Sea Level Rise
Defra (2006) recommends an allowance for future mean sea level rise for the North Wales coast of 3.5, 8.0, 11.5 and 14.5mm/year for
the periods 1990-2025, 2025-2055, 2055-2085 and 2085-2115, respectively. Sea water levels used in this study have been increased
appropriately for the relevant period into the future. For example, to represent sea level rise over 50 years (relative to 2006) 0.318m
is added to all present-day sea levels, or for 100 years 0.956m is added.
Wave Climate - Inter Annual Variability in the Deep Water Wave Conditions
The uncertainties involved in the prediction of future wave climate change are too great to attempt a "prediction" of future wave
conditions. However, it is useful to consider inter annual variability and use this to assist in the consideration of future wave climate
scenarios.
Two offshore datasets were therefore analysed to assess the trend (if any) that can be observed from the past wave climate.
The first dataset covers a period from January 1970 to January 1993. The second covers the period from January 1987 to December
2001. Although the two datasets are each internally consistent they cannot be considered as one since they do not pertain to the same precise
location.
The analysis consists of calculating the average of the wave heights for the 10% and 1% exceedance levels for a period of 5 years (a five
year rolling average is considered to smooth the annual variability and highlight any underlying trend). The natural variability amongst
the 5 years blocks of data was found to be in the order of +/- 10%. Therefore + 10% would be a realistic sensitivity allowance for future
wave height change (hence, + 5% on wave period to retain the same wave steepness). This is now also recommended in Defra (2006) as a
sensitivity allowance to possible future wave climate change.
Limitations and Further Work
Within the original studies, the probability of flooding in 50 years of climate conditions was estimated to compare current and future change in
flood risks. Other TAN 15 criteria such as flood velocity, rate of rise and speed of inundation were not estimated, nor were other
climate change scenarios (e.g. probability of flooding in 100 years of climate change). The maps below illustrate the 50 year flooding scenario from the original studies undertaken. Following on from the original work done for the Conwy Tidal Flood Risk Study, additional flood inundation modelling and mapping work has been undertaken for the Pensarn to Kinmel Bay area considering 100 years of climate change to produce maps in accordance with TAN15 guidance on flood risk. A pdf copy of this report can be viewed in the 'HR Wallingford Reports and Drawings' section of this website.
