How our engine couples SWAT+ and MODFLOW 6
Our engine runs SWAT+ and MODFLOW 6 as one program. SWAT+ loads MODFLOW 6 as a library, through MODFLOW 6's own programming interface, and the two step forward together, one day at a time. Each day, the water that drains below the soil of each land unit becomes recharge, shared among the aquifer cells that land unit covers in proportion to the area they overlap, and MODFLOW 6 then solves the aquifer for that day. Its streams are SWAT+'s own channels, cut where they cross each cell: one river network, not two. Each stretch gains water from the aquifer or loses water to it, and that exchange flows back into the SWAT+ channel on the next day. The model shown is our Michigan model of the Rogue River basin: about 85,000 links from 18,000 land units onto 11,000 cells. The full two-way water balance is still being validated. A SWAT+ with MODFLOW order, in the states where it is offered, adds a steady-state MODFLOW 6 model; the daily two-way run is not yet part of an order.
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Transcript
Our engine runs SWAT+ and MODFLOW 6 as one program. SWAT+ loads MODFLOW 6 as a library, through MODFLOW 6's own programming interface, and the two step forward together, one day at a time. First, SWAT+ runs its day. The water that drains below the soil of each land unit becomes recharge, shared among the aquifer cells that land unit covers, in proportion to the area they overlap. In this Michigan model, of the Rogue River basin, that is about 85,000 links, from 18,000 land units onto 11,000 cells. Then MODFLOW 6 solves the aquifer for that day. Its streams are SWAT+'s own channels, cut where they cross each cell: one river network, not two. Each stretch gains water from the aquifer or loses water to it, and that exchange flows back into the SWAT+ channel on the next day. Then the next day begins. The full two-way water balance is still being validated. SWAT+ and MODFLOW 6: one engine, trading water every day.
Credits
Model: the Rogue River basin, Michigan (land units, grid and stream reaches from its own files). Heads: a 61-day coupled test run of this model (test build). The daily loop and the gain/loss arrows are illustrations.