My WebLink
|
Help
|
About
|
Sign Out
Home
Browse
Search
FLOOD02685
CWCB
>
Floodplain Documents
>
Backfile
>
2001-3000
>
FLOOD02685
Metadata
Thumbnails
Annotations
Entry Properties
Last modified
1/25/2010 6:25:10 PM
Creation date
10/4/2006 11:04:31 PM
Metadata
Fields
Template:
Floodplain Documents
County
Larimer
Basin
South Platte
Title
Flood Geomorphology of Arthurs Rock Gulch: Paleoflood History
Date
1/1/1994
Prepared For
Larimer County
Prepared By
Elsevier Science Publishers
Floodplain - Doc Type
Flood Documentation Report
There are no annotations on this page.
Document management portal powered by Laserfiche WebLink 9 © 1998-2015
Laserfiche.
All rights reserved.
/
26
PDF
Print
Pages to print
Enter page numbers and/or page ranges separated by commas. For example, 1,3,5-12.
After downloading, print the document using a PDF reader (e.g. Adobe Reader).
Show annotations
View images
View plain text
<br />.. <br /> <br />, <br /> <br />C.F. Waythomas. R.D. Jarrelll Geomorphology J I (/994) /5-10 <br /> <br />'" <br />'" ~.." S/rES:J&4. .~T!S <br />WW 10 <br />>~ f-~ <br />g~ . aFBw <br /><% a +:=80 <br />"'- . " FBI <br />:nui <br />..% . ;::S2 <br />~3 . 0 cfI oFS3 <br />~- c J . Fa4 <br />=" <br />\2.. , <br />..~ ......- j <br />~% "./d_.' <br />2- . <br />,,0 , ~ '-a I <br />2" 0 <br />-- <br />x", . . ! <br /><w 0 <br />2~ 0 500 '000 1500 '''''' <br />~ <br /> OISTANCE UPSTREAM FFKJM SITE t, IN METE?S <br /> <br />Fig. 6. Maximum height ofpaleosrage indicators (PSI'3) :1bove the <br />lowest potnt;n the active channel versus distance upsue:tm t'rom site <br />I. <br /> <br />~ < <br />% 100 0 0 o - OE:lAIS ~\,.OW ~ <br />w 0 sm::s j <br />~ '0 0 0 <br />w 1 <br />.. <br />.. 60 ; <br />u: 4() 1 <br />w 1 <br />::; <br />w 0 0 <br />0: '0 .J <br />% <br />" 0 SlTEl-O 0 0 j <br />0: <br />co <br /> FBO FB' F32 FB3 FB4 AC <br />~ 0 <br />% <br />w '0 <br />" ~ <br />0: 0 <br />w 60 o - DURIS FlOW <br />.. S"''' <br />.. 0 <br />'" 4() <br />w <br />> <br />0 '0 <br />" <br />% <br />.. 0 SITE! -0 0 0 <br />i3 0 <br />::; <br /> FBO FB' Fa, Fa. FB4 AC <br />~ <br />% 0 <br />W <br />" 60 0 <br />a: 8 <br />~ <br />.. 4() <br />.J o - QEIAJS FlOW <br />" ."", 1 <br />a: 20 0 <br />" .J <br />.. <br />a: 0 <br />w 0 0 <br />0 0 0 0 0 <br />~ <br />" <br />0 <br />.. <br /> F80 FB, FB2 Fa. FB4 AC <br /> (aides!) RB..Al1VEAGE (yourrqest) <br /> Fig. 1. Selected plots of relative..age data (Ta.ble 2) used [0 differ. <br />ymbols ential:e bouldery ftood deposits in Arthurs Rock Gulch. AC is 3Clive <br /> cbanneL <br /> <br />" -",.;., <br />4 .- ' . ~ :~~;:; - <br /> <br />29 <br /> <br />1.7 m of alluvium. Three alluvial units appear in the <br />trench (Fig. 8), Unit A consists of massive orange- <br />brown silty sand to sandy silt. Wood fragments col- <br />lected from unit A (about 1.6 m depth) yielded a <br />radiocarbon age of ca. 4868 yr BP . (GX-15643, Table <br />2). Unit B is about 1.4 m thick and consists of massive. <br />slightly organic. silty sand and sandy silt with a few <br />granules and pebbles. Detrital wood and charcoal sam- <br />ples from unit B yielded radiocarbon ages of ca. 297 yr <br />BP (l.l mdepth; GX-15641; Table 2), and ca. 517 yr <br />BP (25 cm depth; GX-15640; Table 2). The radiocar- <br />bon ages indicate that a period of aggradation in. the <br />lower pan of Arthurs Rock Gulch was in progress by <br />ca. 4800 yr BP. A nonconformity of about 4500 yr BP <br />is denoted by an abrupt erosional contact separating <br />units A and B. Unit B is evidence for an interval of <br />stream alluviation that commenced at least 300 years <br />ago that we interpret as reworked colluvial sediment <br />formed by gully erosion of colluvial deposits upstream <br />from Site 5, Numerous relict gullies that expose silty <br />organic sediment are present in this pan of the basin. <br />The lack of coarse sediment in unit B indicates that it <br />probably did not form by flash flooding. Unit C consists <br />of well-sorted pebbly gravel composed of > 95% peg- <br />matite clasts. Unit C is equivalent to FB3 and records <br />at least one episode of overbank flood deposition that <br />occurred sometime after 297 yr BP. <br />FB4 deposits are present along the active channel <br />margin and consist of small clusters of imbricate boul- <br />ders and cobbles (Fig. 5a). FB4 deposits are unweath- <br />ered and are about 60 cm lower than FB3 deposits (Fig. <br />6; Table 2). <br /> <br />5.2. Sire 2 <br /> <br />Site 2 is located in the lower part of the basin about <br />0.5 Ian upstream from Site I (Fig. 2). Bouldery flood <br />deposits of different ages are present at this site, but <br />were not studied in detail. The channel lacks a straight <br />reach suitable for making hydraulic computations and <br />the PSI's are located only on the outside bend of the <br />channel. <br /> <br />. All rodioc:ubon dates given in text :l.re caJibr.u:ed to the dendro- <br />chronologie timescale according to the method ofStuiverand Reimer <br />( 1987). <br /> <br /><:;';:~:';~4h~.~..~~::'~(:;:'~ ... .:', ".; 'f"':':'::' . <br />
The URL can be used to link to this page
Your browser does not support the video tag.