developed with GRASS5.0

Interpolation and simulation of terrain development with hedges

Helena Mitasova, Lubos Mitas, University of Illinois at Urbana-Champaign
in cooperation with Seth M. Dabney, USDA-ARS National Sedimentation Lab, Oxford, MS

1. Digital elevation model, slope and curvature

DEMs and topographic parameters were computed from field measured point data by the RST method (s.surf.rst) in GRASS5.0, at 0.4m resolution, displayed at 2x vertical exagerration

contours for 1993 and 1996
DEM with slope draped as color for 1993 and 1996
DEM with profile curvature for 1993 and 1996
Crossection of DEM for 93 (blue) and DEM for 96(red), 7x vertical exagerration, blue on top are eroded areas, red on top are areas with aggradation.

Dynamics of DEM and slope development on a tilled hillslope with hedges from 1993 - 1996

movie in mpeg format or animated gif

Notes on interpolation

2. Simulation experiments

The SIMWE model (Mitas and Mitasova 1998) was used to simulate the impact of hedges under various simplified conditions. Hedges are 3 cells (1.2m) wide located along contourline running through the 3rd site from the bottom of each profile. Red spheres show the measured elevation in 1996, green spheres show elevation in 1993 at the start of simulation. Cyan - blue is deposition, yellow-red is erosion.

Terrain and erosion/deposition pattern development for 7 steady-state events with uniform rainfall excess 36mm/hr, and Mannings n=0.2(hedge) and n=0.15(field), with elevation change proportional to predicted erosion/deposition rate.

1 2 3

Animation of terrain and erosion/deposition pattern development for all 7 events

animated gif or mpeg movie

Note, that without the smoothing effect of tillage, smaller events, wind or other phenomena between the rainfall events the model predicts development of rills, in spite of the fact that rilling is not explicitely incorporated into the model - it appears spontaneously. Closer look at the model is needed to find out whether the method really simulates (at least approximately) the development of rills or whether this is just the effect of the numerical solution of the equations governing the overland flow.

Terrain and erosion/deposition pattern for one steady-state event with uniform rainfall excess 36mm/hr and Mannings for hedge 0.2 and for the field 0.05. The four times higher Mannings for hedge (without taking into account higher infiltration) causes sharp increase in water depth within the hedge and consequent erosion ABOVE and below the hedge. In the field experiment, hay bales were placed each 9m perpedicular to the hedge to prevent the water flow along the hedge, so the predicted effect seems to be realistic.
Erosion/deposition pattern for this case, draped over terrain 1993
same as previous with variable rainfall excess - 4 times smaller in the hedge due to infiltration.
Erosion/deposition pattern for spatially variable infiltration

Note: The simplified conditions were chosen so that the impact and interaction of different properties can be studied and demonstrated.

References

Seth M. Dabney et al. 1999 Lanscape Benching from Tillage Erosion Between Grass Hedges, in press
Mitas, L., Mitasova, H., 1999, Spatial Interpolation. In: P.Longley, M.F. Goodchild, D.J. Maguire, D.W.Rhind (Eds.), Geographical Information Systems: Principles, Techniques, Management and Applications, GeoInformation International, Wiley, 481-492.
Mitas, L., Mitasova, H., 1998, Distributed erosion modeling for effective erosion prevention Water Resources Research Vol. 34, No. 3, pp. 505-516.

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