Saturated hydraulic conductivity and its impact on simulated runoff for claypan soils

Saturated hydraulic conductivity (K-sat) is an essential parameter for understanding soil hydrology. This study evaluated the K., of in situ monoliths and intact cores and compared the results with other studies for Missouri claypan soils. These K-sat values were used as runoff-model inputs to assess the impact of K-sat variation on simulated runoff. Lateral in situ K-sat of the topsoil was determined on 250 by 500 by 230 rum deep monoliths. These values were compared with the K. of 76 by 76 mm diam. intact cores with and without bentonite to seal macropores. Mean (+/- SD) lateral in situ K-sat was 72 +/- 0.7 mm h(-1) and mean intact core K-sat without bentonite was 312 +/- 58 mm h(-1). The mean intact core K-sat without bentonite was significantly larger than the lateral in situ K-sat (P = 0.03). The lateral in situ K-sat was not different from core K-sat with bentonite (71 +/- 1.1 mm h(-1)). The intact core K-sat with bentonite differed from previous studies by 10 times. This was attributed to the variations in soil depth to claypan, macropore presence, and methodology. The impact of using an effective hydraulic conductivity (K-eff) computed from measured K-sat on intact cores without bentonite underestimated the Water Erosion Prediction Project (WEPP) simulated runoff by 28% for a measured runoff event of 40 mm. The core K-sat with bentonite was correlated with measured runoff from long-term erosion-runoff plots. A quadratic regression explained 95% of the variability between measured and simulated runoff.