Morphological assessment of reconstructed lowland streams in the Netherlands |
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| Institution: | 1. Department of Hydraulics and Hydrology, University of Valladolid, Avenida de Madrid 44, Campus La Yutera, 34004 Palencia, Spain;2. Grupo de Pesquisa em Tecnologia em Ecohidráulica e Conservação de Recursos Pesqueiros e Hídricos – GETECH, Universidade Estadual do Oeste do Paraná, Jardim Santa Maria, Toledo, Brazil;3. Gestión Ambiental de Navarra, S.A. Calle Padre Adoain, 219 bajo, 31015 Pamplona/Iruña, Spain;1. Centre Européen de Recherche et d''Enseignement des Géosciences et de l''Environnement, UMR 34, Europôle de l''Arbois, B.P.80, 13545 Aix-en-Provence Cedex 04, France;2. UMR CNRS 6554 LETG Rennes COSTEL/Université Rennes 2, place recteur Le Moal, 35000 Rennes, France |
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| Abstract: | Channelisation measures taken halfway the 20th century have had destructive consequences for the diversity of the ecology in the majority of the lowland streams in countries such as the Netherlands. Re-meandering is the common practice in restoring these lowland streams. Three reconstructed streams were monitored during the initial two years after construction of a new channel. The monitoring program included morphological surveys, sediment sampling, habitat pattern surveys, and discharge and water level measurements. Adjustments of the longitudinal bed profile formed the main morphological response. These adjustments were most likely caused by a lack of longitudinal connectivity of the streams as a whole, interrupting transport of sediment at locations of weirs and culverts. Bank erosion was observed only in a limited number of channel bends, and was often related to floodplain heterogeneity. Longitudinal channel bed adjustments and bank erosion were mainly caused by exogenous influences. In channel bends, the cross-sectional shape transformed from trapezoidal to the typical asymmetrical shape as found in meandering rivers. This behaviour can be attributed to an autogenous response to the prevailing flow conditions. Due to the prevailing fine sediment characteristics, bed material is readily set in motion and is being transported during the entire year. The existing design principles fail to address the initial morphological development after reconstruction. An evaluation of pre-set targets to realise water depth and flow velocity ranges shows the current procedures to be deficient. Based on this unfavourable evaluation, and the two-dimensional nature of habitat patterns needed to improve the conditions for stream organisms, we recommend to predict morphological developments as part of the design procedures for lowland stream restoration in the Netherlands. |
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| Keywords: | Stream restoration Lowland streams Morphodynamics Re-meandering Water management |
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