Warren Falls Solutions

The strange history of Warren Falls began shortly after completion of the Historic Columbia River Highway in the 1920s, when unruly Warren Creek repeatedly pushed debris against the modest new highway bridge that spanned the stream.

The first Warren Creek bridge was replaced as part of the waterfall diversion; no photos of the original structure survive

Oregon highway engineers subsequently diverted the creek in 1939 through a bizarre tunnel that survives to this day. The diversion created today’s manmade Hole-in-the-Wall Falls when an accompanying flume was removed sometime in the early 1960s, leaving an eerie, dry cliff where Warren Falls once thundered.

This article proposes a few solutions for restoring Warren Falls to its former glory in tandem with the ongoing ODOT project to restore the Historic Columbia River Highway.

Option A: Let Nature Take Her Course

The simplest solution for restoring Warren Falls is to simply wait for the “trash rack” diversion structure to rust away, eventually collapsing into the tunnel intake under the weight of a heavy winter flood or debris flow. Surprisingly, this hasn’t already happened over the 73-year life of the diversion project, but it is inevitable.

Debris flows periodically clog the brink of Oneonta Falls; a similar event is inevitable at Warren Falls

This is the least desirable option because it leaves the maintenance and safety liability of the diversion tunnel in ODOT’s hands, and the removal of obsolete structures to chance. The dry falls and diversion tunnel are visited regularly by curious hikers, canyoneers and rock climbers, so the unresolved safety liability the tunnel presents for ODOT is quite real.

Option B: A Large Cork

Short of waiting for the “trash rack” diversion structure to collapse on its own, the simplest option for restoring Warren Falls is to cork the tunnel intake. A vault carved like a rocky bathtub into the bedrock brink of the falls forms the tunnel intake, and provides for the “cork” solution.

Though the metal “trash rack” covers an opening of roughly 20×20 feet square, the rock vault is tapered in a v-shape, narrowing to the 5 foot width of the tunnel at the bottom of the vault. The “cork” would be a series of stacked basalt columns filling the vault and blocking the bypass tunnel opening. Approximately twenty 6-foot columns, each about 18 inches in diameter would do the job.

The 1939 construction drawings for the diversion project show the v-shaped vault carved into the lip of Warren Falls, leading to the diversion tunnel (cross-section view)

Mother Nature would provide the assist for this solution once the basalt columns are in place, with the hydraulic force of Warren Creek filling the spaces between columns with fine gravels and sediment over time. Eventually, the voids between the columns would fill completely, plugging the bypass tunnel to all but a small amount of seepage.

The lower end of the corked bypass tunnel would also be covered with a protective grate to prevent curious explorers from entering, just as a number of lava tubes in Oregon have been gated to public access. The bonus? A very large, secured bat cave is created in the process!

A stack of basalt columns like these would form the “cork” that plugs the bypass tunnel forever (Wikipedia)

How would the basalt columns get up there? The best plan would be an air crane, as the rock columns would be comparable in size and weight to the timber loads that are routinely lifted in Oregon’s helicopter logging operations.

ODOT maintains an open maintenance field just a few hundred yards from the falls site, with direct freeway access for delivering the columns to a staging area. On-the-ground workers could access the top of the falls from the Starvation Ridge Trail, but a mechanical lift from the base of the falls would be more practical.

Option C: Colossal Dental Work

The third option is the best plan for fully restoring Warren Falls to near-natural conditions. This design would “fill the cavity” of the entire bypass tunnel, permanently.

Construction detail of the lip of the masonry dam that supports the “trash rack” (cross-section view)

This solution uses the original masonry dam at the head of the bypass tunnel to temporarily pipe Warren Creek over the natural falls during the construction phase, allowing for concrete work to proceed within the bypass tunnel.

The tunnel would be plugged in two steps. First, a reinforced concrete plug would be poured at the lower opening of the bypass tunnel, sealing the tunnel exit. The plug would be disguised on the outside to match the color and texture of the basalt cliff.

Next, the rest of the tunnel would be filled with mixture of concrete and rock cobbles — roughly 100 cubic yards worth. Once the tunnel “cavity” is filled, the vault at the top of the falls would be filled with basalt columns, using the same method described in the “cork” scenario. In this case, they could be mortared in place, since this approach would already have concrete pouring equipment on site.

Wanted: dentist with masonry skills and a helicopter pilot license… (photo: Zach Forsyth)

The “dental work” option has the benefit of stabilizing basalt cliffs that form the western wall of Warren Falls by permanently filling the man-made cavity behind them. This option allows ODOT to walk away from the Warren Tunnel site forever, with almost no trace of the old stream diversion left behind.

How would ODOT move the concrete and rock to the top of the falls? Fortunately, much has changed since the tunnel was originally created, and today there is portable equipment specifically designed for the task.

First up is a truck-mounted concrete pump, normally used for precision pouring in building construction, but increasingly used to minimize environmental impacts at construction sites.

This truck-mounted concrete pump would easily reach the top of Warren Falls (Wikipedia)

Moving rock to the top of the falls would be a bit more cumbersome, but could employ a portable rock conveyor. These are widely used in commercial aggregate operations, and could conceivably be used at the Warren Falls site. A low-budget alternative is to us rock from Warren Creek’s streambed above the falls.

Moving heavy equipment to the site would drive up the cost of restoring Warren Falls, so the “dental work” option for completely decommissioning the old tunnel is probably the least viable alternative, given funding constraints. But it’s also possible that ODOT will already have equipment required to do the job in the area as part of the project to restore the historic highway.

A telescoping rock conveyor could be the solution for loading aggregate into the Warren Tunnel (Wikipedia)

Next Steps?

Why link restoration of Warren Falls to the Historic Columbia River Highway project? The answer lies in the intertwined history of the falls and the highway department: now is the time for ODOT to undo an unfortunate environmental travesty from another era.

The historic Columbia River Highway restoration project provides a once-in-a-lifetime opportunity to provide the resources needed to restore the falls. It also allows ODOT to demonstrate how much highway planning has evolved since the diversion project was conceived, more than 70 years ago.

I will be making another pitch to restore Warren Falls at the Historic Columbia River Highway advisory committee meeting on March 16 (in Hood River). Hopefully, I’ll be able to capture the imagination of the citizens and ODOT staff charged with returning the old highway to its former glory, and make the case that restoring Warren Falls ought to be part of the larger restoration effort.

More to come…

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2 Comments on “Warren Falls Solutions”


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