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<br />2" 19 <br /> <br />event comparing volume of sediment, areas of inundation, and maximum depths. <br />For a more complete discussion of the Cornet Creek' simulation, see SLA and <br />O'Brien (1989). <br />A second simulation of a historical event using the MUDFLOW model was <br />performed for the 1983 Rudd Creek mud flow in Davi s County, Utah. The flood <br />hydrograph and data used in the simulation wer'e developed by the U.S. Army Corps <br />of Engineers (USCOE, 1988). The criteria to be replicated was <br /> <br />1. The area of inundation. <br /> <br />2. A survl!yed volume of the mud flow deposit of approximately 84,000 yd3. <br /> <br />3. A mud flow frontal velocity on the alluv'jal fan of approximately the speed <br />that a man could walk (eyewitness account). <br /> <br />4. Observed mud flow depths that ranged from approximately 12 feet at the apex <br />of the alluvial fan to approximately 2 or 3 feet at the front. <br /> <br />The simulated maximum depths and area of inundation results shown in Figure <br />2.4 is excel'lent. The maximum simulated depth at the fan apex was 12.3 feet. <br />Mud flow velocities on the fan ranged from about 1 to 4 fps. The maximum flow <br />velocity at the fan apex was predicted to be about 20 fps. Frontal lobe depths <br />ranged from 1 to 4 feet deep depending on the spatial and temporal distribution <br />of the flow. Figure 2.5 shows the final deposit depths after flow was predicted <br />on the fan to cease. The excellent results were obtained by varying the fan <br />roughness (SLA and O'Brien, 1989). <br />A third application of the MUDFLOW model was the s'imulation of a 100'year <br />mud fl ood on Hi ko Spri ngs Wash, near Laugh 1 in, Nevada (0' Bri en and Full erton, <br />1989). <br /> <br />2.8 Hodel Sensitivity <br />The MUDFLOW model employs an explicit numerical advancement scheme, thus <br />the choice of time increment and grid size is theoretically dependent on the <br />Courant condition, which states that <br /> <br />Ce At < 1 <br />Ax <br /> <br />(2.25) <br /> <br />where Ce is the wave celerity. The celerity is the velocity of a wave relative <br />to the velocity of the flow. For small waves in shallow channels, it is defi ned <br /> <br /><<'" <br />