Sedimentation balance

Figure 1: Division of the area of interest into three parts for volume analysis: Part 1: outer area, Part 2 pond area and Part 3 intertidal area (Boersema et al. 2016).

The volume changes reflect the relaxation of the volume changes in time. The outer area (Part 1) loses sediment, while the inner parts (Parts 2 and 3) gain sediment (see figure 1). The sediment volume of the inner area, Parts 2 and 3, increases with 107 x 10³ m³ between June 2015 and April 2016, or 130 x 10³ m³/year (figure 2). This sediment comes from local erosion of the inlet (sand and mud) and the net suspended sediment inflow (mostly mud). The initial sedimentation in Perkpolder is dominated by the local erosion effect; therefore the second process is more important.

The sediment volume of the inner area increases with 57 x 10³ m³ between July (T1) and April 2016, i.e. 78 x 10³ m³/year (figure 2). This corresponds to 47 x 10³ tons/year, assuming a dry bed density of 600 kg/m³ (in between the density of freshly deposited mud and a consolidated muddy bed). The tidal prism is approx. 1.7 million m³. For a typical mud concentration of 50 mg/l, this corresponds to a maximum net sediment influx of 85 tons/tide or 60 x 10³ tons/year, implying a trapping efficiency of about 80%.

Figure 2: Sediment volume development over time for the three parts of the Perkpolder tidal basin (Boersema et al. 2016).

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.

Sedimentation balance

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