CHAPTER 8: FLUVIAL PROCESSES, PATTERNS AND LANDFORMS River capture of the River Suir
In parts of Munster and Leinster several rivers flow in a north-south direction (e.g. Rivers Barrow, Nore and Slaney). Other rivers in Munster (e.g. the River Suir) show unusual bends in their course. The Suir flows south for a distance and then suddenly turns to flow east towards the sea. The unusual drainage system of this river can be explained by looking at the processes of superimposition and river capture – a part of the ancient development of Irish rivers.
1. The ancient south-flowing (consequent) Rivers Suir and Barrow cut down and both superimposed themselves into folded rocks that had an east-west trend.
2. A young east-flowing (subsequent/tributary) stream of the Barrow flowed in an east- west trending valley. This river entered the sea at Waterford.
3. By a process of headward erosion this younger subsequent stream of the Barrow met up with the south-flowing River Suir and captured its water. This created a sudden right- angled bend in the River Suir near Clonmel.
4. The point of capture is called an elbow of capture.
5. The beheaded River Suir is now much smaller than it once was, since it has lost much of its water to the subsequent stream. It is now too small for its valley. This river is known as a misfit stream (e.g. the River Blackwater south of Cappoquin).
6. The empty part of the valley south of the elbow of capture is known as a windgap.
7. In the past, the River Suir entered the sea at Youghal. Today, due to river capture it has a longer course and reaches the sea at Waterford.
Before river capture Consequent R. Barrow Consequent R. Suir CS CS
Subsequent tributary of R. Barrow
Clonmel
A tributary of R. Suir
SS SS
Youghal Cappoquin
CS = consequent stream SS = subsequent stream
Fig. 60 Diagrams to show the course of the River Suir and River Blackwater SS SS Waterford
Present day R. Blackwater
E W
Cappoquin M
Youghal
E = elbow of capture W = windgap M = misfit stream
Clonmel Waterford After river capture Consequent R. Barrow