The first misconception is that we need a new spillway, and the second is that corrugated metal pipe causes roadway washouts.
The new spillway to be built is to withstand a 100-year flood and will give a new golf cart path at a cost of approximately $3 million.
Those who propose the new construction fail to mention that the old spillway has withstood one 500-year flood and two 100-year floods within the last 10 years. Not bad for a spillway built around 1960.
About three or four years ago a maintenance problem showed up at the spillway: a large void was found under the concrete spillway. This maintenance repair should have been an easy fix by our construction people with approximately 14 cubic yards of flowable fill concrete, but our city officials opted to bid out the repair to a contractor because they felt a pressurized grout mix would be a better choice.
This process is equivalent to using a pressure grouting machine to fill a swimming pool when backing concrete trucks up to the pool and dumping the concrete directly into the pool would be quicker and far less expensive. Thank you, Chip Conner, for a well-built and well-designed spillway.
Regarding the misconception that roadway washouts are caused by corrugated metal pipes and that because some CMPs (corrugated metal pipes) rust out at the bottom they are unsafe and dangerous, both statements are simply false.
Washouts at pipe culverts result from bad or no planning, improper installation and no authoritative inspector checking the plan and installation. Driving south on Ga. Highway 74 from the 54/74 intersection you will see discolored spots on the roadway caused by oil from vehicles when they hit a good-sized bump in the road. Each of these bumps is found in a low spot in the road directly where a concrete pipe culvert has been improperly installed. These pipes, whether concrete or CMPs, are not the cause of the road’s settlement.
Washouts where CMPs or concrete pipes are used are due to bad or no compaction of the soil or gravel filling the trench around the pipe. In a flood situation or when the upstream end of a pipe is plugged by debris, water will find its way to the outside of the pipe, eventually leading to a washout. The pipe will be as good as new but the roadway will still be washed out.
A CMP that is rusted out in the bottom still retains its structural strength and will not collapse. There are reasons to use CMP and reasons to use concrete pipe. Either is acceptable in its proper place.
Charles Phillis
Peachtree City, Ga.
