PORTRUSH AND PORTSTEWART OUTFALLS, DEPARTMENT OF THE ENVIRONMENT FOR NORTHERN IRELAND
The Challenge
The Department of the Environment for Northern Ireland needed
to understand the effects of a new sewage disposal strategy
scheme on coastal water quality. The work was carried out in
connection with the EC Bathing Water Directive to ensure compliance
with bacteriological standards at a number of beaches in the
area.
Our Solution
An initial marine survey was carried out to establish the
hydrodynamic characteristics of the area, which are affected
by the presence of an amphidromic point (a location with no
tidal range at all) close to Portrush. Detailed measurements
of tidal elevation were taken at a number of locations along
the coast, revealing a complex tidal regime in the area.
We also measured the current at a number of offshore locations.
The results showed currents affected by the proximity of a
large estuary, a group of islands close to the shore and the
rapidly varying bed profile in the area. Bathymetric surveying
was also carried out to obtain detailed information on sea
bed profiles in the area of the main existing outfall. We also
scanned, georegistered and reprojected a large number of Admiralty
charts so that they could be digitized into our GIS ; the contours
were used to create a grid of depths that could be used in
the wave refraction model to assess effluent movement and deposition.
We were able to confirm the suitability of the recommended
outfall location and to provide detailed information for outfall
design.