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JRBM vol 6 Issue 1

Determination of apparent and composite friction factors for flooded equatorial natural rivers
By Lai Sai Hin, Nabil Bessaih, Law Puong Ling, Aminuddin Ab. Ghani and Mahyau Seng
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This paper presents results, calculated from field measurements taken in several frequently flooded natural rivers, which include D and R relationships, variation of flow resistance with depth of flow, the apparent friction factor, and the composite friction factor for flooded natural rivers. The results obtained have shown the complexity of flow resistance in natural rivers due to the interaction between the main channel and floodplain flow. The interaction has given rise to a pair of apparent shear stresses at the interface region, which can significantly reduce the discharge capacity of the rivers. The apparent shear was quantified in terms of an apparent friction factor, f_a , and it was found that the apparent shear stress is many times greater than the averaged boundary shear stress of the rivers. Based on the averaged boundary shear stress and apparent shear stress, the composite (actual) friction factor for the rivers can be estimated accurately (R² =0 99 using a statistical method that had been derived.
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Discharge estimation for equatorial natural rivers with overbank flow
By Lai Sai Hin, Nabil Bessaih, Law Puong Ling, Aminuddin Ab. Ghani, Nor Azazi Zakaria and Mahyau Seng
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The estimation of discharge capacity in river channels is complicated by variations in geometry and boundary roughness. Estimating flood flows is particularly difficult because of compound cross-sectional geometries and because of the difficulties of flow gauging. Results are presented of a field study including the stage-discharge relationships and surface roughness in term of the Darcy-Weisbach friction factor, f_a for several frequently flooded equatorial natural rivers. Equations are presented giving the apparent shear force acting on the vertical interface between the main channel and floodplain. The resulted apparent friction factor, fa is shown to increase rapidly for low relative depth. A method for predicting the discharge of overbank flow of natural rivers is then presented, by means of a composite friction, f_c , which represents the actual resistance to flow due to the averaged boundary shear force and the apparent shear force. Equations are also presented giving the composite friction factor from easily calculated parameters for overbank flow of natural rivers. The results obtained using the methods proposed show that a significant improvement has been achieved compare to the discharge obtained using traditional methods, with an averaged error of 2.7%.
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Sediment deposition in a rigid monsoon drain
By Aminuddin Ab. Ghani, Nor Azazi Zakaria and Mahathir Kassim
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Field data collections to study the physical sediment characteristics and trends of sediment deposition were carried out at Raja River monsoon drain made up of concrete channels for the period of 2000 and 2001. Assessments of the existing incipient motion equations developed from experimental works were made using the measured field data. The results show that equations by Novak & Nalluri (1975), El-Zaemey (1991) and Ab. Ghani et al. (1999) are able to predict satisfactorily the sediment deposition in rigid channel.
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Understanding sediment dynamics using geological and engineering approaches: A case study of the Buffalo River area of concern, Buffalo, NewYork
By Jill Singer, Joseph Atkinson, Patricia Manley and Patrick McLaren
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A combination of geological and engineering approaches was applied to better understand sediment movement along a contaminated river bed and provide support for remediation decision making. The geological approach, using sediment trend analysis (STA) and side-scan sonar mapping, helps interpret sedimentary processes acting over longer terms, while the engineering approach, based on a three-dimensional sediment transport model, illustrates sediment movement over shorter times, such as might be driven by storm events. The study site was the lower portions of the Buffalo River (Buffalo, NY), which is a tributary to Lake Erie and is an Area of Concern (AoC), as identified by the International Joint Commission due to beneficial use impairments primarily associated with contaminated sediment. Results from STA indicate two distinct flow regimes: a downstream regime dominated by fluvial processes and an upstream regime driven by changes in the level of Lake Erie. Where the two flow regimes intersect, sediment furrows are found. These features have been observed in this portion of the river over the past fifteen years and show characteristic ‘tuning forks’ opening in both upstream and downstream directions, indicating a bidirectional flow regime. Upstream movement of sediment also was found with the sediment transport model, which links hydrodynamic and particle tracking components to calculate transport pathways. Such movement is apparently generated by high amplitude seiches common to Lake Erie. Upstream sediment transport was not expected, but is consistent with the interpretation of results from each of the three different approaches. This combination of techniques has provided insights about short-term and longer-term sedimentation processes, which is helpful in choosing among management and remediation options for river restoration.
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Flood warning – on the value of local information
By Günter Blöschl
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Based on the experience with the flood forecasting system of the Kamp catchment in Austria the role of local information in warning is discussed.
