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<br />w. D. White and S. G. Wells <br /> <br />Table 3 <br /> <br />Average Length of Overland Flow on Interfluves <br />within the Burnt Mesa Watersheds <br /> <br />Light <br /> <br /> Mean Overland <br /> Flow Distance <br />Location (m) <br />Headwaters 5 <br />Mid-basin 16 <br />Basin mouth 10 <br />Headwaters 10 <br />Mid-basin 12 <br />i <br />Basin mouth 8 <br />Headwaters 26 <br />Mid-basin 14 <br />Basin mouth 6 <br /> <br />Watershed <br /> <br />Burnt Mesa, Intense <br /> <br />Moderate <br /> <br />Overland flow is more effective on the hydrophobic layers. _ After the fire., <br />hydrOphobic layers were eroded and the underlying unconsolidated material <br />was available for transportation. Hydrophobic layers on steep slopes were <br />eroded by rilling as flow was concentrated into minute channels (fig ~ 5). <br />Sheetwash erosion and rilling destroyed the impervious layers on gentle and <br />steep slopes,__respectively. Fire-induc;:ed grain size reduction most likely con- <br />tributed to the supply of easily-erodible material. <br /> <br />EROSION INDEYEGET A TED ' WATERSHEDS <br /> <br />In undisturbed watersheds, the sediment supply to the fluviai systems is <br />sporadic thr9ugh time and is commonly dependent upon geomorphic events <br />which attain threshold conditions (Schumm, 1973: Scott and Williams, 1974: <br />Schick, -.1974). --Sediment sources, such as. hillsiopes and valley margins, are <br />stable over longer time periods because threshold conditiol?-s are infreque~tly <br />attained. Stress applied ~.2 'undisturbed watersheds must be of higher -magni- <br />tude than that applied to devegetate_9, watersheds if a given amount of erosion <br />is to occur. Drainage basin devegetation results in an increase of sediment <br />delivery because lower threshold conditions are required to produce and to <br />entrain sediment. in the forest-fire devegetated watersheds of the Jemez <br />Mountains, movement of sediment supplying fluvial systems has increased in <br />frequency and has become more dependent upon seasonal variations in weather- <br />ing and runoff. <br /> <br />?l1A <br />