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Assessment of Flow Paths in Upland Areas and Vegetated Buffers
August 2, 2004
I.J. Kim, S.L. Hutchinson, and J.M.S. Hutchinson*
The department of Biological and Agricultural Engineering*The department of Geography
Kansas State University, Manhattan, KS
ASAE Annual Meeting 2004
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Research Background (1)
Model assumption:– Uniform overland flow– Ex) WEPP, REMM, VFSMOD
Reality:– Concentrated surface runoff in fields– Dillaha, 1986 / Fabis et al, 1993 / Dosskey, 2002
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Research Background (2)
Digital elevation model (DEM)– Calculation of hydrological attributes
• Slope, contour line, hill shade, aspect, etc• Flow path and length • LS factor
– Delineating contributing area (e.g. watershed)– Risk assessment for landscape susceptibility
30 m DEM widely used for GIS-Hydrologic model– Accessible data source (i.e., USGS 30m DEM)– Less costly
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Typical grid resolution in DEM
SourcesSatellite imagery
Digitizing contour line
GPSLaser
system
Resolution 100(~1) 30~1 10~1 <100
Unit m m m cm or mm
High Cost and data storage
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Purposes of Study
Delineating flow path networks and drainage boundaries for hillside areas and vegetated buffers
Determining a suitable grid size for parameterizing model inputs at field scale site
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The study area: Fort Riley NE
Kansas River
NIR Image
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Study Site
Hillside: grass
Buffer: brushes / trees
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GPS Receiver Settings
Model PDOP* Operating mode
Trimble XR and XRS
<4.0Uncorrected GPS &
Post-processing(Differential Correction, DC)
•Date: March 24Date: March 24thth, 25, 25thth and April 14 and April 14thth 2004 2004
•Base station for DC: Range Control Office Station, Ft. RileyBase station for DC: Range Control Office Station, Ft. Riley
•PDOPPDOP**: position dilution of precision: position dilution of precision
•Accuracy: ± 50 cmAccuracy: ± 50 cm
•Vertical accuracy errorVertical accuracy error—a vertical control point (KF0640)a vertical control point (KF0640) —root mean square error (RMSE)root mean square error (RMSE)
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Elevation Data Collection
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Method for Creating DEM
Interpolation TOPOGRID in ArcInfo
Grid size (m) USGS 30 30 10 3
Accumulating Area (# of cell)
900 m2
( 1 )900 m2
( 1 )900 m2
( 9 )900 m2 ( 100 )
Delineating method(Arc Workstation)
D8
TOPOGRID is essentially based on a discretised thin plate spline technique and an iterative finite difference interpolation.
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Limitations and Assumption
Accuracy of grid DEM is dependent on GPS accuracy Becoming overland flow to channel flow is dependent on the
contributing area (the number of cells)
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Drainage network delineation:Eight direction (D8) model
E, 20
S, 22
W, 24
N, 26
•FILL / FLOWDIRECTION / FLOWACCUMULATION•Define flow paths from the specific accumulation area (# cell)•BASIN / FLOWLENGTH
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Hillside and Buffer Zone Data Points
# of points: 2998AVG PDOP: 2.68Highest: 399.0 mLowest: 382.5 mRMSE - 0.307 (XRS) - 0.526 (XR)
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Surface Elevation Variability
USGS 30m DEM 30m DEM
10m DEM 3 m DEM
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Highest and Lowest Elevationat the Entire Areas and within the Buffers
Grid sizeHighest
(m)Lowest
(m)Difference
(m)Total Buffer Total Buffer Total Buffer
USGS 30m 399 389 387 388 8 1
30 m 399 386 384 385 15 1
10 m 399 388 384 385 15 3
3 m 399 388 382 384 17 4
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Flow Path and Catchment Area Boundary (CAB)
USGS 30m DEM
30m DEM
10m DEM 3 m DEM
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Longest Flow Length & CAB
Grid size # of CABFlow length*
(m)
USGS 30m 7 324.9
30 m 2 379.9
10 m 7 239.0
3 m 22 228.3
*Flow length is the longest in the catchment boundary
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Flow Path and CAB (3 m DEM)
TH:9m2 TH:90m2
TH:450m2 TH:900m2
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Conclusions 30m resolution should be avoided for determining flow
paths, especially in the buffer areas Grid size significantly influences flow direction,
catchment area shape, and surface terrain complexity on the hillside and buffer areas.
3m DEM provides the most detailed flow paths and catchment area boundaries
90m2 (10 cells) in 3m DEM required for flow path delineation with in the buffer
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Future Studies,,, Applying larger resolution (e.g. 1m DEM) to the area
and/or Ft. Riley
Applying advanced method to the flow direction
Evaluating effects of the flow length to hydrologic responses in a model
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Acknowledgements
The Strategic Environmental Research Development Program (SERDP)
Kansas State University Agricultural Experiment Station
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Questions and Comments?
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Study Site
Hillside: grass
Buffer: brushes / trees