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Location Name: Lookout Creek (Lower Reach cross-sections) - HJALOL

Parent: Lookout Creek - LOOKOUT

Site Description:
Spatial coordinates determined from the location of stake 001Z (downstream end), 012X, and 014X (upstream end) of Lower Lookout Creek cross-sections
Bounding Coordinates (decimal degrees):
North: 44.21565800
South: 44.21291400
East: -122.25173300
West: -122.25325300
Elevation (meters):
Minimum:   437
Maximum:   448
Landform:
The lower Lookout Creek (LOL) site consists of 14 cross sections along a 470 m long reach of 5th-order Lookout Creek located approximately 450 m upstream of the Lookout Creek gaging station. The upstream drainage area is approximately 61.5 km2, very nearly double that of the LOM site, while the average channel gradient is slightly less than half that of the LOM site at 1.5%. With an average channel width of approximately 27.3 m, however, it is only slightly wider than the LOM site (24.7 m), although the lower two-thirds of the reach is slightly wider (29.3 m).

A sharp (>90°) left bend, in which the channel has been pinched against a bedrock wall on the right bank by an alluvial fan (currently inactive) on the left bank, divides the reach into two distinct parts. In the upper part, the stream flows to the northwest, bending slightly toward the west before entering the sharp southward bend. The channel runs along the foot of a steep hillslope on the right, while the left bank is bordered by a more gently sloping surface that is probably an inactive alluvial fan. Downstream of the sharp bedrock bend, the channel abruptly widens and the stream flows nearly due south for approximately 230 m. A large, high bar, approximately 130 m long by up to 20 m wide, separates the current channel along the east bank from the former main channel (abandoned during the February 1996 flood) along the west bank. Downstream of this bar, the channel narrows and bends approximately 25° toward the west. About 90 m downstream of this second bend, the channel enters a narrow bedrock gorge just below the lowermost cross section (XS 1).

Downstream of the bedrock bend, the left (east) bank of the channel is a 4- to 6-m high terrace in which fluvial sediments (presumably older Lookout Creek sediments) unconformably overlie a debris flow deposit, which presumably originated in watershed 2 (WS 2), and varved glaciolacustrine sediments (Gottesfeld et al., 1981). Gottesfeld et al. reported a piece of wood from the debris flow deposit to have a carbon 14 date of greater than 35,500 years B.P. The stream appears to be actively eroding the terrace for approximately 200 m from the bedrock bend downstream to a bedrock projection just upstream of XS 3. On the right (west) bank downstream of the bedrock bend, a low terrace or floodplain surface approximately 1.5 to 2.5 m above the low-flow channel extends downstream from the vicinity of XS 8 to XS 1, reaching a maximum width of about 30 m. This surface is covered with old-growth conifer forest and is bordered on the west by a high terrace on which the H.J. Andrews headquarter facilities are located.

Prior to the flood of February 1996, LWD was fairly abundant within the portion of the LOL reach downstream of the bedrock bend, including a number of old-growth Douglas fir and cedar logs, which spanned the channel or projected from the banks into the channel, but most of this wood was evacuated from the reach during the flood.

The LOL site differs from the LOM site in that it is much more highly constrained by adjacent valley walls and valley floor landforms (i.e., alluvial fans and terraces), although the abrupt local widening in channel and valley floor width downstream of the sharp bend at the LOL site may cause the portion of the reach downstream of this feature to behave more like an unconstrained reach. The LOL site is downstream of numerous documented debris flows, many of which have reached Lookout Creek. One unique aspect of the LOL site is the clearing for the Andrews Forest headquarters to the northwest, which may conceivably have exacerbated windthrow in this reach, causing LWD input to be higher than it otherwise would be. Overall, the LOL site is probably more representative of "typical" 4th to 5th-order mainstem channels in the western Oregon Cascades than is the LOM reach.