This chapter discusses the implications of the
route options on surface water quality and drainage. Surface waterbodies
affected are identified and the potential impacts arising from the construction
and operation of the various options are examined.
The assessment has been based on a review of
available water quality data from the Environmental Protection Agency (EPA
1999). Hydrological studies have also
been undertaken for the Rivers Lee, Bride, Sullane and their tributaries.
In assessing impacts, the following significance
criteria have been used:
|
Significance Criteria |
Impact |
|
Severe adverse impact |
Permanent significant impact on a Class A
(unpolluted) river or designated salmonid river under the Freshwater Fish
Directive (78/659/EEC) which would affect its designation as such. Permanent
loss of a major strategic potable surface water source. High potential for
increased flooding of large number of residential properties, roads, and
agricultural land, with no potential for mitigation. |
|
Major adverse impact |
Temporary impacts on a Class A river or
designated salmonid river. Permanent impact on a Class B (slightly
polluted/eutrophic) river and watercourses not classified but used as nursery
grounds for protected fish species. Permanent significant impact on a major
strategic potable surface water source. Significant potential for increased
flooding of residential properties, roads and agricultural land, with limited
scope for mitigation. |
|
Moderate adverse impact |
Temporary impacts on a Class B river or watercourses
used as a nursery ground for protected fish species. Permanent impacts on a
Class C (moderately polluted) watercourse. Temporary impact on major potable
water source. Permanent impact on local potable surface water source.
Increased flood risk for small number of properties, gardens / pathways,
roads and agricultural land but with scope for partial mitigation. |
|
Minor adverse impact |
Temporary impacts on a Class C river or
watercourse. Permanent or temporary impacts on a Class D (seriously polluted)
or unclassified waterbody. Temporary impact on local potable water source.
Localised and limited change to the flood risk for agricultural land, with
scope for mitigation. |
|
No impact |
Changes that are unlikely to affect the integrity
of a resource or feature. No change to the existing flood risk (within the
limitations of modelling accuracy). |
|
Minor beneficial impact |
Reduction in the potential pollution of
waterbodies such as by the provision of pollution control measures where none
exist. Localised reduction in flood risk for agricultural land. |
|
Moderate beneficial impact |
The removal of polluting discharges to Class A
rivers and designated salmonid waters. Widespread reduction in flood risk or localised
reduction in flood risk of residential properties, roads, areas of special
importance and agricultural land. |
The main surface waterbodies within the study area
are shown on Figure 6.1. There are three main river systems (the Rivers
Sullane, Lee and Bride), and a number of lakes, described below.
The Sullane River flows from west to east along the
path of the existing N22, and is part of the River Lee system, and joins the
Carrigadrohid Reservoir south of Macroom. For the whole of its length, (for the
period 1990-99) it has Class A water quality. This classification is according
to the EPA’s Biological River Quality classification system (EPA 1999), details
of which are presented in Appendix 6 (unless stated otherwise all river classes are for
the period 1990-1999).
The Sullane’s main tributaries (within the study
area) are listed below:
·
River Douglas - Class
A quality
·
River Dangansallagh -
unmonitored by EPA
·
Sullane Beg –
unmonitored by EPA
·
Foherish River -
Class A quality
·
Finnow River - Class
A tributary of the R. Foherish
·
River Laney - Class A
river
·
Clashavoon Stream -
unmonitored tributary of the River Laney
The River Lee flows from Lough Allua, approximately
17km to the south west of Macroom. The River Lee is part of the EPA’s sampling
programme and generally records a water quality of Class A, except at Inishcarra
Bridge, where the water quality has been Class B for the past 10 years. For the
study area however, the River Lee’s water quality has been at Class A for the
period 1990-1999.
The Lee Valley was flooded in the 1950s when two
dams were constructed, one at Carrigadrohid, and one at Inishcarra, forming two
reservoirs, named after the villages where the dams were built. The reservoirs
were constructed to produce hydro-electric power, but are also used for water
supply and recreation, and are recognised as contributing greatly to the scenic
resource of the area. The river itself is designated as a salmonid fishery
under the EC (Quality of Salmonid Waters) Regulations of 1988 (SI 84 of 1988),
implementing the Freshwater Fish Directive (78/659/EEC).
