A method and system is provided for producing erosionally stable fluvial geomorphic landscape designs in a computer aided design environment. A topography input module is configured to access a three-dimensional model of existing topography of a site, while a data input module is configured to receive climatic and hydrological data associated with the site. A channel geometry module is configured to utilize the three-dimensional model and the data to generate dimensions for one or more proposed ephemeral channels. A design surface module generates a graphical view of a proposed landform at the site using the existing topography, the proposed ephemeral channels, and optionally, various complementary topographic features.