Castlewarden Flood Study


Client: Kildare County Council
Location: Kildare, Ireland
Value: €200,000 (Estimated)
Scope: Stage (i) to (iii) including PSDP



The culverts under the N7 were designed in accordance with Section 50 of the Arterial Drainage Act. However, throttles were placed on the culverts to limit flows to existing levels until a flood alleviation scheme could be implemented further downstream. Localised flooding of the N7 and a nearby house occurred during severe rainfall events and, in 2009, Kildare County Council commissioned JBB to assess the effect of moving the throttle on the culvert further downstream and to recommend local flood alleviation measures to protect the N7 from flooding. The culvert is located where the Slane River passes under the N7 at Castlewarden, Co. Kildare.

The scope of the overall study was as follows:

  • Investigation of the flooding mechanism through site visit and discussion with local authority staff and residents;
  • Detailed topographic survey of the culvert, river channel and floodplain area;
  • Review of existing hydrometric data the collection of new data;
  • Review of changes to the river and culvert arising from the road improvements;
  • Determination of flows during recent flood events and severity of the event;
  • Development of a HecRas model from the area upstream of the N7 crossing to the next culvert to assess the effect of moving the throttle;
  • Sizing of new culvert openings, design of floodplain area and embankments, other bank protection works;
  • Consultation with Inland Fisheries Ireland;
  • Development of a cost estimate;
  • Presentation of a report detailing the flooding mechanism, assessment of the effect of various solutions and the recommendation of the preferred solution;
  • Preparation of tender documents (new PWC).