Matt Hogan, Project Engineer in our Site Engineering [...]
By: Darren Hamrick, PE, MS, LEED AP
The City of Birmingham engaged Sain Associates to review the existing drainage conditions at 6th Avenue South near UAB, which experiences frequent flooding. These flooding problems are related to the large watershed draining to this location and the lack of storm water management which was implemented many decades ago when this area was originally developed.
There are three areas in this vicinity where flooding is frequently occurring: 1) at the intersection of 6th Street South and 8th Street South; 2) at the railroad underpass on 6th Ave South; and 3) immediately upstream of the railroad crossing, near 6th Street South. Needless to say, this is a significant problem that needs to be corrected.
Furthermore, on the immediate downstream side of the railroad are several building facilities which also experience some drainage problems. These areas flood less frequently because the railroad immediately upstream acts as a dam, which in turn, causes more flooding to occur upstream.
All of these areas eventually flow into an existing 5’x10’ box culvert downstream, which has capacity to carry larger storms as flooding has not been experienced in this downstream location. One concern we wanted to consider was the possibility of overloading this 5’x10’ box culvert if we simply increase pipe sizes in the flooded areas immediately upstream.
In order to analyze this system, we developed a watershed model that includes the entire drainage area that contributes flow to the flooded area. This model has watershed areas that contribute to the flooding ranging from 4 acres to 282 acres in size. Because of the significant sizes of these watersheds, we had to consider the timing of each watershed and how long it takes for drainage to arrive in the flooded areas.
Findings and Proposed Solutions
Because we did not want to simply push this problem downstream by increasing pipe sizes in our study area, we looked for areas where we could capture and hold as much runoff as possible without flooding any streets. Fortunately, we identified vacant utility areas beneath an overhead transmission line which provided enough space where we could install a large storm water holding area. This area was designed to temporarily flood immediately after large storms, thus providing a place for the excess runoff to be held short term without flooding the roads. This Green Infrastructure project will improve drainage in areas that have previously had water flooding 2 feet deep in roadways allowing the drainage system to function without flooding these areas during a 10-Year Storm.
This project will re-purpose an under-utilized vacant utility area beneath an overhead transmission line and create an open green space where storm water can be managed to reduce flooding problems in the vicinity of 6th Avenue South. The result of this project will be a safer and more aesthetic environment in the vicinity of 6th Avenue South near UAB.