The River Lee also has a number of tributaries
within the study area. The principle tributaries are:
·
Cummer/ Buingea River
- generally Class A quality, (at Atholis Bridge, water quality was Class B in
1990)
·
Sullane River -
(described above)
·
Aghthying Stream –
unmonitored by EPA
·
Glashagarriff River –
unmonitored by EPA (pNHA, see Chapter 8:
Ecology)
·
River Dripsey -
generally Class A (the water quality at Luskins and Dripsey Bridges was Class B
in 1997)
·
River Kame -
unmonitored by EPA.
·
River Bride –
generally Class A (see below)
The River Bride is the most easterly tributary of
the Lee within the study area, joining the Lee east of Ovens. The River Bride
does not have any monitored tributaries within the study area. Although
generally Class A within the study area, one site along its length, the bridge
at Crookstown, was recorded as having between Classes B and C water quality for
the period 1994-1999. This is understood to be due to a sewage discharge, but
the classification improves to satisfactory conditions (Class A) downstream.
The River Bride has one major tributary within the study area, the River
Ochaul, which joins approximately 0.75 km north west of Aherla, but is not
monitored by the EPA.
In addition to the Carrigadrohid and Inishcarra
reservoirs, there are a number of other lakes within the study area. Lough Gal,
situated close to the village of Bealnamorive is actually two lakes in close
proximity, and is a pNHA, as it has floating fen, extensive freshwater marsh
and scrub, and is also used by birds for feeding and nesting (Chapter 8: Ecology). There are also a couple of bodies of standing water to
the north and west of Ovens, which are abandoned quarries.
The Electricity Supply Board (ESB), operates two
hydroelectric generating stations at Carrigadrohid and Inishcarra. Significant
operating rules are included in Appendix 6.
The Reservoirs are the main source of water to Cork
City and its environs.
The new Macroom Water Treatment Works (completed in
1998) currently abstracts water from the River Sullane, although this is
expected to be replaced by abstraction from the River Laney within 10 years.
The town’s current water demand is 3,000 m3/day, rising to 10,000 m3/day
in 30 years (Cork C.C. pers comm). Further planned improvements to water supply
in the study area are listed in Appendix 6 (Cork C.C. 1996).
There may be additional abstractions from the
surface watercourses within the study area for public or private uses. At
present no further information is available.
Macroom Waste Water Treatment Works discharges to
the River Sullane at the eastern edge of the town. There are a number of
improvements to the sewage treatment facilities within the region detailed in Appendix 6 (Cork C.C.)There are several other effluent
discharges in the region, listed in Appendix 6.
Carrigadrohid reservoir is used for recreation,
including rowing and water skiing. Inishcarra reservoir is not promoted for
recreation due to the recent occurrence of toxic algal blooms (Cork CC
1996). The new National Rowing Centre
is currently under construction at Farran Wood, with the Irish National rowing
team expected to begin training there from April 2002. The reservoirs and watercourses are popular
fisheries with anglers, some are game fisheries, the remainder are
predominantly coarse fisheries (Chapter
8: Ecology).
There is an ESB smolt (juvenile salmon) rearing
facility situated at Carrigadrohid.
There are few recurring flooding problems in the
study area. Areas that experience flooding generally have an appropriate land
use, for example, agricultural land on the River Bride floodplain and
recognised floodable areas adjacent to the two hydroelectric reservoirs.
Localised flooding has been noted at Crookstown
adjacent to the River Bride and at Ballyvourney adjacent to the River Sullane.
Isolated houses/buildings appear to be at some existing risk of flooding
adjacent to the River Bride (at Killumney and near the Kilcrea Friary), on the
Kame River, on the Finnow River (at Gortnalicky) and possibly near the River
Laney and River Sullane confluence (Mill and downstream end of Macroom). The
drainage around Clondrohid is understood to be a cause of concern.
With the inclusion of appropriate drainage and
associated pollution control measures into the design of the scheme there would
be potential for minor or moderate beneficial impacts to the River Lee
reservoirs, and other rivers currently affected by run-off from the existing
N22. Although the existing N22 will be
left in situ, the volume of traffic using the road would greatly decrease
following the construction of any of the options, and hence the level of
potentially polluting run-off from the road would also decrease.
