As a result of its unusual topography, the city of New Orleans is prone to flooding from the Mississippi River and Lake Pontchartrain, as well as frequent inundation from high intensity rainfall. Since the late 1800s, New Orleans Sewerage and Water Board (NOSWB) has been tasked with providing the city adequate drainage, sewerage collection and drinking water while mitigating flooding risks and drinking water contamination.
In September 2017, the NOSWB began a comprehensive review of its storm water system. It was an ideal time to test the system—right in the middle of hurricane season.
CC Lynch was brought in to test 23 pumping stations. The board also tested a series of control rooms and a power plant through separate contractors.
CC Lynch selected two main methods for measuring flow at each pump station, testing with an ADCP (acoustic doppler current profiler) or an ultrasonic clamp-on flow-meter. There were also a couple of unique scenarios that called for two additional open channel flow measuring techniques using Teledyne Isco’s 2150 AV sensor and their Non-Contact LaserFlow Velocity Sensor. The method deployed depended on the pumping station’s physical configuration and access. In some cases, multiple methods were used to generate the most accurate reading.
At larger pump stations with sufficient access, the CC Lynch crew conducted the ADCP method, applying USGS best practices. A tag line was installed across the station’s influent channel. A floating platform, with the ADCP sensor mounted to it, ran along the line while the ADCP sensors collected velocity, area and flow measurements.
To execute this method, the crew used Teledyne RDI’s RiverPro ADCP as well as the StreamPro for shallower channels. The product’s auto-adaptive sampling feature helped improve the accuracy of discharge measurements while its 20-degree beam enabled data collection from the bottom of the channel.
At stations containing influent closed pipes with sufficient access, we used a Flexim ultrasonic flow meter. This clamp-on process was non-invasive to the pipe and enabled water to continue to flow throughout testing.
CC Lynch has seen the Flexim meters outperform competing units in accuracy on numerous applications. While in use, Flexim meters document many QA/QC parameters, enabling operators to verify reading quality.
The CC Lynch crew reviewed these parameters after each reading. At stations where the ADCP method was deployed, we ran the data through separate QA/QC procedures.
Our team put together detailed summaries on each pumping station, listing our findings and highlighting vulnerabilities. This documentation was added into a larger report on the entire storm water system.
CC Lynch was able to serve as a one stop shop for all the flow-monitoring needs of the NOSWB. Our team designed a testing approach that would accommodate the physical configuration of each station, operated all the measuring equipment, analyzed flow data and compiled findings into a simplified format for the board.
In December, the board received a report detailing the performance of the entire storm-water system. This research and analysis will help the NOSWB address system weaknesses over the coming year.