I am currently trying to create an erosion model of the mound of Oymaagac Höyük (Samsun, Turkey) to investigate the relation between the distribution of the survey findings there collected and the potential erosion of the tell. After some bibliographic research, I decided to try two different methods:

  1. Combining the RUSLE formula with GIS tools as in Howland 2018 (Howland, M. D. et al. 2018, Quantifying the effects of erosion on archaeological sites with low-altitude aerial photography, structure from motion, and GIS: A case study from southern Jordan. JOURNAL OF ARCHAEOLOGICAL SCIENCE, 90 (Antiquity 84 2010) https://escholarship.org/uc/item/27q3f2vt);
  2. Calculating the Topographic Index with GRASS r.topidx.

As it concerns the 1st method, the Revised Universal Soil Loss Equation (RUSLE) is a mathematical model used to predict rates of soil erosion caused by rainfall and land use. I am still working on the calculation of the RUSLE factors (A=  R K LS C P, where A = average annual soil loss, R= rainfall erosivity factor K = soil erodibility factor, L = slope length factor, S = slope steepness factor, C = cover-management factor, and P = supporting practices factor). If R can be easily computed via GRASS r.usler, and L and S gained through the DEM, K is more complicated than expected, as I do not have the data necessary for the calculation of the K factor (that would be otherwise easier to calculate - GRASS r.uslek). I only have the rough archaeological description "clay loam".

Does anyone have an idea about how to correctly calculate it? 

Considering the difficulties in calculating the RUSLE factors, I decided to try with the Topographic Index (GRASS r.topidx). Assuming that topography drives the flow, the topographic index predicts the flow accumulation in topological low spots. As the slope increases, the potential of accumulation decreases. Here you can see the final result.

Does anyone know why I get negative values? I have read that I am supposed to gain only positive values (I am using high-resolution DTM - pixel size 15 cm-). And moreover, can I actually connect it with the erosion of the mound and use it to predict where the survey findings will most probably accumulate?

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4 Kommentare

  1. Anonym sagt:

    Back in the day, I used USPED, since it has a little more modelling power than RUSLE (it provides net erosion/deposition values that are easy to interpret), but is not more difficult to parametrize.

    There is a summary in the proceedings volume available here:

    https://oar.onroerenderfgoed.be/item/330


  2. Benjamin Ducke sagt:

    I have attached a PDF of my master's thesis (in German) which contains the full details.

  3. Benjamin Ducke sagt:

    Figuring out in which directions and how far material was most likely displaced would be another issue, however. You could use USPED's values as an approximation (potentially, stuff was moved from areas with high erosion to areas with high deposition values). But I think a more exact approach would be to compute flowlines and directions using other GRASS tools. You could also ask on the GRASS user mailing list.

  4. Margherita Andrea Valsecchi Gillmeister sagt: Autor

    Thank you very much for the hints and your MA thesis! I will then try to use USPED, and then try with the computation of flowlines and directions.