Local hydrological process information from field surveys can be used to build more reliable models than is possible with regional data bases. River basin management processes are difficult to quantify in a general way, so familiarity with the local situation and interaction with local stakeholders will help to more accurately quantify the effects of river basin management on the flood situation. Local real time data, such as runoff data and water levels of reservoirs, can be used to improve forecasts by updating the routing and rainfall runoff models. Communication and the credibility of warnings may be strongly enhanced by local human forecasters that are familiar both with the model and the flood situation in the area of interest. Global information can assist at the local scale to extend lead times by precipitation forecasts and to assess forecast uncertainty by ensemble forecasts but much additional information at the local scale is needed to maximise the credibility of the forecasts.
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Hydrological modelling to assist water management in the Usangu wetlands, Tanzania
By M.P. McCartney, J.J. Kashaigili, B.A. Lankford and H.F. Mahoo
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The Usangu wetlands, containing the Ihefu swamp, are one of the most valuable inland wetlands in Tanzania. Over the last decade, outflow from the swamp has ceased for extended periods in the dry season. This has had severe consequences for downstream ecosystems, including the Ruaha National Park. Results from a simple hydrological model developed for the Ihefu swamp indicate that, between 1958 and 2004, dry season inflows declined by approximately 60% and the dry season area of the swamp decreased by approximately 40% (i.e. from 160 km² to 93 km² ). The model also shows that to maintain minimum downstream environmental flows requires a minimum inflow of 7 m 3s-1, which is approximately 65% greater than occurs currently. There is significant potential for improving water use efficiency. However, given the socio-economic importance of current levels of water withdrawal, this inflow may be difficult to achieve. Consequently consideration needs to be given to other options, including upstream storage and water management within the wetland itself. This paper highlights that a simple model supplying relatively low-confidence, but indicative, results can provide a useful basis for contemplating water management options.
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Evaluation of the reduction in the water storage capacity of Black Lake, AK
By Mohamed Elhakeem and Athanasios N. Papanicolaou
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The paper provides a systematic evaluation of the causes that trigger reduction of a lake’s water storage volume. This evaluation is demonstrated herein through combined numerical analysis and field work conducted on the south side of the Alaska Peninsula to address the reduction in the water storage volume of Black Lake. The contribution of this research was the development of an integrated approach that adequately quantifies the causes of reduction of water storage volume of lakes. For this purpose, a set of established routing, erosion, riverine, and lake models were integrated to identify quantitatively the causes of the Black Lake water storage reduction. Selection of the models was a compromise between their complexity, compatibility, capability, and available input data. The results of this study suggest that contrary to what has been long thought the lake receives sufficient water influx to maintain its maximum storage capacity. In addition, sedimentation was not found to the cause, because siltation since 1950 has reduced the storage capacity by only 1.0%. The reduction in the lake storage was mainly attributed to severe degradation at the lake outlet. The outlet elevation of the lake has decreased by at least 1.0 m over the past 55 years. This study recommended that a gated weir could be used as a control structure to maintain the elevation at the lake’s outlet. In addition, an erosion model predicted that the lake may loose 80% of its current storage capacity within a 100-year period causing a complete destruction of the ecosystem, if no action is taken.
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JRBM vol 6 Issue 2

A framework for uncertainty analysis in flood risk management decisions
By Jim Hall and Dimitri Solomatine
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Modern flood risk management involves responding sustainably to flood risk with portfolios of structural and non-structural measures. Under these circumstances of multi-attribute choice between portfolios of options, the motivation for uncertainty analysis becomes more compelling than ever. Uncertainty analysis is required in order to understand the implications for decision makers of limited data, model uncertainties, changes in the flooding system over the long term, incommensurate scales of appraisal and potentially conflicting decision objectives. In recognition of the importance of uncertainty analysis as an integral aspect of sustainable flood risk management, a new framework for uncertainty analysis within flood risk management decisions has been established. The proliferation of methods for uncertainty analysis can be placed within the coherent framework. As well as estimating the amount of uncertainty associated with key decision variables, the framework supports the decision making process by identifying the most influential sources of uncertainty, and the implications of uncertainty for the preference ordering between options. The challenges posed by severe uncertainty about the potential for long term changes in the flooding system are discussed and robustness analysis is advocated in response to these uncertainties.
