Many programs that are used for storm water management are intended primarily for analysis or simulation. The MIDUSS program facilitates the design of conveyance or detention storage elements in a tree network. The program is command driven and allows the design to proceed in a traditional manner by allowing the user to define individual subcatchments to generate the overland flow. The resulting hydrographs may be manipulated and used to design pipe and pond elements of a drainage network. The user can experiment with alternative trial designs.As the design proceeds, a file records the data input and design decisions made by the user. This file may be used in subsequent design sessions during which the user may switch from manual (i.e., keyboard) to automatic (i.e., file) input. This allows continuation of a previous design session, testing of a prior design with a different storm, or redesign of specific elements of the system.In either mode, the user can monitor progress at each step and take corrective action in the event of bad data or incorrect design decisions. Key words: computer, design, storm water, sewer, detention, pond.