7773

• UCREFRP Catalog Number: 7773
• Author: Many
• Title: Hydroecologie Appliquee
• USFW Year: 1993
• USFW - Doc Type: 2‎(5)‎
• Copyright Material: YES

The Enhancement of Drained Salmonid Rivers in Ireland 13
physical and hydraulic terms from the
fisheries perspective. Aquatic floristic
and macro-invertebrate records are
also most desirable as is a description
of the riparian zone. Quantitative
assessments of salmonid stocks and,
where possible, all other fish species
are essential. The compilation of this
type of data base is essential in un-
derstanding how a catchment func-
tions in fisheries terms. An example
of the level of sampling required in an
Irish catchment (650 km2) to comply
with this type of strategy is outlined
(fig. 4a) (from O'Grady, 1991(c)) and
some of the findings in relation to
variation in salmonid habitat and sub-
strate type are illustrated (fig. 4b
and c).
3. EXAMINATION AND
ADJUSTMENT OF DRAINAGE
DESIGN PRE-WORKS
The priorities of the drainage en-
gineers and the fishery biologist are
very different. The former is con-
cerned primarily with ensuring that the
designed peak discharges are main-
tained within bank height and outfall
is provided for in marginal lands. The
fishery biologist is primarily concerned
with the ecological conditions in mean
summer flow conditions. If the physi-
cal and ecological date bases outlined
in Section 2 have been compiled it is
possible for the engineer and biolo-
gist, working in collaboration, to adjust
the first phase design to the advan-
tage of fisheries interests. This con-
cept is now an accepted part of en-
vironmental impact assessment stu-
dies (C.E.C., 1978).
The drainage design in engineering
terms seeks to find the minimum cost
option to achieve the required outfall
and discharge objectives. In channels
of fishery value, hydraulic data, for
mean summer flow levels, should be
used to assist in the examination of
the likely effects of the drainage de-
sign on a fishery. Such calculations
may allow one to adjust design, and
while still attaining the drainage ob-
jectives, reduce the longterm impact
on the fishery resource or, at least,
create a physical regime which can be
rehabilitated post-works. This pro-
posal, while very effective, is likely to
result in increased engineering costs.
However, these must be weighed
against the permanent fishery losses
which may otherwise be incurred.
There is now widespread recognition
of the problems created by not taking
cognisance of the importance of re-
taining many natural features of chan-
nels (meanders, bank slope, etc.)
when draining rivers (Boon et al.,
1992).
Apart from the aforementioned con-
siderations in relation to backwater
analysis the baseline physical, hydro-
logical and biological data can be
used in a number of ways to adjust
the first phase design to the advan-
tage of fishery interests. A few ex-
amples of how this can be done in a
practical way are outlined here.
The physical data compiled will
illustrate the depth of stony deposits
on a particular river bed section and