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The importance of statistical uncertainties in selecting appropriate methods for estimation of extremes
By P.H.A.J.M. van Gelder
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Statistical uncertainties in the estimation of extremes are normally not well considered in present practice or even present research. This paper shows the application of extreme distributions to river variables with non negligible levels of uncertainty and presents an approach to deal with them. Four distribution types (Gumbel, Pearson III (log shifted Gamma), Lognormal and Generalised Pareto) are fitted to peaks over threshold or annual maxima data sets of river discharges. Piecewise exponential distributions are used to summarise the four distribution types and bootstrapping methods for quantifying the uncertainty in the design discharges. The paper furthermore presents relationships between probability density functions, convergence theorems and statistical tests to judge the goodness of fits.
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Data-driven approaches for estimating uncertainty in rainfall-runoff modelling
By Durga Lal Shrestha and Dimitri P. Solomatine
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This paper presents application of the method for assessment of predictive uncertainty of a rainfall-runoff model using data-driven modelling techniques. Historical model errors which are mismatch between observed and simulated values of runoff by rainfall-runoff models are assumed to be indicators of total model uncertainty. Uncertainty is represented by the model prediction interval. Different data-driven techniques used to determine the interval are compared. The method is tested to estimate uncertainty of runoff simulations by conceptual rainfall-runoff model with application to Brue catchment in the United Kingdom; it is also compared with other uncertainty estimation methods.
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A model conditional processor to assess predictive uncertainty in flood forecasting
By E. Todini
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This paper briefly discusses the nature, the causes and the role of predictive uncertainty in flood forecasting and proposes a novel approach to its estimation. Following the definition of predictive uncertainty, its importance in the decision process is highlighted in relation to the different sources of errors (model, parameter, observations, boundary conditions) that affect flood forecasting. Moreover, the paper briefly analyses the importance of using a full predictive uncertainty, obtained by marginalising the parameter uncertainty, instead of the predictive uncertainty conditional to a single parameter set. Finally, a new Model Conditional Processor (MCP) for the assessment of predictive uncertainty is then proposed as an alternative to the Hydrologic Uncertainty Processor (HUP) introduced by Krzysztofowicz as well as to the Bayesian Model Averaging (BMA) approach due to Raftery et al. The new MCP approach, which aims at assessing, and possibly reducing, predictive uncertainty, allows combination of the observations with one or several models’ forecasts in a multi-Normal space, by transforming observations and model forecasts in a multivariate Normal space by means of the Normal Quantile Transform. The results of the new approach are shown for the case of the River Po in Italy, and compared with the results obtainable both with the HUP and the BMA.
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Uncertainty in flood damage estimation
By Regina Egorova, Jan M. van Noortwijk and Stephanie R. Holterman
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The aim of this article is to incorporate uncertainty into the currently used method for estimating the economic damage of floods in the Netherlands. Using a high-water information system, this so-called Standard Method computes the expected flood damage per damage category on the basis of the number of objects subject to flooding, the maximum damage per object, and the relative damage depending on the water depth. Using a probabilistic approach, the Standard Method is extended by taking account of the uncertainties in the maximum damage per object (maximum possible damage per unit object; e.g., house, production facility, meter road) and the damage function (describing the proportion of the maximum damage incurred to an object due to flooding as a function of the water depth). In estimating the damage in a flooded area, it is also important to take account of the spatial dependence between flood damages at different locations. For this purpose, the following three types of spatial dependence are considered: complete spatial dependence, spatial independence, and partial spatial dependence (for which the damage functions are completely dependent for independent water-depth classes). Using Monte-Carlo simulation, probability distributions of the flood damage are determined. The new uncertainty-based model for predicting flood damage is applied in a case study and the results of a sensitivity analysis are reported.
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Quantification of uncertainties in flood risk assessments
By Heiko Apel, Bruno Merz and Annegret H. Thieken,
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By a common definition, flood risk assessments are comprised of two parts: a hazard and vulnerability assessment. The hazard assessment investigates the extent and magnitude of usually large flood events, which are associated to a certain exceedance probability, whereas the vulnerability part assesses the impact of the flooding on specified targets, e.g., building, people or infrastructure. Being inherently speculative flood risk assessments should always be accompanied by an uncertainty assessment in order to assist consequent decision properly. In this paper a dynamic-probabilistic method is proposed, which enables a cumulated flood risk assessment of a complete river reach considering dike failures at all dike locations. The model uses simple but computational efficient modules to simulate the complete process chain of flooding. These modules are embedded into a Monte Carlo framework thus enabling a risk assessment which is physically based thus mapping the real flooding process, and which is also probabilistic and not based on scenarios. The model also provides uncertainty estimates by quantifying various epistemic uncertainty sources of the hazard as well as the vulnerability part in a second layer of Monte Carlo simulations. These uncertainty estimates are associated to defined return intervals of the model outputs, i.e., the derived flood frequencies at the end of the reach and the risk curves for the complete reach, thus providing valuable information for the interpretation of the results. By separating single uncertainty sources a comparison of the contribution of different uncertainty sources to the overall predictive uncertainty in terms of derived flood frequencies and monetary risks could be performed. This revealed that the major uncertainties are extreme value statistics, resp. the length of the data series used and the discharge-stage relation used for the transformation of discharge into water levels in the river.
