- 10th November 2020
- Posted by: Miranda Pont
- Category: Blog
We were commissioned by Manx Utilities to conduct a feasibility study for a Flood Alleviation Scheme in the village of Laxey, Isle of Man.
The overall aim of the project was to determine the scheme options required to provide a standard of protection of 1% AEP (Annual Exceedance Probability) plus climate change for the village. To achieve this, the project involved:
- Reviewing the existing risk and mechanisms for fluvial, surface water and tidal flooding
- Developing a baseline assessment of the existing flood risk and damages considering economic, environmental and social effects
- Developing a long list of all potential flood mitigation measures
- Screening the long list to determine a short list of options
- Determining the economic viability of the short list
- Summarising the findings for public consultation
Why flood alleviation?
Laxey is located on the downstream reaches of the Laxey River. The catchment is predominantly rural, with steep valley sides. These factors, combined with an extensive arterial drainage network, result in a rapid response to rainfall events. Laxey has been affected by four flood events in the past five years.
We wrote a flood incident review for the 1 October 2019 event, establishing a timeline of events and mechanisms for the flood event.
The baseline assessment incorporated the impacts of climate change over the next 100 years and processes of deterioration, including gravel accumulation, vegetation growth, debris blockage of bridges and culverts, and structural collapse of walls. The baseline scenario provided the justification against which the options were compared. Hydraulic modelling was undertaken to represent the baseline scenario for fluvial, surface water and tidal flood events.
Potential measures which could be implemented were considered as evidenced by the baseline assessment. Criteria such as environmental considerations and technical difficulties were then used to determine whether the options were suitable to be taken into the short list of options. These options were then costed and appraised for viability. The options were added to the hydraulic model and the results compared to the baseline assessment. The options which provided a benefit and were deemed economically viable were presented at the public consultation.
For the public consultation, we summarised the findings of the project into various media, including a video, posters and leaflets. Click on the links below to view each of these:
These visualisations provided residents with a representation of how the scheme would affect the landscape of the village, while the posters and video justified the need for the scheme.
The feasibility study demonstrated that there is a good economic case to provide a Flood Alleviation Scheme to Laxey. Some of the options considered as part of the scheme, such as the debris catcher in Glen Roy and replacement of the Gretch Veg culvert, have been installed by the Department of Infrastructure.
The proposed Flood Alleviation scheme also generated interest from the press. Click on the links below to find out more:
- BBC website coverage
- Isle of Man TV coverage of the public engagement event
- Manx Radio coverage
- IOM Today press article
Want to know more?
Email Gavin Hodson for more information about the Laxey Flood Alleviation Scheme.
You can also find out more on our Flood and Water Management webpages.