ARCHIVED REPORTS_DRAFT ENVIRONMENTAL IMPACT REPORT

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seek the coldest water temperatures available along their migration route.Numerous studies have shown that fish, when presented with a range of temperatures,will seek a temperature that is preferred, and will not submit themselves to temperatures sufficiently high to cause adverse physiological effects when given options(Cherry et al. 1975; Gray et al. 1977; Biro 1998). As fish migrate upstream and begin to encounter and move into the thermal plume,temperature differences from river background become greater and they may gradually encounter unfavorably high water temperatures. These fish would either move laterally within the river channel until they encounter either more tolerable temperatures or the unaffected zone of passage along the other shoreline, or they would move higher or lower in the water column seeking more favorable temperatures. Because a zone of passage (unaffected by the effluent plume) remains along the west river margin under all conditions modeled and it is sufficiently wide(i.e., 150 feet) (Appendix F),the fish would be allowed to move laterally and continue upstream with minimal delay. Additionally,because the thermal waters of the plume are more buoyant and therefore, spread wider at the surface of the water column,they could move into deeper water and continue along more of a mid-channel migration route that would expose them to temperatures less different, or even no different, from river background. In either case, should fish swim or"drift"back toward the affected area of the plume before passing the discharge outfall, the same behavioral response would be repeated until the fish moved past the outfall. If fish were to move into the plume, exposure time would be expected to be limited based on their ability to swim rapidly. Cruising speeds (i.e.,the speed at which a fish can swim for an extended period of time) for adult chinook salmon and steelhead typically fall within 2 to 4 body lengths/second or approximately 1.5 to 3 feet/second(fps) (based on size) (Bell 1986). Adult salmonids are capable of maintaining sustained swimming velocities of up to 4.6 fps and burst speeds in excess of 20 fps,depending on water velocity and temperature(Powers and Orsborn 1990). Therefore, if fish were to move into the thermal plume,their ability to rapidly move out of the elevated water temperatures would result in short exposure time(e.g., on the order of minutes). An example of this movement tendency was documented by Becker(1973). Based on tracking studies of Chinook salmon and steelhead migration past the discharge of heated effluent in the Columbia River, it was concluded that (a)no complete thermal barrier to salmonid migration existed, (b)upstream spawning was not affected, (c) fish were capable of detecting temperature change and changing migration paths, and(d)there was no detectable difference in migration rates when water temperatures downstream of the discharge were elevated by 3.57 to 5.5°F above ambient summer water temperatures of 68°F measured upstream of the discharge. Analysis Summary At approximately 1,500 feet downstream of the discharge outfall, approximately half(i.e., 51%)of the river cross- sectional area(along the east bank river margin)would be affected by the effluent plume(Appendix F). As such, an approximate 150-foot zone of passage exists for the fish species in the west margin of the water column.As the fish move closer to the discharge,the portion of the water column(i.e., cross-sectional area)affected by the effluent plume decreases slightly. Within 450 feet of the discharge outfall,47%of the water column is affected by the plume.At 250 feet downstream of the discharge,where internal plume temperatures can show substantial differences from river background,particularly under the"worst-case"scenario(Appendix F), 59% of the river cross-section along the west margin of the river is unaffected by the plume. Based on the plume dynamics simulated within the river channel under the"worst-case"conditions, adult fish undertaking upstream spawning migrations past the WQCF discharge outfall would be presented with an adequate zone of passage during winter months. Based on results of this assessment,the discharge plume associated with build-out of the proposed project (increased capacity up to 27 mgd)has the potential to result in behavioral avoidance of elevated water temperatures within the plume of thermal water downstream from the point of discharge.Avoidance of the plume is considered to be a short-duration impediment to migration. The plume would not result in a complete barrier to migration. Based on the area of the river cross-section affected by elevated water temperatures,the unaffected EDAW Manteca WQCF and Collection System Master Plans EIR Fisheries and Aquatic Resources 4.13-22 City of Manteca