Morphology and water movement processes

The largest morphological change in the new Perkpolder area occurred during the first 1-2 months following the opening on June 25, 2015. The inlet eroded and this sediment dropt into the deep pond just inside Perkpolder area. Thereafter, the inlet was more or less in equilibrium and further sedimentation of Perkpolder was controlled be net sediment influx from outside, which is probably mainly muddy. Every tide about 1.7 million m³ water flows in and out. With a typical mud concentration of 50 mg/l, we can estimate the net sediment influx to be 60 x 103 tons/year. Assuming a dry bed density of 600 kg/m³, this implies that about 80% of the incoming sediment was trapped inside Perkpolder area between 30 July 2015 (T1) and April 2016 (T4). A 2DH Delft3D model was set up to simulate hydrodynamics, sediment dynamics and morphodynamics due to tidal forcing. The model reproduces the measured velocities and the inlet reasonably well, and was further calibrated on the estimated net sediment influx and the morphological changes between June 2015 and April 2016. Thereafter, the model was used to better understand how the new intertidal area develops. It was shown than a 50% volume reduction of creeks and pond hardly affects the sedimentation, which is also the case for a 50% change in inlet width. The latter does influence the more local sedimentation and erosion patterns, i.e. close to the inlet (Boersema et al. 2016, page 23-26).

Referenties

Perkpolder tidal restauration, one year after realisation, draft progress report, Boersema, M., J. van der werf, P. de Louw, T. Ysebaert, T. Bouma, Centre of expertise Delta Technology, 27 november 2016.

Morphology and water movement processes

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