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

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

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

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)

Elevation Data Collection

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.

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, 20

S, 22

W, 24

N, 26

•FILL / FLOWDIRECTION / FLOWACCUMULATION•Define flow paths from the specific accumulation area (# cell)•BASIN / FLOWLENGTH

Hillside and Buffer Zone Data Points

# of points: 2998AVG PDOP: 2.68Highest: 399.0 mLowest: 382.5 mRMSE - 0.307 (XRS) - 0.526 (XR)

Surface Elevation Variability

USGS 30m DEM 30m DEM

10m DEM 3 m DEM

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

Flow Path and Catchment Area Boundary (CAB)

USGS 30m DEM

30m DEM

10m DEM 3 m DEM

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

Flow Path and CAB (3 m DEM)

TH:9m2 TH:90m2

TH:450m2 TH:900m2

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

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