My WebLink
|
Help
|
About
|
Sign Out
Home
Browse
Search
FLOOD03686
CWCB
>
Floodplain Documents
>
Backfile
>
3001-4000
>
FLOOD03686
Metadata
Thumbnails
Annotations
Entry Properties
Last modified
1/25/2010 6:28:00 PM
Creation date
10/4/2006 11:56:22 PM
Metadata
Fields
Template:
Floodplain Documents
County
Statewide
Community
Nationwide
Basin
Statewide
Title
Guide for Selecting Manning's Roughness Coefficients for Natural Channels and Flood Plains
Date
4/1/1984
Prepared By
USDOT - Federal Highway Administration
Floodplain - Doc Type
Educational/Technical/Reference Information
There are no annotations on this page.
Document management portal powered by Laserfiche WebLink 9 © 1998-2015
Laserfiche.
All rights reserved.
/
16
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 />COSTA AND JARRETT-DEBRIS FLOWS <br /> <br /> <br />Figure 11. Old debris-flow levee along Red Dirt Creek tributary <br />near Toponas, Colo.. area I on Figure 3. <br /> <br />the left, and not flow onto the adjacent ground on <br />the right. <br />In many basins, old (vegetated) levees indicate <br />debris flows have occurred in the recent geologic <br />past (Figure II). Several such older levees may be <br />found along the same channel. No attempt was <br />made to date these older debris flows. The geo- <br />morphic freshness and number of older levees in- <br />dicate that debris flows would not be considered <br />unique in these, or other similar mountain basins. <br /> <br />GAGING STATION EVIDENCE <br /> <br />Gaging-station records in conjunction with up- <br />stream slope-area estimates of peak flows also can <br />be used to differentiate debris flows from water- <br />floods, even where a gaging station is located sev- <br />eral kilometers downstream from the site. The ef- <br />fects of debris flows generally are limited to <br />headwater debris fans and channels, while the ef- <br />fects of waterfloods can occur far downstream be- <br />fore attenuating. An investigation of the nearest <br />gaging-station records downstream of the affected <br />tributary may show a rise in stage signifying pas- <br />sage of the flood wave. <br />Hydrograph shape also can be used to identify <br />the occurrence of a debris flow upstream of a gaging <br />station if the debris flow temporarily dams the flow <br />of the main stream. As an example, hydrographs <br />are shown for two stations on the Crystal River in <br />the vicinity of Redstone, Colo, Figure 12 is a hy- <br />drograph of diurnal snowmelt-runoff peaks and of <br />a rainfall peak resulting from convectional showers <br />on July 21, 1951, for the Crystal River near Red- <br />stone, Colo, Note that the discharge following the <br />rain decreased to about the same as the prerunoff <br /> <br />" <br /> <br />317 <br /> <br />" <br /> <br />Q <br />Z <br />~ 40 <br />~ <br />~ <br />w <br />. <br />~ <br />~ <br />~ 35 <br />> <br />u <br />. <br />o <br />u30 <br />. <br /> <br /> <br />w <br />'" <br />c <br />< <br />325 <br />~ <br />Q <br /> <br />20 <br />19 <br /> <br />20 <br /> <br />21 <br /> <br />JULY <br /> <br />Figure 12. Hydrograph of rainfall flood for Crystal River near <br />Red:<.tone, Colo.. July 1951. <br /> <br />low-flow stage, A second hydrograph for the Crys- <br />tal River above Avalanche Creek near Redstone for <br />the same time of year in 1959 is shown in Figure 13, <br />A rainstorm upstream of the gage resulted in the <br />first rise. The discharge following the rain however, <br />decreased to less than one-half the normal baseflow <br />and then increased to more than 14 m3/s (500 ft3/s). <br />Our interpretation of this hydrograph is that a de- <br />bris flow from a small tributary upstream from the <br />gaging station temporarily dammed the Crystal Riv- <br />er. The dam was subsequently breached and the <br />sharp flood peak resulted. Because of the remole <br />location and lack of rainfall data in this mountain- <br />ous area, the amount of rain that fell on the tribu- <br />tary which generated the debris flow is unknown, <br />Hydrographs similar to Figure 13 have been incor- <br />rectly interpreted as waterfloods resulting from in- <br />tense rainfalls, Some of these peaks have been used <br />in annual flood series in flood-frequency analyses. <br />The important distinction is that the hydrograph re- <br />flecting the debris-flow dam effect has a brief drop <br />to well below the base flow before rising to the high <br />peak, <br />The temporary damming of stream channels by <br />debris flows is not an isolated phenomenon. In <br />1971, a local newspaper in Ouray, Colo., reported <br />that Oak Creek, a small tributary to the Uncom- <br />pahgre River in southwestern Colorado, dammed <br />the Uncompahgre River with large boulders and <br />debris, forming a temporary lake. In 1976, Lucky <br />Gulch, a small tributary to Sweetwater Creek, <br />dammed Sweetwater Creek with sediment and de- <br />bris, <br />
The URL can be used to link to this page
Your browser does not support the video tag.