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Parameter Sensitivity in Hydrologic Modeling - page 26 / 163

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certain computed topographic parameters (such as longest flow path), and the inability to adjust the grid size to the dimensions of topographic land surface features (Garbrecht et al., 1999).

Miller et al. (1999) explored the effects of spatial resolution and accuracy of DEMs on hydrologic characterization using GIS. The study analyzed the area, slope, drainage density, and surface variation for watersheds ranging in size from

    • 0.0016

      km2 to 146 km2, using 2.5, 10. 30, and 40 meter DEMs. Miller et al.

  • (1999)

    noted an overall reduction in slope with increasing cell size. In Miller’s

study, both the mean and standard deviation of watershed slopes are highest for

IFSAR

DEMs

(highest

resolution

DEMs).

A

deviation implies that much of the natural surface

reduction in slope standard has been simplified to a more

continuous

smooth

surface

(Miller

et

al.,

1999).

Another observation drawn by Miller et al. (1999) is that the high resolution DEMs create more tortuous flow paths, more complex routing, and longer drainage networks. Total drainage lengths were found to be considerably different among four DEMs of different cell sizes on smaller watersheds as described by the drainage density (length/area). Mean drainage density is higher for watersheds and channels created with high resolution DEMs than for other surfaces (0.0104 m for the 2.5 m IFSAR DEM as compared to 0.0085 m for the 40 m DEM).

Miller et al. (1999) found that the high resolution IFSAR DEM provided significantly different results at small scales when compared to other surfaces, while the differences among DEMs at larger scales were reduced. The final

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