Ecological engineering in a new town development: Drainage design in The Woodlands, Texas

This paper presents a comparative study of two different drainage designs in a 10,930-ha new town development of The Woodlands, Texas. Open surface drainage by shallow grassed swales was used in the first two subdivisions that were developed with ecological approaches. Open surface drainage mimics the natural flow regime and is regarded to mitigate development impacts on watershed. In other later subdivisions, the drainage design shifted back to a conventional stormwater drainage system, that is, curb and gutter, drop inlet, and underground piping, known to concentrate stormwater and lead to downstream flooding. The objective of this study is to compare The Woodlands’ two drainage systems on their correlation with downstream floods. Two sub-watersheds within The Woodlands that used different drainage designs were compared. U.S. Geological Survey stream data from the gauge station at the outlet of each sub-watershed were used for analysis. Geographic Information System was used to quantify the development conditions. Correlation analysis was performed using measured precipitation and streamflow data. Results show that open drainage watershed generated less storm runoff than the conventional drainage watershed, given the similar impervious area in both watersheds. Furthermore, the open surface drainage watershed responded to rainfall in a way similar to its predevelopment natural forest conditions, indicating effective flood mitigation post development. In contrast, in the conventional drainage watershed, the precipitation–streamflow correlations increased enormously after development. The open drainage system presents an advantage over the conventional drainage one in mitigating flood problems in urban development.