Stable bay theory and integrated coastal development: A case study

摘要

In this study we have investigated the sensitivity of the results obtained using static equilibrium bay shape theory to the choice of model parameters and environmental variables. This included the examination of how sensitive the shapes predicted are to slight changes in the variables that might accompany climate change. The results of the sensitivity analysis showed that the existing configuration of the bay near Beadnell harbour is close to equilibrium. However, significant adjustment in shoreline position may be expected should the predominant wave direction change from its current sector by a little as 10°. Agreement between the current MHWL and the position suggested by equilibrium theory in the southern part of the bay is not as good, but is best towards the centre of Beadnell Bay, where there is plenty of sand. Near Snook Point there are large rocky outcrops that are not adjusting to equilibrium as fast as the sandy beach. We have also investigated the sensitivity of the equilibrium bay to the choice of down coast point. This is normally taken to be a point where the shoreline is parallel to the incoming wave crests. From an inspection of the MHWL in Beadnell Bay, (see Figure 2), it is evident that there is a sharp change in alignment of the MHWL where Long Nanny Burn reaches the sea. The current bay shape appears to be the result of shoreline response to different predominant wave directions reaching the northern and southern parts of the bay. However, one would expect to see a smooth change in shoreline orientation in the area where the two different wave climates meet, but such a region is not observed. This suggests that the Long Nanny Bum plays an important morphological role in sustaining a longshore gradient of sediment transport by transporting sediment in the upstream/cross-shore direction. It must be remembered that the theory for static equilibrium bays considers the predominant wave climate for a particular bay. Fluctuations in the variables over the timescale of tides, storms and seasons can be anticipated to lead to significant variation from static equilibrium. In this case, equilibrium theory provides a useful first order estimate of the likely range of coastal response to fluctuations in wave climate.