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Regional Hydraulic
Geometry Curves of the South Umpqua Area in Southwestern Oregon
by Todd D. Kuck
The Roseburg District Bureau of Land
Management (BLM) has conducted stream surveys at gaging stations
in the South Umpqua River basin to produce regional hydraulic geometry
curves. These curves provide information to estimate bankfull discharge,
mean depth, width, and cross-sectional area at ungaged sites within
the watershed. The regional curves were developed using methodology
from Dunne and Leopold (1978) and Rosgen (1996).
Eight active gaging stations were surveyed
to develop the regional curve relating bankfull discharge to drainage
area. Drainage areas for these sites ranged from 54.4 to 456 square
miles. All of the gaging stations are maintained by the U.S Geological
Survey (USGS) or the Water Resources Division, Douglas County, Oregon
Surveys were also conducted at discontinued gaging stations and
ungaged streams where restoration activities are planned. These
four additional sites allowed us to include data from smaller streams
and were used in conjunction with data from active gaging stations
to develop the regional curves of mean depth, width, and cross-sectional
area plotted against drainage area. These relationships are therefore
based on 12 sites which range in basin area from 0.42 square miles
up to 456 square miles.
Figure 1. Regional curve for the South Umpqua Area, Oregon.
The relation
between bankfull discharge and drainage area determined for the
South Umpqua area is Qbkf
= 44.8 DA0.918 , where Qbkf
is bankfull discharge in cubic feet per second (cfs) and DA is the
drainage area in square miles. The regression equation has a correlation
coefficient (R2) of 0.85.
Figures
2, 3, and 4 show regional hydraulic geometry curves for the South
Umpqua area (and curves from other studies) for mean bankfull depth,
bankfull width, and bankfull cross-sectional area as a function
of drainage area.
The relation
between mean depth (D) in feet and drainage area (DA) in square
miles for the South Umpqua area is D = 0.9 DA0.389 (R2
= 0.97). The relation between bankfull width (W) in feet and drainage
area is W = 11.5 DA0.419 (R2 = 0.94). The relation between bankfull
cross-sectional area (A) in feet and drainage area is A =10.8 DA0.809 (R2
= 0.98.)
The slope of the regional curve for
bankfull discharge of the South Umpqua area is very similar to the
slope for the West Cascades and Puget Lowlands in Washington state
(Figure 1). The intercept for the South Umpqua area curve is, however,
slightly lower than the other Washington site. Comparing the South
Umpqua curve to those from Wyoming and Idaho shows them to be generally
higher as expected indicating higher unit discharges and larger
channel dimensions for similar watershed areas.
For the other regional curves (Figures 2, 3 & 4), slopes for
the South Umpqua area with respect to bankfull depth, width, and
cross-sectional area were generally steeper than curves from other
western U.S. regions. Unfortunately, data from Washington state
for these parameters were unavailable for direct comparison.
Figures 2, 3, and 4. South Umpqua regional hydraulic geometry
curves of mean bankfull depth, bankfull width, and bankfull cross-sectional
area as a function of drainage area, respectively.
Conclusions and Recommendations
The regional hydraulic geometry curves
of the South Umpqua River in southwestern Oregon will allow hydrologists
and others to estimate a number of bankfull characteristics based
on data from ungaged streams in the region. Since all of the curves
are estimated using drainage area, it will be relatively simple
to check expected bankfull characteristics in the field. This in
turn will facilitate interpretation and design of stream restoration
projects, assessment of stream health and future project planning.
Currently, the Roseburg District BLM
is conducting similar surveys of gaging stations in the North Umpqua
River basin. These surveys will be used to produce hydraulic geometry
relations for comparison purposes to determine if there are differences
in the two basins.
Additional data needs for the Umpqua
basin include the development of dimensionless rating curves using
stream survey and gaging station data (as described in Dunne and
Leopold, 1978) and the development of dimensionless ratios for reference
reaches by stream types (Rosgen, 1996). In addition, reestablishing
discontinued gaging stations on small streams and establishing crest-stage
gages on small streams will provide invaluable data that is currently
unavailable.
References Cited:
Castro, Janine M., 1997. Stream classification in the Pacific
Northwest: Methodologies, regional analyses, and applications.
Doctor of Philosophy thesis, Oregon State University, Corvallis,
OR.
Dunne, Thomas, and L.B. Leopold, 1978. Water in Environmental
Planning. Freeman and Co., San Francisco, CA, 818 p.
Rosgen, D.L., 1996. Applied River Morphology. Wildland Hydrology,
Pagosa Springs, CO.
USDA Forest Service, 1995. A guide to field identification of
bankfull stage in the western United States (video). Rocky Mountain
Forest and Range Experiment Station, Stream Systems Technology Center,
Fort Collins, CO.
Todd D. Kuck is a
hydrologist with the Bureau of Land Management, Roseburg District,
in Roseburg, Oregon. Tel: (541) 440-4931; e-mail: Todd_Kuck@blm.gov
Editor’s Note:
The utility of channel geometry curves has been widely recognized
by hydrologists and others as a valuable tool. At the present time,
channel geometry curves are being developed in many parts of the
United States in large part due to the influence of Dave Rosgen
and Luna Leopold.
Recently published channel geometry relationships include those
for streams in the upland Ozarks (Manner, 1999), southern California
(Azary, 1999), North Carolina (Harman et al., 1999), and the Southwest
United States (Odem and Moody, 1999). All of the above papers can
be found in: Darren S. Olsen and John P. Potyondy (Editors), 1999.
Wildland Hydrology, AWRA Specialty Conference Proceedings, June
30-July 2, 1999, Bozeman, Montana, TPS-99-3, 536 pp.
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