In Namibia, the Ugab river cuts across titled layers of sedimentary rock as seen in this Google Maps (Links to an external site.) view.. In contrast to this main stream, the tributaries tend to flow parallel to one another in weaker layers of rock. This general pattern is best described as .

The Ugab river and its tributaries show a Trellis Drainage Pattern.

Explanation:

The name tellis comes form the Trellis structure in a garden. This is because in this drainage pattern, the tributaries enter the main river at an angle of approximately 90 degrees.

This pattern occurs when the main river cuts across hard rock, while the tributaries flow accross layers of soft rock, as it happens northwestern Namibia, where the Ugab river is located.