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JRBM vol 5 Issue 1

The GLOWA Volta Project: Interdisciplinary analysis of the impact of global change on a river basin in West Africa
By NICK VAN DE GIESEN, CHARLES RODGERS and PAUL VLEK
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This article gives an overview of the structure of the interdisciplinary GLOWA Volta Project and its main scientific outputs. The article serves to provide the context for a set of articles written by project scientists for this special issue of the Journal of River Basin Management. After a brief introduction, a description is given of the Volta Basin in West Africa. The main issues related to changes in water supply and demand are presented. Climate change and variability, landuse change, and increasing competition for water between sectors are especially relevant. The integrative approach followed within the GLOWA Volta Project is given in detail. The choice was made to focus on conceptual integration early on, rather than at the end of the project. This led to a network structure for communication between disciplinary research modules. Finally, a listing of the individual articles in the special section is given, together with overall conclusions.
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Influence of soil-moisture and land use change on precipitation in the Volta Basin of West Africa
By HARALD KUNSTMANN and GERLINDE JUNG
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An ongoing intensification of agriculture in West Africa has lead to changes in surface and subsurface characteristics that may directly affect evaporation rates and, in turn, regional rainfall patterns. To investigate the effects of those changes, the Penn State University/National Center for Atmospheric Research (NCAR) mesoscale meteorological model (MM5) was applied for the identification of feedback mechanisms between land surface (soil and vegetation) and atmosphere. MM5 was applied in three different resolutions (81 x 81, 27 x 27, and 9 x 9 km2) with 2-way interactive grids. The objective of this work was to learn to what extent regional (intra-domain) evaporation determines rainfall within the domains. The effect of decreased and increased initial soil moisture on total rainfall and on precipitation recycling indicators was investigated. Scale dependent, positive (increased precipitation at increased initial soil moisture) as well as negative (decreased precipitation at increased initial soil moisture) feedback mechanisms were found. Detailed atmospheric water budget analysis showed that negative feedback mechanisms on the small domain appeared to have been caused by an increased inflow of atmospherc moisture. Sensitivity of precipitation with respect to soil moisture was very variable over space. Both negative and positive sensitivities were observed. To investigate the effect of land use change, the total rainfall distribution was computed under the assumption of the observed land use substitution from cropland woodland mosaic into shrub land and finally into grassland. Sensitivity of precipitation with respect to land use change was very heterogeneous. Total precipitation change was of the same order of magnitude as in case of the initial soil moisture perturbations.
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Climate trends of temperature, precipitation and river discharge in the Volta Basin of West Africa
By REBEKKA NEUMANN, GERLINDE JUNG, PATRICK LAUX and HARALD KUNSTMANN
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The impact of climate change on precipitation and water availability is of major concern for policy makers in the Volta Basin of West Africa, whose economy mainly depends on rainfed agriculture and hydropower generation. It is therefore essential to know if, and to which extent climate trends in the Volta Basin exist that impact water availability. In this study, the present trends in precipitation, temperature, and river discharge for the Volta Basin were analysed. Linear trend and corresponding levels of significance were calculated for time series of annual and monthly maxima and corresponding means respectively. Trends of total annual precipitation and standard deviations for all considered variables were analysed. In addition, the stability of linear trends was considered via reverse arrangement test. Clear positive trends with high levels of significance were found for temperature time series. Precipitation time series showed both positive and negative trends, whereas most significant trends were negative. However, due to the small number of significant cases, only weak trends towards a decrease in precipitation can be concluded. Most of the significant trends of the standard deviation in precipitation were negative. Due to this observation a trend towards a decrease in the variability of precipitation is concluded. In case of discharge time series, a small amount of (predominantly positive) significant trends for the wet season was observed. The majority of the significant trends for the dry season were negative. For discharge no clear trend could be evaluated though, as the anthropogenic influences (e.g. building of dams, intensified irrigation) could not be quantified. Both, standard deviation of temperature and of river discharge show positive and negative significant trends. Thus one can not draw the conclusion of a change in temperature and river discharge variability. It is additionally shown that monthly precipitation trends can be weakly linked to climate indices. This was achieved by linear correlation analysis between monthly precipitation amounts and the climate indices NAO, SOI, TNA, TSA.
