Sensitivity testing the effect of breach representation for two contrasting coastal floodplains

Sensitivity testing the effect of breach representation for two contrasting coastal floodplains

Marshman, S.J.

Stive, M.J.F. (mentor)
Nicholls, R.J. (mentor)

Civil Engineering and Geosciences

Hydraulic Engineering

CoMEM - Coastal and Marine Engineering and Management

2010-06-24

Coastal floodplains in the south of England are at high risk of tidal flooding due to extreme water levels. The breaching of coastal defences is the most dominant source of floodwater and is a spatially and temporally uncertain process. However, there is an increasing requirement for predictive breach modelling for the simulation of coastal flood inundation. The main aim of this project is to investigate how the LISFLOOD-FP models predictions of flood inundation are affected by the variation of simplified breach representations. The research focuses on how the time varying representation of inflow discharge (represented by the QVAR boundary condition type in the model) can be utilised in a range of different breach scenarios, and how in turn this affects the flood inundation characteristics for a rural floodplain at Lymington/Pennington and an urban floodplain at Old Portsmouth. An inflow model based on an offline weir discharge equation was derived and validated in a simulation of the December 1989 storm surge event at Lymington/Pennington. The different breach scenarios then utilised this proposed inflow model and systematically varied the two breach parameters of breach growth and breach initiation timing for a 1 in 200 year extreme water level condition at both study sites. Analysis of the results indicate that the rate of breach development and the timing of breach initiation has a considerable effect on the overall flood extents and the rate and pattern of inundation at both the rural and urban study sites. Furthermore, comparison of the two study sites using individual benchmark floodplain compartments and simulations with a combined rural/urban DEM showed that the presence of elevated urban features on the floodplain has a significant influence on the flood inundation characteristics. Further research is required to assess the limitations and the validity of the proposed QVAR inflow model for modelling breaching events. Also, the evaluation of the two breach parameters in a probabilistic setting is recommended to assist in managing future coastal flood risk on both rural and urban floodplains.

Floodplain
LISFLOOD-FP
Digital Elevation Model
Breach

http://resolver.tudelft.nl/uuid:16ac3bb6-c3dd-4318-afc4-648cc9c255ed

Student theses

master thesis

(c) 2010 Marshman, S.J.