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Last modified
1/25/2010 7:11:15 PM
Creation date
10/5/2006 2:50:16 AM
Metadata
Fields
Template:
Floodplain Documents
County
Jefferson
Community
Buffalo Creek
Basin
South Platte
Title
Wildfire Flood-Hazard and Watershed-Rehabilitation Monitoring
Date
1/8/1998
Prepared For
CWCB
Prepared By
USGS
Floodplain - Doc Type
Flood Mitigation/Flood Warning/Watershed Restoration
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<br />preserved in stream channels and is particularly useful in providing hydrometeorologic data for ungaged <br /> <br /> <br />basins (Jarrett, 1990, 1991). Most studies involve prehistoric floods, but the methodology also is <br /> <br /> <br />applicable to studying modern floods in remote areas. Rainfall amounts on sparsely vegetated hillslopes <br /> <br /> <br />(burned or unbumed) can be inferred from the amount of hillslope erosion (rills, gullies, and headcuts), <br /> <br /> <br />maximum size of sediments transported, and deposttional characteristics. The paleoflood rainfall <br /> <br /> <br />estimates can be compared with other sources of rainfall data (gaged, bucket survey, and radar) or they <br /> <br /> <br />can provide rainfall data when no other source exists. <br /> <br />Because of the hazards and flashy nature of floods in burned areas, peak discharges were estimated <br /> <br /> <br />using the slope-conveyance method (Barnes and Davidian, 1978) for streams in the Buffalo Creek area <br /> <br /> <br />after each rainstorm. Sites were selected primarily where bedrock is exposed across the channel. A few <br /> <br /> <br />sites were located in alluvial channels; reaches selected were relatively straight and uniform, which <br /> <br /> <br />reduces potential errors due to channel change. In such reaches, net change in total-flow area probably <br /> <br /> <br />are small for one flood, atthough sediment loads may be large. Cross section data were collected for <br /> <br /> <br />channels in burned and adjacent unbumed basins. Monitored basins range from about 0.1 km2 to the <br /> <br /> <br />total burned area of about 50 km2. The bumed area is located just upstream from the South Platte River at <br /> <br /> <br />South Platte streamflow-gaging station (06707500) shown on figure 1, which has a total drainage area of <br /> <br /> <br />6,680 km2 The flood of record is 53 m3 Is, which resutted from snowmett, since the gage was installed in <br /> <br /> <br />1904. Peak-discharge data were estimated for 75 sub-basins in the study area having different basin <br /> <br /> <br />characteristics such as vegetation cover, burn intensity, watershed aspect and slope, sediment sizes, and <br /> <br /> <br />watershed-rehabilitation measures. Onsite data also were collected for subsequent storms that produced <br /> <br /> <br />runoff. Monitoring is planned until water and sediment runoff in the burned area has returned to near- <br /> <br /> <br />normal. <br /> <br />For burned and unburned basins, data also were collected to: a.) estimate hillslope erosion; b.) estimate <br /> <br /> <br />channel agradation and degradation; c.) approximate volumes of channel and alluvial-fan depostts; and d.) <br /> <br /> <br />identify past fire and flood depostt sequences in the alluvial stratigraphy. This monitoring complements <br /> <br /> <br />sediment studies being conducted by other USGS and USFS scientists and to help validate channel <br /> <br />7 <br />
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