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Demand and supply of improved water in the Ghanaian Volta Basin
By STEFANIE ENGEL, MARIA ISKANDARANI and MARIA DEL PILAR USECHE
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Growing efforts are undertaken at the local, national, and international level to improve water supply in developing countries and thereby help people to satisfy their basic water needs. This study aims at an evaluation of households' actual access to and use of improved water sources in rural communities in the Ghanaian Volta basin. A statistical analysis of a household survey conducted in the Volta Basin helps to demonstrate that access to improved water does not automatically translate into use of it for all households. Our analysis shows that 43 per cent of those households that had access to an improved source still use unsafe water as their main domestic water source. Relative distance to improved and unimproved sources, the pricing system established locally, and quality perceptions all are likely to influence household water source choices.
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Water and electricity sector reforms in Ghana: Back on track?
By SUSANNAWOLF, VERONIKA FUEST and FELIX ASANTE
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The lack of continuous and reliable supply of energy and water is a major hindrance to industrial and agricultural productivity in Ghana. Similar to the public utility management problems found in most developing countries, the electrical and water utility companies of Ghana have suffered from a number of institutional and operational shortcomings, including low collection rates, high wastage, operational losses, and inadequate staffs. Reforms of the energy and water sectors have been under way since the beginning of the nineties. Prices have increased significantly, but there has been little or no improvement in services. This analysis will focus on on-going reforms, their likely effects on different user groups and the obstacles for their implementation. Those who provided water and electricity were plagued with institutional weaknesses, and regulating agencies did not perform according to their mandates. The regulating agencies were lacking financial and human resources for monitoring, and their functioning suffered from principal agent problems. The government policy of private sector participation in utility provision has been only partially implemented for various reasons: the providers of water and electricity and the government agents that manage the reform process have a greater effect on manufacturers than they do on agriculture because the former have the greater need for regular supplies of water and electricity. The potentials and interest of the clients, regulating agencies and providers as well as the relationships between them have to become a key issue in the reform process. There is a need for more transparency and accountability on the part of politicians and providing agencies - whether public or private, local or national.
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Hydrological parameterization through remote sensing in Volta Basin, West Africa
By MOHSIN HAFEEZ, MARC ANDREINI, JENS LIEBE, JAN FRIESEN, ANDREAS MARX and NICK VAN DE GIESEN
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Ground-based hydrological data collection tends to be difficult and costly, especially in developing countries such as Ghana and Burkina Faso where the infrastructure for scientific monitoring is limited. Remote sensing has the potential to fill the gaps in observation networks. The GLOWA Volta Project (GVP) seeks to maximize the information to be gained from satellite imagery by combining remotely sensed data with strategically chosen ground observations. However, there is very limited information about the coupling of remotely sensed data with ground based data over the mixed savanna terrain of West Africa. This paper provides an overview of innovative techniques to measure hydrological parameters as actual evapotranspiration, rainfall, and surface runoff over mixed savanna terrain in a semi-arid region in West Africa, and their potential use. Evapotranspiration - The Surface Energy Balance Algorithm for Land (SEBAL) was used to calculate sensible heat flux and evapotranspiration through the energy balance. The SEBAL parameterization is an iterative and feedback-based numerical procedure that deduces the radiation, heat and evaporation fluxes. Along a 1,000 km gradient in the Volta Basin, three scintillometers were installed to measure sensible heat flux over distances comparable to NOAA-AVHRR pixels, approximately two kilometers. The comparison of sensible heat flux measured from remotely sensed data and scintillometers provide accurate results. This will help to increase the reliability of SEBAL parameterization. Rainfall - Depending on the region within the Volta Basin, up to 90% of the precipitation in originates from squall-lines. The Tropical Rainfall Measuring Mission (TRMM) imagery provides a valuable tool to monitor such squall lines. However, the TRMM signal should be validated for squall line rainfall. To increase the reliability of space-based rainfall measurements, TRMM based rainfall rate estimates were calibrated with rainfall measurements from a dense network of rain gauges. Surface Runoff - Remote sensing has limited value in estimating surface runoff. The savanna of West Africa, however, is dotted with a large number of small reservoirs used to supply water for households, cattle, and small scale irrigation. Bathymetry of sixty reservoirs in Ghana's Upper-East Region produced a very regular correlation between surface area, as observable by satellites, and volumes. By using all-weather RADAR imagery and the measured surface/volume curves, surface runoff volumes can be monitored throughout the year. These indirect runoff measurements will help researchers to develop surface-runoff models for the Volta Basin.
