CARDIGAN TIDAL FLOOD RISK MANAGEMENT
PROJECT OVERVIEW
In January 2021, CJ Associates were instructed by Binnies on behalf of Natural Resource Wales to undertake a ground investigation in Aberteifi, Cardigan, Wales. The purpose of the GI was to provide ground data for designs for the improvements to the existing flood defences, thereby ensuring properties within the town are adequately protected from tidal flooding from the River Teifi. The GI scope designed by Binnies comprised 3 no. boreholes to 15 m bgl, 6 no. overwater cone penetration tests (CPT) to 20 m bgl, post-fieldwork monitoring, variable head permeability testing, laboratory testing (contam and geotech), and factual reporting.
The site is designated as a site of special scientific interest within the River Teifi. In order to undertake the works, CJA applied for the Flood Risk Activities Permit (FRAP). The FRAP required CJA to demonstrate how biological and ecological risks would be managed, which included the use of wheel washing, avoiding invasive species, and only using agreed access routes as determined by an ecologist.
During the tender period, the CJA project manager visited the site along with members of the supply chain (pontoon and CPT provision) to agree on the access routes and meet with stakeholders affected by the GI operations. Maps were annotated in real time on site by our project manager with respect to the agreed access routes, location of the site compound, along with any time restrictions as requested by local businesses. We also had to plan the GI works around the optimum tidal regime, thereby ensuring the pontoon could be floated to each of the CPT locations during a high tide and in daylight.
The site visit determined that access around the town was not suitable for a wheeled cable percussive rig due to narrow streets and tight corners. CJA recommended and implemented a tracked Commachio 205 drilling rig that could be mobilised to the site and tracked along the narrow streets with appropriate traffic management. To reduce the amount of manual handling associated with the GI, we allowed for a third operative within our pricing, which also improved productivity, ensuring the work was completed within the agreed programme.
Each of the borehole locations was surrounded with heras fencing with the ground protected with heavy-duty plastic sheeting formed into a bund to prevent discharge to the nearby River Teifi. Vegetable-based lubricants were used with the rig with strict procedures for the refuelling of plant and the management of spills.
The overwater CPTs were undertaken from a double-stacked floating pontoon that was constructed at a nearby slipway. The CPT rig was mobilised onto the pontoon via ramps with edge protection in place, complete with a support boat during operations. In order to provide sufficient kentledge of the CPT, we strategically placed 4 no. IBCS filled with water that were connected to the CPT unit via chains. We completed 8 no. CPTs to the required refusal depth within the agreed programme (one week).
The samples retrieved from the boreholes were logged and photographed on site, and data was issued in real time so that timeous decisions could be made by Binnies with respect to termination depths and the design instrumentation, thereby removing any associated delays.
The boreholes were installed with a 50 mm ID standpipe following a strict installation procedure. The boreholes were retrofitted with a groundwater monitoring logger. Variable head permeability testing was undertaken during the post-fieldwork monitoring period.
A factual report complete with lab testing was produced, and the data from the site has been both comprehensive and reliable and allowed Binnies to progress their design within their agreed programme with NRW.
GENERAL PROJECT DETAILS
Location: Cardigan, Wales
Sector: Flood Defence
Client: Natural Resource Wales (NRW)
Consultant: Binnies
Contract Value: £60,000
Services: Dynamic sampling, rotary coring, overwater pontoon, cone penetration testing, permeability testing
PROJECT HIGHLIGHTS
- Embracing early contractor involvement (ECI) and instigating site visits during the tender and mobilisation period with NRW and Binnies.
- The timeous completion of the ground investigation with the successful implementation of a floating pontoon.
- Regular checkpoint calls with the client team from tender award through to project completion with clear lines of communication and team ethos maintained.
- The real-time data flow from site during the fieldwork and monitoring period.