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Reframe: a software system supporting flood risk analysis
By Hamish Harvey, Roger Peppé and Jim Hall
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There exists a growing range of powerful quantitative uncertainty, sensitivity, risk and decision analysis techniques, on which flood risk management has begun to draw. A number of factors conspire to limit the rate and the extent of their uptake. One is the difficulty of applying them to the software systems already used to support flood risk management decisions. Another is the problem of communication, often recognised as a lack of transparency, which arises when increasingly elaborate analyses are constructed by coupling computations from multi-disciplinary teams, which may also be geographically distributed. We outline the design of a prototype system, Reframe, designed to address both of these issues, and develop an example of its use in the implementation of an idealised but realistic flood risk analysis. The system is designed to be deployed on a server and provides its user interface through a web browser, enabling shared access. Diagrammatic representation of calculations are generated automatically, enhancing transparency and aiding communication. Detailed provenance information is maintained for all data, and can be explored by following hyperlinks in the interface.
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Learning how to deal with uncertainty of flood risk in long-term planning
By Gérard Hutter and Jochen Schanze
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Long-term planning in the context of Flood Risk Management (FRM) necessarily involves dealing with considerable uncertainties. In the past, there have been general doubts about the usefulness of long-term plans as guiding frameworks for decision makers. Since the mid-1990s, there has been a revival of long-term planning to shape the future of European societies and cities. This revival will last in flood risk management only if the implications of dealing with uncertainty for practitioners can be specified. The paper explores learning as one reason to consider developments in the long run. It draws a distinction between exploiting what is already known and exploring what might come to be known in the future. Based upon theoretical reasoning and findings from case studies in London and Dresden, three recommendations to long-term planners are derived to handle uncertainty in planning: (1) Balance learning to exploit a certain past and learning to explore uncertain futures, (2) Use forums for learning about uncertainties in long-term strategies of FRM, and (3) Think of dealing with uncertainty in long-term FRM as a social process prone to interruption, irrelevance for ongoing decision making, and post-disaster politics.
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JRBM vol 6 Issue 3

Evaluating uncertain flood inundation predictions with uncertain remotely sensed water stages
By Guy Schumann, Mark Cutler, Andrew Black, Patrick Matgen, Laurent Pfister, Lucien Hoffmann and Florian Pappenberger
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On January 2 2003 the Advanced Synthetic Aperture Radar (ASAR) instrument onboard ENVISAT captured a high magnitude flood event on a reach of the Alzette River (G.D. of Luxembourg) at the time of flood peak. This opportunity enables hydraulic analyses with spatially distributed information. This study investigates the utility of uncertain (i.e. non error-free) remotely sensed water stages to evaluate uncertain flood inundation predictions. A procedure to obtain distributed water stage data consists of an overlay operation of satellite radar-extracted flood boundaries with a LiDAR DEM followed by integration of flood detection uncertainties using minimum and maximum water stage values at each modelled river cross section. Applying the concept of the extended GLUE methodology, behavioural models are required to fall within the uncertainty range of remotely sensed water stages. It is shown that in order to constrain model parameter uncertainty and at the same time increase parameter identifiability as much as possible, models need to satisfy the behavioural criterion at all locations. However, a clear difference between the parameter identifiability and the final model uncertainty estimation exists due to ‘secondary’ effects such as channel conveyance. From this, it can be argued that it is necessary not only to evaluate models at a high number of locations using observational error ranges but also to examine where the model would require additional degrees of freedom to generate low model uncertainty at every location. Remote sensing offers this possibility, as it provides highly distributed evaluation data, which are however not error-free, and therefore an approach like the extended GLUE should be adopted in model evaluation.
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Does reconnection mean restoration for an oxbow lake, Hungary?
By J. Fisher and C. Stratford
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This paper presents the results of a case study in which a simple one-dimensional lumped hydro-ecological model, OxbowSim, is developed in order to predict the hydrological, nutrient and ecological impact of different management scenarios on a floodplain oxbow in the River Tisza basin, Hungary. The impact of the various lake managements on the value of the Tisza oxbows as local fisheries, areas of biodiversity, possible flood retention reservoirs and their threat from pollution incidents in the River Tisza is considered. This case study also highlights the problems of limited data availability and lack of shallow lake research in this region especially now that EU environmental legislation, such as the Water Framework Directive 2000/60/EC, has to be met.
