Roughness indices for estimation of depression storage capacity of tilled soil surfaces

Information on the depression storage capacity (DSC) of soil surfaces is ne eded for modelling surface runoff and erosion. However, time-consuming meas urements of the soil surface microrelief in a two-dimensional grid are nece ssary to obtain accurate estimates. Therefore, estimation of DSC from rough ness indices requiring fewer measurements is desirable. In this study a new simple and physically based roughness index was developed and tested. Thir ty-two soil surface microreliefs were determined in Danish erosion study pl ots on two sandy loam soil types, Humic Acrosol and Haplic Luvisol accordin g to the FAO soil classification. The soil treatments were: cultivated up-a nd-down the slope (black fallow), mouldboard ploughed up-and-down the slope , winter wheat (Triticum aestivum L.) drilled up-and-down the slope and win ter wheat drilled across the slope. The slope was ca. 10% for all plots. Da ta were treated initially by removing the slope after which 20 artificial s lopes (1-20%) were introduced producing 640 data sets. The DSC was calculat ed for each data set and a number of roughness indices were related to the calculated DSC. The best correlation to DSC was obtained by the newly devel oped index, mean upslope depression, MUD (R-2 = 0.86), followed by the geos tatistically based limiting elevation difference, LD, and limiting slope, L S (R-2 = 0.76), and some statistically based parameters as standard deviati on adjusted for oriented roughness up-and-down the slope (R-2 = 0.76), rand om roughness, RR (R-2 = 0.67), and standard deviation adjusted for oriented roughness both up-and-down and across the slope (R-2 = 0.62). Furthermore, MUD appeared to give less biased estimates than other indices, which overe stimated small DSC-values and underestimated larger DSC-values. Calculation s showed that the MUD index required relatively few measurements. MUD based on less than 200 surface elevation readings gave a good prediction (R-2 > 0.7) of DSC of tilled soil surfaces. (C) 1999 Elsevier Science B.V. All rig hts reserved.