Effective Flood Mitigation Research Articles

Combining Ecosystem Services with Cost-Benefit Analysis for Selection of Green and Grey Infrastructure for Flood Protection in a Cultural Setting

The present paper describes a methodological framework that combines ecosystem services (flood protection, education, art/culture, recreation and tourism) with economic analysis for selection of multifunctional measures for flood resilience. The framework includes active stakeholder participation and it consists of the four main components: (1) identification and valuation of ecosystem services pertinent to the project site under various mitigation scenarios, including baseline (pre-mitigation conditions); (2) evaluation of most effective flood mitigation measures through hydrodynamic simulations, and evaluation of economic viability using cost-benefit analysis; (3) selection of measures through consideration of ecosystem services, and solicitation of stakeholders’ inputs; (4) development of the conceptual landscape design. Application of the framework was demonstrated in a case study of Ayutthaya Island, Thailand. Results of our research suggest that taking a holistic perspective of ecosystem services and economic assessments, marshalled through active stakeholder participation, has the potential to achieve more ecologically sustainable and socially acceptable solutions for flood protection in areas with cultural heritage. However, there is still a considerable challenge in taking this framework to a full-scale practical implementation, and this mainly relates to the selection of indicators that can enable proper application of ecosystem services.

Global-scale river flood vulnerability in the last 50 years.

The impacts of flooding are expected to rise due to population increases, economic growth and climate change. Hence, understanding the physical and spatiotemporal characteristics of risk drivers (hazard, exposure and vulnerability) is required to develop effective flood mitigation measures. Here, the long-term trend in flood vulnerability was analysed globally, calculated from the ratio of the reported flood loss or damage to the modelled flood exposure using a global river and inundation model. A previous study showed decreasing global flood vulnerability over a shorter period using different disaster data. The long-term analysis demonstrated for the first time that flood vulnerability to economic losses in upper-middle, lower-middle and low-income countries shows an inverted U-shape, as a result of the balance between economic growth and various historical socioeconomic efforts to reduce damage, leading to non-significant upward or downward trends. We also show that the flood-exposed population is affected by historical changes in population distribution, with changes in flood vulnerability of up to 48.9%. Both increasing and decreasing trends in flood vulnerability were observed in different countries, implying that population growth scenarios considering spatial distribution changes could affect flood risk projections.

내배수시설 경계 재설정에 따른 내수침수 저감효과 분석

In this study, we effectively reduce the flood damage through a revise the border for district unit urban drainage system and propose a design technique over the configuration of the sewer network. It was selected in adjacent urban drainage system, analysis the results for the revise of the watershed boundary and inundation reduction effect. The main nodes were chosen to generate a flood damage, the flood mitigation effect was verified. It proposed a emphasis point for revise the border for urban drainage system.

Assessment of People’s Awareness and Perception of Flooding in Donga Town, Taraba State, Nigeria

Flooding is now an annual occurring event in Donga Town especially after heavy rainstorm which is further worsened by the nature of the topography of the area. The knowledge of how the public view flooding is considered a crucial aspect in modern flood management as it steers the development of effective and efficient flood mitigation strategies. This study therefore assessed public perception of flooding in Donga town. Two wards were purposively drawn out of ten wards (Gata Aure and Fada ward). The survey design method was employed in this study. Yamane (1967) method of sample size determination was used to arrive at a sample size of 130 for the study. Systematic random sampling was used in the administration of 130 questionnaires to respondents. Non parametric statistics of Spear Man rank correlation and descriptive statistics (percentages, tables, pie and bar charts) were used to analyze the data. The result of the findings showed that 95% of the respondents were male, 88.4% of the respondents were aware that the area was prone to flooding. Also, about 46.2% perceived that rainfall was the major cause of flooding in the study area. Correlation analysis result was insignificant which implied that in Donga town, educational level of respondents did not influence respondent’s awareness level of flooding and that people’s perception of flooding was influenced by factors other than respondent’s literacy level. The conclusion from the study is that rainfall intensity and amount is the main cause of flooding in Donga town and also individual’s response to flooding in the study area is poor. This study recommends the need to educate the people living in the flood plain on the dangers of continuous occupation of the area.

