To allow for different pressure gradients over the two inlets the water motion in the double inlet system is described by the 2D shallow water wave equations. The double inlet system is schematized to four compartments: the ocean, the two inlets and the basin. The model is forced at the ocean boundary by a Kelvin wave travelling past the two inlets. The equations are solved using a semi-analytical technique, which is computationally efficient allowing a large number of calculations in a short period of time. Using this process-based exploratory model with parameter values of the Texel-Vlie Inlet system, the effect of basin depth, Coriolis acceleration, radiation damping and basin geometry on the spatial variation in basin water level and the stability of the double inlet system are investigated. It is shown that for relatively shallow basin depth stable inlet cross-sectional areas are present. Adding the Coriolis acceleration, accounting for radiation damping and different basin geometries does not change this conclusion and only slightly affects the size of the stable cross-sectional areas. An application of the model to a multiple inlet system is described.