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A study of hydraulic characteristics for flow in equatorial rivers
By Lai Sai Hin, Nabil Bessaih, Law Puong Ling, Aminuddin Ab. Ghani, Nor Azazi Zakaria and Mah Yau Seng
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This paper presents the results obtained from field measurements taken in several frequently flooded equitorial rivers, including velocity distributions, stage discharge relationships, roughness behaviours and discharge estimation. These have illustrated the large difference in velocity between the main channel and floodplain under flood conditions, and the effects of momentum transfer between deep and shallow flow, which include reduction in main channel velocity and discharge capacity, leading to a reduction in compound section capacity at depth above bankfull. Another significant characteristic that has been found is that the floodplain regions behave as storage reservoirs (V = 0 m/s) in most cases due to high resistance of long and thick grasses along the flood plains (n = 0.07−0.1). Flow resistance relationships have been presented in terms of Manning’s coefficient and Darcy-Weisbach friction factor, showing the complex nature of flow resistance in the rivers and further explaining the danger inherent in the conventional practices of extrapolating inbank data for the analysis of overbank flows. Results for discharge estimation have been shown for comparison with actual data, the errors incurred by applying empirical methods to compound channel flows have been quantified and found to depend on the particular method used.
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Field experiment to restore a gravel bar and control growth of trees in the Asahi River
By Shiro Maeno and Satoshi Watanabe
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The number of active gravel bars on the Asahi River in Okayama Prefecture (located in western Japan) has continuously decreased over the last 20 years, whereas stable vegetated areas have rapidly expanded on river bars during the same period. In a basic study to examine the re-establishment of gravel bars as a river restoration technique, an artificial gravel bar was experimentally created in the field. The effect of flood flows on the bar was then examined. Preliminary numerical simulations of the annual scale flood predicted that flooding strong enough to move stones would uniformly flow over the restored gravel bar and that the gravel bed could be maintained due to the increase of shear stress on the bed. However, monitoring of the restored bar showed that branches of Salicaceous species (willows) and seeds of Eragrostis curvula (weeping love-grass) quickly re-vegetated the downstream part of the test area. Additional numerical simulations, using the observed hydrograph, suggested that branches and seeds would be brought to the bar during the flood recession period.
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A linear geospatial streamflow modeling system for data sparse environments
By Kwabena O. Asante, Guleid A. Artan, Shahriar Pervez and James Rowland
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In many river basins around the world, inaccessibility of flow data is a major obstacle to water resource studies and operational monitoring. This paper describes a geospatial streamflow modeling system which is parameterized with global terrain, soils and land cover data and run operationally with satellite-derived precipitation and evapotranspiration datasets. Simple linear methods transfer water through the subsurface, overland and river flow phases, and the resulting flows are expressed in terms of standard deviations from mean annual flow. In sample applications, the modeling system was used to simulate flow variations in the Congo, Niger, Nile, Zambezi, Orange and Lake Chad basins between 1998 and 2005, and the resulting flows were compared with mean monthly values from the open-access Global River Discharge Database. While the uncalibrated model cannot predict the absolute magnitude of flow, it can quantify flow anomalies in terms of relative departures from mean flow. Most of the severe flood events identified in the flow anomalies were independently verified by the Dartmouth Flood Observatory (DFO) and the Emergency Disaster Database (EM-DAT). Despite its limitations, the modeling system is valuable for rapid characterization of the relative magnitude of flood hazards and seasonal flow changes in data sparse settings.
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Predicting effects of best management practices on sediment loads to improve watershed management in the Midwest, USA
By T. Kevin O’Donnell, Claire Baffaut and David L. Galat
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Targeted implementation of agricultural best management practices (BMPs) to reduce non-point source pollution is the most recent strategy to improve U.S. surface waters. Little empirical evidence exists documenting effectiveness of U.S. BMP programs at the basin-scale. This knowledge gap hampers the ability of future programs to adapt implementation strategies. Additionally, U.S. agencies may lack sufficient knowledge of upstream processes necessary to plan enhancement of downstream large rivers. This study used the Soil andWater Assessment Tool (SWAT), a deterministic hydrologic model, to predict reduction of sediment erosion and transport over a 30-year period due to grass and woody-riparian establishment on cropland in the La Moine River Basin, U.S.A. Mean annual sediment reduction due to BMPs was predicted to be 3.6% at the downstream watershed gage. Identification of sediment sources in this watershed based on predicted hillslope erosion indicated a cost-effective strategy to reduce sediment load may be constrained by BMP placement primarily in the 100-year floodplain. This study indicated upland areas should be targeted for BMP establishment. Better representation of channel and floodplain sediment processes in SWAT and other hydrological models may be required if BMP targeting in agricultural settings will be assessed by computer simulations instead of on-the-ground monitoring.