수치모형 적용을 통한 나주 강변저류지 홍수위 저감효과 분석

강변저류지는 일정 규모 이상의 홍수를 하도로부터 분배하여 홍수량을 저감시킴으로써 홍수위험을 저감시키는 수공 구조물이다. 본 연구에서는 강변저류지에 의한 홍수저감효과를 분석하기 위하여 수치모의를 수행하였다. 기후변화에 의한 이상홍수 발생시, 홍수저감효과를 분석하기 위하여 계획빈도를 상회하는 수문조건에 대한 검토를 수행하여 강변저류지의 홍수조절능력을 분석하였다. 또한, 강변저류지가 설치된 하천은 복잡한 지형과 횡월류위어를 통하여 강변저류지로 분배되는 흐름이 동시에 발생하므로 복잡한 흐름현상을 구현하기 위하여 2차원 모형의 적용성을 검토하였다. 기존 강변저류지 홍수저감효과 분석시 주로 활용되는 1차원 모형과 2차원 모형의 결과를 비교 및 검토하였다. 본 연구결과 강변저류지에 의한 홍수저감효과를 모의하기 위해서는 지형 및 횡월류 흐름을 공간적으로 구현할 수 있는 2차원 모형을 활용하는 것이 합리적인 것으로 판단된다. The retention basin is a hydraulic structure for flood mitigation by storing river flow over a design flood. In this study, numerical models were adopted to simulate the flood mitigation effects by a retention basin. The large flood condition was applied as a boundary condition to consider an abnormal flood caused by climate change. Furthermore, the two-dimensional numerical model was adopted to regenerate the complex flow pattern due to the topography and lateral flow near the retention basin. The numerical results of the one- and two-dimensional model were analyzed and compared. The results showed that the two-dimensional model is more applicable to assessing flood mitigation by the retention basin with a complex topography and lateral flow patterns.

FLOOD MODELING OF RIVER GODAVARI USING HEC-RAS

Many cities and towns are developed on downstream side of dams. Some of them are established on the banks of river. During the monsoon period, when the dam is full at its Maximum Reservoir Level (MRL) and still the surplus floods are approaching into dam submergence, the maximum discharge is released from the dam to avoid the overtopping. This results into floods on downstream and may cause the disaster in cities or towns settled on banks of rivers. To facilitate the appropriate measures for effective flood mitigation in advance, there is a need to model the flood plain. With the advent of modern technology, the use of sophisticated softwares in flood modeling helps in getting an idea of extent of flood at its submergence. This paper presents a case study of Godavari river flood modeling using HEC-RAS software. The flood released for Gangapur dam, which is constructed on upstream of Nashik city at 14 km distance is considered for the modeling. The flood discharge is based on the worst discharge of 1969 flood. The river, 14 bridges across the river and the flood plain are modeled. The model facilitates to locate the flood plain and its extent for effective flood mitigation measures.

The English floodplain

English floodplains are platforms for flood risk vulnerability; they are varied in form and in the timing of their development, both naturally and in terms of human occupation. An understanding of floodplain generation is one of the diverse research areas that can contribute towards effective flood mitigation efforts. The performance of remedial measures like catchment sediment management, flood embanking and channel dredging need to be evaluated with regard to active fluvial process systems so that they may be applied appropriately, particularly given uncertain future environmental changes.

Progress in natural flood retention at the Bavarian Danube

The public generally expects restoring natural flood retention as an effective flood mitigation measure, given that river regulation or losses of natural retention storage space through human intervention of nature are often perceived as the cause of recent disastrous floodings. In order to investigate the above mentioned hypotheses and to investigate the retention potential of a large natural river before the river was modified by man, we developed a 2D-hydrodynamic model for a 270 km section of the Bavarian Danube under its historical and present states. In other words, we modeled the flooding of the river prior to the implementation of any river regulation measure, i.e., a state at around 1,800, and compared the results with the present state. Surprisingly, even though the retention volume during the historical state was much larger compared to the present (approximately 350 million m3 of additional retention space during a 100-year flood event), only minimal or even negative effects on the damping of flood peaks could be detected for some cross sections. The delay of the flood peak in the historic scenario, however, conforms with general expectations. Two main hydraulic effects could be observed: Firstly, overtopping of the accompanying floodplains is nowadays delayed by dikes, so that the smaller retention volume is activated very efficiently during times of flood peak passage. Secondly, the timely interaction of the Danube flood wave propagation with flood waves from tributaries and with bypass-overland-flows parallel to the main channel is important. We furthermore performed steady-state simulations to show the process of overtopping, the activation of retention volume and the flow velocities on the floodplains for both states and quantify the loss of retention volume over the last 200 years. This consideration explains the natural retention effects in more detail.

