CHAPTER 8: FLUVIAL PROCESSES, PATTERNS AND LANDFORMS
get through it quickly enough, leading to a back-up of water upstream. This causes flooding (much like too many people trying to get through a narrow doorway).
The weir causes a back-up of flow and flooding occurs. Disturbance of
the
riverbed by the construction of the New Quay area could have led to an increase in the river’s load, leading to deposition and flooding.
Natural factors leading to flooding in Clonmel
1. The Suir valley is very flat. The gradient falls only 15 m in a 23 km stretch between Clonmel and Carrick- on-Suir. The gradient over this reach is 1:1,500 which is extremely flat for a river flood plain.
2. Climate change has led to increased rainfall which triggers more floods.
3. The volume of water is increased due to the meeting (confluence) of the south channel and the main river channel at the town.
The combined flow of water from the two channels is funnelled through the Gashouse Bridge. The increased volume leads to flooding of the town centre, Suir Island and South Channel as the water squeezes under the bridge. When the soil and bedrock are saturated, heavy rainfall has nowhere to go except over the land and into rivers.
Fig. 50 Extent of flooding in Clonmel town centre
How can the human impact on the river be reduced? 1. Remove blockage points on the river The Office of Public Works (OPW) recommended that the Old Bridge, Cooney’s Weir and the Old Mill be removed. However, the Old Bridge is of historical importance and has not been removed. The weir has been modified to allow more water to flow over it. Removing it would damage salmon fishing in the river.