What are the physical characteristics of the habitats on the Missouri River and its floodplain? A triangulated irregular network (TIN) was needed for a surface water model to inventory depth and velocity at varying discharges. Our challenge was to combine floodplain topography (feet above mean sea level) from a DEM and river bathymetry (feet below the water surface) into a TIN. Complicating factors include differential slope of the water surface applied along its linear length. Grids of cost-distance, down-river source-point elevation, and depth were combined to produce a bathymetric surface in topographic units, which was combined with the floodplain grid and converted to a TIN.