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<br />III. DESCRIPTION OF STUDY RIVERS <br /> <br />A. Study Rivers. The study rivers were selected on the basis of the <br />foll owi ng three criteria. Fi rst, the Federal Emergency Management Agency <br />(FEMA) requested that rivers be selected which historically have experienced <br />flash-flood type events with appreciable river-bed changes and channel <br />migration during floods. Such rivers are found typically in the western <br />United States. Second, the Committee Members wanted to include two different <br />types of ri vers:. those which are characteri zed by stabl e, confi ned channel s; <br />and those which have unstable, disturbed channels. Third, and most <br />important ly, it was necessary that adequate input i nformat i on on the study <br />rivers be available for testing the different numerical models. The input <br />data generally had to satisfy the requirements of the individual numerical <br />model s, as set forth in Chapter II. In the search for app rap ri ate study <br />ri vers whi ch sat i sfy these condit ions, vari ous regi ana I FEMA offi ces were <br />contacted, including Denton, Texas; Bothell, Washington; San Francisco, <br />California; and Denver, Colorado. After reviewing the recommended rivers, the <br />San Lorenzo River (SLR), the San Dieguito River (SDR), and the Salt River (SR) <br />were selected by the Committee. Note that these rivers had been previously <br />invest i gated usi ng movabl e-bed numeri cal model s by Corps of Engi neers (COE), <br />San Diego State University (SDSU), and Simons, Li & Associates (SLA), <br />respecti ve ly. Among these three ri vers, SLR is a channel i zed, stable, sand- <br />bed river; SDR is characterized by an unstable, disturbed, sand-bed channel <br />conditions; and SR is an unstable, gravel-bed river. Other characteristics of <br />these rivers are as follows: <br /> <br />1. San Lorenzo River. The San Lorenzo River is located in Santa Cruz County <br />in northern California, and meets the Pacific Ocean at the northern end of <br />Monterey Bay in the City of Santa Cruz, as shown in figure 1. SLR <br />historically has flooded frequently and caused substantial flood damage to the <br />City of Santa Cruz before the COE' s f1 ood-control project, which i ncl uded a <br />leveed channel, was completed in 1959. Since completion of the project, <br />sediment has accumul ated in the channel, result i ng in a loss of channel <br />capacity. A photograph of the river supplied by COE, San Francisco District, <br />taken upstream of the Water Street Bridge looking downstream, is shown in <br /> <br />31 <br />