A Comparison of Hydrology and Channel Hydraulics in
Headwater Streams of the Central Oregon Cascades
Laura A.
Gordon E.
a,b
Grant ,
State University, College of Earth, Ocean, and Atmospheric Sciences, Corvallis OR;
b
b
Lewis
USDA Forest Service, Watershed Processes Group, Corvallis, OR
Observations
Introduction
Discussion
1. Geomorphology
•
Developing a quantitative framework that relates multiple
geomorphic thresholds set by the hydrograph to channel form would
be invaluable for predicting habitat quality and channel stability
under changing flow regimes
•
Surface runoff channels are distinguished from spring-fed systems by the presence of developed bed forms (i.e., steps , pools, and gravel bars), a
single-thread thalweg, infrequent wood spacing, a coarser bed, and a wider grain size range
Surface Runoff (Boulder Creek)
Spring-fed (Jack Creek)
Grain Size Distribution Comparison
100
90
80
70
60
50
40
30
20
10
0
How does the hydrologic regime
shape gravel-bed channels?
Study Site
Particle Size Distribution for Mobile Fraction
100
100
Spring-fed (Jack 1)
Spring-fed (Jack 2)
Spring-fed (Anderson 1)
Spring-fed (Anderson 2)
Surface Runoff (Boulder 1)
Surface Runoff (Boulder 2)
Surface Runoff (Boulder 3)
Surface Runoff (Canyon 1)
Surface Runoff (Canyon 2)
Spring-fed
90
90
Surface Runoff
80
80
Qb=jQβ
70
70
60
60
50
50
40
40
30
30
20
20
2. Hydraulic and cross-sectional geometries
10
10
• Spring-fed channels are wider than surface runoff channels for a given discharge
• Depth− and consequently boundary shear stress− increase more rapidly with discharge at a cross-section in surface runoff channels due to narrower
cross section width
• Channel configuration reflects a specific range of transport thresholds set by the hydrograph
0
0
10
100
Grain Size (mm)
1,000
10,000
Grain size statistics for surface runoff channels: D16=40mm, D50 =91 mm, D84=229mm;
and spring-fed channels: D16=84mm, D50=26 mm, D84=84mm
1.8
Spring-fed
Example Cross-section
0.5
Hydraulic Geometry of Surveyed Reaches
100
1.4
0.4
1.2
0.35
1
0.3
0.8
0.6
0.4
0.2
0
0
5
Station (m)
10
Surface Runoff
Example Cross-section
1.8
1.6
Elevation (m)
1.4
5.3264x0.2459
y=
R² = 0.4506
y = 16.854x1.2463
R² = 0.552
10
250
1
y = 0.3563x0.3598
R² = 0.402
y = 0.5479x0.3187
R² = 0.051
0.8
0.6
Width (Surface Runoff)
Depth (Spring-fed)
Depth (Surface Runoff)
0.1
0.1
0
5
Station (m)
0.15
0
0.001
1
0
0.2
1
10
Bankfull Discharge (m3/s)
10
100
200
150
Bedload (Surface Runoff)
Surface (Spring-fed)
0
20
40
60
80
Cumulative Percent of Dicharge
100
Bedload rating analysis following Whiting and Moog (2001) to explore relative
differences in theoretical transport regimes (j=1 and β=2.5). In spring-fed
channels, lower flows transport a relatively greater proportion of the bedload.
Bedload (Spring-fed)
1
10
100
Grain Size (mm)
1,000
10,000
Implementation of the Parker (1990) bedload transport relation for gravel
mixtures (Parker, 2013)
Motivating questions for future work:
1. How are interactions among multiple hydrologic and
geomorphic thresholds expressed in channel form?
2. Which thresholds are most sensitive to changes in the
hydrologic regime?
Spring-fed
Surface Runoff
0.01
0.1
Discharge (m3/s)
1
10
Future Work
Boundary Shear Stress vs. Q
Surface Runoff
•
y=
Flow Record Analysis: Analyze discharge records to quantify and
compare hydrologic and geomorphic thresholds
2D Flow Modeling: Examine hydraulic and geomorphic response to
varied flow and sediment regimes; test channel and habitat stability
under different climate/flow scenarios
126.28x0.496
Spring-fed
•
100
50
0
0.001
Surface (Surface Runoff)
y = 0.2113x0.496
0.05
Width (Spring-fed)
0.2
y = 0.368x0.1762
0.25
0.1
1.2
0.4
Cross-sectional depth vs. Q
0.45
Depth (m)
Elevation (m)
1.6
Spring-fed
Surface Runoff
Percent of Discharge used to Transport
Percentages of Bedload
1
Bankfull Width (m)
Bankfull Depth (m)
The Central Oregon Cascades are composed of two geologically
distinct provinces: the highly permeable, low relief High Cascades
and the resistant, deeply dissected Western Cascades (Harr, 1977;
Priest et al., 1983; Jefferson et al., 2006)
• In headwater streams of the Oregon Cascades, the flow regime dictates how often
and by how much geomorphic thresholds, like initiation of transport, are exceeded
• Because spring-fed channels are very near critical and are therefore adjusted to a
narrower range of thresholds, their bed texture and geometry could be more sensitive
to small changes in the hydrograph caused by climate change or flow regulation
• Surface runoff channels may be comparatively less sensitive to changes in the flow
regime because they are adjusted to a wider spectrum of hydrologic events
Cumulative Percent of Bedload
Channel form and organization reflect the full hydrologic regime
Percent Finer
•
•
Sarah L.
