Floodplain Rehabilitation Research Articles

Pastoralist Responses to Floodplain Rehabilitation in North Cameroon

This paper examines the responses of mobile pastoralists to a floodplain rehabilitation program in north Cameroon. From 1993 to 1999, we measured changes in number of camps and herds, and the time they spent in the 600 km 2 of the Logone floodplain that was reflooded in 1994. The first year, few pastoralists anticipated the reflooding or its impact, and the increase in grazing intensity was caused by a prolonged stay of pastoralists who already used the area for transit. The following three years showed a sharp increase in the number of camps and herds, which stabilized from 1997 onwards. Overall, grazing intensity increased threefold, following the gradually recovering perennial grasslands, with no signs of overexploitation of the area. These developments closely match the ideal preemptive distribution model. We also examined how reflooding affected pastoral incursions in the Waza National Park located in the floodplain.

A geomorphic monitoring and adaptive assessment framework to assess the effect of lowland floodplain river restoration on channel–floodplain sediment continuity

AbstractThe state of the science of lowland river floodplain restoration reflects the relatively new and experimental nature of large river floodplain rehabilitation efforts. Based on results of a case study of floodplain restoration at the lowland Cosumnes River, California, we present a geomorphic monitoring and adaptive assessment framework that addresses the need to inform and utilize scientific knowledge in lowland floodplain river restoration activities. Highlighting hydrogeomorphic processes that lead to habitat creation, we identify a discharge threshold for connectivity and sediment transfer from the channel to the floodplain and integrate discharge magnitude and duration to quantify a threshold to aid determination of when geomorphic monitoring is warranted. Using floodplain sand deposition volume in splay complexes as one indicator of dynamic floodplain habitat, we develop a model to aid prediction of the sand deposition volume as an assessment tool to use to analyze future monitoring data. Because geomorphic processes that form the physical structure of a habitat are dynamic, and because the most successful restoration projects accommodate this fundamental characteristic of ecosystems, monitoring designs must both identify trends and be adapted iteratively so that relevant features continue to be measured. Thus, in this paper, adaptive assessment is defined as the modification of monitoring and analysis methods as a dynamic system evolves following restoration activities. The adaptive monitoring and assessment methods proposed facilitate long‐term measurements of channel–floodplain sediment transfer, and changes in sediment storage and morphology unique to lowland river–floodplain interactions and the habitat that these physical processes support. The adaptive assessment framework should be integrated with biological and chemical elements of an interdisciplinary ecosystem monitoring program to answer research hypotheses and to advance restoration science in lowland floodplain river systems. Copyright © 2005 John Wiley & Sons, Ltd.

Integration of ecological aspects in flood protection strategies: defining an ecological minimum

AbstractPolicy makers are confronted with the question of how to combine sustainable flood protection and floodplain rehabilitation in the best possible way. Both topics deal with spatial planning aspects in a range of scales. This question was the starting point for the development of an evaluation method within the IRMA/SPONGE project INTERMEUSE, illustrated on the basis of assumed flood protection strategies in the Meuse river basin (the ‘sponge’ strategy, the ‘retention’ strategy, and the ‘floodplain lowering’ or ‘winter bed’ strategy). The integration of flood protection and floodplain rehabilitation can be performed on two scale levels that are interrelated: on the regional level the focus is on (large parts of) an entire stream basin; on the local level specific site conditions are taken as starting point. Ecological aspects under study are spatial cohesion of habitats as identified by species population persistence modelling (regional, longitudinal level) and required habitat quality for carabid beetles and for meadow vegetation gradients as assessed by correspondence analysis (local, transversal level). The carabid beetles are taken as indicative for the ecological integrity of the river bed, the meadow vegetation for that of the floodplain.A unifying concept in the evaluation of ecological integrity is the ecological minimum: the critical boundary or minimum level of habitat conditions for a potentially good ecological functioning. It is the least acceptable state for a river ecosystem that is still functional to some extent, compared to a natural river ecosystem. The results of this study show clearly that there is a good chance to combine floodplain rehabilitation aims with flood protection activities, both on a local and on an international scale. Although ecological effect assessment and ecological optimizing (referring to a natural reference state) remain basic, additionally the assessment of the ecological minimum helps to define design strategies for integrated flood protection, especially in situations where there is an opportunity for river rehabilitation. Copyright © 2004 John Wiley & Sons, Ltd.

