The present invention is a method of hydrodynamics-based gridding (Hydro-Grids) for creating geologic models of subsurface volumes, such as reservoirs. Vertical grid surfaces may be chosen in an unstructured fashion to provide lateral resolution where needed. Lateral grid surfaces are created to represent surfaces of constant geologic time based on simulation of the depositional processes that created the subsurface volume. The values of geologic properties are then specified within each cell created by the intersections of the vertical and lateral surfaces. The geologic data may include, for example, seismic data, outcrop studies, well log data, core data, numerical modeling data, and interpreted stratigraphic surfaces based on seismic data. The modeled geologic properties of the subsurface volume may include, for example, grain size distribution, connectivity, net-to-gross, porosity, permeability and pore pressure.