Natural Stream Design Opens Gate for Thoroughbred Racetrack

By Shawn Keough, PE, and Mark Pribak, PE

A 2-stage channel design enables the relocated Blakely Drain to convey both low and high flows within a 100-foot-wide drain corridor. Adequate storm water drainage is critical to keeping Pinnacle Race Course in peak condition for events. (Photo courtesy of Pinnacle Race Course)

Horse racing and water don’t mix. After heavy rains, racetracks that don’t drain well are often forced to cancel races due to water logged tracks that threaten horse and jockey safety. Drainage concerns went beyond the track at Michigan’s new Pinnacle Race Course in Huron Township near Detroit Metropolitan Wayne County Airport. Located within a 100-year floodplain, the site required an innovative storm water management design to make one of the country’s premier Thoroughbred racing tracks possible. The Pinnacle Race Course was developed by Post It Stables, Inc., as the anchor tenant of the Pinnacle Aeropark development being undertaken by the Wayne County Department of Jobs and Economic Development to capitalize on this desirable location and bring more economic activity into the County. The existing land was undeveloped and primarily used for agriculture. In addition to the race course, the master plan and design guidelines developed for Phase I are shaping the land use concept into a mixed-use development that features opportunities for office, high-tech, industrial and governmental uses with a significant amount of preservation and open space. Bounded by roads and/or high tension power lines on all four sides, five drain crossings, and multiple wetland areas, the 320-acre site required significant reconfiguration to accommodate the mile-long race course. The site’s proximity to the airport was an additional constraint that had to be considered during planning and design. The Federal Aviation Administration (FAA) regulates that property located within 10,000 feet of runways cannot feature open storm water ponds because they attract wildlife that could be hazardous to air travel. A hydrologic/hydraulic analysis of the drain network confirmed that the majority of the site is within the 100-year flood boundary and that a series of drain relocations, drain widening, culvert improvements, downstream storage basin and drain cleanouts would be necessary to contain the 100-year flood level impacts within a 100-foot-wide drain corridor.

To make way for the track without affecting existing roads, portions of the Blakely Drain to the north and Silver Drain to the south were relocated and widened from 20 to 100 feet. Both drains were reconfigured from simple engineered trapezoid cross-sections to natural stream designs.

The Blakely Drain serves a large watershed and has flowing water during each season. It was redesigned as a Rosgen 2-stage, C-type channel that features a double trapezoid cross-section. The low-flow channel is intended to carry the 1.2-year flood flow within its width to depth ratio of 12:1. This channel meanders through the larger flood-flow channel that has a 100-foot top width. The serpentine shape of the Blakely Drain relocation was designed in cooperation with the Michigan Department of Environmental Quality (MDEQ) to represent a more natural stream design instead of simply relocating the drain in a straight line around the race track. Over time, it will act like a natural stream as water flow in the low-flow channel ultimately defines the new location of the stream. FAA concerns were addressed through this design since water is temporarily stored within the stream channel rather than a large pond.

The Silver Drain was designed using a 100-foot-wide, single trapezoid cross-section primarily due to its shallower profile. Though shorter than the Blakely Drain relocation, the design for this widening also took advantage of additional storm water storage within the wider cross-section to mitigate flood flows across the race course site and Pinnacle Aeropark area. MDEQ is allowing this shallower drain to create its own low-flow channel over time.

The natural stream design approach will return the relocated drains to more natural conditions with good flow characteristics during periods of low and high flow. The 100-foot width provides more riparian environment and a natural buffer area to help meet the requirements of the Wayne County Storm Water Management Plan. Widened stream banks were stabilized through the use of seeded mulch blankets pegged in place. Small native trees and plantings will create shade and introduce additional root structure into the stream banks for increased slope stabilization. Water quality benefits are expected from the vegetative buffer that reduces erosion and increases nutrient removal from the water.

In addition, a linear wetland comprised of Wayne County Drain Numbers 1 and 3 was shortened during the Blakely Drain relocation. Flows from these drains are tributary to the Blakely Drain and wetland mitigation was proposed on another portion of the site to meet MDEQ requirements. The Reisner Drain and Evans Drain were also relocated slightly during construction.

A compressed schedule for the project was needed to retain federal funding through the Michigan Gaming Control Board and prepare the facility for the 2008 racing season. The closure of a Thoroughbred racing facility in another part of the state made funding available if the Pinnacle Race Course could open in mid summer 2008. Planning and design efforts were compressed into four months leading up to and continuing into an extremely condensed construction period. To expedite the schedule, MDEQ and Wayne County allowed construction to progress in areas without wetlands and streams, while permits for the other areas were still in process.

Pinnacle Race Course held its opening day of racing on July 18, 2008. With the economy in the State of Michigan searching for opportunities for growth, this project was completed as a cooperative effort between all reviewing agencies, designers and contractors to meet the aggressive deadline while protecting the environment, improving water quality and enhancing the natural stream corridors.

Originally published in Innerview Vol. 23, No. 1, 2009

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