field is "Head", "PorePressure", "Speed", or "Gradient".
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For an unconfined solution, "PorePressure" extends above the water table into the unsaturated zone, contouring negative pore pressure (suction) with a tension cut-off at "SuctionCap" metres of head (default 1 m ≈ 9.81 kPa); set "IncludeSuction" ->