Description
Background:
The Hinkley BEEMS (British EDF Estuarine and Marine Studies) programme is funded by New Nuclear Build Generation Company (HPC) Ltd. Through this programme, Cefas provide authoritative scientific information on the marine and transitional waters in the vicinity of potential new build nuclear power stations and require a competent supplier to deliver the element described below.
Requirement:
Bathymetric surveys in the Severn Estuary are required to be completed during the construction phase of the Hinkley Point C (HPC) build programme. A total of two surveys are required in 2025.
The supplier will undertake two multibeam echo sounder (MBES) bathymetric surveys. The first survey is expected between January to March 2025 which will serve as a pre-disposal for the placement of dredged material survey at the Portishead dredge disposal site (LU070) and King Road and Avonmouth Harbour Approaches area in the Severn Estuary, Somerset (see Figure 1). The second survey will be completed within two months of completion of initial capital dredge works (estimated September / October 2025).
The bathymetric survey area covers the entire Kings Road and Avonmouth Approaches area, which encompasses the dredge disposal site LU070 (Portishead). With regard to the Portishead disposal site, data is officially required for the disposal area plus a 100m buffer of the Northern, Eastern, and Southern boundary and a 250m buffer on the Western boundary (Figure 1). Figure 1 shows that the Southern 'buffer' boundary runs parallel with the edge of the Southern boundary of the wider Kings Road and Avonmouth Approaches area. This Southern boundary skirts the intertidal zone but it is important to gather data here if safe to do so. Table 1 gives the bounding coordinates for the Kings Road and Avonmouth Approaches Area.
Given the presence of fluid mud in the area (causing false bed heights during low energy periods), and the proximity of the Southern boundary to the intertidal zone, the survey must be undertaken during a period of Spring tides.
As the two survey datasets will be directly compared with each other, and used for volumetric analysis, suppliers who commit the same vessel to both surveys would be more favourable.
Cefas require the vessel(s), vessel crew, hydrographic survey team, and suitable equipment to undertake the surveys described. Cefas also require a lead hydrographic surveyor, with at least 5 years industry experience, to be present on the vessel(s) for the duration of each of the above surveys. Suppliers should also be aware that a client representative may join for part, or all, of the surveys. This will be confirmed within the pre-survey meeting.
For full details download the Bidder Pack at https://defra-family.force.com/s/Welcome and search for CEFAS24-144 under opportunities.