The following general potential impacts have been
identified for all route options during construction and operation:
·
Increased pollution
loading in surface waterbodies as a result of construction or road run-off;
·
Increases in spillage
and pollution incidences;
·
Contamination or
disruption to public and/or private water supplies;
·
Physical changes to
watercourse hydrology or to habitats;
The significance of the impact would depend on the
sensitivity of the receptor. Where road run-off is discharged to a river, the
greatest impacts could be expected to occur in the smallest rivers, depending
on the length of road discharging to the river. Particularly sensitive
receptors that have been identified within the study area include:
·
Carrigadrohid
Reservoir (recreation)
·
ESB salmonid rearing
facility
·
Inishcarra Reservoir
(reservoir for potable water);
·
Sullane River
(potable water source)
·
River Lee (potable
water source and designated salmonid river)
·
River Bride (notable
salmonid nursery and spawning habitat);
·
Salmonid spawning and
nursery tributaries (Agthying Stream, River Dripsey, Sullane Beg, River
Foherish, River Finnow, River Douglas, River Dangansallagh River Buingea, &
River Kame)
Crossing a river may well affect its water quality during
the construction phase. Provided that suitable mitigation mechanisms are put in
place to minimise discharge to rivers from road-run off or accidental pollution
incidents, the river’s water quality should not be permanently affected by the
operation of the road. However, where a stretch of route runs alongside a
river, the risk of road run-off and accidental pollution incidents discharging
to the water body is increased. This may increase the likelihood of a long-term
change in water quality, such that it cannot support the functions (whether
amenity, potable water source, or ecological) that it currently maintains.
All options are likely to produce an increase in
runoff from the road surface that would contribute to an overall increase in
flow rate in the traversed catchments as a whole. The impact is likely to be greatest for the options that pass
along river valleys with small catchments or where there are very long lengths
within the catchment (Finnow, Kame, Bride), but in every case would be likely
to constitute only a small proportion of major flows. There would generally be
negligible impact (including impact on the reservoirs) or only a minor adverse
impact on flood risk downstream. The potentially significant river crossings and
floodplain incursions due to the various route options are presented in Appendix 6.
Of the major river crossings proposed for the
various routes, two of the crossings on the River Bride are the ones most
likely to add to existing flooding problems as they are close to existing
infrastructure. A crossing immediately below Crookstown has the potential to
cause the greatest problems (Blue Route, Nodes 11 to 12a, see Figure 3.4), since there is more vulnerable infrastructure
than at other locations. A crossing near Kilcrea Friary (Blue Route, Nodes 11
to 12a, see Figure 3.4) has one house that may be vulnerable immediately
upstream of an existing bridge. All
crossings shall be designed as to prevent, where possible, flow increases up to
flood levels for a chosen design return period.
In a few instances, there is the potential for
diversion of water through a new road drainage system to reduce risks of
flooding in localised problem areas (e.g. Clondrohid school). Generally this would be achieved with only
localised increases in water levels in other nearby/adjacent channels.
Several of the options potentially involve crossing
of floodplains, embankments along the length of floodplains, or incursion into
the flood storage areas provided for in the design of the hydroelectric
reservoirs. Local effects would be greatest from embankments down the Finnow or
Kame floodplains (since road embankments could take up or isolate a significant
proportion of the flood storage area). Lengthy incursions into the
Carrigadrohid or Inishcarra Reservoir flood storage areas could lead to very
small increases in level over a wide area. The Finnow and Kame floodplains
include some existing infrastructure that could be at risk if flood levels
increased.
In general, the risk of contamination of
watercourses (e.g. discharge of sediment, oils and/or hydrocarbons into the
watercourses) by flooding would increase very slightly if road embankments are
constructed on floodplains. During
construction, both the risk of flooding and the consequences of flooding on
water quality, are potentially greater for the options with longer lengths of
embankment within the floodplain. The staging of some construction activities
could reduce the potential for adverse impacts. There would generally be little
difference in the flood risk between construction and operation (unless large
areas of floodplains are prevented from flooding by the construction of
embankments).
