Predicting depressional storage from soil surface roughness

Runoff may be reduced by temporal water storage in depressions at the soil surface. Depressional storage is difficult to measure and is usually estima ted from some roughness index. The objective of this study was to compare t he ability of selected roughness indices to describe maximum depressional s torage (MDS). Height measurements were taken on 221 tilled soil surfaces ac ross a range of roughnesses. Maximum depressional storage was determined fr om digital elevation models (DEMs), The MDS values ranged from 0 to 13 mm. Five roughness indices were calculated Dom transects across these DEMs: ran dom roughness (RR), tortuosity (T), limiting elevation difference (LD) and slope (LS), and mean upslope depression (MUD). Regression analysis of RIDS on each of five roughness indices showed that RR best described depressiona l storage (r(2) = 0.80). Prediction of RIDS in the field based on RR has an uncertainty of +/- 3 mm (95% confidence interval). Variation was due to RR and its nonspatial nature. To improve predictions of RIDS, the spatial con figuration of the surface has to be taken into account.