2004-5 Pipe

Background

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There is a small creek that flows along the river side of the street here. It is “open” until it reaches a point about 80 feet west of the drive to the house, where it enters a 24” concrete pipe. This pipe continues along the street, makes a gradual right turn towards the river as it goes under the drive, and then continues along the lot line before emptying out into a ravine that flows into the Kanawa canal. The total length of the pipe is about 275 feet. There is (was) also a concrete manhole box about 75 feet up from the canal end of the pipe. It appears that the pipe was installed sometime in the very early 50s, although it could be earlier. The manhole box and the pipe from the manhole box to the ravine is newer than the rest of the pipe, but it is not clear how much newer. It may have been installed in the early 80s, but it is not known why.

There is also a concrete dam that runs along the river side of the property. This dam is completely buried, and no longer has a function. At one time there was an artificial pond on the property. The dam appears to be about 18” thick at the top, about 3 feet thick at the base, and is about 12 feet tall. It sits on a concrete base that is about 4 feet tall and about 8 feet thick. (We only know this as a result of the excavation we had to do as part of this project.)

The existing house (that we are in) was built in 1992-5, and replaced a house that was in essentially the same location. The existing house is built on top of the buried dam.

The previous owners (and builders) of the house experienced some over-land flooding of the creek at least once during the time they (or their family) owned the property. One of these incidents, in the mid 80s, may have prompted the partial replacement of some the original 24” pipe with newer pipe, as well as the installation of the manhole structure.

The neighbors have reported that on several occasions the road has flooded, although it is not known if any of these incidents also produced over-land water flow at the house.

The reason for all of the flooding in this location is fairly clear. The existing 24” pipe that is intended to carry the creek into the ravine (and into the canal) is simply inadequate. Richmond DPW, as well as a professional engineer with Timmons Engineering, have determined that the creek drains about 130 acres of the City of Richmond. During very heavy rains, or lighter rains when the soil is completely saturated, the pipe simply cannot handle the flow.

Summer 2004

Late in the afternoon of July 27, 2004, about 4 in. of rain fell at the house in about 45 minutes. The creek rose very quickly, overwhelmed the culvert, and flowed over the east side of the property. It was about 8-10 inches deep and fast moving. Within 90 minutes of the rain starting, the flood was over. It was during this flood that about 8 feet of dirt bank and riprap were eroded at the tail end of the existing 24” pipe. In addition there was extensive erosion around the concrete manhole box, although no actual damage to it was apparent. However, the manhole box was now very susceptible to further erosion, since water could easily dig into the earth around it.

In August of 2004 Hurricane Gaston dropped 10 to 12 inches of rain in a few hours in central Richmond. Again the existing 24 inch pipe was overwhelmed and there was overland flooding. (I am sure it was much worse and much scarier than the flooding of July 27. We were out of town for it.) During this storm the concrete manhole box failed and collapsed, and about 80 feet of the pipe were destroyed. A canyon about 15 feet deep and about 80 feet long resulted. Again no water got into the house.

All of this damage was photographed, and the actual flooding in the July storm was photographed.

The Problem

The destruction of the 24 inch pipe and the severe erosion left the property much more vulnerable to further damage, although no actual damage to the house had occurred.

After the July storm I contacted Richmond DPW, and an engineer made several visits to the property. He concluded that the existing pipe was “grossly inadequate”, and that at least a 54” pipe was needed. He also made the initial estimate of 100-130 acres of Richmond draining through this creek.

However, after some research the DPW engineer concluded that the existing pipe did not belong to the city, had not been installed by the city, and that no city right of way existed. He said that the city could not do anything for us. He did suggest that we could offer a right of way to the City, but that there was no guarantee it would be accepted and that even if it was there was no guarantee what might be done in the way of repairs, or when.

The Solution

When it became apparent that this was “our problem” I began a search for help. We quickly found Timmons Engineering, and an engineer was assigned to the job.

We went through about two months of design work, exploring replacing the existing pipe with a larger pipe, as well as making an open rock lined channel.

The rock lined open channel had advantages, but would have been far too wide and too expensive. This was rejected in favor of replacing the existing 24 inch pipe with a 60 inch pipe. At the head end of the new pipe there will be two six foot square boxes with walls that taper away towards the entrance. Behind that is a formed structure that forces water into the pipe. At the tail end of the pipe is a “vee” shaped wall structure and a large amount of granite riprap.

We have bid out this project and it is currently underway. I believe it will be substantially done by the end of the third week of January. At that point we will have to landscape the yard again and get some driveway work done.

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