Southwest - ValleyFloor_TellurideStreamRestoration_Final Report

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J ORIC RANGE OF VARIABILITY AS A CONTEXT FOR RESTORATION 215 diffractions from cobbles or larger material (Clement and west, where debris-flow deposits are visible in aerial photos Murray, 2007) and are more likely to demonstrate fluvial from 1953,1969,1987,and 2004,there is a surficial sequence, reworking that prevents horizontally continuous reflections.In as expected,of several deposits containing gravels and cobbles some cases, reflections from debris-flow deposits were free that fine down-valley from gravel/cobble at the north end to from the diffractions caused by large clasts and thus appeared sand/gravel at the southern end. From XSO to XS2 at the north similar to low-energy overbank deposits. The similarity of end of the wetland, the surficial sequence of coarse deposits debris-flow and overbank deposits is probably a result of sorting makes up the entire imaged sequence of 2-4m. At XS3, the and fining that occurs as debris flows move down valley and debris-flow sequence is underlain by peat and vegetated fine behave progressively more like fluvial processes (Nakamura sediments that were crossed by channels. At XS4, debris-flow et al., 2000). In cases where subdivisions within the low- or deposits comprise the upper —1.5 m. Below, pond sediments high-energy categories were possible, we noted gyttja, peat, were identified by an auger core at XS4 Q 112.5 m (Figure 2). and coarse(cobble or boulder)sediment deposits. Below that is a sequence of debris-flow or other colluvial depos- Distinct differences are apparent between deposits on the its.At XS5, recent debris-flow deposits composed of sorted sand west and east sides throughout most of the wetland(Figure 4). and gravel comprise the upper —1 m. Below is a sequence of The east side of the wetland from cross-sections XS1 to XS5 is peat,gyttja,and overbank deposits 1-2 m thick.This is underlain characterized by horizontal and laterally continuous reflections by what we interpret as poorly sorted hillslope sediment derived through the entire vertical section imaged by the GPR(Figure 4). directly from the valley wall. XS6 is different from upstream This reflection pattern is interpreted to represent stable, low cross-sections on both west and east sides of the valley, with energy environments without any fluvial reworking or channel direct inputs suggested by the alluvial fan on the east and by migration.The west side of the valley is more complex. In the dipping strata on the west. The center of XS6 has debris-flow a)GPR overview xs o ■Gyttja or massive peat . ■Debris flows and overbank deposits XS 1 ■Peat and overbank deposits ®Coarse channel or alluvial fan deposits XS 2 Flow - XS 3 y XS4 North XS 5 /S6 Not to scale Pit 24 XS401150 XS4 @112.5X54 @55 0 XS4 26 3 s b)XS4 Sg 6 245 205 155 105 SS 5 West Position(m) East Figure 4. (a)GPR surveys show distinctly different facies on the west and east sides of the Lulu City wetland.The east is dominated by peat and overbank deposits between XS1 and XS5 with no fluvial reworking. The west is vertically and laterally heterogeneous, although deposits are debris-flow dominated. GPR data have been corrected for low-frequency system noise(WOW),time-zero and topographic variations,and have had automatic gain control(AGC)and migration filters applied.(b)The GPR survey of XS4 penetrated up to 4 m on the east side of the valley.Labels at the top of the image are excavator or auger-hole identifiers.Yellow lines are to scale and represent the depth of those holes.At the bottom of the image,lines denote where XS4 crosses the Long W and Long E transects.Gray bars are areas where GPR data could not be collected.The west side of the valley is dominated by debris flows and overbank deposition.The east side is stable,non-erosional,peat and overbank deposition.This figure is available in colour online at wileyonlinelibrary.com/journal/espl Copyright©2011 John Wiley&Sons,Ltd. Earth Surf.Process.Landforins,Vol.37,209-222(2012)