Ecohydrological and hydraulic river modelling for describing aquatic habitats

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Natural catchments, rivers and aquatic biodiversity have been strongly degraded due to the negative effects of industrial and urban development as well as the intensification of agriculture. River and catchment rehabilitation measures are necessary in order to improve these depleted river conditions.  


In practice there is a lack of tools that are capable of describing the effects of such measures on the aquatic habitat. Central objective of this project which is funded by the German Federal Environmental Foundation (DBU) is the compilation of an integrated GIS-based modelling system that can be used to depicting the influences of changes in catchment water balance and morphological river structure on the habitat of certain benthic organisms. The approach is to couple an ecohydrological and two hydraulic model to depict certain parameters that are
most important for benthic invertebrates. The parameters discharge dynamics, water depth, flow velocity, substrate stability, sediment transport and the morphological river structure with information about the substrate, river banks and vegetation have to be connected with the demand of the organisms on their natural habitat. These habitat functions are derived from an autecological database as well as from regional macroinvertebrate sampling.

 

The Soil and Water Assessment Tool (SWAT) is applied to depict the discharge regime and erosion processes in the study area, which is the rural Kielstau catchment in northern Germany. Drainages and landscape depressions are two main regional characteristics and have a significant influence on hydrologic processes there and thus have to be considered in the modeling approach. Furthermore, the SWAT model is used to depict sediment input from the catchment into the river, which is governed by erosion from agricultural fields and drainages. Using the resulting hydrographs and sediment graphs for each tributary as boundary conditions, the main river channel is modelled with the 1D model HEC-RAS and certain hotspots with the 2D ADaptive Hydraulic modelling system (ADH). The models calculate water depth, flow velocity, substrate and bank stability as well as sediment transport in variable resolutions.

 

Functions, which describe deadly, uncomfortable, comfortable and optimum ranges for each modelled organism and each parameter are then applied on the parameter maps for further habitat evaluation in the GIS. 

 

Sediment measurements for validating the model outputs are carried out at the Department of Hydrology and Water Resources Management, University of Kiel. Biological sampling and data on organism preferences are supplied by the Institute for Hydrobiology and Zoology, University of Duisburg-Essen. River topography, hydromorphological and hydrological data are collected during own measurement campaigns and provided by the Land Survey Office Kiel, soilAQUA, the State Agency for Coastal Protection, National Park and Marine Protection as well as the Department of Nature and Environment Schleswig-Holstein.