AECOM's coastal processes study identified erosion threats and informed strategic coastal defence planning for Allerdale Coast.
AECOM was commissioned by Cumbria County Council to conduct a comprehensive coastal processes study for the Allerdale Coast. The main objective was to develop sediment transport models, both one-dimensional (1D) and two-dimensional (2D), to investigate ongoing erosion processes and provide crucial insights for decision-making concerning the future of important assets, such as the B5300 road.
Study objectives
The study aimed to achieve the following objectives: • Development of a regional 2D tide, wave, and sediment transport model. • Identification of erosion causes and estimation of erosion rates. • Assessment of potential impacts of coastal erosion on the B5300 road. • Establishment of a baseline for future management studies in key areas, including Beckfoot, Crosscanonby, Dubmill Point, and Allonby.
Model development
Our team successfully developed a fully integrated 2D model encompassing tides, waves, and sediment transport for the Solway Firth. The hydrodynamic model incorporated the latest bathymetric surveys, including LiDAR and beach monitoring datasets. The model provided a 5-meter resolution in the nearshore region.
Following calibration and validation of the hydrodynamic model, the wave model was coupled and validated using storm data from the winter of 2013/14. The sediment transport model was then validated using pre- and post-storm beach profile data. Cross-shore profiles analysis demonstrated that the 2D sediment transport model accurately represented bed level changes, consistent with the measured data.
Similarly, the 1D cross-shore model was validated by comparing predicted changes to storm-induced beach profiles. The 1D longshore sediment transport model utilised historical shoreline change data to predict erosion/accretion rates over the long term.
Application and findings
The validated 1D and 2D sediment transport models were subsequently employed to analyse the response of coastal processes to various coastal defence options, including the implementation of hard defences to prevent erosion and sediment movement along the coast.
The modelling results confirmed that without extending or maintaining coastal defences, the B5300 road would eventually face the threat of coastal erosion. The study also identified critical locations along the coastline and informed the development of an optimised, phased response for implementing coastal defence schemes. The combination of 1D and 2D models proved to be a powerful tool for evaluating coastal protection options. By comparing the results of different schemes, the relative impacts of alternative options could be better understood in terms of their potential future consequences.
In addition, the modelling approach facilitated the consideration of future climate change scenarios, enabling an understanding of the potential consequences of a passive approach to coastal management. This information was crucial for supporting funding applications for the necessary capital works.
Informing coastal management strategies
AECOM's coastal processes study for the Allerdale Coast provided Cumbria County Council with valuable insights into erosion processes, their impacts on the B5300 road, and the effectiveness of different coastal defence options. The combination of 1D and 2D sediment transport models allowed for informed decision-making and strategic planning to mitigate future risks. The study's findings will play a crucial role in developing sustainable and effective coastal management strategies for the Allerdale Coast area.