In 2009, the former Velt en Vecht Water Board (now part of the Vechtstromen Water Board) and in consultation with the municipalities of Emmen, Coevorden, Hardenberg and Ommen concluded an agreement in which agreements were made about the scope and interpretation of the development of storm water retention areas. This agreement was called the Local Government Agreement Water (LBW). From 2015, the Vechtstromen Water Board has started to review the LBW. In 2020, the Vechtstromen Water Board commissioned FutureWater to support the recalibration of the LBW.
The purpose of these calculations was to provide a definite answer about the usefulness and necessity of the proposed storm water retention areas that were seen as necessary in 2009. Various scenario calculations were performed using a Sobek model in which water levels and discharges were compared under the current and future climate and with and without integration of the storm water retention areas.
The activities in this project included:
- Testing of discharge and water levels at critical locations for the climate scenario at different recurrence times (flood risk assessment using climate scenario),
- Comparison to the results of the flood risk assessment using historical climate data,
- Integration of storm water retention areas in the Sobek model and analysis of their impact on water levels, discharge at critical locations (usefulness and necessity for storm water retention areas, answer to LBW),
- An initial estimate of critical locations along specific flood defense barriers for the different scenarios (high resolution comparison of water levels and defenses barrier heights) and
- A comparison of the results with a number of previously conducted studies.
During the project, the flood risk assessment method, which was developed by Arcadis in 2020, was (further) automated, so that the method can be applied more quickly and for other comparable projects within Vechtstromen Water Board. Based on the results of the calculations, clear advice could be given on the usefulness and necessity of the proposed storm water retention areas as they were proposed in 2009.
More information about the method for standardizing regional flooding that is used by the Vechtstromen Water Board can be found on the following website (in Dutch): https://www.vechtstromen.nl/over/klimaat/wateroverlast/normering/werkt-normering/