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A hybrid metric-conceptual (HMC) model for monthly riverflow prediction in the semi-arid Volta Basin of West Africa
By B.A. AMISIGO and NICK VAN DE GIESEN
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Data-based mechanistic modelling techniques have been applied to catchment monthly runoff, potential evaporation and rainfall time series to model monthly catchment runoff at selected gauging sites in the Volta Basin of West Africa. The aim of the study was to obtain a modelling framework that not only accounts for the rainfall-runoff non-linearity in the basin and provides acceptable predictions of the monthly catchment runoff for the sub-basins studied, but also reveals the necessary insights for a plausible interpretation of the rainfall-runoff mechanism in the basin. The rainfall-runoff process was considered in two stages - a nonlinear transformation from rainfall to effective rainfall and then a linear transformation from effective rainfall to runoff. First a linear time varying, state dependent parameter (LTV-SDP) transfer function model was applied to the monthly rainfall-runoff calibration series of each sub-basin to determine the form of the rainfall-effective rainfall non-linear transformation. The observed series (runoff or rainfall) that was significantly related to effective rainfall was then identified. Next, the functional form of this relationship was established and used to fit linear time invariant (LTI) transfer function models relating monthly runoff to monthly effective rainfall and potential evaporation. The best estimate of the monthly effective rainfall from the nonlinear modelling was obtained from the product of monthly rainfall and a fractional power of monthly runoff - the runoff acting as surrogate for catchment wetness. Since this form of effective rainfall cannot be used for simulation in validation mode (as the runoff series is unknown then), a non-linear rainfall filter used in the Identification of unit Hydrographs And Component flows from Rainfall, Evaporation and Streamflow data (IHACRES) application was used to model effective rainfall in this mode. The study showed that monthly catchment runoff in the basin can be decomposed into two parallel flows, an instantaneous (within a month) and a slower (with one month delay) flow components. These results suggest that baseflow contribution to streamflow is insignificant in the Volta Basin.
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JRBM vol 5 Issue 2

Probability of flooding upstream from a bridge as a function of its construction
By Marek Sowinski
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The main objective of this paper is to compare the probability of flooding areas upstream from a bridge without piers (with a deck supported only by abutments), with a bridge of the same width with piers (which deck is supported additionally by piers). However, the problem was treated broadly and an analysis contained an influential investigation of different factors affecting probability of flooding not only piers width and shape. The paper starts with the formulation of performance function used in reliability analysis. Then, after the short characteristics of the methods of this analysis, one of them – the advanced first-order second-moments (AFOSM) method chosen for solution to the problem is briefly described. The second part of the paper contains a case study of a bridge designed in town Srem on Warta River (Poland). Two models used for computation of hydraulic losses, which are required for determination of the performance function, are described. The first one is based on the energy equation (solved by the standard step method) and used for a bridge supported only by abutments, the second one applied for computation of losses in the inner section of a bridge supported by piers is based on the momentum equation. Computer simulations performed for the considered variants of bridge projects were used for comparison. The computations results were presented in the form of the exceedance probability curves (EPC) of the water level upstream from a bridge. It was found that application of piers to the construction of a bridge can significantly increase the probability of flooding, depending on the constriction effect of the piers. The performed analysis allowed to quantify the influence of factors deciding on this effect.
