Closure of Point Defiance’s Five Mile Drive a surprise? Here’s how we got to this point

Tacoma Metro Parks announced the permanent closing of a beautiful drive along Point Defiance Park’s bluffs on May 17.

The closing came after the release of a geotechnical report in January from GeoEngineers, an engineering and earth science consulting firm in Tacoma, which found that the bluffs have experienced “several episodes of erosion and bluff retreat in recent history”.

“Nobody knows when that cliff might suddenly give way, and our primary goal is to keep park visitors safe, as well as making our parks more resilient to climate change,” Metro Park’s website stated.

The outer loop of Five Mile Drive in Point Defiance Park will be permanently closed on May 20 for all motorized traffic, the Metro Parks Tacoma website states. Pedestrians, bikers and other non-motorized traffic will still be allowed on the loop.

The 103-page report recorded some early signs of erosion in 2004, which have continually been monitored since. The erosion has caused major damage, according to the monitoring and new reports.

“These episodes have brought the crest of the bluff closer and closer to the viewpoint and the paved edge of Five Mile Drive. The bluff crest is currently about 20 feet away from the edge of Five Mile Drive,” the report states.

The report also notes that the main reason for the erosion as natural weathering.

“Surficial erosion and sloughing typically occur due to natural weathering processes such as seepage, saturation of shallow soils during heavy rain events, decay of roots, and root removal of blown down trees. The magnitude and volume of material involved in surficial sloughing depends on several factors including steepness of slope, time of year, rainfall, saturation of ground, and activity of burrowing animals,” the report stated.

Another reason the report cited for the erosion was storm drain outfall. Certain storm drains had been flowing out onto the bluff, causing the erosion to increase and accelerate.

Since the bluff is visited frequently and has already receded so much, the report stated, the “consequences of the continued slope erosion could be severe.”

Officials say there are only three approaches to potentially reduce the effects of erosion. The report suggests improving the bluff stability through engineering measures, slope setbacks or closing the Five Mile Drive and eliminating all public access to the area.

Engineering measures to improve the stability of the bluff could be undertaken, but it would not be economically feasible, according to the findings of the report. The plan would include constructing a retaining wall that is at least 50 feet tall to lessen the bluff erosion. Although this could help with erosion issues, the report states that the required large equipment, possible reinforcements and the present erosion make this plan less effective than others.

Instead, experts recommend creating a slope setback to solve the erosion problem. The setback would be 150 feet from the eroded edge of the bluff and would decrease the risk of erosion reaching the viewpoint.

The setback would require Five Mile Drive, parking lots and other existing structures to be setback and relocated, but would cost significantly less than building the retaining wall and provide a long-term solution to preventing erosion.

The Metro Parks has rejected this plan, saying the 150-foot setback recommendation would require the removal of trees and habitats, which would go again the Metro Parks’ stewardship commitments, the agency’s website stated.

Instead, the agency is looking at different plans to create a different route for motorized vehicles on an existing service road. The 1.5-mile road would require less removal of trees and habitats.