FLOOD01619 - Laserfiche WebLink

Home Browse Search

I I I I I I I I I I I I I I I I I I I v-a vides. The longer the warning time, the more possibilities there are for preventing damage. Warning systems are essential for some types of flood protection and require action immediately before a flood to make it effec- tive. The cost of a flood warning system can vary from a minimal amount to a significant amount depending on the degree of sophistication desired. A system using non-recording gages and sensors and vol unteers can be very inexpensive. A sophisticated system with automatic sensors, and real time computer predictions, and flood inundation maps which can be related to the flood peak flow predicted could be quite expensive. In addition, a warning and evacuation plan must include maintenance and management of vital services (telephone, sewage, water, traffic, hospitals, and police and fire protection) before, during, and after the flood and during post flood re-occupation and recovery. The crucial feature of any flood warning system is a reliable method for transmitting the alarm to the publ ic. A method must be chosen which wi 11 be immedi ately understood by the public and not confused with other sorts of warnings. For example, use of Civil Defense sirens could be confused with other sorts of warnings. On the other hand, a warning given over radio or television stations may not be received by anyone if the flood occurs in the middle of the night. The success of a flood warning system also depends on knowledge of the exact areas that will be flooded by a flood of the predicted size. A flood warning system should be developed and implemented in the Ralston/ Leyden/Van Bibber drai nage bas in. The system chosen shoul d be based on defined needs along the drainageways and the budget available to implement the system. In the case of Ralston Creek, a warning system would need to rely on pre- cipitation gages and water level sensors located upstream of the hogback in order to provide a meaningful amount of warning time. The precipitation gages and water level sensors could be monitored by radio by the police or by a system of volunteers. In any case, it is necessary to have frequent drills to insure the adequacy of the systems operation. It would be essen- tial for the person in charge of disseminating the warnings to be cautious about false alarms since a number of false alarms can result in people ignoring future warnings. The National Weather Service provides flood warnings for localities based on the occurrence of intense rainfall cells. This sort of warning could be useful for saving lives in flash floods resulting from rainfall downstream of the hogback on Ralston Creek.