A BOUNDARY-ELEMENT METHOD FOR STOCHASTIC FLOW PROBLEMS IN A SEMICONFINED AQUIFER WITH RANDOM BOUNDARY-CONDITIONS

A boundary element technique will be developed to deal with steady sta te flows through a shallow aquifer with random boundary conditions. Th e aquifer is bounded by a leaky layer above, and an impervious stratum below. The flow problem is formulated in terms of a stochastic bounda ry value problem involving a Helmholtz equation. A formulation of the boundary element method for the stochastic mixed boundary value proble m is presented. The moments of unknown random hydraulic head can be ob tained by application of an expectation operation to the boundary elem ent formulations. A numerical method to evaluate hydraulic head moment s on boundaries and inside the domain is then developed. The influence of the spatial structure of the boundary conditions on the hydraulic head statistics is discussed and the results are compared with some an alytical solutions for one-dimensional flow problems for the purpose o f verification of the numerical algorithm. The significance of the pre sence of the leaky layer on the hydraulic head statistics is also inve stigated. A numerical example for more general steady state flows thro ugh a semiconfined aquifer is presented. (C) 1997 Elsevier Science Ltd .