Deltares Starts Scale Model Tests for Unique Inlet Work Flood Channel

Scale Model Tests for Unique Inlet Work Flood Channel

After weeks of preparation research institute Deltares started discharge tests on a scale model of a planned adjustable inlet work for the new 8 km long flood channel Veessen-Wapenveld, by-passing the river IJssel just south of Zwolle, the Netherlands.

The flood channel is one of 30 projects of the national flood protection programme Room for the River and is designed - in case of extreme discharges - to lower the level on the river IJssel by 71 cm.

A unique 800 m wide inlet work has been designed to create an additional river discharge capacity up to 1145 m3/s. That is 45% of the total discharge capacity of the river at that specific location.

Works on the flood channel will start this summer and it is scheduled to be ready by late 2016

Scale model
Last year IJsselweide construction consortium (Boskalis and Van Hattum en Blankevoort, a Volker Wessels Company) was contracted for the construction of the flood channel, including the building of 8 km dikes, an inlet work, an outlet work, two pumping stations and two bridges.

The consortium has been obliged to do scale model testing to show that the inlet work is well dimensioned and can handle the required 1145 m3/s to flow into the channel.

Research institute Deltares has built a 1:10 scale model of the planned inlet work and started the first discharge tests recently.

Project manager Judith van Os from Deltares: "The scale model study can be used to in detail simulate structures in the channel such as the dike and the bridge piers. This gives us a more precise idea than computer models of how much water can actually pass over the inlet and the exact velocity of the water."

Agriculture land use
Under normal conditions the flood channel is used by meadowland farmers. In the decision making and design phase of the project the local farmers were involved as stakeholders and it was agreed that the flood channel would be used as little as possible.

Subsequently the inlet work consite of 60 adjustable openings. In normal upward position 1,05 m high rotatable boards withhold the river water to flow into the flood channel so farmers can continue their daily business. Only in case of an extremely high water level, the boards will be lowered and allow the river water to stream into the flood channel.

The inlet work has been designed on the probability this will happen only once every 100 years.

Critical operational phase
When the flood channel is put into operation, the lowering of the boards is the most critical phase. At that moment there is no water in the flood channel and the 1 meter high water column against the boards will suddenly flush into the channel.

The difference in water levels will create a hydraulic jump. The scale model tests allow a more detailed study of the behaviour of this jump.

Location of stilling basin
The flow velocity and the turbulence of the hydraulic jump causes erosion and - without protection - will damage the grass surface in the flood channel and possibly influence the stability of the inlet. To prevent this from happening, a stilling basin has been planned. This is a deepened area just after the inlet work that will reduce the velocity of the flow and fix the location of the hydraulic jump.

One of the objectives of the scale model test for Deltares is to optimize the dimensions and the location of this stilling basin.

Source: Dutch Water Sector

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Taxonomy

• Job Function
• Flood Management