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Stakeholder participation in modelling for integrated catchment assessment and management: An Australian case study
By L.T.H. NEWHAM, A.J. JAKEMAN and R.A. LETCHER
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This paper addresses issues of participation in the development of integrated assessment and modelling approaches in catchment management, drawing on lessons from an Australian case study in the management of diffuse source pollutants in the Ben Chifley Dam catchment of south-eastern Australia. In discussing the nature and outcomes of the interactions with catchment managers and the catchment community, particular emphasis is given to activities associated with the development of a scenario-based modelling tool that enables users to evaluate the biophysical and economic trade-offs associated with a range of potential management changes. The case study demonstrates the extent to which the development of models and software can provide a focus for communication between researchers, catchment managers and the catchment community. Benefits of the participatory activities included: (i) ensuring that the research addressed the primary concerns of catchment stakeholders, (ii) improving the flow of information between researchers and catchment stakeholders, and (iii) fostering cross-agency collaboration. However, there were substantial resources required for participatory activities; these were initially underestimated. Features of the participatory processes which contributed to their success included: (i) early identification of the need for participatory activities and their continuation over the course of the case study (ii) incorporating a broad range of catchment stakeholders in participatory activities, (iii) tailoring participatory activities to specific groups of catchment stakeholders, and (iv) gaining the higher level support of local management organisations. Improvements to the process which were identified included reducing the reliance on a single management organisation and establishing an ‘exit strategy’ in the initial planning of the case study.
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Assessment of flood risk accounting for river system behaviour
By M.C.L.M. VAN MIERLO, A.C.W.M. VROUWENVELDER, E.O.F. CALLE, J.K. VRIJLING, S.N. JONKMAN, K.M. DE BRUIJN, A.H. WEERTS.
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In this paper “river system behaviour” is defined as the complex interaction between river flow and the flooding of flood prone areas. A basic aspect of river system behaviour is that a local dike breach may affect hydraulic loads and hence dike failure probabilities at other locations. Important aspects in river system behaviour are discussed as well as the fact that effects of river system behaviour on flood risk may be both beneficial as well as adverse. This paper presents a conceptual approach to quantify effects of river system behaviour on probabilities of dike breach and flood risk. It was successfully applied to two example river configurations. The results of these examples are discussed. It is concluded that for proper flood risk assessment all relevant failure mechanisms, uncertainties as well as all proposed safety improvement measures are to be jointly taken into account. The conceptual approach enable all this. In the authors’ views, there is a need for developing models that account for effects of river system behaviour on flood risk. Such models can serve as a tool for policy makers in evaluating the effects that (regional) safety improvement measures have on the flood risk in the entire river basin.
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Development of a non-intrusive and efficient flow monitoring technique: The space-time image velocimetry (STIV)
By ICHIRO FUJITA, HIDEKI WATANABE, RYOTA TSUBAKI.
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A novel image analysis technique for measuring river surface flow is proposed. When we assume that the brightness distribution of river surface image is convected with the surface velocity, a space-time image for a searching line set parallel to the main flow would indicate velocity information as its image orientation. The new technique, the space-time image velocimetry (STIV), is capable to measure the orientation angle of the pattern using the eigenvalue analysis of the local space-time image. The performance of STIV is compared with the other image analysis technique, the large-scale particle image velocimetry (LSPIV), previously proposed by the authors and it is shown that STIV is an alternative image analysis method for measuring streamwise velocity distributions efficiently.
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The Ythan Project: A case study of public participation in river restoration
By C.T. MORRIS
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TheYthan Project (2001–2005) was a catchment-scale partnership project based in northeast Scotland, which aimed to involve local people in a variety of river management related activities, including the implementation of a number of river restoration projects. The project originally developed from an increased public interest in the river in response to a perceived deterioration in water and habitat quality, most notably in terms of increased nutrient levels in the river waters, as a result of diffuse pollution. The extent of this public interest led to the project facilitating public participation throughout a series of actions designed to protect and enhance the river. This paper describes the project’s actions to involve local people in the river restoration element of the Ythan Project and looks at some of the wider lessons learnt during this process and their relevance to the implementation of the Water Framework Directive in Europe.
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Institutional drivers and constraints of floodplain restoration in Europe
By TIMOTHY MOSS
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The task of restoring floodplains, as a means of improving flood protection or providing other benefits, poses multi-dimensional challenges to policymakers and project managers alike. Involving essentially a reconfiguration of the interaction between a river and adjacent low-lying land, floodplain restoration affects a wide range of institutions designed to secure a variety of private and public goods associated with water and land use. A scheme to restore a floodplain requires the successful enrolment of these institutions in such a way as to create a result acceptable to the principal stakeholders. This is a highly complex process. This paper, based on EU-funded research on the policy contexts and selected pilot schemes of floodplain restoration in Germany, France and England and Wales, provides a critical appraisal of the institutional drivers and constraints of floodplain restoration. In particular, it explores how recent shifts in problem awareness and problem-solving in a number of relevant policy fields are creating windows of opportunity for more integrated approaches to restoring floodplains but problematises the emergence of a new policy delivery gap emanating from the growing complexity of new generation floodplain restoration schemes.