Guiding principles for choices in floodplain rehabilitation.

This paper presents a set of seven guiding principles for the ecological rehabilitation of the floodplains of large rivers. The principles are derived from existing policies (Dutch and European) and general ecological knowledge. When choices have to be made about projects to carry out or between possible measures within projects, the set of principles can be a helpful tool for policy makers and project designers. By bridging the gap between general policies and practical dilemmas, the principles can help to structure complex discussions.

The River Elbe in Germany - present state, conflicting goals, and perspectives of rehabilitation.

Based on an overview of the present state of the Middle Elbe River and existing management objectives concerning nature protection, navigation, and flood control, we describe conflicting goals. Regarding the course and structure of the river channel and floodplain, we will propose strategies and measures for integrated river management. We will focus on several scenarios of dyke relocation, which have been studied from a hydrological, ecological, and socioeconomic point of view. The retention effect of dyke relocation depends nor only on the spatial situation (e.g., river section, area size), but also on the type of measure (controlled retention in storage holders or dyke relocation). Socioeconomic studies have shown a willingness by society to pay for dyke relocation amounting to about 108 million?.a -1 . The economic value of floodplain rehabilitation due to nutrient removal is assessed at 7 million?. annually. Benefit-cost analyses were performed for several scenarios of dyke relocation and indicated a positive benefit-cost ratio even for the scenario with the highest costs. Finally, we report on experiences concerning administrative aspects of implementation of measures and discuss future perspectives of rehabilitation for the Middle Elbe River.

An evaluation of the benefits of lowland river-floodplain rehabilitation (the Rhine, the Netherlands).

Water quality of the Rhine has improved significantly since 1970, but its landscape was highly altered with a shortage of dynamic processes, characteristic landscape elements and biodiversity. During the last decade manifold floodplain rehabilitation projects have been planned and realized in the Netherlands. Yardsticks for recovery are naturalness, biodiversity and spatial connectivity, but actually there is no clear end-point or reference to assess its success. Constraints for rehabilitation are flood protection and shipping. The benefits of a subset of rehabilitation projects situated along the largest flee-flowing Rhine branch, that has an open connection to the North Sea, were assessed at two landscape levels: the project itself (1-10 kin) and the river stretch (> 100 km) using five parameters (landscape mosaic, vegetation, macro-invertebrates, fish and birds). The assessment yielded comparable marks among the parameters, so the overall appraisal is considered to be robust. However, the scarcity and incompleteness of the underlying data forced us to use a fair amount of expert judgement. Generally terrestrialized floodplains have been set back to more frequently flooded (semi-) aquatic habitats. Especially dynamic, shallow water habitats emerged. Vegetation quickly responded when management changed from farming to extensive grazing. Rheophilic fish and macro-invertebrates immediately colonised side channels. At present, more than 40 % of the present floodplain area consists fo deep water and 30 % of agricultural land and built up areas, and typical floodplain habitats (such as shallow riverbed, river banks and dunes and herbaceous floodplains) are still underrepresented. Within rehabilitation projects the landscape significantly changed, but the projects do not yet significantly contribute to the ecological recovery of the whole river stretch. Moreover, biological indicators point to a moderate or even poor ecological state.

Evaluation of floodplain rehabilitation: a comparison of ecological and policy-based biodiversity assessment.

This study evaluates the effects of ecological rehabilitation on biodiversity in floodplains along lowland rivers in the Netherlands, using two different approaches. Species richness was compared with a policy and legislation based index, calculated by means of BID-SAFE. BIO-SAFE is a valuation model that incorporates only protected and endangered river species, derived from Red Lists, the European Habitats directive, the European Birds directive and the conventions of Bern and Bonn. The study included higher plants, birds, mammals, herpetofauna, odonates and butterflies. In some cases, biodiversity in the floodplains significantly increased after rehabilitation. However, the outcome of the evaluation differs per taxonomic group and approach. The results show positive temporal trends with respect to species richness of higher plants, herpetofauna and odonates, and to a lesser degree mammals and butterflies. The policy and legislation based index increased to some extent, but not significantly, for higher plants, herpetofauna and butterflies. Correlation between species richness and policy-based values was found in all sites for birds, herpetofauna, odonates and, to a lesser degree, higher plants. For higher plants, positive as well as negative correlations were found, depending on the site. Based on these results, we argue that an ecological approach and a policy based approach yield complementary information. Therefore, it is recommended to apply a multi-approach methodology in monitoring and evaluation of restoration projects.

