Heavy cracking and a sunken road grade on the north (right) side of Scenic Drive just west of Esther Way, above, was caused in part by damage and runoff from the Kelly Avenue landslide that occurred in the 1980's, some of which can be seen in the background. That slide is stable, but plans are underway to investigate adding a retaining wall to the right side to stabilize Scenic Drive itself.
Photo by Mark Gibson.
The Dalles The City of The Dalles is taking steps to shore up an unstable embankment along the ridge of East Scenic Drive that is in a landslide zone.
Geotechnical consultants have monitored the 600 to 900 blocks of Scenic Drive for the past several decades. These experts do not believe the current movement of pavement and curb line on the north and downhill side of a one-fourth mile section of roadway is associated with the old Kelly Avenue Landslide.
The slide that occurred in the 1980s was determined by geologists to have been caused by excessive groundwater and deep wells were dug to stabilize the terrain that are still in operation.
Dave Anderson, public works director, told the city council in January the current earth shifting activity is occurring about 10 feet below ground level; whereas, the landslide movement had been at a depth of about 180 feet.
He is concerned that continued shifting of the ground, even if slight, will eventually destroy underground utilities and the roadway in the area. If a catastrophic failure of the embankment were to occur, Anderson told Mayor Steve Lawrence and the city council in January that homes on the north side of the street could be severely damaged or destroyed.
Following his report Jan. 28, Anderson gained agreement from the elected body to hire Shannon and Wilson, Inc., to design a retaining wall and come up with a cost estimate for its construction.
The geotechnical firm based in Lake Oswego has worked with the city since the 1980s to monitor the site of the former landslide, so is familiar with the problems of ground movement.
Anderson expects the design work to be completed within the next three months. He said the city will then advertise for a contractor to erect the wall, which is expected to be in place during fiscal year 2014-15.
Anderson said the $58,776 being paid to Shannon and Wilson and subcontractor Quincy Engineering is money from the Transportation Systems Reserve Fund. That capital had once been set aside to upgrade Thompson Street and extend 19th Street.
However, citizens rejected the formation of a Local Improvement District to improve Thompson, considered a substandard street by city officials, due primarily to the high cost of the work. The majority of landowners along the roadway would have been charged $7,000-$8, 000 as their share of improvements but about one-third would have ended up with an assessment of more than $10,000.
North Wasco County School District vetoed the city’s offer of $294,148 to purchase the southern 42-feet of property along Thompson Track for the 19th Street Extension. The plan of municipal officials is to one day extend 19th eastward, from where it dead ends by Mid-Columbia Medical Center at Oakwood Drive to connect with Thompson Street.
In exchange for the right-of-way purchase, the city offered to pick up the district’s $78,000 share of Thompson Street improvements.
When the city mothballed the improvements for both streets in early 2012, the council made it clear that the cost to perform the work in two to five years was likely to be higher. They said there was no guarantee that the money set aside for upgrades would still be available when the plans were revisited.
Anderson said there is about $600,000 in transportation reserves, although about $500,000 has been generated by new developments and can only be used for projects that enhance roadway capacity.