Due to recent EU policies and regulations, such as the Water Framework Directive, Habitat Directive and Bird Directive, river basin managers must to take measures to improve the ecological quality and functioning of rivers and adjacent wetlands. Water quality improvement and restoration of hydro- and morphodynamic conditions are inevitable in order to achieve those objectives. Moreover, river managers emphasised the need for measures to reduce the flood risks by increasing the conveyance capacity on the one hand and improving the ecological quality of the rivers and floodplains on the other in order to meet the environmental requirements of EU policies and regulations. A research project was set up to (a) develop knowledge on the interactions between hydro- and morphodynamic processes, physio-chemical processes and ecological processes and (b) to implement this knowledge in the Delft modelling software. To improve and validate the quantified relationships between floodplain vegetation and hydro- and morphodynamic processes in Delft3D, the following activities were carried out:
- Simulation of flume experiment on sediment transport on a vegetated bed. A thorough quantitative comparison of the simulations with the data of the flume experiment is pending.
- Improvement of analytical formulae for the hydraulic resistance of vegetation and for the bed shear stress on a vegetated bed. Three different expressions for the vegetation resistance were developed and compared with the modelled data from 1-DV model for different types of Dutch floodplain vegetation and combinations of water depth and bed roughness. Surprisingly, the results show that the simplified equation of the complex analytical formula provided the best agreement. Moreover, the test results of the new analytical formulae for bed shear stress show an improvement. Based on the results of this analysis, the formulae for hydraulic roughness of vegetation and bed shear stress in Delft3D and SOBEK are / will be improved. To provide underpinning for one of the key principles on which the Water Framework Directive is based, research activities were initiated to quantify the relationships between the biological quality elements and the physio-chemical and hydromorphological quality elements. Research activities focused on (a) chronic toxic pressures from contaminated soils and (b) hydromorphological requirements related to availability and suitability of habitats for fish species. Research activities are linked with European research projects: REBECCA and FLOODSITE. The first results will become available in 2005.
The applicability of the recently developed ecological modelling tool HABITAT was tested in different case studies. For example, HABITAT was applied for the Taquari River, Brazil, to analyse the habitat availability for characteristic fish species, such as the Piranha. In this case study HABITAT was applied in combination with SOBEK2D. |
