ATKINS

A drainage strategy was prepared for each site which identified connection points to local watercourses or to the Council’s drainage network and quantified the anticipated foul and surface water flows. The proposed surface water attenuation required for each site was determined to avoid increasing the risk of flooding in the receiving watercourses and the sewerage networks. A preliminary design was carried out for areas where it was necessary to extend and locally upgrade the Council’s existing drainage networks in order to service these sites.

The assessment identified over 5km of foul sewerage and 6.5km of surface water pipework (up to 1200mm diameter) necessary to service the 26 developments. The IR£4m total cost of the work (including surveys, design fees and contract supervision costs) was distributed amongst the developments contributing to each pipe length on a pro rata basis by flow. This approach provides incentive for future developers to attenuate surface water runoff from the sites thereby limiting the downstream impacts of these developments on existing watercourses or existing drainage networks.

All relevant data was presented on a single ‘quick reference’ plan for easy reference by Council Engineers when in discussion with potential developers. For each development the plan indicated:  

• The anticipated unrestricted flows from each site and the proposed level of surface water attenuation to be imposed by the planning authority
• Necessary extensions and upgrades to the council’s drainage networks to accommodate the new developments, including pipe routes and sizes
• The developer's contributions necessary to cover all costs to the council, including survey costs, design fees (and the cost of this assessment) and site supervision

The findings of the assessment have been used as the basis for successful funding applications under the serviced lands initiative resulting in funding grants to the Council of over €1 million.