The River Velpe and it’s side rivers are part of the Belgian Demer catchment. The River Velpe has a specific design with a long and a practically unbranched river course, into which many small rivers flow. Especially the downstream part of the river Velpe reacts quite severly to rain or snow, resulting in high flow-rates and water-levels. One of the reasons is the development of spatial use in the whole catchment area. The percentage of paved surface increases. This is why rainwater will flow quickly as surface run-off while at the same time the natural water retentioncapacity of the valley decreases. An extra storage capacity in the area of Halen will increase the retention capacity and decrease the risk of flooding.Why >
During the past years , many floods have occured in the basin of the Velpe river. The biggest problems occure at two locations: the Aarschotsesteenweg (a road) in the city of Vissenaken and the city centre of Halen. In this centre many neighbourhoods have been flooded more than once. Thanks to the construction of this new retention area, the road and the neighbourhoods will be better protected. The capacity of the retention area is nearly 200.000 m3 water, or 200 miljon litres of water.
The flood problems in Halen reflect the flood problems in the whole Demer area, upstream from Diest. In this area the rivers Velpe, Herk and Gete flow together in the river Demer. Already a few different retention areas have been built in the river Demer and it’s siderivers, to control the flooding porblems in the whole valley.< What How >
- Decreasing floodrisk by constructing a retention area with a volume of 200.00 m3
- Constructing a sediment trap; sedimentation in the river reduces its water drainage and water retention capacities. A sediment trap is made by a local widening of the river. Because of the increased width, water will flow more slowly depositing its sediment composed of sand and sil . The sand trap can be cl;eared easily of sediment.
The sediment trap has a length of approximately 150 meter and is about 20 meter wide. The sediment trap has a capacity of 3.000 tons of sediment. To build the sediment trap, 10.000 tons of soil have been removed. This soil has been re-used for the construction of embankments.
- Integration of land use, combining a natural garden and pool with water retention.
project by ALFA partner(s):