Evaluating RZ-SHAW model for simulating surface runoff and subsurface tile drainage under regular and controlled drainage with subirrigation in southern Ontario

The response of both surface runoff and subsurface drainage as affected by water table management practices in tile-drained fields is poorly documented. Widely used to simulate management effects on crop production and water quality, the Root Zone Water Quality Model (RZWQM2) has recently been equipped with a subirrigation component. Coupled with Simultaneous Heat and Water (SHAW) model to improve its hydrological responses to cold climates, the hybrid RZ-SHAW has never been tested for simulating surface runoff and subsurface drainage under controlled drainage with subirrigation system. The objective of this study was to evaluate the model performance in predicting surface runoff, subsurface tile drainage, and crop yield under regular drainage (DR) and controlled drainage with subirrigation (CDS) for the first time. The RZ-SHAW model was calibrated and validated against tile drainage, surface runoff and crop yield data collected in a tile-drained field in Harrow, Ontario from June 2008 to December 2011 under DR and CDS treatments. Despite occasional underestimation in winter and overestimation in summer, the model was performing generally satisfactorily in simulating the accumulated subsurface drainage and runoff under both DR and CDS treatments with percent bias (PBIAS) within ±15 %, Nash-Sutcliffe model efficiency coefficient (NSE) >0.5 and the index of agreement (IoA) >0.75. Overall, the RZ-SHAW was capable of predicting the subsurface drainage and surface runoff under both DR and CDS treatment, and it provided reliable estimation for the impact of water table management practice on ET and crop yield, but its accuracy for simulating events of peak flow was not as precise for the CDS treatment than DR treatment.