Using FIGURE 7.1, outline flood prevention methods that can be implemented to reduce the risk of flooding in this drainage basin.

7.11 A drainage basin is the total land area drained by a river and all its tributaries. It is the region enclosed by a watershed divide from which all precipitation flows into the river system. 7.12 One reason for the dendritic drainage pattern assumed by the river system is the uniform geology/rock type in the basin. 7.13 The dendritic pattern is visible in Figure 7.1 as the tributaries branch out in a tree-like manner without a preferred direction. 7.14 The drainage density at S is low. This is the case because S is located in the forested area where high interception and infiltration rates by vegetation reduce surface runoff and limit stream channel development. 7.15 The stream order of the main river (outlet to sea) is 4th order: Smallest tributaries: 1st order. Junction of two 1st order streams: 2nd order. Junction of 2nd and 1st: 3rd order. Main channel: 4th order. 7.16 (a) S 7.16 (b) There is a greater risk of flooding at S because it is at the basin outlet where the entire drainage basin contributes water, resulting in the highest peak discharge and volume. 7.16 (c) Flood prevention methods that could be implemented to reduce the risk of flooding in this drainage basin include constructing upstream dams and reservoirs to store excess water and release it gradually, building levees and embankments along the main river channel near S to contain high flows, increasing afforestation especially in the upper basin to enhance interception and infiltration reducing runoff, widening and straightening river channels to increase capacity and flow velocity, and installing flood warning systems with monitoring gauges to allow timely evacuations and preparations.