WALRUS-paddy model for simulating the hydrological processes of lowland polders with paddy fields and pumping stations

• WALRUS‐paddy for hydrological modeling of lowland polders with paddy fields and pumping stations was developed.
• The model accounts for the complex irrigation and drainage practices in paddy fields and human-induced polder discharge.
• The model was tested and applied to a typical Chinese polder.
• The model is available for water resources management of Chinese polders.

Simulating the rain-runoff process in lowland polder will lead to improvements to hydrological modeling of entire floodplain catchments. The lumped Wageningen Lowland Runoff Simulator (WALRUS) provides an efficient and reliable model for simulating the hydrological processes in lowland catchment with shallow groundwater. However, this model needs to be improved before being applied to Chinese polders, which have multiple land use types and pumping stations. This study proposes an improved version called WALRUS-paddy that accounts for the discharge from multi-sources, including drylands, paddy fields, residential areas, and water areas. A water management scheme is incorporated to control the irrigation and drainage operation in paddy rice fields and the groundwater flow between the paddy field and the adjacent dryland is considered. In addition, a new stage-discharge relation function is introduced to represent the discharge process of the polder with pumping stations and culverts. Then, the model is validated in the Jianwei polder of east China. The modeled results agree well with the observed discharge and show that the improved model can provide good estimates of the discharge in this polder district. Thus, the improved model is feasible and helpful for water resources management of Chinese polders.