Selection of Best Channel Design Alternative for Watercourse Master Plan

Optimization modeling can be used as a design and a planning tool in the selection of the "best" drainage alternatives for engineering projects. The approach was used for the Middle New River Watercourse Plan to evaluate five drainage design concepts that would safely convey design floods previously defined in studies conducted by the U.S. Army Corps of Engineers and the Flood Emergency Management Agency (FEMA). Due to varying development density along the Middle New River, the entire study reach was divided into sub-reaches. Each sub-reach was subject to site-specific design requirements and therefore modeled accordingly. The optimization models searched for and evaluated optimum design configurations for the drainage project based on the governing system equations employed. Important governing equations used in the procedure included the continuity and Bernoulli's equations for flow hydraulics, and scour equations for bed dynamics and channel mobility. Using economic performance as the objective function, the optimization models were formulated to evaluate the optimum channel configuration that provided the least project cost. Cost components included channel excavation and earthwork, hydraulic structures, acquisition of right-of-way and drainage easements, revegetation work, salvage, mobilization, engineering, contingency, operation, maintenance and repair. The resulting nonlinear optimization problems associated with the five design alternatives considered were solved using GAMS-MINOS, an optimizer code developed by Brooke et al.