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Table 3. Recent projects in which restoration of some component(s) of natural flow regimes has occurred or been proposed for specific ecological benefits. Location Flow component(s) Ecological purpose(s) Reference Trinity River, CA Mimic timing and magnitude of peak Rejuvenate in-channel gravel habitats; restore riparian succession; provide migration earl Barinaga 1996, flow y flows for juvenile salmon Truckee River, CA Mimic timing, magnitude, and duration Restore riparian trees, especially cottonwoods Klotz and Swanson 1997 of peak flow, and its rate of change during recession Owens River, CA Increase base flows; partially restore Restore riparian vegetation and habitat for e fishes and non-native brown trout ti Hill and Plaits in press overbank flows v na Rush Creek, CA (and other Increase minimum flows Restore riparian vegetation and habitat for waterfowl and non-native fishes LADWP 1995 tributaries to Mono Lake) Oldman River and tributaries, Increase summer flows; reduce rates of southern Alberta, Canada Rows stage decline; mimic natural flows in wet years Green River, UT Mimic timing and duration of peak flow and duration and timing of nonpeak flows; reduce rapid baseflow fluctu- ations from hydropower generation San Juan River, UT/NM Gunnison River, CO Rio Grande River, NM Pecos River, NM Colorado River, AZ na ey Ily by ns re- ms .ed an )se ids on In ta, w- ng of Bey A ng on nia sh- )n- Restore riparian vegetation (cottonwoods) Rood et al. 1995 and cold-water (trout) fisheries Recovery of endangered fish species; enhance Stanford 1994 other native fishes Mimic magnitude, timing, and duration Recovery of endangered fish species of peak flow; restore low winter baseflows Mimic magnitude, timing, and duration Recovery of endangered fish species of peak flow; mimic duration and timing of nonpeak flows Mimic timing and duration of flood- plain inundation Regulate duration and magnitude of summer irrigation releases to mimic spawning flow "spikes"; maintain minimum flows Mimic magnitude and timing Bill Williams River, AZ Mimic natural flood peak timing (proposed) and duration Pemigewasset River, NH Reduce frequency (i.e., to no more than natural frequency) of high flows during summer low-flow season; reduce rate of change between low and high flows during hydropower cycles Roanoke River, VA Restore more natural patterning of monthly flows in spring; reduce rate of change between low and high flows during hydropower cycles Ecosystem processes (e.g., nitrogen flux, microbial activity, litter decomposition) Determine spawning and habitat needs for threatened fish species Restore habitat for endangered fish species and scour riparian zone Promote establishment of native trees Enhance native Atlantic salmon recovery Increased reproduction of striped bass Kissimmee River, FL Mimic magnitude, duration, rate of Restore floodplain inundation to recover change, and timing of high- and low- wetland functions; reestablish in-channel flow periods habitats for fish and other aquatic species •J. Polos, 1997, personal communication. US Fish & Wildlife Service, Arcata, CA. bF. Pfeifer, 1997, personal communication. US Fish & Wildlife Service, Grand Junction, CO. wood trees (Klotz and Swanson 1997). Recent approaches to streamflow management Methods to estimate environmental flow requirements for rivers focus primarily on one or a few species that live in the wetted river channel. Most of these methods have the nar- row intent of establishing minimum allowable flows. The simplest make use of easily analyzed flow data, of assumptions about the regional simi- larity of rivers, and of professional b b Molles et al. 1995 Robertson 1997 Collier et al. 1997 USCOE 1996 FERC 1995 Rulifson and Manooch 1993 Toth 1995 opinions of the minimal flow needs for certain fish species (e.g., Larson 1981). A more sophisticated assessment of how changes in river flow affect aquatic habitat is provided by the Instream Flow Incremental Method- ology (IFIM; Bovee and Milhous 779 11 December 1997