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<br />Proposed Water Year 200S-2b06 Experimental Actions <br /> <br />6 <br /> <br />high experimental flow, there would be an increase of between 140% and 234% in <br />suspended sand export over releases that would otherwise occur under the No Action <br />(0, Topping, personal communication), For a 600,000 acre-foot month, this increase is <br />predicted to be between 216% and 390% above export under the No Action, <br /> <br />The volume of fine sediment export from Marble Canyon that occurs under the <br />Proposed Action will depend on the prior history of Paria River fine sediment <br />production, Fine sediment export volumes measured at the Grand Canyon gage will <br />depend on fine sediment production from both the Paria and Little Colorado Rivers, If <br />non-native fish suppression flows are preceded by a high experimental flow in <br />November, the net volume of fine sediment exported during the January-early April <br />fluctuations should be reduced owing to the potential for newly input fine sediment to <br />be stored along shorelines above the 20,000 cfs slage, <br /> <br />Erosion of sand bars likely will be increased when non-native fish suppression flows <br />occur in the absence of a high experimental flow. Fine sediments will not have been <br />elevated above the reach of the non-native fish suppression flows and the daily stage <br />will reach higher onto sand bars than would Record of Decision fluctuating flows, <br /> <br />Aquatic and Terrestrial Food Base <br /> <br />Alternating Low Steady and Low Fluctuating Flows <br /> <br />These releases can occur under both the No Action and Proposed Action alternatives, <br />but only with a sediment trigger in the former. Two-week periods of these flows are not <br />likely long enough to produce measurable differences in the biomass or growth of <br />aquatic or terrestrial food base species, There likely will be measurable differences <br />between the two flow regimes in the physical environments of near shore habitats <br />occupied by rearing native fish, and there will be an added benefit under the Proposed <br />Action in being able to compare these differences under both clear water and turbid <br />water conditions, <br /> <br />High Experimental Flow <br /> <br />Effects of the No Action January flow and the Proposed Action November-December <br />flow are anticipated 10 be similar, The food base along the river varies from a <br />predominately autotrophic (powered by sunlight) system in Glen Canyon to a partially <br />autotrophic or primarily allochthonous (powered by organic matter produced <br />elsewhere) system below Glen Canyon, In both reaches, drift plays a role in food <br />delivery 10 the fishery, The timing of a late fall or winter flood coincides with reduced <br />productivity and abundance associated with invertebrates (McKinney et a!. 1999, Rogers <br />et al. 2003). The short duration disturbance would have a measurable, but temporary <br />effect on the bottom-dwelling algae and invertebrate community, Silt and sand will be <br />