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A service and value based approach to estimating environmental flows
By Louise Korsgaard, Roar A. Jensen, Torkil Jønch-Clausen, Dan Rosbjerg and Jesper S. Schou
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An important challenge of Integrated Water Resources Management (IWRM) is to balance water allocation between different users and uses. While economically and/or politically powerful users have relatively well developed methods for quantifying and justifying their water needs, this is not the case for ecosystems – the silent water user. Therefore, ecosystems are frequently omitted from water allocation decision-making. In IWRM, environmental flows may serve to represent water for ecosystems. As ecosystems, in turn, provide services to people, providing for environmental flows is not exclusively a matter of sustaining ecosystems but also a matter of supporting humankind/livelihoods. One reason for the marginalisation of environmental flows is the lack of operational methods to demonstrate the inherently multi-disciplinary link between environmental flows, ecosystem services and economic value. This paper aims at filling that gap by presenting a new environmental flows assessment approach that explicitly links environmental flows to (socio)-economic values by focusing on ecosystem services. This Service Provision Index (SPI) approach is a novel contribution to the existing field of environmental flows assessment methodologies. The SPI approach is a pragmatic and transparent tool for incorporating ecosystems and environmental flows into the evaluation of water allocation scenarios, negotiations of trade-offs and decision-making in IWRM.
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Integrated water resources management in the cross river basin, Nigeria: How can we reconcile institutional boundaries and interests?
By Emmanuel M. Akpabio
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This paper examines the practice of IntegratedWater Resources Management (IWRM) in the Cross River Basin (CRB), Nigeria. Nigerian Government Decree 101 of 1993 vests all rights and control of Nigeria’s water resources in the federal government, with the Cross River Basin Development Authority (CRBDA) mandated with the power of administration within its area of jurisdiction. Considering the various other agencies and bodies with similar management interests in the basin, this paper examines the implication of institutional boundary problems.A wide range of methods, including semi-structured interviews, stakeholder meetings, observations and secondary data were used to collect data. In the result, a complicated system of institutional arrangements was identified at vertical and horizontal levels, with similar management interests and functions creating coordination problems for the CRBDA. The paper traces these problems to weak and inadequate legal, legislative and enforcement apparatus for IWRM. In addition, many other administrative and political issues such as corruption and insufficient understanding of IWRM were noted to be accountable to and complicating the observed problems. The paper calls for urgent institutional reforms in the basin area.
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Trends of fish resources in the Tonle sap basin – their correlation with the hydrological conditions of the Mekong river
By Sokhem Pech, Kengo Sunada, Satoru Oishi, Naoki Miyazawa and Daisuke Tanaka
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By using a simple ecosystem model, the study grasps the relationship between the change in inundated areas (water level and flood extends) and the level of fish production in the Tonle Sap Basin (TSB). The model produces the fish production trends that can reflect the changes in key parameters such as flood extent and relative fish area density. The results show the continued dominance of the opportunist/white migratory species in the TSB’s fish composition. It reconfirms the hydrological and biological linkages between the TSB and the Mekong River that require a cross-sectoral and cross-boundary integrated planning and development.
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Conceptual design and modeling of restored coastal wetlands
By Robert E. Odell, Brad R. Hall and Peter C. Brooks
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This paper presents a conceptual design methodology together with a simplified numerical modeling technique for evaluating, designing, and restoring coastal wetlands. The conceptual design methodology uses specific geomorphic relationships observed in neighboring mature marsh basins to develop a synthetic tidal channel network for the restoration site that reasonably predicts its characteristics once fully functional. The numerical modelling methodology consists of three uncoupled models applied iteratively that describe the hydrodynamics, supply channel erosion, and marsh plain accretion of the developing basin over time. The results from the conceptual design and modeling methodologies can be directly applied to the prediction and quantification of subtidal and intertidal habitat area that is likely to emerge in the restored site as it evolves and ultimately reaches a state of dynamic equilibrium.
