Integrating Surface Sediment Flow Modeling into the Root Zone Water Quality Model.

Pesticide and sediment runoff has been a concern in surface water systems. Many studies focus on modeling these runoffs, however, there was no right tool available for scenario assessment. The Root Zone Water Quality Model (RZWQM), a vertical 1-D, agricultural, field scale water, crop, and solute model, was extended to support surface runoff including sediment load at various grain sizes as well as dissolved and sorbed chemical runoff from pesticide applications. Sediment routines from the Groundwater Loading Effects of Agricultural Management Systems (GLEAMS) were integrated into the RZQWM sub-daily execution loop in order to calculate the bulk sediment runoff for each storm or irrigation event. The calculated water and sediment runoff values are then used in conjunction with RZWQM's pesticide fate and transport calculations to determine the amount of specified pesticides or their daughter products that exist in the tail water or sorbed to the sediment runoff. The joint model underwent a sensitivity analysis for variables affecting surface water and sediment runoff. Results from the sensitivity analysis were used to inform calibration against several field experiments which were then validated against either subsequent years at the same site or on a neighboring, contemporary field. The integrated model will be useful to predict pesticide and sediment runoffs from agricultural fields for management.