NDM completed the Feasibility Study which included the hydrologic evaluation using XP-STORM for drainage within the uptown area. The study included the hydraulic evaluation of the existing discharge tunnel system (14-foot diameter tunnel) and the preliminary design of an additional 17-foot relief tunnel to the Trinity River. Alternatives considered included parallel relief systems, underground detention basins, and combined detention and relief systems. The project included the hydraulic modeling of these d systems. The project also included the evaluation of subsurface conditions related to boring through various materials with necessary access shafts and appropriate boring machines. Vertical and horizontal alignments were evaluated for the relief tunnel. Additional considerations included the potential of project phasing, outfall structures, and pumping system for the underground detention basin and tunnel.

The design phase included revised the tunnel alignment and size.  The tunnel was combined with the Mill Creek/Peaks Branch tunnel and increased in size to 30-foot diameter. NDM services during the design phase included 2D modeling of the contributing system to the tunnel using XP-Storm, evaluation of overland flow and flooding limits, development of a Drainage Master Plan for the contributing State Thomas system, preparation of construction plans for a local 14-foot diameter horseshoe tunnel, tunnel plan and profile sheets for the 30-foot diameter tunnel, road improvement plans, structural design for tunnel upper shaft support/inlet structure, and survey for and preparation of easement documents.