英语翻译

英语翻译
Abstract
Based on a stochastic approach,drainage in a layered soil profile with macropores waspredicted using a one-dimensional numerical flow model.Soil hydraulic functions,0(~) andK(~b),were obtained from laboratory measurements on undisturbed 100 cm 3 soil cores.The coreswere collected in 60 different locations for each of three soil horizons along a 31 m transect on asandy loam soil.The effect of a stochastic description of 0(~b) and K(~b) on predicted fluxes andwater content profiles was evaluated with the aid of Monte-Carlo simulations.Initially simulationswere carried out with the actual field data.Alternatively,500 sets of the multi-normal parametervector P = {0 s,a,n,K s} were generated and used in a Monte-Carlo simulation approach.Inaddition,deterministic calculations were carried out using (1) arithmetic mean values of untransformedhydraulic parameters,(2) arithmetic mean values obtained after backtransformation ofGaussian distributed parameters,and (3) alternatively using a set of mean bimodal retention andconductivity curves.Predictions obtained with the two stochastic methods and the deterministiccases are compared with measured cumulative outflow and moisture content profiles from fifteen1m long undisturbed soil columns collected along the same transect.All simulations based onunimodal hydraulic functions underestimated the mean observed drainage.If actual field data areused,the mean outflow is 74% of the mean measured cumulative outflow,compared to 70% forthe Monte-Carlo simulation.The range mean -I- two standard deviations of the simulated outflowfor both methods is considerably smaller compared to the measured range of variation.Deterministicpredictions of the total drainage amounted to 83,83,and 127% of the observed drainage forthe cases 1,2,and 3,respectively.Observed outflow curves displaying macropore flow could not be predicted with the unimodal Richards' flow equation.The results indicate that the field-scale unsaturated flow behaviour in soils with macropores cannot be accurately predicted assuming aunimodal retention characteristic.This is true for both the mean drainage but even more so for the extremes.The use of bimodal hydraulic functions considerably increased the total drainage,resulting in an overprediction of the mean measured drainage.Predicted soil water contents in the 1 m deep soil profile are mostly higher than the measurements.Contrary to the drainage,the range of variation of the predicted water contents is always larger than the measured variability,except for the surface values.