Hydrological impacts of floodplain restoration: a case study of the River Cherwell, UK

Abstract. This paper investigates the impacts on floods of hypothetical changes to river channel geometry by construction or removal of embankments to prevent water spreading onto the floodplain at high flows. A numerical model is applied to the River Cherwell between Oxford and Banbury to simulate changes to flood hydrographs. Embanking the river increases the peak flows downstream by 50-150%. Restoring the river channel through the floodplain to pre-engineered dimensions reduces peak flow by around 10-15% and increases peak water levels within the floodplain by 0.5-1.6 m. These results suggest that floodplain rehabilitation, in terms of embankment removal or returning the channel to pre-engineered dimensions, can be a valuable part of the flood management strategy of a catchment. Both measures lead to increased inundation of the floodplain, which can be positive for ecological restoration. Keywords: floodplains, hydrological impacts, rehabilitation, flood frequency

Dam, Environment and Regional Development: Case Study of the Logone Floodplain in Northern Cameroon

The purpose of this paper is a study of environmental change in the Logone floodplain in northern Cameroon following the construction in the 1970s of a dam for a rice irrigation project. This unique ecosystem, designated as a biosphere reserve for supporting an impressive wildlife population, depends on the annual overflowing of the lowland. Several communities living in the plain rely upon water and natural resources of the floodplain to support recession agriculture, the fisheries, wetland rice and livestock. But both persistently poor rainfalls in the Sahel and the adverse impacts of the dam have devastated the area, forcing a large number of people to leave. This paper gives the scope of this situation based on geospatial information and field investigation, and also early results of the floodplain rehabilitation programme conducted since 1994 under the supervision of the World Wildlife Fund. In addition to demonstrating the potential of geomatics technology in environmental hazard assessment, this case study highlights the complexity of water-related issues in areas of conflicting interests. Despite significant improvements achieved by the rehabilitation programme, there is still much work to complete for the area to recover its former biodiversity.

Australia's Environmental Flow Initiative: filling some knowledge gaps and exposing others

Many of Australia's river systems have been seriously degraded by inappropriate management of regulated flows. Other systems are facing threats from future water resources developments. There is a lack of information available to aid in allocation of environmental flows to rivers in order that they are managed in an ecologically sustainable manner. The Environmental Flows Initiative (EFI) is a major Australia-wide R&D program into environmental flows, funded through the Natural Heritage Trust (NHT), and administered by Environment Australia (EA). The program aims to identify environmental values, undertake targeted research to identify risks to river systems and flow requirements to sustain environmental values, to trial flow management options, and to evaluate these trials. The NHT relies on matching funding provided by the State and Territory authorities, and supports integrative approaches with emphasis on works on-the-ground where possible. While the EFI will close significant knowledge gaps, other gaps remain. Some of these relate to development and validation of rapid assessment techniques, understanding the importance of flow variability and how to define it, manipulation of flows to control alien species, developing a system of prioritising rivers for environmental flows, and enhancing flows with other catchment, channel and floodplain rehabilitation measures.

