Weverstraat pluvial flooding
This project has been prompted by two consecutive incidents (2008 and 2013) occurring in the Weverstraat in the town of Oosterbeek within a 5-year timeframe. On Sunday, 22 June 2008, heavy hail, rain and thunder storms moved across Oosterbeek. Hail stones, heavy downpours, numerous thunderbolts and fierce gusts of wind caused a great deal of damage. In 2013, extreme weather once more produced heavy downpours. In the afternoon of Saturday, 28 July and in the night of Sunday, 29 July heavy thunder storms moved across the province, causing a great deal of pluvial flooding and storm damage. In the Weverstraat, the basements of lower-lying houses flooded once again.
Results
In November 2013, the municipal authorities conducted a “Pluvial Flooding” survey among the residents of the Weverstraat. All 103 addresses were approached, of which 30 responded and completed the survey. This survey mapped out the problems experienced in that current situation. Residents submitted potentially promising solutions. The conclusion was that at least 10 per cent of the houses are flooded during heavy downpours or thunder / hail storms. The outcomes of the survey constitute the basis for a possible approach to tackling pluvial flooding caused by extreme downpours.
Wareco Engineers have conducted an analysis of the scope of the rain water run-off area, followed by a realistic theoretical computation of the volumes of rainwater running off towards the Weverstraat. On the basis of this computation, potential measures have been developed that contribute to solving the water issue. The impact of each measure on reducing pluvial flooding has been determined. Each separate measure has a certain (major or minor) impact on the desired result. For that reason, it was important that the measures to be taken should tie in with the needs of residents / stakeholders, yet be justifiable in societal and economic respects.
The measures and their impact on pluvial flooding have been presented during the residents meeting. For each measure, its effect on pluvial flooding has been indicated, as well as its consequences for the scope of the work to be carried out in the Weverstraat. Six scenarios have been discussed during the round of dialogue (see download).
A working group has been set up to elaborate the final design. This working group is expected to provide input for the final design. The set of measures has been compiled in consultation with these residents.
Three main strategies have been identified that contribute to partially resolving the water issue.
• Using peak water storage / WADIs in the Zweiersdal valley;
• Adapting the profile of the Weverstraat;
• In more elevated areas, directing and collecting water at an earlier stage.
These can be reduced back to the scenarios as presented by Wareco Consultants during the residents meeting in May 2015.
• Scenario 2: “Lowering thresholds in alleys”
• Scenario 5: “Lowering the road” (in combination with 1 V profile)
• Scenario 6: “Diverting water from the Poststraat”
The point of departure is that the above scenarios constitute guidelines for the further elaboration of the measures into a final design.
Based on a “tour” with the stakeholders, promising locations for rainwater storage have been surveyed. In addition, the working group has endorsed the Spatial Planning Preconditions (as set down by the municipality).
A “sketching session” with the working group has generated a first survey for the Preliminary Design. The members of the working group had been divided into two sub-teams. Each team was given over an hour to present and draw out ideas and wishes. The rationale was set out in a brief pitch. Working group A was tasked with posing additional or clarifying questions to working group B and vice versa. This eventually resulted in some consensus regarding the ideas and wishes submitted. These will be elaborated further into a Preliminary Design.
Contact person
Bas Jansen
Gemeente Renkum
+31(0)26 33 48 403
ba.jansen@renkum.nl