Author(s): D. Stephenson; Mr. M. Furumele
Keywords: Floods; Hazard; Risk; Rivers; Waterways
Abstract: Increasing urbanization, in particular low-cost housing along the banks of streams, is leading to increased flooding. Consequent damage and health hazards need careful consideration. This planning process should be formalized in order to decide the localities for housing and other urban development. The standard method of deciding water levels is to estimate floods from either an existing flow record or preferably by synthesising from rainfall records. The latter is preferable because the model can then account for increasing urbanization and other structural changes such as channelization, bridges, waterways and management structures. The hydrologic analysis yields the flow rates with different probabilities of exceedance and a subsequent hydraulic analysis will indicate the corresponding water levels for different recurrence intervals. The latter is also dependent on the roughness of the channels and the geometric cross-section. By coupling the hydraulic model to a GIS system, it is possible to depict the extent of the flood plains for various recurrence intervals with different colours. The risk of flooding of any locality is at plotted. The hazard of flooding is another factor to consider. That is, whether there is avoidable damage, tolerable damage, serious damage or catastrophic damage. Thus an index of different hazard levels can be obtained. The hazard index should be coupled with the risk index in order to establish a hazard-risk index which in turn should indicate the desirability of development at different distances from waterway.