Print Email Facebook Twitter A parametric study concerning estuary mouth dynamics and inlet closure Title A parametric study concerning estuary mouth dynamics and inlet closure Author Moerland, V.D. Contributor Stive, M.J.F. (mentor) Wang, Z.B. (mentor) Slinger, J.H. (mentor) Luijendijk, A.P. (mentor) Faculty Civil Engineering and Geosciences Department Hydraulic Engineering Date 2013-01-14 Abstract With the development of a process-based model (Delft3D) of the St Lucia Estuary inlet, a first approach is made with regard to the estuary mouth dynamics and closure mechanisms that are observed at St Lucia inlet. The purpose of this thesis is to get a better understanding of the hydrodynamic and morphological behaviour of the St Lucia inlet with the additional effect of the Mfolozi River discharge. The focus in this thesis is on the period after 2001 till present, where the management policy is to let the St Lucia inlet function in its natural state and with the possibility to join with the Mfolozi River. A model with a schematized situation of the estuary with representative inlet geometry is forced with representative waves and tide conditions. Important factors determining the inlet stability such as tidal prism, longshore sediment transport, inlet geometry and river discharge are investigated in this thesis. The Mfolozi River mouth and St Lucia Estuary entrance are situated in a seasonal varying climatic regime with long drought periods with low riverine flows followed by wet periods and cyclonic events. A high energy wave climate in combination with a micro-tidal regime and a high rate of longshore sediment transport are the most important factors of the instability of the St Lucia inlet. According to Bruun (1978) inlets that are classified with a P/M ratio below twenty are found to be unstable and the inlet may be closed by deposition of sediment during a storm event because the tidal prism is relative small. In line with Bruun, the St Lucia inlet can be classified as an unstable inlet with a low P/M ratio of approximately two. Three scenarios were developed with different estuary dimensions; a small, a medium and a large basin. The inlet geometry is the same in the scenarios and each scenario is modelled with five different simulations. The simulations are forced at the boundaries by a varying range of tide and wave conditions. The tide is varied from average to neap and spring tide. The wave height is varied from average to higher and extreme wave heights. Higher waves are responsible for a higher rate of longshore sediment transport and with both varying tide and wave conditions a wide range of P/M ratios are modelled. In addition the influence of a lower D50 was investigated, and the influence of the Mfolozi River was simulated. The results of the simulations show that they are in line with expectations. Small P/M ratios show that inlets are unstable and different closure mechanisms are observed. Similar to what is found in nature regarding the A-P relationship, a decreasing cross-sectional area with a lowering tidal prism, is also found with the Delft3D models which suggest that the model is capable of giving a good representation of the morphodynamics. Subject St LuciaMfolozi Riverclosure mechanismstidal inlet stabilityprocess-based modelingDelft3D To reference this document use: http://resolver.tudelft.nl/uuid:400c301c-250d-46d0-ab87-3348141becf3 Embargo date 2013-01-31 Part of collection Student theses Document type master thesis Rights (c) 2013 Moerland, V.D. Files PDF MSc_Thesis_St_Lucia_Inlet ... erland.pdf 10.61 MB Close viewer /islandora/object/uuid:400c301c-250d-46d0-ab87-3348141becf3/datastream/OBJ/view