Floodplain rehabilitation in North Cameroon: Impact on vegetation dynamics

Abstract. Since the construction in 1979 of a dam in the Logone floodplain in the Sahelo‐Sudanian zone of Cameroon, annual inundations have decreased, reducing perennial vegetation as important grazing source for nomadic herds and wildlife during the dry season. Presently, possibilities exist to release excess water for floodplain rehabilitation. In 1994 a pilot release was executed, reflooding 200 km2, to verify predicted advantages. Vegetation has been studied from 1984 onwards along a transect covering flooded, recently reflooded and desiccated parts of the floodplain. Since 1993, the floristic composition has also been monitored in a grid in the centre of the impact zone. Cover of perennial grasses, most notably Echinochloa pyr amidalis and Oryza longistaminata increased from 41 to 61% in the reflooded zone. Vetiveria nigritana, a tussock grass that used to be dominant, disappeared slowly after the dam construction and has not shown a comeback. The cover of annual species, most notably Sorghum arundinaceum, a dominant annual grass only since the mid‐1980s, decreased in the reflooded zone from 58% to 34%. If the present conversion rate of annual into perennial grassland is extrapolated, recovery towards a 100% perennial state may be reached after the 2003 flooding season. Apart from favourable climatic conditions, recovery might be dependent on the restoration of soil fertility, limiting an approach focusing on flooding depth only.

Floodplain rehabilitation in Far North Cameroon: expected impact on bird life

Scholte, P., de Kort, S. & van Weerd, M. 2000. Floodplain rehabilitation in Far North Cameroon: expected impact on bird life. Ostrich 7 (1): 112–117. The Logone floodplain in the sahelo-Sudanian zone of Cameroon used to be a highly productive ecosystem. Perennial pastures and fish played a crucial role for fishermen, pastoralists and wildlife. The construction of an upstream dam reduced inundation causing widespread degradation Nonetheless, approximately 350 bird species have still been observed. They include eleven waterfowl species which surpass the IWRB/Ramsar criterion one % of West African population). The few available surveys suggest that prior to the dam construction, the area harbored an even more abundant birdlife. Presently possibilities exist to release excess water for floodplain rehabilitation. In 1994, a pilot release has been executed to verify predicted advantages for men and wildlife. Larger scale rehabilitation of the Logone floodplain is formulated, based on the pilot release results. Annual total waterfowl, as well as heron colony counts have been executed showing an increase in bird numbers. Data variability questions somewhat the conclusion that this has been exclusively due to increased flooding. Additionally, bird populations of degraded annual grasslands and well flooded perennial grasslands have been assessed by line transacts. Results showed the much higher numbers of waterfowl and passerines in perennial grassland. Hydrological and vegetation monitoring showed a change of annual into perennial grassland due to the re-flooding, which might lead to increased bird populations. Questions remain how to extrapolate these findings to the entire area to be re-flooded, justifying continuous counting and studying factors limiting bird populations. Such a study started for the Black Crowned Crane, a resident flagship species. For migratory species, surveys are recommended to assess the role of other wetlands in the Lake Chad basin.

Potential for floodplain rehabilitation based on historical maps and present-day processes along the River Rhine, The Netherlands

Abstract For the purpose of restoration, a process-based geomorphological and ecological classification of rivers and river reaches has been developed to help identify both past and present-day geomorphological processes along lower branches of the Rhine. Historical maps are used to analyse floodplain development since 1600. The series of maps shows development and erosion of bars and floodplains, and land use reflects both vegetation and geomorphological patterns and indicates that the ecological succession was strongly related to geomorphology. Historical measurements (early 19th century) of the water depth and water levels are used to derive historical river profiles and water duration curves. Present-day hydraulic parameters were calculated which show that they are not related to the geomorphological patterns in floodplains. Changes in the geomorphological activity of the river are strongly related to changes of the width-depth ratio of the main channel. Potentials for bar and levee development are therefore based on differences between the width-depth ratio of the Rhine branches.

River and floodplain rehabilitation in Western Europe: opportunities and constraints

River and floodplain rehabilitation in Western Europe: opportunities and constraints

The Gemenc Floodplain Rehabilitation Project: A Policy Analysis for the Rehabilitation of a Danube Floodplain, Hungary

In 1992 the Hungarian Ministry of Transport, Communication and Water and the Ministry of Environment and Regional Policy, sponsored by the Dutch Government, commissioned a combination of Dutch and Hungarian institutes to execute a study into the possibilities for the rehabilitation of the Gemenc floodplain. It was agreed that the study would focus on the water -management of the area, but nevertheless take into account the wider scope of other management areas and interests such as the forestry, hunting, fisheries and recreation as well. The study used a policy analysis approach for formulating and analyzing three different alternatives. The results showed that rehabilitation of the Gemenc area has a good perspective, especially when the most promising elements from each of the alternatives are combined.