle these problems.Particular emphases in this paper are laid on(1) learning from previous flooding events in the UK and China,and(2) which management methodologies are commonly used to reduce flood risk.The paper concludes with a strategic research plan suggested by the authors,together with proposed ways to overcome identified knowledge gaps in flood management.Recommendations briefly comprise the engagement of all stakeholders to ensure a proactive approach to land use planning,early warning systems,and water-sensitive urban design or redesign through more effective policy,multi-level flood models,and data driven models of water quantity and quality.     

基于两种建模方式的嵌套式城市雨洪模型研究与应用

全球气候变化和快速城镇化打破了城市水循环平衡,造成近些年来我国城市暴雨洪涝事件频繁发生。城市暴雨洪涝(雨洪)模型是应对城市洪涝事件的重要技术保障。然而,对于城市暴雨洪涝模拟,模拟精度和计算效率往往是一对矛盾体。本文总结了目前两种应用比较广泛的建模方式,即基于部分物理机制的水文单向驱动水动力模拟方式和基于完整物理机制的全过程双向耦合模拟方式。在此基础上,为了提高防汛应急处置工作的前瞻性和准确性,本文提出基于上述两种建模方式的嵌套式模拟方法。针对昆明主城区及其局部汇水区的模拟应用研究表明,嵌套式模拟方法在一定程度上缓解了城市雨洪模型在“整体”和“局部”、“精度”和“效率”之间的矛盾,具有较好的实用价值。     

城市河流面源污染控制技术

随着点源污染得到逐步治理,面源污染已成为水体污染的主要原因,并有逐渐恶化的趋势.主要讨论城市河流流域范围内的面源污染控制问题,从污染物输送入河前的源头控制和污染物集中入河的末端控制两方面,分别阐述了目前城市河流面源污染控制的技术性措施.     

黄河下游滩区漫滩概率分析

根据对新中国成立以来黄河下游历次漫滩资料的分析，小浪底水库建成前约2年漫滩一次，建成后约3年漫滩一次。随着黄河调水调沙的继续实施，黄河下游河道的过洪能力将会得到进一步提高，加上工农业用水的增加、中游水土保持工程建设的不断完善．小浪底水库对中常洪水的拦蓄率将会提高，发生大于平滩流量洪水的概率会更低，有希望达到5年一遇。因此。从技术角度分析黄河下游滩区具备享受国家蓄滞洪区运用补偿政策是可行的。     

城市构筑物暴雨内涝分层模拟技术及应用

气候变化和城市快速发展,导致我国城市洪涝问题日益突出。城市洪涝模拟是当前城市洪涝灾害风险管理领域研究热点,但国内外依然缺乏针对城市多层构筑物的精细模拟技术和方法。城市立交桥,是一种典型的城市多层构筑物,极易遭受洪涝灾害,并对城市交通造成严重影响。以城市立交桥为代表,在现有全分布式城市暴雨内涝模型基础上,结合城市立交桥的特点,提出一种分层模拟技术,并从网格分层构建、分层产汇流计算、地表与管网分层耦合和上层网格排水等方面详细阐述了分层模拟技术。将该分层模拟技术应用于深圳市罗芳立交桥2018年“8.29”暴雨积水过程模拟,与单层模拟方法相比,多层模拟结果更接近上报积水信息。研究表明,分层模拟技术更能准确表达城市复杂多层建筑物的实际暴雨内涝过程。     

关于城市排水(雨水)防涝规划编制的思考

随着城市雨水系统规划设计的范围扩大,已经逐渐超过了基于推理公式法的雨水系统规划设计方法的适用范围,导致计算结果出现偏差,影响雨水系统的安全性。同时,目前全国开展的城市排水防涝规划中,要求转变思路以及加强数学模型等新技术的应用,但由于规划的编制和模型等新技术的应用在我国还处于起步阶段,很多具体技术问题有待探讨。总结了排水防涝规划的核心问题及思路,对规划编制的重点问题以及数学模型的应用等几个关键问题进行探讨。     

建筑物密集城区溃堤水流二维数值模拟

本文对建筑物高度密集的城区溃堤洪水进行了数值模拟。模型采用有限体积法对二维浅水方程进行了非结构离散，以Roe格式的近似Riemann解为基础计算界面通量。为考虑社区和楼房的容水性能引入了侵入系数的概念，采用物理模型试验结果验证了该数学模型的准确性和稳定性。应用该模型对哈尔滨市未来可能发生的溃堤洪水进行了模拟，研究表明，以二维路网为主要计算区域时，网格尺寸的大小对计算结果影响并不明显，而不同的侵入系数则对其影响较大。     

