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Modelling an Anthropogenic Effect of a tidal basin evolution applying tidal and wave boundary forcings: Ley Bay, East Frisian Wadden Sea

Abstract Potential physical impacts of an Anthropogenic Effect on a tidal basin evolution are investigated applying the Delft3D model suite under both tidal and wave boundary forcings. Study area is based on a peninsula construction of the Ley Bay in the East Frisian Wadden Sea. Model simulation spans from 1975 to 1990 in two stages of which the second stage begins with the implemented peninsula on the 1984 predicted morphology. The model bed consists of initially distributed three sediment fractions. Sensitivity of the Ley Bay evolution is analysed under three different sediment transport formulations: 1) Van Rijn, 1993 (VR93), 2) Soulsby, 1997 (SVR) and 3) Van Rijn et al., 2004 (VR04). Offshore tides and waves are transformed up to the model boundaries via a nested modelling approach and a statistically derived highly schematised wave climate is adopted in the simulations. Predicted morphologies indicate lower agreement with the measured morphology due to including very sparse data. Despite this discrepancy, they reproduce the major changes in the Ley Bay caused by the peninsula construction while each formula results in a slightly different channel/shoal pattern. Predicted evolution under the SVR shows the strongest sediment exporting system and therefore the lowest agreement with the 1990 measured morphology. Both VR93 and VR04 formulas resulted in marginal exporting systems and more or less similar morphologies. In fact, only the VR04 prediction indicates a fair agreement with the 1990 data. Temporal evolution under the VR04 shows concentrated velocity patterns at the bay entrance and in the eastward bay channel resulting in the development of this channel and sedimentation in the southern part of the bay as found in the data.

MODELLING Anthropogenic Effect OF A TIDAL BASIN EVOLUTION

A numerical approach was undertaken to investigate an Anthropogenic Effect (i.e., construction of a peninsula in 1984) on the tidal basin evolution of the Ley Bay in the East Frisian Wadden Sea. Coupled hydro-morphodynamic model runs span from 1975 to 1990 applying both tidal and wave boundary forcings with a multiple-sediment bed. The offshore tidal force was transformed to the study area applying a cascade modeling approach while a highly schematised wave climate was adopted in this simulation. Two bathymetries (i.e., 1975 and 1990) were available for this study and therefore the peninsula was implemented based on the 1984 predicted bed. Resulting morphodynamic evolution indicates that the deeper areas (channels) are well reproduced by the model rather than the shallow areas (inter-tidal areas). In addition to the peninsula construction, the human interference by dredging and dumping appears to have influenced the Ley Bay evolution. Due to the lack of data availability, such information was not incorporated in this study. Comparisons of predicted and measured 1990 topographies in terms of qualitative and quantitative parameters show that the predicted bathymetry sufficiently resembles with the data. Application of a highly schematised wave climate affects on the bed evolution. Further investigation on the wave schematization could help to optimize the model prediction. On-going work uses this model set-up in order to forecast the Ley Bay evolution under future sea level rise scenarios.

modelling morphodynamic response of a tidal basin to an Anthropogenic Effect ley bay east frisian wadden sea applying tidal forcing only and different sediment fractions

Morphodynamic response to an Anthropogenic Effect (construction of a peninsula) is investigated using the state-of-the-art Delft3D numerical model based on the Ley Bay area in the East Frisian Wadden Sea. Model simulations span a duration of 15 years applying tidal boundary forcing only and two bed sediment compositions; single (d50 = 0.2 mm)- and multiple (mud, fine-sand (0.25 mm) and coarse-sand (0.60 mm))-fractions. Finally, the Effect of the initial distribution of sediment fractions is investigated.

Application of the multiple sediment fractions resulted in strong sediment import into the Ley Bay in contrast with the case for a single sediment fraction. Temporal and spatial evolution of larger-scale basin elements (e.g. channels, tidal flats) indicate that the impact of the peninsula is better predicted using the multiple sediment approach. Agreement between the predicted morphology and the data is fair in deep water areas (> 3 m) compared to the shallow water areas (< 2 m) in the bay. These predictions are further improved after application of an initially distributed bed sediment composition. Therefore, the optimal prediction of the Anthropogenic Effect is obtained under the latter case implying the requirement of applying a stable bed sediment composition in line with the imposed boundary forcings.

On-going work focuses on more detailed bed configuration around the peninsula (e.g. including possible dredging and dumping Effects) and the wave boundary forcing.

modelling morphodynamic response of a tidal basin to an Anthropogenic Effect ley bay east frisian wadden sea applying tidal forcing only and different sediment fractions

Morphodynamic response to an Anthropogenic Effect (construction of a peninsula) is investigated using the state-of-the-art Delft3D numerical model based on the Ley Bay area in the East Frisian Wadden Sea. Model simulations span a duration of 15 years applying tidal boundary forcing only and two bed sediment compositions; single (d50 = 0.2 mm)- and multiple (mud, fine-sand (0.25 mm) and coarse-sand (0.60 mm))-fractions. Finally, the Effect of the initial distribution of sediment fractions is investigated.

Application of the multiple sediment fractions resulted in strong sediment import into the Ley Bay in contrast with the case for a single sediment fraction. Temporal and spatial evolution of larger-scale basin elements (e.g. channels, tidal flats) indicate that the impact of the peninsula is better predicted using the multiple sediment approach. Agreement between the predicted morphology and the data is fair in deep water areas (> 3 m) compared to the shallow water areas (< 2 m) in the bay. These predictions are further improved after application of an initially distributed bed sediment composition. Therefore, the optimal prediction of the Anthropogenic Effect is obtained under the latter case implying the requirement of applying a stable bed sediment composition in line with the imposed boundary forcings.

