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<br />could be reproduced almost exactly (lriq. 12). The maximum computed <br />depth fan apex was 12" 3 feet which c:orrelated well with the 12 foot <br />observed depth (Fig. 12). Mudflow velocities on the fan ranged <br />from 1 to 4 feet per second (about walking speed). The maximum <br />flow velocity at the fan apex was computed to be about 20 fps. <br />Frontal lobe depths ranged from 1 'to 4 feet deep depending on the <br />spatial distribution of the flow on the fan. The progression of <br />the mudflow across the fan in 1.2 minute increments is shown in <br />Fig. 13. The excellent results wen~ obtained by slightly varying <br />the fan roughness within realistic limits and using a constant <br />sediment concentration of 45 percent by volume (SLA and O'Brien, <br />1989). The choice of a uniforlll sediment concentration was <br />appropriate in this case because "the mudflow was initiated by a <br />landslide instead of a rainstorm, usually a more common cause of <br />mudflows. <br /> <br />10000 <br /> <br /> - <br /> ~----- \ <br /> --- <br />/ <br /> \ <br /> \ <br /> <br />9000 <br /> <br />8000 <br /> <br />7000 <br />,..., <br />en <br />b 6000 <br /> <br />~ <br /> <br />liJ 5000 <br />e:: <br />a: <br />o 4000 <br />en <br />- <br />o 3000 <br /> <br />2000 <br /> <br />1000 <br /> <br />o <br />o <br /> <br />50 <br /> <br />I 00 q 150 200 250 300 350 400 450 500 <br />TIME (SECONDS) <br /> <br />Figure 11. <br /> <br />J__ <br /> . <br />,-- <br />,- -- <br />'- <br />,- -- <br />,- <br />.~ <br />,- ~ <br /> - <br /> <br />~ <br /> <br />1983 Mudflow Hydrograpl1. for Rudd Creek, Davis county, <br />Utah, Developed by th,e AJ:my Corps of Engineers. <br /> <br />Three tests were employed to v,erify the FLO-2D model: (1) the <br />channel routing component for wat:e,r was compared to the HEC-2 <br />model; (2) the two-dimensional floodplain component was correlated <br />with the area of inundation predicted by the HEC-2 model for the <br />Poudre River; and (3) a simulation of an actual mudflow event at <br />Rudd Creek, Utah was conducted. The excellent correlation <br />demonstrated in all three cases support the verification of the <br />model and justify its application t,o more diverse alluvial fan and <br />urban flooding problems. <br /> <br />29 <br />