The verification of NAMMU using HYDROCOIN Level 1 cases 1 and 7: transient flow from a borehole and saturated flow through a shallow land disposal facility

The numerical accuracy of the finite-element groundwater flow code NAMMU has been verified using test cases 1 and 7 from HYDROCOIN Level 1. Case 1 compares calculated results with an analytic solution to an idealised transient borehole experiment in a porous medium with a single horizontal fracture. The numerical results are in excellent agreement with the analytic solution, both for the pressure values and for the gradients. Our use of lower-dimensional elements to represent fractures is also verified in this test case, again with excellent agreement. Case 7 involves calculating flow through an idealised shallow land disposal facility in argillaceous media, and verifies a code's ability to model the spacially varying permeabilities which would be found in the vicinity of this type of facility. Since there is no analytical solution for this case, the results from independently developed codes have been intercompared. Considerable refinement of the grid was found necessary in the neighbourhood of the concrete engineered barriers, and near the outflow. With this refinement, the results from NAMMU compared well with results from other codes participating in the HYDROCOIN project. (author)