Environmental Engineering Reference
In-Depth Information
Plans (CHaMPs) such as those produced for the
Thames (ABPmer 2008) and the Solent (Bray and
Cottle 2003; Hodge and Johnson 2007) as well as
Flood Management Strategies such as the Essex
Estuaries Strategy (Ahlhorn and Meyerdirk 2007)
or
Selecting a Site for Realignment
When selecting locations for realignment there
are a number of site characteristics that are rel-
evant, of which the existing land use and the land
elevation in relation to the tidal frame are prob-
ably of greatest importance. The existing land use
is clearly critical andwill influence the economic
rationalefortheworkandthefeasibilityofun-
dertaking the projects, with aspects such as the
presence of infrastructure, the proximity of road
or rail lines, and the alignment of gas and electric
pipelines or pylons all being relevant. Land ele-
vation is also important both to engineering fea-
sibility and to potential nature conservation
outcomes. Other considerations include mini-
mizing the engineering costs; reducing the
length, and maintenance cost, of the new sea
wall; the potential to impact on thewider estuary
or coast; or the effect on the stability and protec-
tion afforded by sea walls in the vicinity (Dixon
et al. 2008).
These aspects usually form the core selection
criteria but numerous others may also be relevant
depending on the scheme objectives, as indicated
in Table 4.1. The site selection process also varies,
most obviously, in terms of the spatial coverage
and level of detail applied; for instance, they range
from:
.
High-level strategic audits of the national hab-
itat creation resource: An example of this in-
cludes the Royal Society for the Protection of
Birds' (RSPB's) reviewof intertidal habitat creation
sites across mainland Britain, which used criteria
such as the absence of infrastructure and the need
to avoid increasing the length of flood defence
(Pilcher et al. 2002). This study identified an area
of around 33,000 ha that was potentially suitable
for realignment.
.
Individual strategies covering a single estuary or
coastal management area: Such studies are de-
signed to identify a set of sites that will contri-
bute to the strategic management of coasts and
estuaries while also providing compensation sites
to offset past habitat losses and the effects of
coastal squeeze. They include Shoreline Manage-
ment Plans (SMPs); Coastal Habitat Management
the Solent Dynamic Coast Project
(Cope
et al. 2007).
.
Project-specific compensation site reviews:
These are studies designed to identify a single
compensation site that will offset habitat losses
froma specific coastal development, inwhich case
the search is centred on the location where the
losses take place. A relatively detailed example of
this includes the UK government's search for
compensatory sites that would offset loss of inter-
tidal habitats from port developments at Lappel
Bank (Medway Estuary) and Fagbury Flats (Orwell
Estuary). This search extended from north Kent to
southern Suffolk and ended with the selection of
the 115-ha Wallasea North Bank realignment site
that was breached in 2006 (ABPmer 2003, 2004a).
For simplicity, the process ismost easily viewed
in two stages. Thefirst stage is a 'Screening' process
at which searches of varying detail (national, re-
gional, coastal cell, estuary) are undertakenusually
making use of geographical information system
(GIS)mapping techniques. The second stage is then
a 'Scoping' exercise during which the feasibility of
an individual site, or selection of sites, is consid-
ered throughconsultationand site investigation, as
set out in the next section.
Most screening studies beginwith a floodplain
map and use a range of criteria to select the most
suitable sites (e.g. by avoiding built-up areas,
roads or railways; identifying areas with eleva-
tions suitable for intertidal habitat creation, and
considering land use and land ownership issues).
To understand the sorts of issues that are rele-
vant, Table 4.2 shows the criteria that were ap-
plied in a range of studies. In most instances the
criteria used are broadly similar but there is often
considerable variability in the emphasis that was
put on physical and/or anthropogenic factors as
well as in the stage in the hierarchical process at
which certain criteria have been used. Such flex-
ibility is to be expected given the variability of
objectives, and the list in Table 4.1 can be seen as
