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Apeldoorn, Netherlands

Ruessink B.G.,University Utrecht | Ramaekers G.,Rijkswaterstaat Waterdienst | Van Rijn L.C.,University Utrecht | Van Rijn L.C.,Deltares
Coastal Engineering | Year: 2012

Nearshore morphodynamic models are computationally demanding, especially when the time scale of interest is weeks or longer. Hence, they often rely on a simple parameterization or non-linear wave theory to estimate the skewed-asymmetric shape of the near-bed, free-stream wave orbital motion, relevant to the prediction of onshore sand transport during mild wave conditions. Recently, Abreu et al. (2010) presented a simple analytical expression for this shape. Here, we present parameterizations to estimate the non-linearity parameter r and phase φ in this expression, such that the non-linear orbital motion can be estimated efficiently from values of the significant wave height H s, wave period T, and water depth h, standard output of nearshore morphodynamic models. The parameterizations are based on a data set of 30.000+ field observations of the orbital skewness S u and asymmetry A u, collected under non-breaking and breaking wave conditions. Consistent with earlier observations, we find that the Ursell number, which includes H s, T and h, describes the variability in S u and A u well and we use it to link H s, T and h to r and φ. The comparison of our findings to another large field data set suggests that wave non-linearity depends weakly on wave directional spread and that our parameterizations may underestimate S u for narrow-banded swell and (unidirectional) laboratory conditions. Furthermore, the use of the parameterizations is not advised on bed slopes steeper than in our data set (i.e., >1:30). © 2012 Elsevier B.V. Source

Verbiest H.,Research Institute for Nature and Forest | Breukelaar A.,Rijkswaterstaat Waterdienst | Ovidio M.,University of Liege | Philippart J.-C.,University of Liege | Belpaire C.,Research Institute for Nature and Forest
Ecology of Freshwater Fish | Year: 2012

Downstream migration of female silver eel Anguilla anguilla (L.) was studied by remote telemetry in the lower part of the River Meuse (Belgium and the Netherlands) using a combination of nine detection stations and manual tracking. N=31 eels (L T 64-90cm) were implanted with active transponders and released in 2007 into the River Berwijn, a small Belgian tributary of the River Meuse, 326km from the North Sea. From August 2007 till April 2008, 13 eels (42%) started their downstream migration and were detected at two or more stations. Mean migration speed was 0.62m·s -1 (or 53km·day -1). Only two eels (15%) arrived at the North Sea, the others being held up or killed at hydroelectric power stations, caught by fishermen or by predators or stopped their migration and settled in the river delta. A majority (58%) of the eels classified as potential migrants did not start their migration and settled in the River Berwijn or upper Meuse as verified by additional manual tracking. © 2012 John Wiley & Sons A/S. Source

Borcherding J.,University of Cologne | Breukelaar A.W.,Rijkswaterstaat Waterdienst | Winter H.V.,Institute for Marine Resources and Ecosystem Studies IMARES | Konig U.,University of Cologne
Ecology of Freshwater Fish | Year: 2014

Anadromous North Sea houting (NSH, Coregonus oxyrinchus) was historically distributed in the Wadden Sea extending from Jutland (Denmark) to the Schelde delta (Netherlands). The species has been considered extinct in the Rhine since the 1940s; however, a successful re-introduction programme re-established a self-reproducing population. Telemetry data of adult NSH (NEDAP TRAIL System®) were used for a first description of the timing of spawning migrations of NSH in winter, but also suggested that the River IJssel, a lower branch of the Rhine, may serve as spawning ground. This was further proven in spring 2010 with drift net catches of 218 freshly hatched NSH larvae sampled directly upstream from Kampen, where the IJssel discharges into Lake IJsselmeer. These larvae did not differ between controls from a hatchery that were about 12 h of age, indicating that the drifting larvae of NSH must have hatched in upstream areas of the River IJssel. © 2013 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd. Source

Platteeuw M.,Rijkswaterstaat Waterdienst | Foppen R.P.B.,Wageningen University | Van Eerden M.R.,Rijkswaterstaat Waterdienst
Ardea | Year: 2010

All over Europe, wetlands have decreased in size, lost their original dynamics and became fragmented as the consequence of an ever increasing human land use. These processes have resulted in losses of nature values, among which declines in marshland bird populations. Ecological restoration of wetland systems follows from initiatives like EU Bird and Habitat Directives and Water Framework Directive, but may be, in itself, too costly to be widely applied. More promising perspectives to reinforce the wetland part of the ecological network Natura 2000 might come into focus when combined with spatial water management which is primarily aimed at more sustainable safety against flooding. In this way, the wetland network may acquire a wider public and political support. Knowledge on scale-related habitat use of wetland birds can play a role in the process of spatial planning. We illustrate this point by distinguishing four levels of spatial and temporal habitat use by wetland birds, and giving examples for each. The four levels are: (1) birds on stopover sites during migration, (2) territorial breeding birds, (3) colonial breeding birds, and (4) staging birds on wintering sites. This asks for ecological coherence on different scales, e.g. on the international level of migration flyways, on the regional level of landscapes and on the local level of individual wetlands. It is advocated that wetland ecologists dedicate themselves more specifically to quantifying the relevant data on habitat use of birds on each of these scale levels. Meanwhile, spatial planners should try to incorporate them into their efforts in realising combinations of ecological restoration or rehabilitation of wetlands and solutions for sustainable water management. These combinations might turn the tide for some seriously threatened species of marshland and wetland birds. Source

Theo Vulink J.,Rijkswaterstaat Waterdienst | Van Eerden M.R.,Rijkswaterstaat Waterdienst | Drent R.H.,University of Groningen
Ardea | Year: 2010

The man-made wetlands in young polders in The Netherlands are important stopover and wintering sites for geese. We studied trends in vegetation composition and goose density in two study areas. One was located in a nature reserve situated in a polder reclaimed from an estuary, the other in a reserve in a polder reclaimed from a freshwater lake. In the former we compared an area of spontaneous vegetation succession with a summer-grazed area. In the latter the effect of reed Phragmites australis cover and height on field selection of geese was studied in an area grazed year-round by cattle and horses. In both study areas the area of short grassland (reed cover about 1%, reed height <0.5 m) was found to be significantly positively related to the grazing density of cattle and horses. Migrating and wintering Greylag Geese Anser anser and Barnacle Geese Branta leucopsis preferred to feed on these extensive short grasslands. In the ungrazed part of the study site in the reclaimed estuarine area, there was an inverse relation between goose density and the ousting of pioneer species of saline habitats and short grasses by tall species such as Calamagrostis epigejos, Phragmites australis, tall herbs and shrubs. Summer grazing by cattle and horses at stocking rates of about 0.4 to 0.9 animals/ha, retarded the vegetation succession to some extent, which resulted in a goose density being higher in the summer-grazed area than in the ungrazed area. The implications for management are that the more desalinated the area becomes and the higher its clay content, the higher the stocking rate must be to retard the vegetation succession. Source

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