NOTE: Dendritic is the most common drainage pattern in Ireland.
The dendritic drainage pattern may be likened to the branches on a tree, as a large number of tributaries join the stream in a random fashion (Fig. 8.2). It’s mainly found on upland areas, where the slope causes tributaries to join at an acute angle. The underlying unconsolidated material or rock can be easily eroded in all directions. The main river has the widest and deepest valley, as it has the greatest volume of water.
Fig. 8.2(a) Dendritic drainage pattern. Notice the way the streams look like the branches of a tree.
Trellis
The trellis drainage pattern displays a large number of right-angled confluences (Fig. 8.3). It can be found where folding has occurred or in places where the hardness of the rock varies. The rivers Bandon, Lee and Blackwater developed in valleys, where the softer limestone which occupied the anticlines was eroded, leaving the more resistant sandstone anticlines standing out.
Fig. 8.2(b) Dendritic drainage pattern on an OS map.
Fig. 8.3(a) Trellis drainage pattern.
Fig. 8.3(b) Trellis drainage pattern on an OS map. Notice the right-angled confluences.
