Monitoring the City’s groundwater levels is essential for us to understand what the water does underneath the surface, where is most vulnerable, and how the groundwater is influenced by rains and infiltration from the canals, Lake Pontchartrain, and the Mississippi River. Here are a few example questions we would like to learn more about:

• Does the brackish water table under Lake Pontchartrain increase the salinity of the groundwater under the city? 
• How much does the height of water in the canals alter the groundwater levels under city blocks nearby?
• During a heavy rain event, what is the storage capacity of the soil to absorb more water, and how long does it take for the water table to re-normalize?
• Where is the water table during a time of prolonged drought?

With the assistance of the Deltares Institute, the City hopes to answer these questions and more by installing a groundwater monitoring network that consists of approximately 30 observational wells across New Orleans, exceeding well beyond the Gentilly Resilience District. These wells will monitor water pressure (depth),  temperature ,and sometimes even salinity and pollution. Deltares is creating a user-friendly portal that can store this data, which needs to be collected across the city every 6 months, and map it so residents can learn more about the groundwater depth and quality in their own neighborhoods. 

Subsidence is the sinking or compaction of land over time, often the result of draining an area that has historically been saturated with water. As the city expanded in the past century, much of the low-lying areas (former swamps and marshlands) were drained to allow for development. These soils are high in organic material like peat and are more prone to reduce in volume when dried out. Constantly draining the city of its water comes at a cost: not only is it expensive to run pumping stations, but the removal of water from the soil compresses it and subsequently reduces its ability to hold water thereafter. Not all soil has the same composition and will respond to this drying out in the same way. Regardless, we can see parts of the city that experience subsidence as concrete and asphalt (impervious surfaces) prevent stormwater from recharging the water table beneath the soil. This affects everything from household foundations to streets to drainage and water pipes.  

 

Feel free to read these reports linked below to learn more about groundwater monitoring and subsidence in the city and region.  

Read the Shallow Subsidence Vulnerability Report (2019)

Read the Groundwater Monitoring Network Report

Read the Assessment of Land Subsidence in New Orleans Report (2023)