Of the possible reservoir crossings, the potential
for adverse impacts in terms of altered water levels is relatively low,
provided the crossings are designed with sufficient waterway area to pass the
major floods the River Lee can produce. Both the Carrigadrohid and Inishcarra
reservoirs have maximum allowable water level ranges of around 5.5m.
The main crossings and potential impacts of each section
of route (without mitigation) are shown in Appendix 6. With mitigation, it is expected that all flood
impacts can be reduced to minor (or negligible) levels.
For each section, the major crossings are tabulated
with an indication of the scale of each crossing and the potential for adverse
impacts. The “acceptable water level increase” for each major crossing is an
interpretation of the Office of Public Works (OPW) policy with regard to new
structures (see section 6.4 below). As an example, a moderate increase might be
of the order of 100-200mm immediately upstream of a structure in a 100 year
event.
The required scale of mitigation is an
interpretation of the difficulty posed in achieving a design that will meet OPW
criteria. The required scale of study is an interpretation of the expected
degree of detail OPW would require for a consent application, in relation to
the other proposed crossings.
Minor Impact. The
route does not cross any rivers along this section.
Minor Adverse Impact. The
route crosses an unclassified tributary of the Sullane (River Bohill). There is
no change to the existing flood risk.
Major Adverse Impact. The
route crosses the River Finnow, classified as a Class A water. Crossing this
river is unlikely to have a permanent impact, such that it loses its Class A
water status, although the construction process may have a temporary affect on
water quality. It also crosses the unclassified Dangansallagh river four times,
and one of its tributaries, also an unclassified river. This is a tributary of
the Finnow, and is known to be a spawning and nursery ground for salmonid
species. Given appropriate design, the increased flood risk is considered to be
localised and limited.
Major Adverse Impact. The
route crosses the River Foherish, classified as a Class A water. Crossing this river
is unlikely to have a permanent impact, such that it loses its Class A water
status, although the construction process may have a temporary effect on water
quality. The route also crosses two unclassified tributaries of the Foherish
and four of the Sullane, resulting in a minor impact on those rivers. There is
likely to be a moderate increase in water level upstream, but given appropriate
design, the increased flood risk is considered to be localised and limited.
Major Adverse Impact. The
route crosses the River Laney which has Class A water quality. Construction
impacts may cause temporary impacts on the river. This section also crosses the
unclassified Clashavoon Stream, two minor unclassified tributaries of this
river, and an unclassified tributary of the Sullane, having a minor adverse
impact on the water quality of each. Localised and limited rises in flood risk
can be expected.
Moderate Adverse Impact. The
route crosses the unclassified Glashagarriff River, and also crosses two more
unclassified Lee tributaries, resulting in a minor adverse impact on all. The
route also crosses the Inishcarra reservoir between Fergus and Ballineadig. The
Inishcarra Reservoir is a major potable water source for the Cork County.
Crossing the reservoir may have a temporary effect on Inishcarra’s role as
potable water source, resulting in a moderate adverse effect. There may be a
very small impact on reservoir water levels, which may cause a limited increase
in flooding risk to agricultural land. Localised and limited rises in flood
risk can be expected elsewhere.
Major Adverse Impact. The
route crosses the River Bride, which is a Class A river for this stretch. There
is the potential for an increased flood risk to a small number of properties
adjacent to the River Bride.
No Impact. The route does not cross any
rivers along this section.
Minor Adverse Impact. The
route crosses a minor, unclassified tributary of the Sullane River (River
Bohill), potentially affecting water quality. There is no change to existing
flood risk.
Minor Adverse Impact. The route
crosses a minor, unclassified tributary of the Sullane River, potentially
affecting water quality. There is no change to existing flood risk.
Major Adverse Impact. The
route runs alongside the Sullane River for approximately 4km. It is possible
that there would be an increase in the potential for pollution of the watercourse
due to accidental spillage, and road run-off, resulting in an overall
cumulative decrease in water quality. However, this is unlikely given that the
new road would incorporate features such as oil interceptors and drainage
ditches, to protect the quality of the receiving water. The existing N22
already runs alongside this stretch of river, and does not incorporate water
pollution protection measures, so that the potential pollution of the Sullane
may decrease.
