Why a 60 inch pipe?
This is the
decision that had the most effect on the expense of this project and
why this may very well be a
disaster for the neighborhood in the future. First I have to wonder who
decided a 60 inch pipe was required for this location. This is some of
the largest drainage pipe made and is rarely used for this type of
situation. Given there is a bunch of 36 inch pipe just downstream from
this project; if in fact there is enough water flow to require this
size pipe,
the county should have constructed a retention pond on the city
property to
control the flow of water into the neighborhood rather than just
dumping all this water into it. Also smooth wall pipe accelerates the
water's speed compared to what a natural stream bed or even corrugated
pipe would be, so this
higher velocity water will now quickly erode the stream bed downstream
of this
project. This in turn will silt up the stream beds and pipes downstream
from
this construction, which will then create future flooding issues. An
open
stream with a rip rap base would have slowed down the water
flowing from the concrete pipes at the wall as it left the catch basin
and stopped this future
erosion
issue. Instead they installed the highest speed pipe at the downstream
end of this
project to make this a "worse case" situation.
Again, the 42 inch pipe under the road was more than adequate in size and if for some reason it wasn't, the solution should have been to design some way to retain this water rather than just dumping it into the neighborhood with the largest, highest speed pipe they could find. Time will tell how big a mistake this is.
What this points to is poor or no design study of what the problem was or even how much water flows into this area and calculating what size pipe was actually required. If the 42 inch pipe was large enough, there was no reason to dig up the street and the 42 inch pipe under it. If the 42 inch pipe wasn't large enough, what about all the old 36 inch pipe downstream from this project? Again, the correct solution would be to create a retention pond to control the influx of water into the neighborhood if there really is this much water, not to install a bigger pipe. Most of this storm water problem stems from the Asian Square and the lack of water control off that property. This type of development can't continue to be built if Doraville is to survive, but that's another topic for another day.
So now that the city decided this project requires a 60 inch pipe, the road has to be dug up and all the problems that entails. Also they decided to replace the pipe on the private property downstream from the actual problem using costly concrete pipe, switching to plastic pipe on the city's property. First lets look at downstream end of the project, which is where they started construction.
Again, the 42 inch pipe under the road was more than adequate in size and if for some reason it wasn't, the solution should have been to design some way to retain this water rather than just dumping it into the neighborhood with the largest, highest speed pipe they could find. Time will tell how big a mistake this is.
What this points to is poor or no design study of what the problem was or even how much water flows into this area and calculating what size pipe was actually required. If the 42 inch pipe was large enough, there was no reason to dig up the street and the 42 inch pipe under it. If the 42 inch pipe wasn't large enough, what about all the old 36 inch pipe downstream from this project? Again, the correct solution would be to create a retention pond to control the influx of water into the neighborhood if there really is this much water, not to install a bigger pipe. Most of this storm water problem stems from the Asian Square and the lack of water control off that property. This type of development can't continue to be built if Doraville is to survive, but that's another topic for another day.
So now that the city decided this project requires a 60 inch pipe, the road has to be dug up and all the problems that entails. Also they decided to replace the pipe on the private property downstream from the actual problem using costly concrete pipe, switching to plastic pipe on the city's property. First lets look at downstream end of the project, which is where they started construction.