CEFAS24-145 Contract for Bathymetry Surveys at Sizewell C

The BEEMS (British Energy Estuarine and Marine Studies) programme is funded by Sizewell C Limited. 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 the Supplier to deliver the elements described below.

Requirement: The purpose of this project is to provide bathymetric data for the Greater Sizewell Bay (GSB) to assess the geomorphological changes of the region, hence contributing to the ongoing monitoring of the Sizewell Coastline.

Cefas require two Multibeam Echosounder (MBES) bathymetric surveys to IHO Special Order (at a minimum) within the Greater Sizewell Bay (GSB) in 2025. Exact survey locations will be agreed between Cefas and the supplier during the pre-survey kick off meetings.

Survey 1 will be in April 2025 and will require nearshore transects to be undertaken to assess the geomorphological changes shown by two longshore bars. Therefore, care should be taken to maximise landward extent, and the survey should be undertaken during a Spring tide window to extend the coverage in the landward sense as far as practicable. Three further East to West Corridors ('Radar Calibration Corridors') are included in the scope for Multibeam survey (Figure 1).

For areas of survey overlap between nearshore or calibration corridors, the expectation is that coverage shall only be acquired once, and hence supplier's should provide details of a proposed survey plan to meet this requirement and ensure that there are no gaps in coverage. Survey 2 would be undertaken in July 2025. The final area to be surveyed will be confirmed by Cefas in spring 2025, but will broadly cover the area between the two lines in Figure 2. The expected maximum survey extent would be 2 km2 but this may be reduced once areas of interest are identified, so therefore expected that this survey to be costed per day. This survey is likely to be required on spring tides to enable any shallow water areas to be accessed. Survey Strategy: Cefas aim to confirm the finalised survey areas in a kick-off meeting with the supplier prior to each of the surveys. The supplier should note that the survey due to occur in April 2025 will be required on Spring Tides. The supplier should provide a line plan two weeks prior to the survey for Cefas to review and provide comment. The regular system of sounding lines shall be supplemented by a series of crosslines for verifying and evaluating the accuracy and reliability of surveyed depths and plotted locations in April. In July, a survey plan and/or dynamic line plans will be required but can be provided nearer the time of survey. The spacing between crosslines should typically be no more than 15 times that of the main sounding lines.

The supplier will be required to attend a Marine Induction meeting with the Sizewell Harbour Master prior to the survey