40
T.N. Burt . I.e. Cruickshank . M.A. Littlewood
5.4
The Issues
It is not possible within the constraints of this chapter to fully discuss all the issues
related to barrages. It is, however appropriate to provide an overview of the complex
interaction of the issues under their generic headings.
5.4.1
Fisheries, Nature and Conservation
Clearly, a barrage whether it fully or partially excludes the tides represents a significant
change to an estuary. The most obvious initial impacts are on the hydrodyn~mics as
already discussed, but estuaries have developed biotas, perhaps over centuries, suited to
the peculiar characteristics of the hydrodynamics as well as climatic and geophysical
conditions of the area. It follows that if the hydrodynamics change, the biota will also
have to adapt, die or vacate the existing habitat and allow new species to move in. In
addition to this, the construction of a barrage will act as a physical obstruction to the
passage of migratory fish.
Biologically, estuaries rank amongst the most productive of natural systems. Primary producers include phytoplankton, free-floating in the water column, microalgae
attached to the surface of sediment and larger plants and macrophytic vegetation such
as saltmarsh and eel grass. Macroalgae (i.e. the typical seaweeds of rocky, coastal shores)
are usually sparsely distributed in estuaries due to the lack of availability of suitable
hard substrates for attachment.
Fig. 5.1. Fish pass on Tawe Barrage, Wales, showing the highly turbulent flows which significantly affect
provision for free passage of fish. (Courtesy of HR Wallingford)
T.N. Burt . I.e. Cruickshank . M.A. Littlewood
5.4
The Issues
It is not possible within the constraints of this chapter to fully discuss all the issues
related to barrages. It is, however appropriate to provide an overview of the complex
interaction of the issues under their generic headings.
5.4.1
Fisheries, Nature and Conservation
Clearly, a barrage whether it fully or partially excludes the tides represents a significant
change to an estuary. The most obvious initial impacts are on the hydrodyn~mics as
already discussed, but estuaries have developed biotas, perhaps over centuries, suited to
the peculiar characteristics of the hydrodynamics as well as climatic and geophysical
conditions of the area. It follows that if the hydrodynamics change, the biota will also
have to adapt, die or vacate the existing habitat and allow new species to move in. In
addition to this, the construction of a barrage will act as a physical obstruction to the
passage of migratory fish.
Biologically, estuaries rank amongst the most productive of natural systems. Primary producers include phytoplankton, free-floating in the water column, microalgae
attached to the surface of sediment and larger plants and macrophytic vegetation such
as saltmarsh and eel grass. Macroalgae (i.e. the typical seaweeds of rocky, coastal shores)
are usually sparsely distributed in estuaries due to the lack of availability of suitable
hard substrates for attachment.
Fig. 5.1. Fish pass on Tawe Barrage, Wales, showing the highly turbulent flows which significantly affect
provision for free passage of fish. (Courtesy of HR Wallingford)