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The mid-channel bars growth toward the surface tends to concentrate flow in the flanking channels, which in turn causes scouring of the channel bed and! or eroding of the channel banks. Bars, especially in rivers with controlled flow regimes such as the Dolores, tend to become stabilized with vegetation, which prevents them from being easily eroded and helps to trap fine materials during high flows. Braided zones resulting from mid-channel bar development usually have steeper channel gradients, and are shallower and wider than unbraided river reaches. A tally of the prominent mid-channel bars in the study area can be found in Table 10. The reach from Bradfield Bridge to Dove Creek Pump Station has approximately 0.50 bars per mile, with most of them being closer to Bradfield Bridge. The bars in this reach appear to be resulting from instabilities in the channel banks, possibly from livestock grazing or recreational use. Unstable or easily eroded channel banks allow the channel to become wider and shallower, promoting the establishment of bars. Consequently, once the bars are formed, channel bank erosion is accelerated. The reach from the Disappointment Creek confluence to the WSA boundary has the highest occurrence of mid-channel bars at one per mile. As with the first reach dis- cussed, the bars in this reach appear to have been enhanced from human related activities. However, this reach is the least confined section in the study area, and it receives a large sediment load from Disappointment Creek, both factors in mid-channel bar development. The reach within the WSA has 0.44 bars per mile, Several of these bars occur downstream from major tributaries (e.g., Spring Canyon, La Sal Creek, etc.) that deposit large sediment loads into the Dolores River. The confine- ment of the river in this reach is partially responsible for the low occurrence of mid-channel bars. Tributary bars are formed where major side canyons deposit their sediment loads when they meet Table 10, Tally of Mid-Channel Bars the Dolores River. Most of the rapids (Bull Canyon, Spring Canyon, La Sal Creek, etc.), especially in the lower part of the study area, are a result of these depositional features. Commonly, these alluvial deposits, extending out from the mouth of the side canyons, push the main stem channel against the opposite bank until it encounters bedrock. High flows in the Dolores River determine channel width and slope through these deposits (rapids). Reducing the occurrence of high flows raises the possibility that the rapids may increase in gradient and decrease in width as tributary flooding adds new debris (Howard and Dolan, 1981). A river channel is considered meandering when the sinuosity (channel length divided by straight-line down-valley distance) exceeds 1.5 (Ruhe, 1975). According to this definition the Dolores River for the entire length of the study area is considered meander- ing, with the exception of a few miles near Bradfield Bridge. Even though some of the sinuosity may be initiated and controlled by the local geologic struc- ture, meandering channels expend large amounts of energy due to the work required when water changes its direction of flow. The meander sequence in alluvial channels has been found to closely correlate to the size and discharge of the river (personal communication, Dr, L. Leopold, 1989). On the average, one meander wavelength is equivalent in length to 10-14 times the bank-full channel width. The bank-full channel width in turn is predominantly controlled by the bank-full discharge, as previously discussed. Pools are most commonly defmed as relatively deep portions of the river channel experiencing converging flow, while riffles are more shallow than pools and occur in zones of diverging flow, In any given river reach, energy loss is greater than the average over riffles and less than the average in pools. In a meandering river, riffles are typically located between successive pools at the "crossover" (or inflection) point of the thalweg (Beschta and River Reach Number River Miles Number Per Mile Bradfield Brdg. to Dove Cr. Pump Sta. g 18 0.50 Dove Cr. Pump Sta. to Disappointment Cr. g 25 0.36 Disappointment Cr. to WSA Boundary 22 22 1.00 WSA Boundary to Bedrock 14 32 0.44 28