The route also crosses the Class A Foherish River,
and three unclassified tributaries of the Sullane. The effect on flood risk on the River Foherish and the River
Sullane due to the crossings is expected to be limited, but could affect a wide
area.
Minor Adverse Impact. The
route crosses 5 unclassified tributaries of the Sullane. There is no change to
existing flood risk.
No Impact. The route does not cross any
rivers along this section.
Major Adverse Impact. The
route runs alongside the Sullane River for approximately 1km, as does the
existing N22. However, the incorporation of pollution control measures in the
new route may reduce the potential for pollution to the Sullane. The route also
crosses the River Laney which is of Class A water quality, and an unclassified
tributary of the reservoir. There is no change to existing flood risk.
Major Adverse Impact. The
route crosses the Sullane River, a Class A waterbody in addition to an
unclassified tributary of the Carrigadrohid Reservoir. It also crosses the
Carrigadrohid Reservoir, and runs alongside the reservoir for approximately
4km. The route may bring about localised and limited changes to the flood risk
to agricultural land.
Major Adverse Impact. The
route crosses the River Cummer/Buingea classified as Class A water quality in
addition to an unclassified tributary of the River Bride which is likely to
have an important function as salmonid spawning habitat. The water level change
may bring about a localised and limited change to the flood risk to
agricultural land.
Major Adverse Impact. The road
runs alongside the Bride for approximately 4km, (as does the existing N22), for
which length the water quality is classified as Class A. Incorporation of
pollution minimisation mechanisms such as oil interceptors and drainage ditches
in the new route may reduce the potential for pollution to the river, as there
are no water pollution control measures in the existing N22.
The route also crosses six unclassified tributaries
of the River Bride. The Bride is the most important salmonid fishery in the
region, and it and its tributaries provide salmonid nursery and spawning habitat.
The combined increase in water level resulting from these crossings, and in
particular the long lengths of embankment within the Bride floodplain, could
potentially contribute to a small, but widespread increase in flood risk to
agricultural land and a small number of properties.
No Impact. The route does not cross any
rivers along this section.
Major Adverse Impact. The route
crosses the River Bride, which is a Class A river for this stretch. There is the
potential for an increased flood risk to a small number of properties adjacent
to the River Bride.
Major Adverse Impact. The
route crosses the River Laney which is of Class A water quality. There is the
potential for an increased flood risk to one property.
Moderate Adverse Impact. The
route crosses two unclassified tributaries of the River Lee. One of these, the
Kame River is a spawning ground for salmonid species. The route runs alongside
its length for approximately 2.5km. The route also crosses the Carrigadrohid
Reservoir, a source of potable water.
Localised and limited increases in flood risk can be expected along the
route, with 2-3 houses potentially affected.
Minor Adverse Impact. The
route crosses 4 unclassified minor tributaries of the River Lee. There may be
localised and limited increase in flood risk for agricultural land.
Moderate Adverse Impact. The
route crosses one unclassified tributary of the Carrigadrohid Reservoir, and
three of the River Bride. The Bride tributaries are part of the Bride system
noted for important salmonid species.
The route also has a major crossing of the Carrigadrohid Reservoir, and
passes close to the reservoir for around 400m. It may be within the flood
storage area of the reservoir over some of this length. Increases in flood risk
would be limited, possibly affecting one property and localised agricultural
areas.
Moderate Adverse Impact. The
route crosses two unclassified tributaries of the River Bride. The Bride is the
most important salmonid river in the region with tributaries providing salmonid
nursery and spawning habitat. There would be no change to the existing flood
risk.
Major Adverse Impact. The
route crosses the River Bride twice. The first crossing is just downstream of
the point at which its water quality is classified as Class B/C. The second is
in the vicinity of Kilcrea, where water quality is classified as Class A. The route also crosses seven unclassified
tributaries of the Bride, which are likely to provide salmonid spawning and
nursery habitats. There is the potential for flooding problems to be exacerbated
at Crookstown, and a few other properties in the area could be affected by
river crossings.
