Arc-GIS hydrological model of small catchments

As we have seen recently, southern Limburg is prone to pluvial flooding. Due to the combination of extreme rainfall and the topography of this area, water concentrates rapidly and causes surface water to overflow its banks. To slow down the concentration process, rainwater buffers can be implemented to temporarily store run-off water during peak discharges. The stored water is, after the highest discharge has been passed, gradually released from the buffer.

The project, which WSP carries out on behalf of Water Board Limburg, focusses on the design of a rainwater buffer along the Mechelderbeek near Vijlen. Preliminary dimensioning of the buffer is done using expert judgement and global rules of thumb. The assignment of my internship is to optimize the hydraulic functioning of the system. Which design principles and what measures in the buffer itself can be adjusted or implemented to attenuate flood waves. Thereby taking into account the adaptability in the Limburg landscape and any linking opportunities that arise in this project.

The construction of a rainwater buffer with a storage capacity of 5000 cubic metres has quite an impact on the community. Therefore, all ideas and values of interest in the area should be included in the design process. Stakeholder participation is key to pursuing dual benefit.

It is relevant for a water buffer that the natural flow of a stream is not affected during periods of low water flow. After all, it is only desirable to allow the buffer to function when the peak discharge threatens to cause flooding. In addition, construction of a buffer might have other beneficial uses.

To model the peak discharges in the Mechelderbeek during extreme precipitation events, the GIS-specialist of WSP has developed an Arc GIS-based tool. The input for this tool only consists of an elevation map of the area of interest and information about therainfallrunoff factor. The output of the tool are hydrographs that each belong to a certain extreme with a specific duration and return period. The direct effects of land use changes or the implementation of water retaining interventions on the discharge in any water system can quickly be analyse dusing this tool.

The internship assignment concerns validating and improving the quality of this GIS-tool.