Modelling human interference on the Ley Bay evolution
Morphodynamische Entwicklung der Leybucht
Human interference (i.e. anthropogenic effect) had and still has a great influence on the present-day morphology of the Wadden Sea tidal basin systems. The present study focussed on one of such systems, the Ley Bay area in the East Frisian Wadden Sea. In 1984, the construction of a peninsula, Leyhörn, took place. The Ley Bay morphological response to the Leyhörn peninsula was investigated using the state-of-the-art Delft3D numerical model. Model simulations span over a duration of 15 years from 1975 to 1990. The resulting bed evolutions are shown for three scenarios in the attached video,
Scenario 1:
Applying tidal boundary forcings only and a spatially uniform bed sediment composition of 0.2 mm (D50)
Scenario 2:
Applying tidal boundary forcings only and a multiple bed sediment composition consisting of mud, fine-sand (D50 = 0.25 mm) and coarse-sand (D50=0.60 mm)
Scenario 3:
Applying tidal and wave boundary forcings and the bed sediment composition is similar to Scenario 2
Analysis of the measured bathymetries at 1975 and 1990 showed that the Ley Bay has experienced strong sediment infilling after the construction of the Leyhörn peninsula. Therefore, the bay channel pattern tends to disappear (see the southward oriented channel), however the eastward oriented channel still dominates the local morphology. These are due to the alteration of the velocity regimes after the peninsula construction as was observed by comparing the velocity patterns prior to and subsequent to the peninsula. Responding bed evolution is further shown by the cross-sectional evolutions of the bay channels; A and B (shown in video), C and D (note, depth strongly decreases from A to D). Strong sedimentation appears at all cross-sections in the measured data.
The predicted bed evolution is very sensitive to the bed composition and the boundary forcing. Under Scenario 1, the results indicated the lowest sediment import into the basin. Resulting cross-sectional evolutions of this scenario are narrow and deeper. In contrast, Scenario 2 developed wider and shallower channel pattern which better resembles the measured data. Specifically, at cross-section D (shallowest section), it was observed that the profile stays at 1975 location rather than deepening as in the first scenario. Therefore, this scenario resulted in strong sediment infilling compared to that of the first scenario. After including the wave effect also into the Scenario 2 (i.e. Scenario 3), the results indicated strong sediment accumulation along the shoreline of the bay. This ultimately resulted in strong sedimentation of the distal parts of both bay channels. At cross-sections, B and C, data showed eastward orientation after the construction of the peninsula and that was not re-produced by the model results. Such phenomenon is expected due to the dredging/ dumping work undertaken at the time of peninsula construction.
Ongoing work focuses on more detailed bed configuration around the Leyhörn peninsula in the simulation after its implementation.
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Climate impact and adaptation research in Lower Saxony
KLIFF Klimafolgenforschung in Niedersachsen
www.kliff-niedersachsen.de
Sprecher des KLIFF-Forschungsthemas A-Küst: Andreas Wurpts
Forschungsstelle Küste im Niedersächsischen Landesbetrieb für Wasserwirtschaft, Küsten- und Naturschutz (NLWKN-FSK) Norderney
Modellierung/ Visualisierung: Pushpa Dissanayake
Forschungsstelle Küste im Niedersächsischen Landesbetrieb für Wasserwirtschaft, Küsten- und Naturschutz (NLWKN-FSK) Norderney
Realisation: Walter Stickan
Zentrum für Biodiversität und nachhaltige Landnutzung, Sektion Waldökosystemforschung, Georg-August-Universität Göttingen
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