Case Studies

Location:  Frisco 3, 4, & 5

Speaker:  James Ensign, PE, CFM (Bergmann) | Jim Washabaugh (Northern Concrete Pipe)

Presentation Description

Enclosed in 1926, Allen Creek now sees frequent stormwater events exceeding its capacity which leads to severe flooding in Ann Arbor. In addition, overland flows are impeded by the railroad berm which parallels the Huron River; exacerbating the local flooding problem. The same railroad berm also serves as a barrier to the trail system which also parallels the river. This project addressed both of these issues by constructing a berm openings within a very short-term track outage.

Like many communities, Ann Arbor started as a mostly rural area with some industrial development mixed with natural areas. Allen Creek was enclosed in 1926, and as development around the City continued at a rapid pace, stormwater flows quickly reached capacity within the constructed enclosure. Extensions and upgrades have been made over the years, but it remains vastly undersized during larger flow events.

The Allen Creek enclosure outlets to the Huron River and when the enclosure reaches capacity, local street sewer systems are not only unable to empty into Allen Creek, but are actually surcharged from the Allen Creek flows. Overland flow in this area cannot directly reach the Huron River due to an existing railroad berm between the developed area and the river. This creates a costly and dangerous localized flooding issue for area businesses and residents. Flooding depths can reach as much as 10-feet in this highly developed area.

In 2015, the City embarked on a study of how to mitigate this issue and improve drainage in the area. The City also investigated a second issue involving safety – illegal railroad crossings by pedestrians and cyclists. The aforementioned railroad berm can serve as a barrier for accessing these trails. The project, which started out as a study to mitigate flood waters, was expanded to allow residents safe access to the trail system located along the river by evaluating alternatives for conveying pedestrians under the tracks as well.

MDOT’s acquisition of the former Norfolk Southern railroad line in 2012 paved the way for development of a High-Speed passenger service that will ultimately connect Detroit to Chicago. The many improvements required for High-Speed service come with increased safety parameters, especially in densely populated areas like Ann Arbor. This project is paving the way for how Michigan can safely incorporate trails within their High-Speed rail corridor.

Establishing the need for a pedestrian crossing and obtaining MDOT’s permission for pedestrians within the RR R/W is one thing but designing and constructing it was a whole other challenge. Bergmann investigated several options for the layout and staging to construct the new pathway on RR property…which was complicated by the requirement to maintain trains at all times, nearby buried fiber optics, and adjoining property land uses. Ultimately, the design team developed staging for limiting impacts to trains and fiber optics by driving sheet piling on both sides of the tracks (between trains). This solution allowed for construction of the wall and pathway without impacting train traffic and is also used to help construct much of the opening near the proposed underpass while trains are running. While construction of the underpass itself is essentially a “cut and cover” used throughout the industry, the unique aspect of this project is that they had to place over 30 large box culvert sections (12’x7’ and 14’x12’) in a short 1 day outage with limited access and live fiber optic cable to work around.

Speaker Bio
Mr. Ensign has a Bachelor of Science in Civil Engineering from Michigan State University with emphasis in structural analysis and water resources. Mr. Ensign’s experience includes maintenance and improvement projects administered under The Drain Code of 1956, dam and lake level projects administered under parts 307 and 315 of the Michigan Environmental Protection Act, and the design of stormwater facilities for highway projects including dam safety improvements, hydrologic and hydraulic analyses, determination of floodplain elevations and delineations, lake and pond design, storm sewer systems, open channel drains and streams, preparing asset management plans, and the preparation and review of storm water management plans. He is a Professional Engineer and a Certified Floodplain Manager.