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Poplar River Crossing

Lutsen, Minnesota


USDA Forest Service


USDA Forest Service


Edwin E. Thoreson Inc.


September 2009

The USDA Forest Service required an environmental solution with an open bottom to replace an undersized, deteriorating structure crossing Poplar River.

The original structure prevented aquatic organisms, including fish, from migrating upstream through the pipe’s opening. This was deemed unacceptable and the replacement structure was required to have a clear span in order to minimize disturbance to the area and to allow fish such as trout to migrate through the structure. In addition, a clear span would not be clogged with debris and would be virtually maintenance free, providing a more environmentally friendly solution.

A 36 x 10 ft CON/SPAN® structure fit the project requirements and was chosen because of its integral end treatment design options. The precast headwalls and wingwalls met the requirements of the USDA. In the end, CON/SPAN’s complete system was the most sound choice for the project due to its innovative, economical design, clear span and precast headwalls and wingwalls.

The design also utilized fast, set-in-place construction, resulting in an overall speedy installation and long life cycle. The CON/SPAN structure, including units, headwalls and wingwalls, was set in approximately 10 hours.


Technical Description:

  • Span: 36 ft
  • Rise: 10 ft
  • Length: 36 ft

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