建筑物密集城区溃堤水流二维数值模拟

通过考虑社区和楼房内部的容水性,引入侵入水量的概念,建立了能够模拟建筑物密集城区溃堤水流运动的数学模型。该模型采用有限体积法对浅水方程进行非结构离散,通过Roe格式计算界面数值通量,给出了侵入水量的合理估算方法。通过物理模型的试验结果验证了本文模型的准确性和稳定性。最后应用该模型对哈尔滨市可能发生的溃堤洪水进行模拟,计算结果表明,该模型能较好地模拟溃堤洪水在城区内的运动过程,侵入系数的变化对计算结果有比较明显的影响。     

上海市区远景防洪标准研究

本文通过对上海市区不同防洪（潮）标准的经济论证，对上海市远景防洪（潮）标准的选用提出参考性建议。在防洪（潮）经济论证中，采用了不确定性的分析方法，在辨识影响防洪（潮）经济效益的不确定性因素基础上，拟定基本风险变量的概率分布，并通过统计试验，以推求防洪（潮）经济指标的概率分布，最终从概率的角度来比较和评价不同防洪（潮）标准的经济合理程度。此外，由于受海平面上升和上海市区地面沉降的影响，某种规模的防洪（潮）设施在其经济分析计算期里各年的防洪（潮）标准也是变化的，因而本研究在计算其防洪（潮）经济效益时也考虑了这种变化。由于本研究考虑了上述因素，从而使结论更趋客观和合理。     

差分模型网格嵌套边界技术在工程潮流计算中的应用

本文对差分模型的网格嵌套技术作了介绍，提出流速梯度项ｕ／ｓ是不可忽视的边界控制条件，并给出了采用线性插值获取ｕ／ｓ值的处理方法，通过实际算例证明网格嵌套技术在实际工程潮流计算中的作用。     

城市突发水涝灾害预防及恢复能力研究

目前,国内关于城市突发水涝灾害防治能力评价的相关研究较少,还没有形成系统的城市突发水涝灾害防治能力评价体系。为进一步推动城市突发水涝灾害定量化研究,对城市突发水涝灾害预防及恢复能力进行了探索性研究。运用信息化手段应对城市内涝问题,首先对城市突发水涝灾害数据及其特征进行了分析,并进一步构建了城市突发水涝灾害预防及恢复能力评价指标体系和评价模型,为各城市评价突发水涝灾害的预防及恢复能力提供一个初步的理论基础和框架。设计了应用于城市突发水涝灾害的混合大数据分析工具,通过搭建系统测试平台对分析工具进行了初步检验。结果表明,大数据技术的应用可以改善城市突发水涝灾害预防工作的技术与装备支持情况,进而有助于城市突发水涝灾害预防能力的提升。     

An alternate approach for transient flow modeling in urban drainage systems

Implementing control structures such as gates at suitable locations in the urban drainage network enables its improved utility by actively controlling and optimizing the flow during a flood event. The successful operation of the control structure is fully governed by the suitability and efficiency of the control strategy adopted, which in turn depends on the response characteristics of the urban drainage system under different flow conditions. For an extreme rainfall event, it is necessary to model the transient flow in the urban drainage system. However, such an exercise is mostly restricted by the limited data and lack of in-depth survey of urban drainage systems in most of the developing countries like India. Taking this into consideration, an alternate approach has been presented in this paper for modeling the transient flow in the urban drainage system under limited data availability. The results obtained have also been compared with the finite difference model using four-point implicit scheme in time domain. The developed model can be used for the computation of temporal distribution of water surface profile with special consideration of lateral inflow. The application has been demonstrated by applying it to a representative catchment in Mumbai, India.     

基于二维浅水方程的城市地面洪水演进数值模拟研究

探究城市内涝灾害数值预报对城市的防洪减灾及灾害评估具有重要意义。基于三角形非结构网格,采用Godunov型有限体积法建立了一个高精度的二维浅水水动力数值模型。该模型使用Roe格式计算界面通量,可以较好地捕捉洪水的动边界运动,模型将静水压力项放入源项中,减少了由于地形底坡项带来的数值解伪震荡。该模型对动边界以及负水深处理技术进行了改进,能够有效提高模型模拟的精确度和静水和谐性。在应用3个算例对模型进行率定的基础上,将模型应用于浑河、太子河之间浑太胡同区域的地表洪水演进的模拟中。结果表明:浑太胡同内洪水演进的水深、流场变化均较为合理,组合溃堤各水深淹没面积均为最大,模拟结果很好地验证了城市区域雨洪的流动演变过程,证明该模型可以用于复杂地形的城市由降水形成的暴雨积水及地表洪水演进模拟过程,模型可快速为城市防汛减灾提供积水情况及涝情信息。     

陆川县城区防洪排涝及水环境治理方案设计

介绍陆川县城区防洪排涝及水环境治理方案。陆川县城区位于九洲江河畔,城区内有9条支流,拦河坝和跨河桥梁众多,由于城区上下游河床浅窄,城区建筑密集,造成洪涝灾害严重。此外,由于九洲江是陆川县和广东省湛江市及雷州半岛人民生活和生产的主要水源,保护水质至关重要,所以在防洪排涝建设同时对水环境进行治理。