On-going work focuses on more detailed bed configuration around the peninsula (e.g. including possible dredging and dumping Effects) and the wave boundary forcing.

Modelling morphodynamic response of a tidal basin to an Anthropogenic Effect: Ley Bay, East Frisian Wadden Sea – applying tidal forcing only and different sediment fractions

Morphodynamic response to an Anthropogenic Effect (construction of a peninsula) is investigated using the state-of-the-art Delft3D numerical model based on the Ley Bay area in the East Frisian Wadden Sea. Model simulations span a duration of 15 years applying tidal boundary forcing only and two bed sediment compositions; single (d50 = 0.2 mm)- and multiple (mud, fine-sand (0.25 mm) and coarse-sand (0.60 mm))-fractions. Finally, the Effect of the initial distribution of sediment fractions is investigated.

Application of the multiple sediment fractions resulted in strong sediment import into the Ley Bay in contrast with the case for a single sediment fraction. Temporal and spatial evolution of larger-scale basin elements (e.g. channels, tidal flats) indicate that the impact of the peninsula is better predicted using the multiple sediment approach. Agreement between the predicted morphology and the data is fair in deep water areas (> 3 m) compared to the shallow water areas (< 2 m) in the bay. These predictions are further improved after application of an initially distributed bed sediment composition. Therefore, the optimal prediction of the Anthropogenic Effect is obtained under the latter case implying the requirement of applying a stable bed sediment composition in line with the imposed boundary forcings.

On-going work focuses on more detailed bed configuration around the peninsula (e.g. including possible dredging and dumping Effects) and the wave boundary forcing.

MODELLING Anthropogenic Effect OF A TIDAL BASIN EVOLUTION

A numerical approach was undertaken to investigate an Anthropogenic Effect (i.e., construction of a peninsula in 1984) on the tidal basin evolution of the Ley Bay in the East Frisian Wadden Sea. Coupled hydro-morphodynamic model runs span from 1975 to 1990 applying both tidal and wave boundary forcings with a multiple-sediment bed. The offshore tidal force was transformed to the study area applying a cascade modeling approach while a highly schematised wave climate was adopted in this simulation. Two bathymetries (i.e., 1975 and 1990) were available for this study and therefore the peninsula was implemented based on the 1984 predicted bed. Resulting morphodynamic evolution indicates that the deeper areas (channels) are well reproduced by the model rather than the shallow areas (inter-tidal areas). In addition to the peninsula construction, the human interference by dredging and dumping appears to have influenced the Ley Bay evolution. Due to the lack of data availability, such information was not incorporated in this study. Comparisons of predicted and measured 1990 topographies in terms of qualitative and quantitative parameters show that the predicted bathymetry sufficiently resembles with the data. Application of a highly schematised wave climate affects on the bed evolution. Further investigation on the wave schematization could help to optimize the model prediction. On-going work uses this model set-up in order to forecast the Ley Bay evolution under future sea level rise scenarios.

modelling morphodynamic response of a tidal basin to an Anthropogenic Effect ley bay east frisian wadden sea applying tidal forcing only and different sediment fractions

Morphodynamic response to an Anthropogenic Effect (construction of a peninsula) is investigated using the state-of-the-art Delft3D numerical model based on the Ley Bay area in the East Frisian Wadden Sea. Model simulations span a duration of 15 years applying tidal boundary forcing only and two bed sediment compositions; single (d50 = 0.2 mm)- and multiple (mud, fine-sand (0.25 mm) and coarse-sand (0.60 mm))-fractions. Finally, the Effect of the initial distribution of sediment fractions is investigated.

Application of the multiple sediment fractions resulted in strong sediment import into the Ley Bay in contrast with the case for a single sediment fraction. Temporal and spatial evolution of larger-scale basin elements (e.g. channels, tidal flats) indicate that the impact of the peninsula is better predicted using the multiple sediment approach. Agreement between the predicted morphology and the data is fair in deep water areas (> 3 m) compared to the shallow water areas (< 2 m) in the bay. These predictions are further improved after application of an initially distributed bed sediment composition. Therefore, the optimal prediction of the Anthropogenic Effect is obtained under the latter case implying the requirement of applying a stable bed sediment composition in line with the imposed boundary forcings.

On-going work focuses on more detailed bed configuration around the peninsula (e.g. including possible dredging and dumping Effects) and the wave boundary forcing.

Modelling morphodynamic response of a tidal basin to an Anthropogenic Effect: Ley Bay, East Frisian Wadden Sea – applying tidal forcing only and different sediment fractions

Morphodynamic response to an Anthropogenic Effect (construction of a peninsula) is investigated using the state-of-the-art Delft3D numerical model based on the Ley Bay area in the East Frisian Wadden Sea. Model simulations span a duration of 15 years applying tidal boundary forcing only and two bed sediment compositions; single (d50 = 0.2 mm)- and multiple (mud, fine-sand (0.25 mm) and coarse-sand (0.60 mm))-fractions. Finally, the Effect of the initial distribution of sediment fractions is investigated.

Application of the multiple sediment fractions resulted in strong sediment import into the Ley Bay in contrast with the case for a single sediment fraction. Temporal and spatial evolution of larger-scale basin elements (e.g. channels, tidal flats) indicate that the impact of the peninsula is better predicted using the multiple sediment approach. Agreement between the predicted morphology and the data is fair in deep water areas (> 3 m) compared to the shallow water areas (< 2 m) in the bay. These predictions are further improved after application of an initially distributed bed sediment composition. Therefore, the optimal prediction of the Anthropogenic Effect is obtained under the latter case implying the requirement of applying a stable bed sediment composition in line with the imposed boundary forcings.

On-going work focuses on more detailed bed configuration around the peninsula (e.g. including possible dredging and dumping Effects) and the wave boundary forcing.