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

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

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

Typical grid resolution in DEM Sources Satellite imagery Digitizing contour line GPS Laser system Resolution 100(~1)30~110~1<100 Unit mmmcm or mm High Cost and data storage

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

The study area: Fort Riley NE Kansas River NIR Image

Study Site Hillside: grass Buffer: brushes / trees

GPS Receiver Settings ModelPDOP * Operating mode Trimble XR and XRS <4.0 Uncorrected GPS & Post-processing (Differential Correction, DC) Date: March 24 th, 25 th and April 14 th 2004Date: March 24 th, 25 th and April 14 th 2004 Base station for DC: Range Control Office Station, Ft. RileyBase station for DC: Range Control Office Station, Ft. Riley PDOP * : position dilution of precisionPDOP * : position dilution of precision Accuracy: ± 50 cmAccuracy: ± 50 cm Vertical accuracy errorVertical accuracy error — a vertical control point (KF0640) — root mean square error (RMSE)

Elevation Data Collection

Method for Creating DEM Interpolation TOPOGRID in ArcInfo Grid size (m) USGS Accumulating Area (# of cell) 900 m 2 ( 1 ) 900 m 2 ( 1 ) 900 m 2 ( 9 ) 900 m 2 ( 100 ) Delineating method (Arc Workstation) D8  TOPOGRID is essentially based on a discretised thin plate spline technique and an iterative finite difference interpolation.

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)

Drainage network delineation: Eight direction (D8) model E, 2 0 S, 2 2 W, 2 4 N, 2 6 FILL / FLOWDIRECTION / FLOWACCUMULATION Define flow paths from the specific accumulation area (# cell) BASIN / FLOWLENGTH

Hillside and Buffer Zone Data Points # of points: 2998 AVG PDOP: 2.68 Highest: m Lowest: m RMSE (XRS) (XR)

Surface Elevation Variability USGS 30m DEM 30m DEM 10m DEM 3 m DEM

Highest and Lowest Elevation at the Entire Areas and within the Buffers Grid size Highest (m) Lowest (m) Difference (m) TotalBufferTotalBufferTotalBuffer USGS 30m m m m

Flow Path and Catchment Area Boundary (CAB) USGS 30m DEM 30m DEM 10m DEM 3 m DEM

Longest Flow Length & CAB Grid size# of CAB Flow length* (m) USGS 30m m m m *Flow length is the longest in the catchment boundary

Flow Path and CAB (3 m DEM) TH:9m 2 TH:90m 2 TH:450m 2 TH:900m 2

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 90m 2 (10 cells) in 3m DEM required for flow path delineation with in the buffer

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

Acknowledgements The Strategic Environmental Research Development Program (SERDP) Kansas State University Agricultural Experiment Station

Questions and Comments?

Study Site Hillside: grass Buffer: brushes / trees