Pipe dreams 

[{
    "name": "Ad - Medium Rectangle CC01 - 300x250",
    "id": "AdMediumRectangleCC01300x250",
    "class": "inlineCenter",
    "insertPoint": "8",
    "component": "2963441",
    "requiredCountToDisplay": "12"
    },{
    "name": "Ad - Medium Rectangle LC01 - 300x250",
    "id": "AdMediumRectangleCC01300x250",
    "class": "inlineCenter",
    "insertPoint": "18",
    "component": "2963441",
    "requiredCountToDisplay": "22"
    },{
    "name": "Ad - Medium Rectangle LC09 - 300x250",
    "id": "AdMediumRectangleLC09300x250",
    "class": "inlineCenter",
    "insertPoint": "28",
    "component": "3252660",
    "requiredCountToDisplay": "32"
    }]

“Ooh, that's worse then the last time I came down here.� Barbara Lynch, city engineer for San Luis Obispo, said as she looked up at the underside of the Marsh Street Bridge, near Santa Rosa Street.

Lynch was particularly concerned with a section of concrete that had fallen off the underside of the bridge. Over time, the steel rebar inside the concrete of the bridge rusts and expands, pushing the concrete off and compromising the structural integrity of the bridge.

The Marsh Street Bridge was built in 1905, and its age, combined with the ongoing erosion of San Luis Obispo creek, has members of the Public Works department a little concerned. They've asked for money from the City Council to fix these infrastructure problems around the city, but there's not much money to be had. City officials are using examples like this in the case for increased sales tax.

The bridge on Marsh Street is easy to miss. Most drivers are probably unaware they are even traveling over a bridge. Similarly, the Higuera Street Bridge could easily go unnoticed.

Don't know where the Higuera Street Bridge is? Don't worry; you're probably not alone. It's actually more like a tunnel underneath the section of sidewalk between Mo's BBQ and Abercrombie and Fitch.

SLO creek disappears under Higuera Street and isn't exposed until is flows out of underneath Mission Grill. McCarthy's regulars know a good look at this hidden section of SLO Creek can be found from a window in the pub's men's room.

Because so many of these bridges go unnoticed, it's likely the public is often unaware or concerned with their conditions. Lynch spends a lot of her time examining the things in that city that often go unnoticed, like storm drains, which happens to be another problem area for the public works department.

About 22 percent of the 59 miles of storm drain pipelines inside the city are CMP, or corrugated metal piping. The CMP pipes were installed 20-30 years ago, and what Lynch is finding, through the use of video cameras mounted on long snaking devices, is that the CMPs are beginning to fail.

So what's the problem? According to Lynch, storm runoff of water and sediment runs down the CMPs, eventually eroding the bottom of the pipe. Once the stream eats through the pipe, the water essentially flows over rocks and sand like an underground river. These streams slowly erode the earth around the pipe, pulling the soil down from above.

Over time, this creates sinkholes and cracked sidewalks, and if a failed pipe is close to a home it can damage the foundation. If one of these failing pipes is below a street, then the pavement on the street can act as a bridge as the soil below slowly sinks.

This in turn eventually drives up the cost of street repairs as streets crack and erode.

“If we could just get rid of this stuff … � Lynch said recently when watching a video of rusted old CMP pipes under Los Osos Valley Road. Lynch is, of course, concerned that if the city doesn't replace the CMP pipes it will lead to more costly road repairs later. There are temporary fixes, like pumping concrete to line the bottom of the eroded pipes, she said.

But Lynch would prefer to replace the pipes.

“Concrete pipe appears to hold up much better,� she said.

For Lynch and Public Works it's difficult to get people to think about pipes that they never see and bridges they don't go under. Bridges, she said, are normally built to last 50 years; then maintenance is usually required. If the proposed sales-tax increase passes next November, the department says it will receive the money it needs to make some of these fixes, she said. ∆

Staff Writer John Peabody can be reached at [email protected].