In coastal and environmental engineering, the closure of tidal inlets entails the deliberate prevention of the entry of seawater into inland areas through the use of fill material and the construction of barriers. The aim of such closures is usually to safeguard inland regions from flooding, thereby protecting ecological integrity and reducing potential harm to human settlements and agricultural areas.
The complexity of inlet closure varies significantly with the size of the estuary involved. For smaller estuaries, which may naturally dry out at low tide, the process can be relatively straightforward. However, the management of larger estuaries demands a sophisticated blend of technical expertise, encapsulating hydrodynamics, sediment transport, as well as mitigation of the potential ecological consequences of such interventions. The development of knowledge around such closures over time reflects a concerted effort to balance flood defence mechanisms with environmental stewardship, leading to the development of both traditional and technologically advanced solutions.
In situations where rivers and inlets pose significant flood risk across large areas, providing protection along the entire length of both banks can be prohibitively expensive. In London, this issue has been addressed by construction of the Thames Barrier, which is only closed during forecasts of extreme water levels in the southern North Sea. In the Netherlands, a number of inlets were closed by fully damming their entrances.[1][2] Since such dams take many months or years to complete, water exchange between the sea and the inlet continues throughout the construction period. It is only during the final stages that the gap is sufficiently narrowed to limit this exchange, presenting unique construction challenges. As the gap diminishes, significant differences in water levels between the sea and the inlet create very strong currents, potentially reaching several metres per second, through the remaining narrow opening.[3]
Special techniques are required during this critical closure phase to prevent severe erosion of existing defences. Two primary methods are used: the abrupt or sudden closure method, which involves positioning prefabricated caissons during a brief period of slack water, and the gradual closure method, which involves progressively building up the last section of the dam, keeping the crest nearly horizontal to prevent strong currents and erosion along any specific section.[4]
- ^ Deltacommissie (1962). Rapport Deltacommissie (in Dutch). The Hague: Staatsdrukkerij- en Uitgeverijbedrijf. Retrieved 22 May 2024.
- ^ Leentvaar, J.; Nijboer, S. M. (1986). "Ecological Impacts of the Construction of Dams in an Estuary". Water Science and Technology. 18 (4–5): 181–191. doi:10.2166/wst.1986.0194. ISSN 0273-1223. Retrieved 22 May 2024.
- ^ Pugh, David (1987). Tides, surges, and mean sea-level. Chichester ; New York: J. Wiley. ISBN 978-0-471-91505-8.
- ^ Dronkers, J.J. (1964). Tidal computations in rivers and coastal waters. Amsterdam; New York: North-Holland Pub. Co.; Interscience Publishers. Retrieved 22 May 2024.