Minor Adverse Impact. The
route does not cross any rivers along this section. However, it lies adjacent
to the River Bride and may have a minor effect on flood levels over a limited
area
Major
Adverse Impact. This link crosses the Rivers Foherish once and
the River Finnow twice, both of which are classified as having Class A water
quality. The route also crosses two unclassified minor tributaries of the
Sullane River. There is the potential for minor increases in flood risk
affecting agricultural areas.
Moderate Adverse Impact. This
link crosses the Inishcarra reservoir, which is a major source of potable water
for Cork County. During the construction process there may be a temporary
impact on the reservoir as a potable water source. There may also be a
temporary impact on the ESB salmon smolt rearing unit, situated downstream of
the route at Carrigadrohid. The link also crosses the unclassified Kame River
which is known to be a spawning ground for salmonid species, a tributary of the
River Lee. There may be an increased localised and limited flood risk for
agricultural land.
Major Adverse Impact. This
link crosses the Cummer/Buingea River, which is classified as having Class A
water quality. The route also crosses an unclassified tributary of the River
Bride twice. The Buingea River crossing has potential for flooding of
properties.
No Impact. The route crosses no rivers
along this section
Since the majority of rivers in the study area are
Class A, any permanent changes to the classification of water quality of any of
these waterbodies would be a severe impact. While this scale of contamination
is not generally expected to result from the operation of the road, providing
that suitable mitigation measures are installed, there may be a temporary
impact on water quality. This may result from construction or an accidental
pollution incident, either prior to installation of mitigation measures, or of
a greater magnitude than for which the mitigation measures are designed. The
pollution impacts of road runoff, such as heavy metals, oil & diesel and
particulates are cumulative with other developments within each catchment and
should be minimised as far as practicable.
The Office of Public Works (OPW), through the
consent process, would control the acceptability of changes to flood risk.
While increases in risk should be minimised, they are most concerned with any
increase in risk to existing infrastructure. Provided culverts and bridges can
pass the appropriate flows (25 year in rural areas and 100 year in urban areas
or areas with houses), with at least 300mm freeboard, minor increases in flood
level in rural areas are likely to be acceptable.
The OPW in their role as Statutory Authority is
responsible for arterial drainage in Ireland.
Under the 1945 Arterial Drainage Act, the OPW were given a supervisory
role in relation to the construction of river bridges and culverts. The act states that no body
“……shall
construct any new bridge or alter, reconstruct or restore any existing bridge
over any watercourses without the consent of the Commissioners…..”.
OPW consent does not confer permission to construct
and does not absolve the developer from fulfilling any other legal obligations
or any third party claims that might arise from the project. Thus, OPW consent requirements should be
regarded as minimum requirements.
OPW consent is usually sought at the detailed
design phase of a project.
The following is a summary of the OPW’s assessment
criteria and design standards:-
·
An appropriate design
flood standard must be selected (i.e. 100 year for urban areas or where
developments are involved; 25 year for rural areas or where developments are
not involved).
·
0.3 m freeboard is
required for bridges (i.e. the bridge soffit must be at least 0.3 m higher than
the design flood level).
·
The structure should
not significantly increase the risk of flooding upstream or downstream.
·
The OPW recommend a
minimum culvert diameter of 1m to ensure accessibility for maintenance and
reduce the risk of blockages
Proposed mitigation measures would be agreed with
the OPW. A consent application would be
made for the preferred route, following further consultation with the OPW and
detailed modelling work showing the impacts on flood level and flood risk.
Modelling could quantify changes to flood level and flood risk, and assess the
sensitivity of floods to any proposed mitigation options. Modelling is likely
to be required to assess the impacts for at least some of the route options.
General mitigation measures to prevent or reduce
potential impacts relevant to all route options for both the construction and
operational phases include:
·
Appropriate design of
structures within watercourses e.g. culverts, bridges; for catchments less than
20km2, OPW locally recommends doubling design flows derived from the
Flood Studies Report methodology;
·
Minimisation of
modification of watercourses (in some locations, for example, slightly higher
flood levels may be more acceptable than disruption to fisheries);
·
Road design
incorporating agreed measures for changes in land drainage and flooding patterns;
·
Road alignment
allowing space between roads and waterbodies to minimise impacts of spillages
and maximise treatment of overland runoff;
·
Consideration of the
type of structures installed within watercourses identified as being spawning nursery
grounds to maintain fish passage;
·
Careful construction
practices e.g. timing of construction works; careful delivery, storage and
usage of materials; use of wheel washing facilities; construction of bunds
around site compounds, haul routes; and management of site drainage including
use of interceptors, settlement tanks, ponds or filters;
·
Installation of
appropriate highway drainage systems, particularly close to sensitive receptors
e.g. oil/water separators, gully pots, catchpits, sedimentation tanks, lined
storage ponds.