A sensitivity analysis approach of multi-attribute decision making technique to rank flood mitigation projects

The goal of this study is to evaluate and rank the effectiveness of the Korean governments’ Four Major River Restoration Projects. A hydraulic simulation model and geographic information system tools are used to analyze the flood mitigation effects provided by these projects. In addition, the rankings of four major rivers are derived using two sensitivity analyses to weight values and performance measures for Multi-Attribute Decision Making (MADM) technique. As a result, the flood risk presented by the Nakdong River can be most effectively decreased when considering these weights, and levee freeboards are the most critical criterion in the effectiveness ranking. The Youngsan River’s flow capacity criterion is also critical for this problem. This study will be helpful in the robust prioritization of various water resources plans.

Quantitative analysis on the urban flood mitigation effect by the extensive green roof system

Extensive green-roof systems are expected to have a synergetic effect in mitigating urban runoff, decreasing temperature and supplying water to a building. Mitigation of runoff through rainwater retention requires the effective design of a green-roof catchment. This study identified how to improve building runoff mitigation through quantitative analysis of an extensive green-roof system. Quantitative analysis of green-roof runoff characteristics indicated that the extensive green roof has a high water-retaining capacity response to rainfall of less than 20 mm/h. As the rainfall intensity increased, the water-retaining capacity decreased. The catchment efficiency of an extensive green roof ranged from 0.44 to 0.52, indicating reduced runoff comparing with efficiency of 0.9 for a concrete roof. Therefore, extensive green roofs are an effective storm water best-management practice and the proposed parameters can be applied to an algorithm for rainwater-harvesting tank design.

SWMM 모형을 이용한 목감천 유역의 LID 시설 적용 홍수저감효과 분석

PURPOSES: In this study, flood mitigation effect of drainage asphalt concrete pavement were analyzed by a SWMM 5.0 program in order to evaluate the low impact development (LID) based on the drainage asphalt concrete pavements. METHODS: In order to determine the porosity parameters of drainage asphalt concretes, the specimen mixtures were manufactured using the conditions presented in the previous study. The numerical simulation was conducted using the SWMM 5.0 program considering the flood mitigation effect of drainage asphalt concrete pavements. The effect of flood reduction can be observed when drainage asphalt concrete pavements were applied to Mokgamcheon watershed. The flood mitigation effect analysis of Mokgamcheon watershed as well as continuous simulation of subwatershed runoff were performed through this study. RESULTS : The analysis of drainage asphalt concrete pavements was carried out for evaluating the effect on runoff, resulting in: the peak flow decreases up to 1.26~9.53% after drainage asphalt concrete pavements applied in the SWMM 5.0 program furthermore, the discharge decreases up to 0.55~4.11%. CONCLUSIONS: As a result, the reduced peak flow and discharge were found through the SWMM 5.0 program. It can be concluded that the flood is effectively reduced when the drainage asphalt concrete pavements are used.

Probability assessment of flood and sediment disasters in Japan using the Total Runoff-Integrating Pathways model

To address many of the problems faced in hydrological engineering planning, design, and management, a detailed knowledge of flood event characteristics, such as flood peak, volume, and duration is required. Flood frequency analysis often focuses on flood peak values and provides a limited assessment of flood events. To develop effective flood management and mitigation policies, estimation of the scale of potential disasters, incorporating the effects of social factors and climate conditions, is required along with quantitative measures of flood frequency. The Japanese flood risk index, the flood disaster occurrence probability (FDOP), was established based on both natural and social factors. It represents the expectation of damage in the case of a single flood occurrence, which is estimated by integrating a physical-based approach as a Total Runoff Integrating Pathways (TRIP) model with Gumbel distribution metrics. The resulting equations are used to predict potential flood damage based on gridded Japanese data for independent variables. This approach is novel in that it targets floods based on units of events instead of a long-term trend. Moreover, the FDOP can express relative potential flood risk while considering flood damage. The significance of the present study is that both the hazard parameters (which contribute directly to flood occurrence) and vulnerability parameters (which reflect conditions of the region where the flood occurred), including residential and social characteristics, were shown quantitatively to affect flood damage. This study examined the probability of flood disaster occurrence using the TRIP model for Japan (J-TRIP), a river routing scheme that provides a digital river network covering Japan. The analysis was based on floods from 1976 to 2004 associated with flood inundation and sediment disasters. Based on these results, we estimated the probability of flood damage officially reported for the whole region of Japan at a grid interval of 0.1 degrees. The relationship between the magnitude of the rain hazard expressed as the probability of exceedance and the probability of flood damage officially reported was expressed as an exponential function by equalizing the whole region of Japan based on excess probability. Moreover, the probabilities of flood damage occurrence according to social factors and changes in climate conditions were also examined. The probability of flood damage occurrence is high, especially in regions of high population density. The results also showed the effect of the dam maintenance ratio on extreme flooding and flood damage frequency. The probability of flood damage occurrence was expected to increase during extreme weather events at the end of this century. These findings provide a sound foundation for use in catchment water resources management.

