In stream restoration projects over the past decennia, the morphology seems to be neglected in the design fase of these projects. The role of morphodynamics in stream restoration projects is discussed with respect to the evaluation criteria of the Water Framework Directive (WFD).
The role of morfodynamics in stream restoration projects
Supervisors: Ton Hoitink, Eisse Wijma (RHDHV), Filip Schuurman (RHDHV)
Starting in the 30s, Dutch streams were normalized and channelized to improve drainage of agricultural land. Straightening of meanders and profile deepening and standardization were common measures to achieve this. Since the 90s the attitude towards the functions of a stream changed. Influenced by National and International regulations, stream restoration projects were initiated.
The key to a successful functioning of a stream system is the combination of hydrology, morphology and ecology. In stream restoration projects over the past decennia, the morphology seems to be neglected. What is the importance of the morphology in stream restoration projects? What knowledge did we obtain so far and can we translate this knowledge into usable design criteria for future projects? Could we even predict the morphological development of a restoration project over time using a simple 1D model? 1D modelling can be done by use of DyMMUS, a meander migration model developed by RHDHV, which is tested in this report. By studying relevant literature, evaluation and design reports and system analyses, the morphodynamic aspects of streams are discussed. An inventory of boundary conditions of the morphology is made, and linked to relevant evaluation criteria and conceptual ideas.
An integrated approach is required for restoration of the morphodynamic system of a stream. The numerous boundary conditions such as discharge, water levels, profile dimensions and valley slope cause restoration of the morphodynamics to be a nontrivial task. Understanding the involved processes is necessary to determine the role of morphodynamics in stream restoration projects and their evaluation criteria.
Morphology and morphodynamics are important elements to reach the objectives of the Water Framework Directive (WFD). Restoration of the morphodynamics is highly dependent on its environment, making it a difficult goal to achieve. Meeting all the boundary conditions is essential for a successful stream restoration project. Water quality appears to be the most important condition, while hydrology and morphology contribute to the habitat conditions within the stream. A dynamic morphology appears to be of less importance to fulfil the objectives of the WFD, than creating the needed habitat conditions. Morphodynamic can be the measure to achieve these habitat conditions, but applicability is highly dependent on location. Stream restoration remains a tailor-made solution, specifically designed to meet the local regulations and requirements.