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Last modified
1/25/2010 6:26:54 PM
Creation date
10/4/2006 11:38:31 PM
Metadata
Fields
Template:
Floodplain Documents
County
San Miguel
Community
Telluride
Stream Name
Cornet Creek
Basin
Gunnison
Title
Flood Hazard Delineation
Date
3/1/1989
Prepared For
FEMA
Prepared By
Simons Li & Associates Inc.
Floodplain - Doc Type
Floodplain Report/Masterplan
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<br />1.6 <br /> <br />volume). Mud flow was categorized as a specific subdivision of landslide where <br />the "transporting mechanism is that of a flow having sufficient viscosity to <br />support large boulders within a matrix of smaller-sized particles." The term <br />"'1 andsl i de" refers to downslope earth movement by such mechan isms as fall i ng, <br />toppling, sliding, and spreading, and may be either wet or dry. <br />Mud flows are nonhomogeneous, nonNewton i an, unsteady flood events whose <br />fluid properties change dramatically as they flow down steep watershed channels <br />or across all uvi a 1 fans. The fl ow behavi or of a mud flow is a function of the <br />nuid matrix properties, channel geometry and roughness. The fluid matrix <br />consi sts of water and fi ne sediments. At suff'i ci ent concent.rat ion, the fi ne <br />sediments alter the properties of the fluid, including density, viscosity, and <br />yield stress. Colloidal forces between fine sediment particles give rise to the <br />nuid's nonNewtonian behavior. <br />The fluid properties of mud flows allow cobbles and boulders to be <br />transported remarkably long distances on relatively mild slopes. Noncohesive <br />sediments in suspension in general do not influence the flow characteristics as <br />long as they do not interlock and strengthen thl? mass. Research has demonstrated <br />that increasing the noncohesive sediment concentration (up to an additional 20 <br />percent volume) has little effect on the fluid matrix properties (O'Brien 'and <br />Julien, 1988). Greater than 2.0 percent noncohesive sediment concentration can <br />incur sign i fi cant momentum transfer from tile fl ow core to the boundary through <br />particle collision and interference. <br />The majority of mud flows occur in stel?p slope an?as and are the result <br />of landslides, prolonged or intense rainfall, snowmelt, or a combination t.hereof. <br />Mud flows can be t.riggered by changes in land use or watershed charact.erist.ics. <br />Infrequent but dramatic illustrations of conditions which have prompted mud <br />flows are associated with catastrophic events such as volcanic eruptions, <br />earthquakes, fi res, rockfalls, and dam fan ures. The vast majority of mud flows, <br />however, originate as rainfall-induced floods in areas of erodible geologic <br />format ions, where failure of soi 1 masses often occur in the form of small <br />landslides or slumps. In general, the propensity for a watershed t.o generate <br />mud fl ows depends on rai nfa 11 or snowmelt, geology, soils, topography, vegeta- <br />tion, and land use. <br />The depositional area for mud flows is often at the mouth of canyons where <br />the channel geometry and slopes transition from a steep, confined watercourse <br />to a relatively flat, unrestricted valley bottom. The aggradation of alluvial <br />
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