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<br />02051 <br /> <br />Potential Implications for Management <br />Objectives <br /> <br />Observations from the three study areas discussed here lead <br />to several implications for management action that could poten- <br />tially help to restore the condition of some archaeological sites. <br />First. based on ohservations relevant to question I above, large <br />areas of fluvial deposits, such as those at Palisades and Arroyo <br />Grande. form the rnos! substantial substrate on Wh1ch archaeo- <br />logical sites are located (see Hereford and others, 1996). The <br />river discharge level represented by high-elevation flood depos- <br />its such as the well.de-fined fluvial terraces at Palisades and <br />Arroyo Grande is substantially above the 1.270 m'/s (45,000 <br />ft'/s) 1996 BHBF ftow and of the 2004 ftood experiment (1,160 <br />mJ/s; 41.000 fills). In order to efTecllarge-scale restoration of <br />the fluvial terraces in these two (and other) areas. a flow level <br />comparable to or exceeding the 1921 ftood slage (4,810 m'/s, <br />or 170,000 11'/s) would likely be needed. In order 10 produce <br />the desired deposition instead of erosion. a flood of this mag- <br />nitude would also require very high sediment concentrations in <br />the f1O\v (see modeling work of Wiele and Franseen, 19(9). An <br />experimental flow of this magnitude is not currently within the <br />management considerations of the Glen Canyon Dam Adaptive <br />Management Program, and it is likely that sediment concentra- <br />tions would be too low in a flow with such high discharge to <br />have a substantial restorative effect. Were a sediment-rich. high- <br />discharge flood to occur, a large volume of new high-elevntion <br />fluvial deposits could then act as a source for aeolian sediment, <br />which could help preserve and protect archaeological sites in <br />areas dominated by aeolian sediments (such as the large dune <br />field at Lower Comanche or smaller coppice dune accumula- <br />tions that overlie f1uvia] telTace sediment at Palisades and <br />Arroyo Grande). Generating a major new fluvial deposit as a <br />source for aeolian sand is anticipated to produce a much greater <br />benefit to the condition of aeolian deposits than creating smaller <br />sources of aeolian sand by simpler methods (for example, <br />removing vegetation from selected channel-margin sand bars). <br />As discussed by previous researchers. Glen Canyon Dam <br />operations are considered to have a potentially large effect on <br />the condition of fluvial deposits (see, for example, Hereford and <br />others, 1993a). By exlension (Thompson and Potochnik, 2000). <br />the operation of the dam has the potential to affect the condition <br />of aeolian deposits as well. In contrast to fluvial and aeolian <br />sediment sources, deposition of locally derived sediment has the <br />least potential to be affected by Glen Canyon Dam operations. <br />Loca] sediment delivery occurs al the sites studied in the fonn <br />of slope-wash events, playa deposition, and distal debris-flow <br />runoff. All of these processes occur irrespective of processes <br />controlled by dam operations. It is possible. however, that the <br />deposits produced by local sedimentation events may vary in <br />their extent nnd locntion from the predam condition it~ as Her- <br />elord and others (1993) and Thompson and Potochnik (2000) <br />proposed, the base ]evel onto which local sediment is delivered <br />has been altered by dam operations. If the configuration of <br />aeolian dunes in a dune field (such as the one at Palisades) has <br /> <br />Discussion and Conclusions <br /> <br />31 <br /> <br />changed, or if a new gully has breached Ihe dune field, local <br />slope-wash events may produce additional gully incision that <br />drains to the river rather than collecting in ponded areas to pro- <br />duce the playa deposits commonly seen at Palisades. The loss of <br />]ocally derivcd sediment would have the greatest effect t:1rthest <br />from the river. where the proponion of local sediment is highest <br />(see discussion of Palisades and Arroyo Grande stratigraphic <br />sections, above). <br />With respect to (he archaeological sites investigated during <br />this work, locally derived sediment was not found to playa <br />volurnetrically significant role in site preservation relativc to <br />the protective cover provided by thicker fluvial and aeolian <br />deposits. However, this research group has observed exposures <br />in other areas of the river corridor in which aeolian and locally <br />derived (slope-wash and debris-flow) sediments interbed. such <br />that a thin cover of coarse, poorly sorted ]ocal sediment fonns <br />a resistant cap that protects more easily erodible aeolian sedi- <br />ment benealh (Heretord and others, 1996). Examples include <br />exposures at the mouths of small tributaries at river mile 60.7 <br />and at Monument Creek, river mile 93.9. By extrapolation, the <br />potential reduction in ]ocal sediment delivery that could follow <br />a reconfiguration of local drainage patterns might lead eventu- <br />ally to reduced preservation of aeolian sediment. <br /> <br />Future Research Directions <br /> <br />It is apparent from the results presented here that sedi- <br />mentary and geomorphic processes that affect archaeological <br />sit~ stability and preservation can vary widely even within a <br />relatively small area. At Lower Comanche, some cultura] fea- <br />hires face erosion because of arroyo incision, while others h,ive <br />become (or have the potential to become) unstable because <br />of dune migration processes. Treatment procedures designed <br />to mitigate erosion at archaeological sites such as these, and <br />others. depend greatly on site-specific parameters. Mitigation <br />measures that increase the preservation potential of one site may <br />be ineffective at others. To this end, the formulation of success- <br />fulmitigation strategies must depend on detailed cooperative <br />field investigations involving both archaeologists and geolo- <br />gists. <br />Sueh ajoint research approach could be lIsed to further <br />elaborate on the sequence of events that has led to the repeated <br />fluvial-subaerial 'f1ood couplet' stratigraphy described at Arroyo <br />Grande. Radiocarbon dating of charcoal and ash material in <br />many of the stratigraphic horizons that represent subaerial expo- <br />sure, both in cultural features (hearth~) and in dispersed occur- <br />rences that like]y represent grass fires, could be used to establish <br />a chronology for flood events in the western canyon. The poten- <br />tial for detailed dating \\'ork in these deposits warrants further <br />investigation, if this can be accomplished without unacceptable <br />risk to the integrity of cultural material and if the collection of <br />carbon samples from this particular area would be acceptable <br />to the Hualapai Nation. The frequency of ftood events, and of <br />burning lncidents during lnterftood times. has the potential to <br />produce a high-resolution record of flood occurrence and to c]u- <br />