Volume II - Kildare.ie

N7 Naas Road Widening & Interchanges Scheme
Upper. This flooding would be further exacerbated by the proposed scheme, and flood
attenuation measures are therefore required for these discharges. John Barry and
Partners Ltd. also examined the effects of enlarging the existing culverts on the N7 and
to develop measures to ensure that this does not exacerbate the downstream flooding
problem.
9.14.3 RECOMMENDATIONS
The surface water runoff volumes from the proposed road should be limited to that of a
Greenfield site. This will result in reduction in runoff from the current situation and
bring some relief to the hydraulics of the system. This can be achieved by the
installation of larger drainage pipes, less steep gradients, French drains, stormwater
tanks, or on-line and off-line storage ponds.
All future urban developments should incorporate flood attenuation measures that limit
stormwater runoff from the site to that of the pre-developed site.
Maintenance should be carried out on all river channels and bridges to remove all debris
and blockages. Vegetation should also be cut back in areas where the growth pattern
could lead to pronounced restrictions in flow, e.g. overhanging branches, dense
entanglements of briars.
The installation of water level recorders and rain gauges is considered essential for
monitoring of the water levels, so that a comparison of current and future water levels
can be made.
A Hydraulic model of the river system is currently being carried out in order to assess
quantitatively the benefits to be obtained from the implementation of flood prevention
measures for the area, and to design effective and optimum combinations of these
measures.
The existing culverts on the N7 should be enlarged so that they have a capacity of 1 in
100 years flood, however it is recommended to temporarily throttle flows through the
new mainline culverts at existing levels until the flood alleviation scheme is
implemented. It is felt that this option is preferable to alternative methods on the basis
that it is more cost effective, uses less land and more importantly will not compromise
the possible options for the flood alleviation scheme.
Environmental Impact Statement 164
June 2001
Volume 2