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JRBM vol 6 Issue 4

Flood risk management in the United States and the impact of Hurricane Katrina
By Gerald E. Galloway
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In 1993, the United States experienced a flood that produced the highest economic damages of the century Large areas of the Midwest were underwater for weeks as the Missouri and Upper Mississippi Rivers left their banks. Over 130 people lost their lives and flood losses grew to over $20 billion (US). For a few years after, national attention was focused on floodplain management, but, as other issues faced the government, efforts to develop a new approach to dealing with flood losses faded. Hurricane Katrina, with the deaths of over 1300 persons and billions of dollars in damages, brought flooding back to the front page of the newspapers and has stirred a new interest in developing a more rational approach to occupancy of the floodplain and to use of new approaches to flood damage reduction. As a result of several recent studies and government actions, attention is now being focused on the use of risk analysis methodologies to support decisions on floodplain use, slowly edging the United States closer to flood risk management and away from floodplain management. This paper discusses the lessons learned from the 1993 flood, the actions taken in the United States since 1993, and the impact Hurricane Katrina is having on bringing risk into the decisions that shape floodplain use in the United States.
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Towards Flood Risk Management in the EU: State of affairs with examples from various European countries
By Frans Klijn, Paul Samuels and Ad van Os
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On 27 June 2006 the Council of the European Union reached political agreement on a draft directive on the assessment and management of flood risks. This directive prescribes approaches and procedures which should be met by the member states. The website of the EU on this directive links to another EU-initiative, the Integrated Project FLOODsite, which aims at providing methodologies for flood risk analysis and management. Obviously, the directive and the IP emerged in a common but much larger context of public and scientific debate on a more integrated and coordinated approach to dealing with flood risks. In this paper we briefly discuss this context and examine a few national cases in order to find out whether flood risk management is already common practice or is still in its infancy, or whether it involves merely good intentions. We base this examination primarily on our experiences within FLOODsite and on presentations held within the special session on River Flood Risk Management which was organised by The Netherlands Centre for River Studies (NCR) during the ISDF3 conference in May 2005. This paper goes into the similarities and differences between some national approaches and tries to place them in a cultural context. It appears that the seemingly most sophisticated management policies do not automatically imply the most comprehensive flood risk management approach. But the intention to evolve from flood management into flood risk management is evident and promising.
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Radar-based flood forecasting in small catchments, exemplified by the Goldersbach catchment, Germany
By Uwe Ehret, Jens Götzinger, András Bárdossy and Geoffrey G.S. Pegram
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Although draining an area of only 75 km2, the Goldersbach caused several times severe flooding in the city of Tübingen, Germany. To cope with this, a flood management was set up based on flood forecasting, partial retention in reservoirs and local flood protection. Due to the small catchment size, the anticipated flood-forecast lead time of three hours could only be achieved by using local, weather-radar based rainfall forecasts for the next 1.5 hours. In short-term rainfall forecasting, knowledge of the current rainfield advection is crucial. Therefore, two advection estimation techniques were applied: one based on the Doppler effect the other on covariance maximization. To combine the advantages of the available sources of rainfall observation, namely radar and rain gauges, a method for ‘geostatistical merging’was developed. It preserves both the relatively reliable mean rainfall measurements from the rain gauges and the high spatial resolution of the radar image. Based on the advection estimates, a short-term, auto-regressive forecast model (SCM, or Spectrum-Corrected Markov chain model) was developed. It follows a two-step hierarchical approach. A bivariate, auto-regressive process forecasts the large-scale development of rainfall in a radar image. The individual development of each gridcell in the image is forecasted by a Markov chain approach. Finally, two rainfall-runoff models are used for short-term flood forecasting. The first, Fgmod, is an event-based model, the second, HBV-IWS, is a continuous water balance model. Both rainfall-runoff models, in combination with the rainfall forecast, allow reasonable discharge estimates for up to three hours.
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Implementing integrated flood risk and land-use management strategies in developed deltaic regions, exemplified by The Netherlands
By H.T.C. van Stokkom and J.V. Witter
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The article presents a short overview of flood risk management in the Netherlands over the past two centuries. The new Netherlands’ policy on river flood management, known as “more space for the rivers” is outlined. A general problem with flood risk management is that flood risk awareness among the public is low and that risk management is seen as the responsibility of the authorities. At the same time, potential damage due to flooding has greatly increased because of economic development, and the risk of casualties due to flooding far exceeds that due to other known external risks. This is particularly true for deltaic regions in developed countries. The article discusses a number of issues relating to an implementation strategy for the new Netherlands’ flood risk management policy, in particular the negotiation processes between water managers and other authorities and stakeholders, the investments involved and aspects of public risk awareness.
