Dolores River Core Science Report

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An inventory would also help to expose ways to maximize the yield on the investment made in efforts to restore certain components of the riparian system. For example, well-established stands of tamarisk along channel margins would probably not respond negatively even to severe flooding. So if the desired goal of a spill were to enhance cottonwood regeneration, an understanding of the non flow-related constraints on cottonwood establishment could prompt some pre-spill investments. Mechanical removal of tamarisk followed by flooding could result in the erosion of bai~lcs and the creation of new sites for cottonwood establishment. Another advantage of having the information from an inventory is that the sites could be re-sampled following such activities to provide a quantification of the vegetative response to various activities (prescribed floods, changes in low flow, mechanical removal of undesirable species, etc.). An approach to inventorying the riparian vegetation of the Dolores River One important aspect of inventorying for the purpose of recording trends through time is to design a network of permanent plots that can be re-sampled at some set time interval or prior to and following management activities. Because riparian plant commuiuties are organized around the geomorphologic features of the channel, floodplain and terraces and are a reflection of the fluvial processes that formed and continue to influence the features, a monitoring protocol should be designed to include a full range of geomorphic settings. The reaches defined in the DRD geomorphic analysis section of this report grossly reflect valley- scale geomorphic patterns but include (in some cases) both confined and unconfined reaches. The reach of the Dolores bet~~~ees~ McPhee Da1~i aszd the Bradfield fridge is a reach characterized by an unconfined river channel that historically meandered across the entire valley bottom and supported extensive cottonwood and willow forests. The reach of the Dolores from Bradfield fridge to the Sari Miguel River is generally higher gradient than the McPhee Dam to Bradfield Bridge Reach, has a narrower valley bottom, and the channel is confined between steep canyon walls (with the exception of the reach through the Big Gypsum Valley). The Big Gypsum Valley is a wide valley with a lower gradient channel and finer textured bed and bai~lcs than the more confined, higher gradient reaches. The San Mig7rel River to the Colorado River reach of the Dolores varies considerably from narrow canyon (upstream from Gateway) to wide valley (downstream from Gateway) and canyon and alluvial reaches until the confluence of the Dolores and Colorado Rivers. A hierarchical geomorphic classification of segments, reaches, and fluvial features would be a useful orgaiuzational tool for stratifying a vegetation sampling protocol for the Dolores River. For example, classifying st~•ean~ segn~e~zts based upon some combination of valley width (degree of confinement), channel gradient, and sinuosity could be the first level in the hierarchy and would likely result in two or three characteristic segment types. The next level in the hierarchy might describe channel form at the reach scale as it is influenced by colluvial deposits adjacent to or in the channel, alluvial fans formed at tributary junctions, and constrictions and expansions that influence hydraulics and scour and deposition. The third tier in the classification could be at 52