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Selecting fluvial geomorphological methods for river management including catchment scale restoration within the Environment Agency of England and Wales
By JIM WALKER, JONTY GIBSON, DAVID BROWN.
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There is a wide diversity of methods for applying fluvial geomorphological techniques to river management within the UK. This paper describes the application of such methods to river management issues at local and national scales, and offers guidance on the application of methods to morphological improvement, restoration and other management issues at the catchment scale. Background is given on the role and development of fluvial geomorphology within UK river management, and the role of recent legislative drivers is reviewed. The scope of current fluvial geomorphological methods which have been applied to river restoration within the Environment Agency over the last decade is described. The processes developed in this paper are drawn from existing Environment Agency guidance, nationally standardised methodologies and, to a limited extent, good practice from other UK sources. At the national scale a framework for developing fluvial geomorphological assessments using desk-based analysis of map and remote sensed data is proposed. At the catchment scale a three-tier system of fluvial geomorphological assessment is proposed for application to river restoration and management. This system provides increasing detail based upon the intensity of the required geomorphological output, and the objectives of the proposed assessment. Also considered are the cost and complexity of proposed activities, and the degree of environmental and economic risk associated with such activities. Methods at a local scale are separated into two tiers; general site assessments that constitute rapid fluvial geomorphological appraisals and geomorphological dynamics assessments that entail a much deeper degree of study. Finally, the future challenges which must be addressed in order to develop and improve the application of fluvial geomorphology to river restoration and management in the Environment Agency are considered. In this context three key issues are apparent; the standardisation of methods, the national collation of data, and the consistency of application of the various approaches.
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River restoration in the UK: Meeting the dual needs of the European Union Water Framework Directive and flood defence?
By GERALDENE WHARTON, DAVID J. GILVEAR.
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A major component of river restoration is the recreation of instream physical habitat heterogeneity and re-establishment of the linkage between the in-channel and adjacent floodplain environment. Re-engineering channels to reinstate a more natural form and the restoration of water and sediment transfer can bring multiple benefits particularly if undertaken as part of an environmental strategy for the whole catchment. The benefits usually include improvements to the ecological quality of rivers and reductions in the severity of flooding downstream. These benefits are achievable because rivers in their natural state are ecosystems that maintain high bio-diversity, floodplains when inundated attenuate flows, and flooding of low-lying areas creates wetlands and washlands of high nature conservation value and flood storage potential. This paper will explore (i) how the European Union Water Framework Directive (WFD) (EC, 2000) will become an increasingly important driver for catchment-based river restoration in the UK, and (ii) how river restoration has the potential to deliver ecological improvements in rivers consistent with WFD targets whilst, at the same time, providing more sustainable flood management.
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Examination of FST-hemispheres for evaluating boundary shear stress in streams
By XIAOLIN WANG, BETTINA BOCKELMANN-EVANS, DONGFANG LIANG.
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In recent years the Fliesswasserstammtisch (FST)-hemispheres have been used increasingly as a device to measure the in-situ bed shear stress for stream restoration. These hemispheres provide a convenient way of estimating the hydraulic characteristics in the near-bed region, which are often needed in river basin management. FST-hemispheres are especially designed for use in the field by environmental engineers and scientists and ecologists. This paper studies the scope and feasibility of using the FST-hemispheres method from the hydraulics perspective. Experiments have been undertaken using FST-hemispheres in a laboratory flume and the results have been compared with published data. Shortcomings have been found in the use of the FST-hemispheres as a means of measuring the boundary shear stress, for which they were originally designed. Through an analysis of the forces acting on the hemispheres in the flow, it has been shown that the FST-hemispheres are more appropriate for use in estimating the flow velocity. The bed shear stress can be related to the near-bed velocity by a bed friction coefficient and thus can be measured indirectly by the hemispheres. Some preliminary numerical model simulations of the flow around a hemisphere have been performed and confirm the aforementioned force-balancing analysis.
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