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We termed the intermediate surface as the low terrace. The low terrace is just above the elevation of the active flood plain and is lower in elevation than the cottonwood terrace. This surt:ace begins to be inundated at approximately 160 m3/s (5700 fe/s), or by the 7 yr. recurrence flood. We believe that the abandonment of this surface coincided with the significant decrease in flood magnitudes which occurred in the mid-1960s in the White-River Basin. Unlike the active flood plain, the low terrace contains mature woody riparian species such as tamarisk, Russian olive and willow (Fig. 14). This terrace is underlain by horizontally-bedded fine-grained alluvium which is well stabilized by thick, abundant riparian vegetation. This surface typically terminates abruptly at a 0.5 m high scarp, which drops to the lower flood plain. Natural levees may be present. Average Boundary And Critical Shear Stress: Average boundary shear stress in the detailed study site was calculated for discharges of 105 and 160 m3/s (3700 and 5700 fe/s), which are the discharges which just inundate the flood plain and low terrace, respectively, at twelve of the measured cross- sections. At 105 m3/s, the average shear stress exerted on the bed ranges from 5.5 to 21.6 N/m2 (Table 3) At 160 m3/s (5700 fe/s), average boundary shear stresses range from 13.1 to 27.3 N/m2. For these high discharges, we assumed that the slope of the water's surface was 0.0014 at each cross-section. Thus, mean depth is the only variable that is different in the calculations and shear stresses are highest where the mean depth was greatest. The critical shear stress necessary to entrain the median particle size was calculated for the 6 pebble counts made at 3 gravel bars in the channel within the study 21