Future Management of the 'Baseline Document for Maintenance Dredging'
In accordance with the Draft Protocol, it is recommended that the baseline document is developed over time to incorporate new information as it becomes available (e.g. from condition monitoring of the SPA). It is also intended to be used in consultation with other operators within the estuary who undertake, or plan to undertake, dredging activity.
It is anticipated that the document should not require substantial revision unless major changes are proposed (e.g. capital works or substantial change to existing maintenance dredging methods or quantities) or significant new information comes to light. It will be important to ensure that future proposals are assessed against the up-dated position and latest information.
It is recommended that the following are taken into account when updating the current baseline:
- London Gateway
- Incorporation of WeBS Data
- Water Framework Directive
- Further Evaluation of water injection dredging (WID)
- Future Research
The London Gateway proposals involve amongst others, a 95ha land claim on the north bank of the Thames and dredging of approximately 30 million m3. A public inquiry into the proposals was completed in September 2003. Since then the Government has announced that it is minded to approve the proposals and therefore it is our understanding that the project will proceed. It is recommended that once the project is complete, this document is revised to take account of the new channel morphology and any changes to the maintenance dredging regime.
Incorporation of WeBS Data
It should also be noted that bird counts are undertaken every year between September and April as part of the WeBS scheme. New bird count data and WeBs alerts data should, therefore, be incorporated into this document as it becomes available. The document should also be reviewed once the six-yearly condition assessment of the SPA has been undertaken by Natural England; where this information will be critical to determining whether existing activities within the estuary are affecting the integrity of the European designated site.
Water Framework Directive
The implementation of the Water Framework Directive is anticipated to have implications on the management of the wider marine resource within the Estuary. While characterisation has now been completed, the implementation process has yet to commence. This document should be developed to address the requirements of the WFD as they become available, to provide a composite baseline for maintenance dredging within the lower Thames Estuary.
Further Evaluation of WID
It is recommended that further evaluation be undertaken to monitor bed level changes adjacent to selected water injection dredge sites themselves, including time-step surveys over a period commencing prior to and concluding a reasonable period after dredging campaign to identify any specific deposition trends arising from the technique and to supplement work previously undertaken by HR Wallingford and Environmental Tracing Systems.
With regard to further work to investigate the estuarine system, an increase in tidal range has taken place which would be worthy of further study, albeit outside the scope of reference for PLA. The predominant causes of the observed increase in tidal range appear to be (although not definitively) anthropogenic in nature; for this reason a simple extrapolation of the observed rates into the future is not appropriate and hence further work is recommended (Littlewood et al., 2003) to:
- Determine the causes of the rise in water levels at Tower Bridge and their relative importance.
- Examine whether a rise at Tower Bridge will continue into the future and if so whether it will continue to be greater than the rise at Southend-on-Sea.