Boundary integral solutions to nearly horizontal flows in multiply zoned aquifers

A general purpose Boundary Integral Equation Method (BIEM) program was developed to solve nearly horizontal flows in multiply zoned, layered and leaky aquifers. A special technique is proposed to handle the large coefficient matrices which are obtained when the BIEM is applied to field problems. The technique involves condensing the matrix equations at the zonal levels before the final global assembling is done. Problems governed by equations with non zero right hand sides lead to BIEM formulation in which domain integrations are required. An automatic mesh generation scheme is proposed in order to maintain the ease of data preparation of the BIEM model. Two methods are proposed to solve the nonlinear equation with the BIEM. In the first method the equation is linearized around the average depth of the zone. The second method involves treating the nonlinear equation as a pseudo Poisson equation in which the right hand side is a function of the dependent variable. The BIEM model is applied to flow problems where analytical solutions are available and also to a groundwater basin in Taiwan.