Fumigant Transport Modeling Using HYDRUS: 4. Development and Testing of Modifications to Enhance Fumigant Field Simulations
Abstract
Several modifications to the HYDRUS1D and HYDRUS2/3D models were proposed by Department of Pesticide Regulation’s (DPR’s) Air and Ground Water Groups to enhance simulation of fumigant vadose zone transport. The modifications were implemented by the models’ primary author, Dr. Jirka Šimůnek, and included various changes to input/output data and file formats, temperature dependence of the stagnant surface boundary layer, ability to simulate tarp removal mid-simulation, ability to simulate incorporated applications mid-simulation, and implementation of dual volatilization boundary conditions at the soil surface. The specific modifications and DPR’s subsequent testing of their computational integrity are documented in this report. In summary, while a few programming errors were initially found and repaired, the testing results reported herein for the final modification versions indicate the modified code works as expected and contains no known errors. The very small deviations between the unmodified and modified model versions observed in some cases were attributable to numerical error as is common with finite element models.