Nonsteady-State Drainage from Porous Media

The validity of numerical solutions of nonsteady-state, one-dimensional, vertical drainage problems was evaluated by comparison with experimental data. Experimental data included simultaneous measurements of fluid pressure using a pressure transducer, and fluid content using gamma radiation. The results of 13 numerical solutions involving five porous media and two or three boundary conditions for each are summarized. Several approximate solutions to the vertical drainage problem were evaluated and the limitations of each discussed. The flow rate was related to the position of the saturated front during primary drainage. During secondary drainage, the change in flow rate was not dependent on the recession of the saturated zone, but was related to the unsaturated hydraulic conductivity and the differential fluid capacity above the saturated zone for the porous material and fluid involved. Characteristic changes in fluid pressure distribution with time are summarized.