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<br />OilJ'i82 <br /> <br />2 <br /> <br />flood-warning have attracted much attention and often overshadow the key <br />aesign consideration which is providing an adequate response time to a flood <br />event, The system must include a component that effectively communicates the <br />flood-warning so that meaningful mitigation action can take place. Given a <br />flood-warning, the effected population must have adequate time to take <br />appropriate action. At a minimum the response time pr'ovided should allow all <br />peop 1 e at ri sk to evacuate the fl ooded area. Th is means repeated warn i ngs <br />from a variety of reliable sources, conveying relevant information (for <br />further discussion see references 1 and 3), Beyond this minimum response <br />time, a reliable warning can provide sufficient time to take action to reduce <br />property damage. Combined with flood proofing (4) and other preflood strate- <br />gies, a significant reduction in flood damage could result. <br />The bottom line therefore is providing an adequate warning time so that <br />all preflood mitigation strategies can be effectively executed. The design of <br />the system must therefore proceed from this condition, beginning with <br />assessment of storm and runoff processes, then to selection of simulation <br />models, then to the computer system that will run the simulation models and <br />manage the data, and finally to the data collection network, If a feasible <br />system cannot be designed then the preflood plans will need to be modified, <br />but the emphasis must always be placed on implementing the best mitigation <br />strategy possible. <br /> <br />Storm and Runoff Processes <br />At the present time measured rainfall and streamflow are the essential <br />data upon which flood forecasts are based. Analysis of the historic measure- <br />ments of storm events and stream flows are the basis for determination of the <br />runoff characteristics of a watershed, Combined with basin information such <br />as topography, soil distribution, channel morphology, vegetation, and urbani- <br />zation, this analysis characterizes individual components of the runoff pro- <br />cess. These components include infiltration, soil moisture, overland flow, <br />channel flow and in some cases reservoir routing. To the extent possible the <br />behavior of as many hydrologic components should be quantified using available <br />historic data. <br />An ana 1 ys is of the meteoro 1 og i c processes shou 1 d be conducted, The <br />nature of flood producing storm events should be determined. An assessment of <br />the regional storm patterns as they relate to the affected watershed should be <br />