Evaluating Simulation Models - Approach

• A suitable approach in such circumstances is to estimate process rate constants (e.g. creep diffusivity) as well as possible and to tune the remaining parameters for a “best fit” to the natural landscape.

• The most common criteria of success are whether the simulated and natural landscapes are morphologically similar.

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Examples of calibrating landscape process rates from field data include:

1) Use of cosmogenic isotopes to date rock exposure ages or to date average exposure age of sediment in alluvial channels. (e.g., Granger, D. and Kirkcher, J, 199?)

2) Use of radiocarbon dating of colluvial fills in hollows to estimate the rate of infilling and thus an effective mass wasting diffusivity. (e.g., Dietrich, W.E., and Dunne, T., Sediment budget for a small catchment in mountainous terrain, Zeitschrift fur Geomorphologie, suppl. 29, 191-206, 1978; Reneau, S.L., Dietrich, W.E., Rubin, M., Donahue, D.J., and Jull, A.J.T., Analysis of hillslope erosion rates using dated colluvial deposits, J. Geology, 97, 45-63, 1989).

3) Measurement of channel and/or slope erosion rates in badlands (Howard, A.D. and Kerby, G., 1983, Channel changes in badlands. Geological Society of America Bulletin, v. 94, p. 739752.)

4) Using radiocarbon dating of old debris flow deposits to estimate recurrence interval of debris flow events (e.g., Eaton, L.S. and McGeehin, J.P., Frequency of debris flows and their role in long term landscape evolution in the central Blue Ridge, Virginia [Abstract], Geol. Soc. America Abstr. Progr., 29(6), A-410, 1997).

5) Assembling statistics of rainfall intensity and frequency, fire recurrence probability, tree root strength, slope hydrology, and soil mechanical properties, etc. to create probabilistic and/or spatially explicit models for slope instability and debris flow generation. (Benda, L., and Dunne, T., Stochastic forcing of sediment supply to channel networks from landsliding and debris flow, Water Resources Research, 33, 2849-2863, 1997; Dietrich, W.E., Reiss, R., Hsu, M-L., and Montgomery, D.R., A process-based model for colluvial soil depth and shallow landsliding using digital elevation data, Hydrological Processes, 9, 383-400, 1995).