Pima County Regional Flood Control District (RFCD) and the Department of Transportation Maintenance Operations Division joined forces to quickly assess and repair damage to Silverbell Road after Sunday’s extreme storm event. On July 29, 2012, Idle Hour Wash peak flow was 5,800 cubic feet per second, equal to a 100-year storm, according to RFCD evaluation of high water marks. Based on comments from neighbors and silt deposits, at least 600 feet of Silverbell Road was covered by flowing water.
Rain gauges upstream from Silverbell Road in the Idle Hour Wash watershed recorded 2.5 to 3.8 inches of rainfall in two to three hours, with most rainfall occurring in the first hour. It is the area’s most damaging storm since the floods of 1993.
The tremendous surge of water eroded the embankment and soil beneath Silverbell Road, approximately .9 miles north of Sunset Road. Pima County Sheriff Department immediately closed this section of Silverbell Road, between Sunset Road and Panorama Road. The road remains closed for repairs; however, local residents still have access to neighborhood streets. This section of Silverbell Road is expected to reopen by Wednesday, August 8. In the event of mechanical failure or inclement weather, the construction schedule is subject to change.
As the supporting soil washed out from beneath Silverbell Road, the pavement cracked and portions were washed out. In addition, Tucson Water lines were exposed. Before road repair work could begin, Tucson Water inspected its water lines and found no apparent damage. Pima County and its contractors have repaired the embankment and will install a new cut-off wall on the east side of the road. The wall, designed to protect the roadway from further erosion, will be approximately 300 feet long and up to eight feet deep. A concrete and cable erosion protection revetment will be added immediately downstream of the newly constructed cut-off wall to protect against future erosion.
The County will also install 600 feet of new pavement beginning this weekend. The road will be reopened to traffic after the paving is complete, but there will still be construction activity along the sides of the road, and the roadway will be subject to construction zone speed restrictions.
The estimated cost of repairing this section of Silverbell Road is $200,000. This does not include utility inspection or repair costs.
In addition, the County will repair Placita del Rio, a local street that also washed out during the storm. Placita del Rio has been temporarily filled in with dirt, so the street is open for local residents. The County will also install pipe culverts on Placita del Rio to allow future storm runoff to flow beneath the street.