The fourth in a four-volume study to assist the Netherlands government in a policy analysis of alternative control strategies for operating the storm-surge barrier across the Oosterschelde basin. This volume describes the simulation model of the storm-surge barrier and basin used to estimate the variation with time of different water levels inside the Oosterschelde, given specified sets of storms outside the barrier. It discusses the capabilities of the model (called SIMPLIC), the storm sets and tidal shapes used, and the model's inputs and outputs. Two sets of storm scenarios were represented in SIMPLIC: a historical storm set comprising 44 storms from 1921 to 1970, and a design storm set including 12 variations of two extreme storm surges. The first storm set was used to evaluate ecological, water management, and shipping impacts and the second to assess safety impacts of the alternative barrier control strategies, as discussed in Vol. I. 92 pp. Ref.