RAINWATER UTILIZATION TO REDUCE FLOODING IN LOW-LYING AREAS OF TAIPEI CITY, TAIWAN

She-Zih is a low-lying area in Taipei City where the Tanshui River and Keelung River meet. Average elevation is about 2.5 m. Perennial flood events occur very often. The only flood prevention facility is the 6 m levee built around the perimeter to overcome 20-yr flood events. The main cause of the flooding problem is the instantaneous extreme high rainfall events that often exceed the drainage capacity of She-Zih. Current solutions to relieve this water hazard, suggested by the Water Resources Agency, include channel widening and many water pumping installations. At present, all emergency facilities are insufficient to combat unexpected heavy storms. Therefore, this study attempts to design drainage systems using the available limited land space, along with rainwater catchment systems, in order to achieve the expected flood prevention goal. These study results may provide adequate references for residents and government agencies to design future flood prevention management plans and strategies.This study gathers information from previous literatures to understand initially the effect of storm runoff in this low-lying area, the flood mitigation benefits of building rooftop catchment systems and the drainage systems. Scaled-down rooftop simulation experiments are then conducted with different rainfall intensities and retention rates to evaluate their effects on flood mitigation. Study results indicate that for low intensity rain, a 55% and 69% flood retention efficiency may be obtained using the lower capping device (2.5 cm) and the higher capping device (5.0 cm), respectively. For medium intensity rain, a 58% and 70% flood retention efficiency may be obtained using the lower capping device and the higher capping device, respectively. For high intensity rain, a 46% and 63% flood retention efficiency may be obtained using the lower capping device and the higher capping device, respectively. In addition, eight locations are selected for temporary retention ponds construction in order to enhance the flood mitigation effect. Stored flood water may then be drained out through pumping or connecting drainages ditches.

Defence measures in flood risk assessment: a case study

Flood defense is a problem of vital importance, for which knowledge and advanced scientific tools play a paramount important role in the strain of coping with flooding problems. In this context, flood modeling represents the basis for effective flood mitigation measures. By using models, an attempt is made to replace trial-and-error-based strategies, as practiced in the past, with more physically based measures of flood management and control. Mathematical models are the best tools, nowadays available, for the design of efficient flood protection strategies and excellent supporters of decision-makers. With reference to these issues, the paper provides a complete application of the procedures, nowadays available, for risk assessment, from catchment to a very local scale, on the Lambro River in Milano, Italy. It is shown that social and political constraints may force risk managers to find different solutions to solve the problems they have to face, which may be related to non-hydraulic issues. Keywords case studies, early warning, flood hazard, mathematical models Language: en

강변저류지에 의한 홍수저감 효과 분석을 위한 수리실험

Detention basin is highly effective hydraulic structure which is available for flood mitigation and ecological characteristics. However, analysis of flood mitigation by detention basin is performed with numerical approaches only, there is not enough data obtained by experimental observation. In this study, physical experiment were performed under unsteady flow condition to analyze flood mitigation with detention basin. Various design factors such as location, later weir height and extent of detention basin were considered in this experimental observations. As the distance from detention base to target location become closer and later weir height become higher, we can expect more effective flood mitigation. As the area of detention basin area become lager, we also expect more higher flood mitigation effects. But, the flood mitigation effects from detention basin would converged to critical value. The obtained data will be useful for following studies about detention basin.

A grid-based rainfall-runoff model for flood simulation including paddy fields

A grid-based, KIneMatic wave STOrm Runoff Model (KIMSTORM) is described. The model adopts the single flow-path algorithm and routes the water balance during the storm period. Manning’s roughness coefficient adjustment function of the paddy cell was applied to simulate the flood mitigation effect of the paddy fields for the grid-based, distributed rainfall-runoff modeling. The model was tested in 2296 km2 dam watershed in South Korea using six typhoon storm events occurring between 2000 and 2007 with 500 m spatial resolution, and the results were tested through the automatic model evaluation functions in the model. The average values of the Nash–Sutcliffe model efficiency (ME), the volume conservation index (VCI), the relative error of peak runoff rate (EQp), and the absolute error of peak runoff (ETp) were 0.974, 1.016, 0.019, and 0.45 h for calibrated storm events and 0.975, 0.951, 0.029, and 0.50 h for verified storm events, respectively. In the simulation of the flood mitigation effect of the paddy fields, the average values of the percentage changes for peak runoff, total runoff volume, and time to peak runoff were only −1.95, −0.93, and 0.19%, respectively.

