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located through archival searches. These photo sites were Located in the field, and photos were <br />matched to identify geomorphic changes that have taken place in the past. <br />Fietd Mapping-Surficial Geology <br />Surficial geology of the alluvial valley in the 4 study reaches was mapped in the field in <br />July and September 1996. Maps were drawn onto a transparent mylar overlay of U.5. Bureau of <br />Reclamation 1:5000 scale air photos taken in 1993 at approximately 2000 ft3/s. The contacts <br />between map units were drawn onto mylar and labeled while viewing the photographs with a <br />stereoscope. Units were distinguished by depositional environment and material. Mapped <br />features were identified on the ground to verify and correct boundary, substrate,-and depositional <br />environment delineations. <br />The extent of the active channel, modern floodplain, and alluvial valley was identified <br />and mapped in each of the 4 study reaches (Fig. 3). The active channel was defined as the <br />approximate extent of the channel which is inundated and reworked with near annual frequency, <br />and was identified in the field from physical evidence of recent inundation. Mapping the active <br />channel occurred at baseflow discharge when the river was low. However, even at baseflow <br />conditions a large area of the active channel is inundated, and much. of the bed was not mapped. <br />Specific deposits mapped in the active channel were: talus, debris fans, gravel bars, eddy- <br />deposited sandbars, and mid-channel and channel-margin sandbars. The modern floodplain is a <br />vegetated, low-elevation terrace-like deposit adjacent to the active channel. It is higher in <br />elevation than the active channel, and. inundated less frequently. The floodplain is identified on <br />the Surficial geologic maps as vegetated channel-margin fine-grained alluvium. The alluvial <br />valley is the low-elevation valley bottom that contains the active channel and the modern <br />floodplain, as well as other higher elevation alluvial deposits which are not inundated and not <br />part of the active channel or floodplain. These deposits include: terraces, debris fans, and eolian <br />sands. More attention was given to mapping the bank-material in the active channel and <br />floodplain, than higher elevation, inactive deposits, which impact fish habitat indirectly. The <br />distribution of vegetation was mapped in the active channel and floodplain, but not on the higher <br />elevation inactive surfaces. <br />Typically inactive deposits include debris fan, terrace or eolian sand. Debris fans are <br />highly dissected and fan surfaces may include deposits of varying ages. Only 3 map units of <br />each fan were distinguished; the most recent incised channel on the debris fan surface, the main <br />~~ fan surface, and the distal portion of the fan which is inundated regularly by the river. Two <br />ten ace levels were also distinguished: an intermediate terrace level characterized by mature <br />r cottonwood forests and a hi her terrace distin <br />g guished by non-riparian vegetation and developed <br />- soils. <br />Fietd Mapping-Flow Patterns and Near-shore Substrate <br />Surface-flow patterns and shoreline substrate were mapped to permit measurement of <br />~_; ~~ relationships between discharge, areas oflow-velocity and recirculating flow, and distribution of <br />`~~~ shoreline habitats. Mapping occurred in the Surprise Canyon, Joe Hutch, and Coal Creek study <br />-, reaches on 6 occasions between 1995 and 1997.. Mapping in the Cedar Ridge reach occurred on <br />,. <br />A-4 <br />