Geologists can study the hydraulic system of an area by focusing on either the streams or the basins in which they lie. On this page, we are most interested in the pattern of streams. A stream network carries water from surface runoff and groundwater discharge, eventually taking it to join the water from other networks on the way to the ocean. The shape and complexity of the network depends on the nature of the rock in the basin, as well as such factors as climate, vegetation, and the erosional history of the region. In general, though, most streams follow a branching pattern.
Small streams join larger ones and are, themselves, joined by even smaller streams.
The exact appearance of the branching pattern, however, varies quite a bit. This pattern develops when streams flow over rocks that are fairly uniform in their resistance to erosion. Flat-lying sedimentary rocks, or massive rocks of any kind fall into this category. Because streams can cut as easily in one place as another, their actual network pattern is the result of random flow. This stream system in Yemen, photographed from orbit, shows a very large dendritic network that carries water toward the Red Sea from the southwestern corner of the Saudi Arabian peninsula.