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The impact of major floods on flood risk policy evolution: Insights from Bangladesh
By Parvin Sultana, Clare Johnson and Paul Thompson
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Building on conceptual work conducted within the UK, the authors examine the incremental and crisis-driven nature of changes in flood risk mitigation policies in Bangladesh since the 1950s. They highlight the key factors which have influenced the incremental and catalytic changes in policy, noting in particular the role and attitudes of international agencies and donors. By exploring incremental changes as a function of coalitions, the authors illustrate the importance of these external forces in their changing alignment with key national-level actors; firstly through an ‘engineering coalition’ and more recently through an ‘environmental coalition’. The extent to which floods act as ‘catalysts’ for changing policy is then evaluated using the four most significant inland floods, or series of floods, in Bangladesh during the time period under investigation. The findings from which endorse many of the conceptual findings in the UK, the main exception being that in Bangladesh factors unconnected with floods continue to be the dominant forces of change – not least significant of which is institutional and political change, resource constraints and the international donor community. In addition, major floods have the capacity to delay policy changes, whilst simultaneously accelerating policy debate, and to destabilise established coalitions.
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On peaks and politics; governance analysis of flood risk management cooperation between Germany and the Netherlands
By Judith A.E.B. Janssen
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Since many rivers do not confine themselves to one country, cross-border cooperation is often required for optimisation of river management. Institutional conditions may either obstruct or motivate this cooperation. By describing the institutional conditions in terms of governance patterns a better understanding of the opportunities and pitfalls for cooperation is obtained. In this paper the cooperation between the Netherlands and Germany in the Rhine River basin serves as a case study. In the Rhine River basin the distribution of competencies over German actors and the threat of an imbalance herein were catalysts for cooperation at a regional level. For the Netherlands the potentially disastrous consequences of flooding and the resultant stringent standards for flood protection make it difficult to enforce Germany’s moral commitment to the Netherlands’ flood protection
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Urban flash flood in Gdańsk – 2001; solutions and measures for city flood management
By Wojciech Majewski
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Floods in urban areas cause considerable economic losses and affect many people. Measures for flood mitigation in urban areas are primarily of an engineering character. Existing city infrastructure very often restricts the introduction of appropriate new constructions. The city of Gdańsk situated at the mouth of the Vistula River, is the most flood-prone agglomeration in Poland. Now there are three possible flood sources. The first is from the moraine hills, in case of intensive precipitation, the second is from the Gulf of Gdansk in case of storm surges and the third is from Vistula River in case of very high discharge or ice jam. In July 2001 a severe flash flood, arising for the first time from the moraine hills, caused by very intensive rainfall, hit Gdansk. In the paper flood run and damages are presented. In situ measurements and hydraulic calculations were carried out to support the best technical solutions to mitigate the consequences of similar floods in the future.
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From reclamation to restoration: Trinity River common vision for the 21st century
By John Promise and John E. Tidwell
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For most of the past 150 years, the dream for the Trinity River in north central Texas was that of a federally-funded navigation canal with barges transporting goods more than 300 miles to and from the Gulf of Mexico. An 1898 promotional button proclaimed the dream: “Dallas – The Inland Seaport of Texas.” Since then the region has grown into America’s largest metropolitan region located on an inland waterway. The region’s population now exceeds 6 million; its area is about 33,000 square kilometres. When the 19th-Century dream of a barge canal died in the early 1980’s because of changing federal priorities, it was replaced by new local pressures to fill and reclaim significant portions of the floodplain. Studies by the US Army Corps of Engineers with the North Central Texas Council of Governments (NCTCOG) demonstrated the devastating effects that massive reclamation would have on existing properties, especially to the downstream Dallas levee system. From these important discussions emerged an unprecedented local/state/federal partnership to more comprehensively address the problems and opportunities of the river corridor and watershed towards a Trinity River Common Vision for the 21st-Century:
• Safe Trinity River, with stabilization and reduction of flooding risks;
• Clean Trinity River, with fishable and swimmable waters;
• Enjoyable Trinity River, with recreational opportunities linked by a Trinity Trails System within a world-class greenway;
• Natural Trinity River, with preservation and restoration of riparian and cultural resources;
• Diverse Trinity River, with local and regional economic, transportation, and other public needs met.
This paper describes the evolution of the Trinity River Common Vision over the past 20 years, highlights successful regionwide projects to stabilize and reduce flood risks such as the innovative Corridor Development Certificate process, and shows the remarkable progress of the region’s three largest cities – Dallas, FortWorth and Arlington. All illustrate the movement from reclamation to restoration, from structural to non-structural, from a 19th-Century barge canal to a 21st-Century Trinity River Common Vision.
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