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Descriptive River Channel Morphology The Dolores River has developed a combination of gradient, pattern, and hydraulic variables that allow it to transport water and sediment loads effiqiently (Le., with a minimum expenditure of potential energy). These fluvial features are closely interrelated and both control and respond to the expenditure of the river's energy. The Dolores River exhibits a classic concave longitudinal profile (see Figure 6), with the channel gradient decreasing from the headwaters to the mouth. This profile is, in part, the river system's means of controlling the rate at which velocity increases downstream. The concave profile is often interrupted locally where gradient steepening and lowering occurs between pools and riffles, and where bedrock outcrops or geologic formations change. River reaches are often classified according to thpir position on the longitudinal profile. Reaches at or near the headwaters typically have fewer deposi- tional features (i.e., riffles, bars, alluvial floodplains, etc.), a lower sinuosity, steeper gradients, and larger bed material, when compared to river reaches closer to the mouth. Even though the study area is located in the middle portion of the Dolores River longitudi- 3.5 nal profile, the channel morphology does exhibit some of these characteristics. As an example, Figure 15 shows a progressive increase in channel sinuosity from Bradfield Bridge to La Sal Creek. The channel gradient above the Disappoint- ment Creek confluence averages 0.4 percent while the gradient below averages 0.2 percent. A signifi- cant difference also occurs in the median bed material size (dSO)' Near the Dove Creek Pump Plant the dSO was measured at 222 mm while the average from several transects near the confluence of Disappoint- ment Creek was 60 mm. Resistance to flow in the Dolores River is caused by both skin friction and form resistance. Skin friction refers to flow resistance caused by obstruc- tions to flow, primarily bed material and vegetation. As shown in the comparison of bedload sizes above, skin friction resulting from bed material decreases downstream. At present, vegetation is not a signifi- cant contributor to the skin friction within the bank- full channel. However, under a reduced flow regime, woody vegetation will invade depositional features such as bars (Figure 16). 1: Bradfield Bridge 10 above glade point 2: Above glade point to Disappointment Creek 3: Disappointment Creek to upper WSA bound 4: Up WSA Bound to LWR WSA bound 3 2.5 ~ 'il) o ::J C Ci5 2 1.5 0.5 o 2 3 4 Figure 15, Dolores River sinuosity McPhee Dam to La Sal Creek. River Station 26