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Assessment and quantification of the waterside slope erosion safety of a fully sandy levee at Kloosterbos

Laar, L.I. van (2021) Assessment and quantification of the waterside slope erosion safety of a fully sandy levee at Kloosterbos.

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Abstract:In this study, a fully sandy levee is quantitatively assessed on its waterside slope erosion safety. It is located within the levee segment 52-4, near Zwolle, and is managed by the water authority Vallei en Veluwe. The levee consists of sand only and does not contain a grass or clay layer. It is therefore considered to be susceptible for erosion of the waterside slope. In previous assessment rounds by Vallei en Veluwe, the levee was considered as concealed levee and wide enough to handle erosion. This is a qualitative judgement of the waterside slope erosion safety and a quantitative analysis was missing. In this study, several existing levee erosion models were investigated to quantify the amount of waterside slope erosion happening at Kloosterbos. At first, two wave models were compared (SWAN and Bretschneider) on their applicability for Kloosterbos. From these, the Bretschneider equations was considered best applicable, since it provided sufficient input data for the erosion model and had a large range of available data sets. The SWAN model gives more options regarding the output, but no SWAN data was available at Kloosterbos. Therefore, the Bretschneider equations were used to provide the input for the erosion model. XBeach1D is used in this study as erosion model for Kloosterbos. This model was compared to four other erosion models (DUROS+, D++, equations of Klein Breteler et al. and DUROSTA), from which XBeach1D came out best to use for Kloosterbos. The other models mainly contained limitations regarding the wave characteristics. Investigation was done on the translation from the coastal to river settings, together with a sensitivity analysis for several parameters within XBeach1D. In the translation to the river settings, the focus was mainly put on the wave generation by JONSWAP (originally meant for the North Sea). It followed that JONSWAP can be used for the Kloosterbos situation. Following from the sensitivity analysis, angled waves would cause more erosion than perpendicular waves. The extension of the angled waves in XBeach1D has not been calibrated nor validated, but is used in the final safety assessment. Further, a weakest link and ultimate limit state (minimum profile left after erosion) was defined for the Kloosterbos situation, which were needed for the eventual safety analysis. The weakest link is defined as the levee location at which the levee is most likely to fail due to erosion of the waterside slope. The weakest link was found to be located east in Kloosterbos. The levee reaches failure at the moment on which the ultimate limit state is exceeded. In this study, the boundary profile used in dune safety is also used as ultimate limit state for the Kloosterbos levee. The boundary profile is the minimum profile that should be left after erosion has happened. All things considered, the waterside slope erosion safety of the levee was determined, using the safety categories stated in WBI2017. The erosion safety of the levee at Kloosterbos complied to the IIIv (1/20,000 years) safety category. This means that the levee complies to the lower threshold for the waterside slope erosion for the levee section. Therefore, no levee measure is needed for Vallei en Veluwe, when looking at the waterside slope erosion.
Item Type:Essay (Bachelor)
Faculty:ET: Engineering Technology
Programme:Civil Engineering BSc (56952)
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