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Mitigation of light rail transit construction on jurisdictional areas in the White Rock Creek floodplain, Dallas, Texas

  • Author(s): Schieffer, Emily
  • Smiley, Jerry
  • et al.
Abstract

In 1994, Dallas Area Rapid Transit (DART) began planning for an 11.8-mile extension of its light rail transit (LRT) system from Dallas to Garland, Texas. The proposed alignment of the LRT extension traversed approximately 1.2-miles of the White Rock Creek floodplain near the confluence of three creeks and adjacent to approximately eight acres of wetlands. Because of the extensive development that has occurred within the watersheds of these creeks over the last 50 years, the conveyance of flood waters within this urban floodplain has been severely constrained. In order to adequately protect the new rail bed from flooding, it needed to be elevated as much as 12 feet above the existing rail bed, nearly 20 feet above the natural surface. This area also serves as part of the Olive Shapiro Nature Preserve and White Rock Park – one of the largest, intact natural areas in the City of Dallas. Thousands of park users cross the proposed alignment daily. In addition to protecting the jurisdictional areas found adjacent to the rail alignment and to preserving the park’s existing flood water storage, project designers wanted to maintain park users’ access to the bike paths and natural areas of the park. All of these concerns were taken into account when evaluating the project design alternatives. The first alternative suggested placing the new alignment on fill with bridges located at the creek crossings. This alternative would restrict park users’ access, destroy adjacent wetlands, and further restrict floodplain storage. The second design option recommended placing the rail line on an aerial structure through the length of the floodplain. This option would minimize permanent impacts to the adjacent jurisdictional areas, maintain the public’s access to all areas of the park, and avoid impacts to floodplain storage within the park. Although the construction costs for this option were higher, DART selected this alternative. The true success of this project, though, was found not in innovative engineering, but in the cooperative efforts between DART, USACE, USFWS and the City of Dallas Parks and Recreation Department. These groups collaborated to develop a mitigation plan that was acceptable to all interested parties, including the general public. The fact that this mitigation occurs within the same watershed and within one-mile of the original impact area is a significant accomplishment. The final mitigation plan has four components: •post-construction restoration of the wetland areas adjacent to the new alignment; •construction of two “educational” wetlands next to the park’s hike-and-bike trail; •restoration of a ten-acre historical wetland within White Rock Creek Park; and •creation of a mitigation monitoring plan to review construction activities. It is our hope that this project will serve as a model for future cooperative work between DART, USACE, USFWS, and the City of Dallas.

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