·
Minimisation of
embankments within the various floodplains and reservoir flood storage areas.
·
Maximisation of use
of existing floodplain storage areas by providing sufficient culverts through
road embankments.
Provided appropriate mitigation measures are taken
to prevent excessive contaminants from entering these rivers, it is not
expected that any river classification would change as a result of any of the
route options.
All of the route options are likely to produce an
increase in run-off that would contribute to an overall increase in flow rate
in the various catchments. However, these impacts are likely to be similar for
each option as roads will contribute a very small proportion of major flows.
There would be negligible or only minor adverse impacts on flood risk
downstream of crossings. Little additional land is likely to be subject to
flooding as a result of increased runoff from any of the route options.
However, the degree of care in design or mitigation
measures that would need to be taken to ensure the impacts are nil, negligible
or acceptable upstream of crossings, would be greatest for the crossings on the
River Bride and down the Finnow or Kame floodplains (see Nodes 4-5, 7b-13,
11-12 and 11-12a, Figure 3.4). The
section of route between Nodes 11 and 12 remains as the greatest potential to
contribute to a widespread increase in flood levels.
The impact of the routes on
surface waters has been considered separately for the western (Ballyvourney
–Macroom) and eastern (Macroom – Ballincollig)
sections.
For the Ballyvourney to Macroom section, between
nodes 1 and 3,the Green and the Yellow route exert the same impact on surface
waters. Between nodes 1 and 6, overall, the Yellow route exerts the least
impact, as it crosses 1 Class A river only, as opposed to 3 Class A rivers
crossed by the Green/Link1/Yellow options and 2 Class A rivers crossed by the
Green route. The Green/Link1/Yellow route is also considered to represent a
localised and limited increase to the flood risk of the Foherish River, and is
the least preferred of the three.
The routes west of Macroom, in order of preference,
are as follows:
·
Yellow (most
preferred)
·
Green
·
Green/Link1/Yellow
For the Macroom to Ballincollig section, the
Yellow, Blue, Yellow/Link4/Blue and Yellow/Link6/Blue routes all exert a
similar effect on surface water, and are least preferred. This is in part due
to the number of times these routes cross the River Bride and its tributaries.
This river is widely regarded as the most productive salmonid river of the
region, and its tributaries, even those which are small or unclassified, serve
as important spawning and nursery habitat (SWRFB pers comm). The South Western
Regional Fisheries Board have stressed the importance of this river system, and
have stated their preference that the preferred route avoids the river
altogether. These routes are also least preferred due to the potential impact
on the River Bride flood plain, and the presence of vulnerable infrastructure
near to the proposed crossings of this river. It is likely that the effects on
flood risk can be more easily mitigated on the Blue route than the Yellow or
Yellow/Link/Blue routes.
The Green and the Red routes both generally avoid
the River Bride system, except at the most easterly end of the route, where
both routes make one crossing of the river. The preferred route option for the
Macroom to Ballincollig section of the proposed road, would be the Green route,
followed by, the Green/Link3/Red route and then the Red route. Each of these
route options cross 2 Class A rivers and also cross either the Inishcarra or
Carrigadrohid reservoirs once. However, the Green/Link3/Red option crosses the
Kame River and its flood plain which is considered to represent a localised and
limited increase in flood risk. The Red route crosses the Kame River and its
floodplain close to existing infrastructure and would have a greater potential
impact in times of flood.
The routes east of Macroom, in order of preference,
are as follows:
·
Green (most
preferred)
·
Green/Link2/Red
·
Red
·
Blue
·
Yellow/Link4/Blue,
Yellow/Link6/Blue and Yellow
Cork County Council 1996. South Cork County
Development Plan
EPA 1999. Water Quality in Ireland 1995-1997