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<br />2,14 <br /> <br />2.6 Model Limitations <br />MUOFLOW is a general i zed rout i ng model vii th the capabil it i es of simul at i ng <br />water and mud flows based on their physical processes. The representation of <br />shear stresses in the mud flow equation are empirical by nature. The viscosity <br />and yield stress relationships, and the turbulent flow Manning's equation all <br />have limitations to their application based on the assumptions inherent in their <br />deviation. <br />The momentum equation is not solved analytically with turbulent and viscous <br />flow stresses included. Rather, approximations of the stresses based on mean <br />flow properties, are employed. The empirical relationships used in calculation <br />of laminar and turbulent flow are intended to give results of a general range '" ' <br />of fl ow values, such as vel oc i ty, depth, and area of i nundat i on. Cali brat ion <br />of the model for a specifi c flood prob 1 {!m wi 11 i nvo 1 ve vary"j ng the roughness <br />values, sediment concentration, or choice of mud flow parameters. <br />The detail and accuracy of the simulation is direct~ly related to the choice <br />of a grid size. Quadrupling the detail of the grid element system may more than <br />quadrupl e the computer time requi red for a s 'j ngl e model i ng run. The time and <br />effort involved in creating a more extensive data file must be weighed against <br />the degree of modeling detail desired. <br />The physical process 1 imitations of the 11UDFLOW model are straightforward. <br />The diffusive wave model has eliminated the inertial acceleration terms from <br />the full dynamic wave equation. Unsteady phenomena such as surging are not <br />s i mul ated. Aggradation and scour, channel avul s ion, flow competence are not <br />simulated. The model assumes a rigid boundary. The model predicts average flow <br />va 1 ues, i ncl udi ng di scharge, depth, velocity, and sed im{!nt concentration between <br />nodes for a chosen time step and channel or alluvial fan reach, The model's <br />useful ness ari ses from its abil ity to accurately s i mul ate average flow propert i es <br />and general areas of inundation quickly and cost effectively. <br /> <br />2.7 Model Verification <br />Hromadka's original OHM model was verified by evalluation of the one, and <br />two,dimensional routing components separately, The diffusion wave approximation <br />to the full dynami c momentum equat i on was evaluated by compari ng the computed <br />flood depths with those of the USGS K,634 dam break model. The K,634 model <br />sol ves the full dynami c wave equat i on coupled with the cont i l1uity equation by <br />a imp 1 i cit di fference techni que and is cons i dE!red an accurate model for unsteady <br />