Ecological engineering in a new town development: Drainage design in The Woodlands, Texas

This paper presents a comparative study of two different drainage designs in a 10,930-ha new town development of The Woodlands, Texas. Open surface drainage by shallow grassed swales was used in the first two subdivisions that were developed with ecological approaches. Open surface drainage mimics the natural flow regime and is regarded to mitigate development impacts on watershed. In other later subdivisions, the drainage design shifted back to a conventional stormwater drainage system, that is, curb and gutter, drop inlet, and underground piping, known to concentrate stormwater and lead to downstream flooding. The objective of this study is to compare The Woodlands’ two drainage systems on their correlation with downstream floods. Two sub-watersheds within The Woodlands that used different drainage designs were compared. U.S. Geological Survey stream data from the gauge station at the outlet of each sub-watershed were used for analysis. Geographic Information System was used to quantify the development conditions. Correlation analysis was performed using measured precipitation and streamflow data. Results show that open drainage watershed generated less storm runoff than the conventional drainage watershed, given the similar impervious area in both watersheds. Furthermore, the open surface drainage watershed responded to rainfall in a way similar to its predevelopment natural forest conditions, indicating effective flood mitigation post development. In contrast, in the conventional drainage watershed, the precipitation–streamflow correlations increased enormously after development. The open drainage system presents an advantage over the conventional drainage one in mitigating flood problems in urban development.

An Information System for Risk-Vulnerability Assessment to Flood

An exhaustive knowledge of flood risk in different spatial locations is essential for developing an effective flood mitigation strategy for a watershed. In the present study, a riskvulnerability analysis to flood is performed. Four components of vulnerability to flood: 1) physical, 2) economic, 3) infrastructure and 4) social; are evaluated individually using a Geographic Information System (GIS) environment. The proposed methodology estimates the impact on infrastructure vulnerability due to inundation of critical facilities, emer gency service stations and bridges. The components of vulnerability are combined to determine an overall vulnerability to flood. The exposures of land use/land cover and soil type (permeability) to flood are also considered to include their effects on severity of flood. The values of probability of occurrence of flood, vulnerability to flood, and exposures of land use and soil type to flood are used to finally compute flood risk at different locations in a watershed. The proposed methodology is implemented for six major damage centers in the Upper Thames River watershed, located in the SouthWestern Ontario, Canada to assess the flood risk. An information system is developed for systematic presentation of the flood risk, probability of occurrence of flood, vulnerability to flood, and exposures of land use and soil type to flood by postal code regions or Forward Sortation Areas (FSAs). The flood information system is designed to provide support for different users, i.e., general public, decisionmakers and water management professionals. An interactive analysis tool is developed within the information system to assist in evaluation of the flood risk in response to a change in land use pattern.

Evaluation of the flood mitigation effect of a Paddy Field Dam project

To mitigate flood damage due to a recent increase in the frequency and magnitude of heavy rainfall events, the Kamihayashi district in Niigata prefecture, Japan, has undertaken flood mitigation measures using paddy fields by installing runoff control devices in drainage boxes of paddy field plots. The purpose of this study is to evaluate the flood mitigation performance of the Paddy Field Dam project in terms of a decrease in discharge volume, drop in channel water level and reduction of inundation damage using combined hydrologic analyses and flood routing. The model constructed for runoff analysis is composed of three modules: a hilly/residential area module in which the overland flow is estimated using the kinematic wave method, a paddy field module in which runoff from paddy fields is calculated using water balance analysis, and a channel network module in which flood routing is performed using a one-dimensional unsteady flow model. The outputs of the first two modules are the input of the third module. The result of the simulation shows the main channel discharge decreased by 26% and the water level dropped by 0.17 m in the case of the largest observed rainfall event. The simulated effect was larger for larger rainfall events. In terms of flood water volume, the runoff control devices have the effect of reducing the flood damage due to the 50-year return period rainfall event to almost that due to the 10-year return period rainfall event.

Local planning practice and flood risk management in England: is there a collective implementation deficit?

Although planning policy enables local planning authorities to influence development with regard to flood risk, in practice there appears to be a number of barriers inhibiting effective flood mitigation, particularly in areas with high development pressures. This research focuses on treatment of flood risk within the English local planning system and discovers that there is a seeming failure to capture strategic, collective flood management opportunities, resulting in an implementation deficit between the aims of planning policy and its practical application. Improvements to local planning policy frameworks are needed therefore, to enable the use of more strategic solutions without compromising local development needs.