The Springfield catchment consists of numerous watercourses and drains, which connect in a complex manner to drain the overall catchment. Springfield is located to the west of the River Shannon approximately 11km downstream of the Parteen Weir. The Shannon flows in a south-south west direction. When the Ardnacrusha head race is at capacity, the excess flood flows are directed downstream via the old River Shannon where it results in overtopping of its banks and encroachment into the Springfield catchment.
A series of streams and drains lie within the Springfield area. The Illaunyregan Stream is the main watercourse in the catchment and rises west of the Ardnacrusha Head Race. It flows under the head race and then under the Errina Canal at Newtoen Loch in a south-east direction past Clonlara and the residential houses and other properties at Springfield. The Illaunyregan Stream continues further south downstream where it receives flows from the Cappavilla Stream and Cottage Stream before discharging to the River Shannon.
The Cappavilla Stream flows west to east and discharges to the Illaunyregan Stream. It has a very flat gradient and small catchment areas and there are typically very low flows in the stream. During all site visits water was observed to be standing still, including during heavy rainfall events.
The Cottage Stream flows in a westerly direction from Clonlara Golf Course where it meets and receives flows from the Springfield stream before discharging to the Illaunyregan stream. There are typically very low flows in the stream, but its acts as important connector channel between flood routes on the Shannon.
The Springfield Stream was originally a natural watercourse running from east to west through Springfield and then south to the Blackwater River. At some point in time the stream was diverted to flow in the opposite direction (west to east) to join the Cottage Stream and now operates as a drainage ditch. The stream is dry for much of the year.
There are numberous other drainage ditches located within the catchment lowlying areas, particularly south of Springfield that interconnect and drain the low lying areas. In wet winter conditions, these drains act as a conduit for flows from the Shannon to reach the Springfield area.
The proposed flood relief scheme involves the construction of a flood defence embankment across the floodplain at Springfield, the construction of a flow control structure on the Illaunyregan Stream and the provision of an over-pumping facility to be used to discharge flows from the Springfield Catchment during flood events.