In the context of the restoration of ecological continuity, it is essential to ensure that fishways be as efficient as possible. The biological efficiency of a vertical slot fishway (VSF) is highly dependent on its hydraulic design. When hydraulic conditions are not satisfied, sills (an insert that functions like a weir) are often introduced at the bottom of the slots, between the pools. In an attempt to facilitate the passage of benthic species, macroroughness (an array of blocks or boulders on the VSF bed) are positioned at the bottom of fishways. The geometry of the pools and the presence of sills or macroroughness have a strong influence on both the discharge through the pass and the flow pattern. Furthermore, the discharge coefficient, which is used by engineers to estimate the discharge through the pass, is affected by the topology of the flow. This paper provides a methodology to predict both the topology of the flow and the discharge coefficient. The methodology could be implemented in design software used to ensure the correct hydraulic performance of the device.