Hocking Hills State Park

On January 7, 1998, a flash flood roared through the Old Man’s Cave Gorge in southeastern Ohio, washing out stairs, portions of trail and bridges – critical links within the hiking system at Hocking Hills State Park. This six-mile loop trail connecting Old Man’s Cave to Cedar Falls is one of the most popular in the Ohio State Park System, visited by nearly 2 million people each year.

The Ohio Department of Natural Resources (ODNR) turned to ms consultants to provide a series of services. ms first prepared a temporary route, emergency improvements and temporary bridges to allow for safe operation during the summer season. Then an improved trail and bridge system was designed to withstand a similar flood and augment the natural beauty of the park.

Assessment and Remedial Design

Timely return of the park to operation was of paramount importance to ODNR. The project team visited the storm-ravaged site less than one month after the flooding to assess the damage. The structural inspection program required in-depth evaluation of seven footbridges, some nearly 50 years old. The team also focused on the trail system, identifying emergency repairs and alternate routes.

A series of in-depth studies was conducted to develop details on the flood. Using computer modeling, engineers simulated the flood to ensure that final and remedial design would not be subject to similar vulnerability.

In another critical remedial measure, a new stair was constructed as an alternate trail route at Cedar Falls to accommodate the thousands of annual hikers. Temporary pedestrian bridges were designed to span the damaged stone arch bridges at Old Man’s Cave and Lower Falls, both critical pedestrian links during the peak visitor season. The emergency repair work was expedited by the partnering efforts of ms, ODNR, and the Civilian Conservation Corps.

Final Design

The second phase of the project included complete trail redevelopment and permanent design of 12 replacement bridges, drainage culverts, various stairs, signage and other features. Stone arch bridges at Upper Falls and Devil’s Bathtub, originally constructed during the 1930s, were restored and improved with installation of drainage and waterproofing systems. A hallmark steel bridge near Cedar Falls, which had been severely bent in a series of floods, was raised, augmented and remains in use, bearing testimony to the park’s colorful history. New stair systems ranged from treated lumber to stone to concrete, depending on the frequency of use, location and acoustic goals to reduce pedestrian noise in the gorge.

ms based bridge designs on survey information and water modeling data with emphasis on aesthetics, longevity in the flood plain and low maintenance needs. ms provided design for trail upgrades, surfacing alternatives, and a comprehensive drainage system consisting of nearly 50 stone-clad drainage culverts. A new directional and interpretive signage program features regional flora, culture and folklore.

Unquestionably one of the project highlights involved the task of developing four signature bridges for the park. A new 80-foot suspension bridge near Cedar Falls serves as a gateway, marking the trailhead back to Old Man’s Cave. The original stone arched bridges at Old Man’s Cave (79-foot span) and Lower Falls (70-foot span) were replaced in their original forms requiring extensive special construction methods including hand-dug foundations due to access constraints.

ms designed the state’s first formally engineered stepping stone crossing, using cantilevered reinforced concrete pedestal abutments. Key materials bolster project aesthetics and maintenance benefits. Weathering steel reduces maintenance upkeep of the steel bridges. Reinforced concrete serves as the structural component for bridge abutments. And the application of Mohican Valley Top Rock sandstone, a naturally occurring “aged” stone harvested exclusively in the state of Ohio, provides a visually pleasing finish material for bridge abutment protection, retaining walls and culverts. Concrete was also used as a replacement material for both treated lumber and railroad ties in locations requiring terrace-grade beam-type steps, eliminating the toxic material issues and extending replacement needs from 5-10 years to 30-50 years.

A summary of bridge types and span lengths follows. All bridges are single spans except where noted.

• Bridge One, steel stringer at 45 feet
• Bridge Three, steel stringer at 68 feet
• Bridge Four, steel stringer at 24 feet
• Bridge Five, concrete stepping stone
• Bridge Six, steel stringer at 39 feet
• Bridge Seven, two-span steel stringer at 26 feet
• Bridge Eight, concrete arch at 79 feet (Old Man’s Cave)
• Bridge Nine, concrete arch at 70 feet (Lower Falls)
• Bridge Twelve, steel stringer at 60 feet
• Bridge Thirteen, two-span steel stringer with new abutments and decking, reused existing stringers
• Bridge Fourteen, steel stringer at 45 feet
• Bridge Fifteen, steel suspension bridge at 80 feet for main span

Drainage

As part of this project the watersheds for the Gulf and Queer Creek were analyzed. Soil conservation service hydrology techniques were utilized for hydrograph development of the various sub-basins. The channels were cross sectioned at various intervals and critical locations in order to perform the hydraulic analysis. XP-SWMM software was used to generate the hydrographs and water surface elevations for the various return frequencies.

Survey

ms consultants prepared topographic mapping of the gorge trails from Old Man’s Cave to Cedar Falls for the preparation of plans to replace walkway bridges destroyed by a storm and to improve existing trails. A Global Positioning System was to establish a control network for aerial mapping. In the gorge, cross sections of the existing streams were collected at 100-foot intervals. The length of the project was approximately three miles and contained approximately 205 acres within the project limits.

Construction Services

After construction document completion, ms provided a series of services to construct both a temporary route to allow safe passage during the busy summer season after the flood and until final improvements could be implemented.

Construction complexities, including extremely challenging access to the six miles of construction area, the sensitive environmental concerns and the natural beauty of the site, were overcome by careful planning of the design team in conjunction with the expertise of ODNR engineering staff and naturalists. All plans were explicit with respect to designated access and construction limits and were well executed by the contractor minimizing any damage to the natural rock surfaces, trees, and plant life. The measure of adding the top rock sandstone as a trail edging feature to direct pedestrians to the preferred trail alignment in high traffic areas enhances the overall natural habitat by allowing the native flora to return to areas damaged over the years by straying hikers.

The Old Man’s Cave Gorge redevelopment program stands as demonstration of a successful enterprise that demanded a complex range of talents and solutions in a high-profile natural treasure.

Services Include: