Evaluation of DRAINMOD using saturated hydraulic conductivity estimated by a pedotransfer function model

Abstract

Direct measurement of soil saturated hydraulic conductivity (Ks) is time-consuming and therefore costly. The ROSETTA pedotransfer function model is able to estimate Ks from soil textural data, bulk density and one or two water retention points. This study evaluated the feasibility of running the DRAINMOD field-scale hydrological model with Ks input produced usingROSETTA.Ahierarchicalapproachwasadoptedto estimateKs usingROSETTA, withfour limited-more extended sets of soil information used as inputs: USDA textural class (H1); texture (H2); texture and bulk density (H3); texture, bulk density, water retention at 33 kPa (u33 kPa) and 1500 kPa (u1500 kPa) (H4). ROSETTA-estimated Ks values from these four groups (H1–H4) were used in DRAINMOD to simulate drain outflows during a 4-year period from a conventional drainage plot (CD) and two controlled drainage plots (CWT1 and CWT2) located in south-east Sweden. The DRAINMOD results using ROSETTA-estimated Ks values were compared with observed values and with model results using laboratory-measured Ks values (H0). Deviations in simulated drainage outflow(D), infiltration (F) and evapotranspiration (ET) resultingfromtheuse ofROSETTA-estimatedrather thanlaboratory-measuredKsvalueswere evaluated. During the study period, statistical comparisons showed good agreement on a monthly basis between observed and DRAINMOD-simulated drainage rates using five soil datasets (H0, H1, H2, H3 and H4). The monthly mean absolute error (MAE) ranged from 0.57 to 0.82 cmfor CD, 0.38 to 0.41 cmforCWT1, and 0.15 to 0.22 cmforCWT2.Onamonthly basis, the modified coefficient efficiency (E0) valueswere in the range of 0.62 to 0.74 for CD, 0.72 to 0.74 for CWT1,and0.79 to 0.86 forCWT2.Themodified index of agreement (d0) formonthly predictions ranged from0.80 to 0.86 cmfor CD, 0.87 to 0.88 cmforCWT1,and 0.89 to 0.93 cmforCWT2. The absolute values of thepercent-normalisederror(NE) onanoverall basiswhenusingROSETTAestimated rather than laboratory-measured Ks values were less than 3% in E, less than 1% in F, and less than 15% in D. The results suggest that ROSETTA-estimated Ks values can be used in DRAINMODto simulate drainageoutflowsas accurately as laboratory-measuredKs values (H0) in coarse-textured soils.