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WSP12656
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Last modified
1/26/2010 4:17:10 PM
Creation date
8/6/2007 1:52:23 PM
Metadata
Fields
Template:
Water Supply Protection
File Number
8220.101.10.B
Description
Colorado River - Water Projects - Glen Canyon Dam-Lake Powell - Glen Canyon TWG
State
CO
Basin
Colorado Mainstem
Water Division
5
Date
7/1/2004
Author
Schmidt - Topping - Grams - Goeking
Title
The Degraded Reach - Rate and Pattern of Bed and Bank Adjustment of the Colorado River in the 25 km Immediately Downstream from Glen Canyon Dam - 07-01-04
Water Supply Pro - Doc Type
Report/Study
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<br />002469 <br /> <br />_~_ ~J <br /> <br />terrace and high terrace. These criteria were used to map the deposits in all of the post- <br />dam photograph series. One additional category was used on the April 1996 <br />photographs, which were taken immediately following the 1996 controlled flood of 1274 <br />m3 Is. These controlled-flood deposits were identified by their appearance as freshly <br />reworked deposits on those photographs. Collectively, the high-flow, flood-sand, and <br />controlled-flood deposits are referred to as post-dam flood deposits. <br />Many of the alluvial deposits in Glen Canyon are steeply sloping or have large <br />cutbanks. It is therefore not possible to assign these banks or slopes to a single elevation <br />category with a known formative discharge. Slopes are, therefore, mapped as a separate <br />facies with deposit level identified as the range between the adjacent deposits at the top <br />and bottom ofthe slope, respectively. <br />The suite of depositional levels identified in the post-dam period does not exist on <br />the 1952 photographs. Deposits on these photographs fall into three easily distinguished <br />categories: (1) wetted sand, interpreted to have been inundated by the peak discharge <br />preceding the photographs of 450 m3 Is, (2) bare sand reworked by that years flood of <br />3483 m3/s, and (3) vegetated terraces. To enable comparison from the pre- to post-dam <br />periods, these deposits have been classified into categories consistent with those used on <br />the post-dam photographs. The wetted sand in 1952 corresponds directly to the post-dam <br />fluctuating-flow deposits. The bare sand encompasses a much broader range of formative <br />discharges, and corresponds to both the fluctuating-flow and post-dam flood categories. <br />We identify the area of pre-dam low sand as a range including, at minimum, the area of <br />wetted sand, and at maximum, the area of wetted sand plus one-half the area of bare sand. <br />We identify the area of pre-dam high sand similarly, including, at minimum, one-half the <br />area of bare sand, and at maximum, all of the bare sand. Error bars around the midpoints <br />of the extremes indicate these ranges. All the vegetated terraces mapped in 1952 are <br />considered equivalent to the pre-dam terraces mapped on the post-dam photographs. <br />In summary, in developing a comprehensive pre- to post-dam time series, we <br />divided the fine-grained deposits into three elevation categories. The pre-dam low sand <br />and the post-damfluctuating-flow deposits correlate and are referred to as low-elevation <br /> <br />19 <br />
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