Laserfiche WebLink
3. TEXT CHANGES <br />TABLE 47A <br />ESTIMATED YELLOW CREEK FLOW DEPLETIONS <br />ProJax Average SeaamY Average Depktionv through <br />AMernaWe Depletloo [ 2 (%) Growing Bannon, AprO-Oat. (%) <br />(Tom/Yr) Sprig Snorer Fat WtoOer A• Years 2 Normal Years 3 Dry Years 3 <br />No Action I - - Negligtble Negligible <br />50,000 2 3 5 7 3.5 2.5 5 <br />125,000 3 5 7 10 5.0 4.0 7 <br />500,000 IS 22 30 29 24.0 18.0 36 <br />l Spring = March to luxe, summer =July to August. till =September to October, winter =November <br />to February. <br />2 Mean of all recorded years (19741982). <br />3 "Normal" years regarded as those disp4yieg c0asistent average flow measurements through the year <br />(water years I974197:i, 1979-1982); "dry" years showing coatpicuously below evetnge Oows through <br />year (19761978). <br />• The pumping rate for the No Action Alternative (Pilot Project) would be no greater dtan the 50,000 <br />TPY Alternative, but would persist for only 120 days instead of 30 years. <br />these alternatives, BLM expects no alterations in the shrub- <br />scrub wetland component. <br />The off channel wetland situated oa Yellow Crcek's <br />alluvial terrace (Table 47A) appears to be maintained by <br />surface runoff Gom adjacent uptends, independent of <br />impactod ground and surface water systems. BLM believes <br />this area would remain unaffected by minirtg-related <br />anivities. <br />Sparse aquatic and semiaquatic plant populations aPPe~ <br />in deeper pools and on stream margins and should not be <br />influenced by flow reductions associated with these <br />alternatives. Similarly, macroinvertebrate populations would <br />be subject to negligible, if any, impacts. Considering the <br />shallow rectangular profile of Yellow Creek's stream bottom, <br />average Bow reductions of 2 to S percent may cause <br />commeasurete decreases in water depth, but would not <br />modify the overall extent of wetted substrate available as <br />invertebrate habitat. <br />BLM considers these potential depletion-related impacts <br />to Yellow Creek's wetland communities functionally <br />inconsequential with respect to wildlife habitat and wetland <br />system function. <br />1.9.6.!.7 500,0007PYAlternarive <br />Groundwater pumping associated with this alternative <br />would be more likely to cause substantial changes in the <br />Yellow Creek's wetland communities, but lacking detailed <br />information on the interaction of ground and surface water <br />systems in Yellow Creek, BLM is unable to quantify such <br />impacts. Confounding impact analysis further is the fact that <br />the stream depletion model used for this alternative was <br />run having assumed all processing water would be obtained <br />from a single well. Incorporating an additional water well <br />(page 2-24 of draft EIS) at ao undetermined location could <br />drastically alter hydrologic effects. Additional analysis would <br />need to be performed before this alternative was approved. <br />Based on the model, average flows in Yellow Creek would <br />be reduced IS to 20 percent during an average growing <br />season (Table 47A), and up to 40 percent during drought <br />inBuencd years. <br />Flow reductions of this magnitude could substantially <br />reduce stream side obligate vegetation. [t is conceivable that <br />attendant changes in channel morphology (e.g., bank <br />sloughing) brought about by long-term alterations in Yellow <br />Crcek's Bow regime could augment sites available for plant <br />establishment, allowing some degree of obligate expansion <br />toward the streambed. <br />3-23 <br />