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11 At the anticipated level of usage of the increase in maximum flow (see Table 4), no impacts should occur to the terrestrial or aquatic resources below the dam. Sustained use of flows at the 25,000 cfs level would cause vegetation currently existing in the 20,000 to 25,000 cfs zone to show some stress from inundation. Limited use is made of this area for nesting, but the vegetation does provide substrate for insect production and for feeding of terrestrial species. Marsh habitats will be temporarily expanded as water seeps into existing backwaters and reattachment areas. Nearshore aquatic habitats will shift in location and size as the maximum flow level is increased, but this should not impact the short-term survival of individual species. No additional erosion of marsh or riparian zones is anticipated to occur. Some individuals have argued that an increase in the maximum flow constraint will lead to increased exchanges of river water with low velocity backwaters, and a corresponding change in backwater temperatures. This outcome is more easily postulated when changing from steady flow conditions. Under fluctuating flow conditions, the extent of differential backwater warming effects remains to be established. In addition, only small numbers of backwaters exist at the present time (only one in the reach near the mouth of the LCR). These backwaters are associated with reattachment bars. Once a reattachment bar is submerged, the exchange rate of water and temperature between the river and the backwater increases. Reattachment bars are normally submerged at flows of 20,000 cfs. Since these bars are submerged at 20,000 cfs, they are also submerged at 25,000 cfs. Y. CONCLUSIONS If the duration of flows between 20,000 and 25,000 cfs is at a low level, and the occurrences are infrequent, then no significant or measurable impacts would occur compared to conditions under interim flows. To the extent that impacts do occur they are not expected to be adverse. Since all canyon resources are linked to sediment, sediment is the key indicator resource. Based on the analysis by Randle, Strand, and Streifel (1993), a maximum flow criteria of 25,000 cfs does not appear to significantly increase the rate of sand transport in the Grand Canyon. Occasional flows between 20,000 and 25,000 cfs may result in minor and localized beach building and provide water to marsh habitats. With the information presently available, the increase in the up-ramping rate from 2,500 cfs/hour to 4,000 cfs/hour and the increase in maximum flow from 20,000 cfs to 25,000 cfs would not lead to long-term degradation of the gains made during interim operations for canyon resources. The final EIS preferred alternative would result in substantial benefits to canyon resources over the short and long term when compared with the no action alternative. Therefore, the final EIS preferred alternative meets the full spirit and intent of the Grand Canyon Protection Act. At the present, we see little evidence that backwater warming will be affected by the. envisioned increases in either the upramp.rate.or the maximum flow