Olathe, Kansas

2014

TransAm Trucking Financial Services selected WRS in conjunction with Napier Engineering as civil engineers to design parking and stormwater management for development of a bare 3.4-acre lot, including a 150-space, 980 square-foot parking lot.

WRS evaluated the pre- and post-development site conditions to develop a mitigation plan to meet the design requirements, including water quality requirements. WinTR-55 modeling and the SCS Curve Number Method were used to analyze pre- and post-development stormwater runoff. The site’s 35% increase in impervious area was large enough to meet the definition of a development, per MARC/APWA BMP manual, necessitating water quality BMPs and stormwater runoff management. WRS completed level of service calculations to determine required total value rating as well as comparative water quality protection value. WRS used U.S. Army Corps of Engineers HEC-HMS modeling to route different storm events and size the stormwater facilities per city design criteria, which required post-development 1-year peak flowrate less than 75% of the pre-development 1-year peak and post-development 10-year peak flowrate no higher than pre-development.

The proposed stormwater management plan included a native vegetated swale and an extended detention wetland to collect, treat, and discharge the stormwater runoff.  The swale was planned with native vegetation and drained to the extended detention wetland.  The extended detention wetland was planted with wetland plant species that naturally treats the stormwater runoff.  The flows from the extended detention wetland are controlled by a Hickenbottom Riser and another separate control structure that connects directly into the existing stormwater system.