36
T.N. Burt . I.C. Cruickshank· M.A. Littlewood
such as the Habitats Directive it is more important than ever to try to understand these
processes and thereby implement best practice. Indeed, future barrage schemes need
to closely embrace the principles of sustainable development, thus ensuring that economic investment and environmental improvement go hand in hand. In assessing the
hydraulic feasibility and environmental impacts of these schemes, some of the issues
required the development of new study techniques to provide predictions of the effects; some issues were virtually unresolvable with present knowledge and even when
established study techniques were used there is still the question of how much confidence could be placed in the results. It is hoped that the guidelines will help facilitate an
integrated approach to the planning and implementation in which the interests of all
the stakeholders are considered and carefully balanced.
This chapter gives an overview of the research project and some of the key issues for
various types of barrages, drawing on illustrations from the authors' research. It makes
a few brief recommendations for future barrages in lieu of these guidelines becoming
formally available.
S.2
Definitions and Purposes of Barrages and Barriers
In order to discuss the environmental issues of barrages it is first important to define
exactly what a barrage is. The definition is open to some debate. The generally accepted
definition of a barrier and a barrage is as follows:
A barrage is an obstruction which permanently excludes all or part of the tidal flow
from all or part of the estuary and through which the freshwater flow down the river
can be passed by sluices or weirs when the tide is lower than the level of the impounded
water behind the barrage. A barrier (sometimes refered to as a tidal surge barrage) can
be considered as a device which is operated only to prevent exceptionally high tides
and surges from passing up the estuary when a surge flood warning is issued: it may be
a permanent structure with moveable gates or it may be of fabric design.
The boundary between the two definitions is not so clear when considering some of
the present day multi-functional structures which are capable of achieving all permutations of tidal and fluvial flow control. Barrages can have significantly more impacts
on the environment than barriers because barriers only temporarily change the natural regime. It is therefore important to retain the distinction between these two types of
structure and the guidelines therefore focus on barrages whilst noting particular issues that relate to barriers. The purposes of the construction of barrages or barriers
can be described as aiming to achieve one or more of the following objectives, each of
which may be applicable in varying degrees:
1. Improved amenity value barrages are constructed to improve the amenity value of the
impounded water and the surrounding land. This may be in the form of: increased
water area for recreational use; improved access to the water area; more stable water
conditions providing opportunity for an aesthetically pleasing waterside development
where both business and housing can thrive. These barrages are often associated with
urban regeneration projects (especially in the UK) where it is seen that the improved
amenity value will act as a catalyst for regeneration. The economic aim is for the
barrage to increase land values which will offset the capital cost of its construction.
T.N. Burt . I.C. Cruickshank· M.A. Littlewood
such as the Habitats Directive it is more important than ever to try to understand these
processes and thereby implement best practice. Indeed, future barrage schemes need
to closely embrace the principles of sustainable development, thus ensuring that economic investment and environmental improvement go hand in hand. In assessing the
hydraulic feasibility and environmental impacts of these schemes, some of the issues
required the development of new study techniques to provide predictions of the effects; some issues were virtually unresolvable with present knowledge and even when
established study techniques were used there is still the question of how much confidence could be placed in the results. It is hoped that the guidelines will help facilitate an
integrated approach to the planning and implementation in which the interests of all
the stakeholders are considered and carefully balanced.
This chapter gives an overview of the research project and some of the key issues for
various types of barrages, drawing on illustrations from the authors' research. It makes
a few brief recommendations for future barrages in lieu of these guidelines becoming
formally available.
S.2
Definitions and Purposes of Barrages and Barriers
In order to discuss the environmental issues of barrages it is first important to define
exactly what a barrage is. The definition is open to some debate. The generally accepted
definition of a barrier and a barrage is as follows:
A barrage is an obstruction which permanently excludes all or part of the tidal flow
from all or part of the estuary and through which the freshwater flow down the river
can be passed by sluices or weirs when the tide is lower than the level of the impounded
water behind the barrage. A barrier (sometimes refered to as a tidal surge barrage) can
be considered as a device which is operated only to prevent exceptionally high tides
and surges from passing up the estuary when a surge flood warning is issued: it may be
a permanent structure with moveable gates or it may be of fabric design.
The boundary between the two definitions is not so clear when considering some of
the present day multi-functional structures which are capable of achieving all permutations of tidal and fluvial flow control. Barrages can have significantly more impacts
on the environment than barriers because barriers only temporarily change the natural regime. It is therefore important to retain the distinction between these two types of
structure and the guidelines therefore focus on barrages whilst noting particular issues that relate to barriers. The purposes of the construction of barrages or barriers
can be described as aiming to achieve one or more of the following objectives, each of
which may be applicable in varying degrees:
1. Improved amenity value barrages are constructed to improve the amenity value of the
impounded water and the surrounding land. This may be in the form of: increased
water area for recreational use; improved access to the water area; more stable water
conditions providing opportunity for an aesthetically pleasing waterside development
where both business and housing can thrive. These barrages are often associated with
urban regeneration projects (especially in the UK) where it is seen that the improved
amenity value will act as a catalyst for regeneration. The economic aim is for the
barrage to increase land values which will offset the capital cost of its construction.