Boundary Shear Stress (τb)
aOregon
a
Hempel ,
% Finer
Abstract ID: EP53B-0831
•
y = 60.274x0.1762
0.01
0.1
Discharge (m3/s)
1
Channel topography will be modeled from total station surveys, Structure from
Motion, and LiDAR
10
3. Transport thresholds derived from the hydrograph
2.5
Surface Runoff Hydrograph with Excess Shear Stress by Grain Size
Flow Duration Curves
Spring-fed Hydrograph with Excess Shear Stress by Grain Size
2.0
(m3/s)
10
Discharge
10
1
1.5
8
6
1.0
4
0.5
1.4
1.2
Discharge (m3/s)
2.0
Spring-fed
Surface Runoff
1.5
1
0.8
1.0
0.6
0.4
0.5
2
0.1
0.0
0
1.8
1.6
12
100
Daily Q / Mean Annual Q
2.5
14
Excess Shear Stress (τb/τcDi)
Consequently, spring-fed systems with stable discharge regimes
(High Cascades) can be found within the same landscape as surface
runoff systems with more variable discharges (Western Cascades)
Excess Shear Stress (τb/τcDi)
•
• Spring-fed systems are poised very close to the critical threshold for transport of framework gravels (D50) most of the time, whereas the threshold for
motion is exceeded less frequently, but to a greater degree, in surface runoff systems
• While the two systems may accomplish similar amounts of work or transport similar amounts of sediment, differences in the distribution of work over
time lead to distinct channel morphologies and compositions
0.2
0.0
0
0.01
0
20
40
60
80
Percent of Time Flow is Equaled or Exceeded
100
Flow data from (Jeffereson et al., 2010)
Discharge
•
•
A combination of both spring-fed and surface runoff channels (12,
60-100m long reaches), located on both the wet and dry sides of the
range, were surveyed during the summer of 2013
Sites on the east side were gaged in the fall of 2012 and about 10
years of flow data exist for sites on the western side of the range
Date
Date
Equations
.
•
τb=τcDi
τb/τcD84
τb/τcD50
Boundary shear stress (τb):
𝜏𝑏 = 𝜌𝑔ℎ𝑆
Where ρ is the density of water, g is acceleration due
to gravity, h is depth and varies with discharge, and S
is bed slope
τb/τcD16
•
Discharge
τb=τcDi
Critical shear stress as a function of grain size (τcDi) is:
𝜏𝑐𝐷𝑖 = 𝜏𝑐 ∗ 𝜌𝑠 − 𝜌 𝑔𝐷𝑖
Where τc* is the critical Shields stress (τc* = 0.047), ρs is the density of
quartz, ρ is the density of water, g is acceleration due to gravity, and Di
is the diameter of the i size fraction (i = 16, 50, and 84)
τb/τcD84
•
τb/τcD50
τb/τcD16
Entrainment of the Di size fraction is likely to occur when:
𝜏𝑏
≥1
𝜏𝑐𝐷𝑖
Or when boundary shear stress equals or exceeds the critical
shear stress
Point cloud of a dry stream reach created with Structure from Motion (SfM), a digital photogrametry technique.
Total Station and SfM data sets will be merged to create a dense topographic map of the surveyed stream reach to
run a 2D flow model
References
.
• Harr RD. 1977. Water flux in soil and subsoil on a steep forested slope. Journal of Hydrology 33: 37–58.
• Jefferson A, Grant GE, Rose TP. 2006. The influence of volcanic history on groundwater patterns on the west slope of the Oregon High Cascades. Water Resources Research 42:
W12411–, DOI:12410Ð11029/12005WR004812.
• Jefferson, A, Grant, GE, Lewis, SL, Lancaster, ST, 2010. Coevolution of hydrology and topography on a basalt landscape in the Oregon Cascade Range, USA. Earth Surface
Processes and Landforms, DOI: 10.1002/esp.1976.
• Julien, PY, 1995. Erosion and sedimentation, Cambridge Univ. Press, Cambridge, England, 280 p.
• Parker, G, 1990. Surface-based bedload transport relation for gravel rivers. Journal of Hydraulic Research, 28: 417-436.
• Parker, G, 2013. 1D Sediment Transport Morphodynamics with applications to Rivers and Turbidity Currents, unpub.
• Priest GR, Woller NM, Black GL, Evans SH. 1983. Overview of the geology of the central Oregon Cascade Range. In Geology and Geothermal Resources of the Central Oregon
Cascade Range, Priest GR, Vogt BF (eds). Oregon Department of Geology and Mineral Industries: Salem, OR; 3–28.
• Whiting, PJ, and Moog, DB, 2001. The geometric, sedimentologic and hydrologic attributes of spring-dominated channels in volcanic areas. Geomoprhology, 39: 131-149.
Acknowledgements
Support for this project is provided by the Northwest Climate Science Center, US Geological Survey, and NSF.
Instrumental field assistance was graciously provided by John Hammond, Keith Jennings, Blake Inglin, Will
L’Hommedieu, Michelle Audie, Jascha Coddington, Michael Forsey, Zach Ferrie, Chris Pope, and Brandon Collins