Coastal Fresh Groundwater Resources Protected From the Impacts of Climate Change
Published: 01/22/2014
Coastal Fresh Groundwater Resources Protected From the Impacts of Climate Change
Published: 01/22/2014
Coastal aquifers face saltwater intrusion threat
The Big Cypress Basin, a coastal freshwater ecosystem located in Southern Florida along the Gulf of Mexico coast, encompasses over 2,400 square miles and includes Naples, a city of about 22,000 people. The very flat basin area is only several feet above sea level. A basin water resources study conducted by a local water management agency concluded that sea level is expected to rise 5 to 20 inches during the next 50 years. The higher sea levels, along with projected increases in population and water supply use, will accelerate saltwater intrusion into the area’s aquifers that currently provide water for the region.
Schlumberger Water Services was hired to help predict the position and movement of the fresh water and salt water interface along the coast in response to the rising sea level and increasing groundwater withdrawals.
Schlumberger experts predict risk of saltwater intrusion
To accurately predict the position and movement of the interface between fresh water and salt water, Schlumberger used the density-dependent groundwater flow and solute transport SEAWAT model developed initially by the U.S. Geological Survey.
Schlumberger collected the existing water level and water quality data for the surficial aquifer system and confirmed that the data were adequate and reliable for calibration and verification purposes.
Within a short timeframe, Schlumberger developed a 3D groundwater flow SEAWAT model, which covered the major water supply well fields and the coastal watershed for the study area (Figure 1). The model used finer layer thicknesses to gain a higher resolution of the major water-producing aquifer, the lower Tamiami aquifer. The model was then calibrated for flow and solute transport using 2 years of transient water level and quality data.
The simulated effects of rising sea levels and human activities (groundwater withdrawals, etc.) clearly showed that saltwater intrusion (Figure 2) was a potential threat to the study area. In an area where the coastal ridge is physically absent and beyond, Schlumberger showed how a twofold increase to the existing groundwater withdrawal rates at the City of Naples Coastal Ridge Wellfield (Figure 3) would result in a significant saltwater intrusion impact along the west coast.
Schlumberger provided model to define long-term water management strategy
By modeling decreased groundwater withdrawals near the coast along with increased brackish groundwater withdrawals from deeper aquifers (Figure 4), Schlumberger enabled the basin’s water managers to strategically define future allocation of sustainable additional groundwater withdrawals.
The modeling and simulation GIS-based database developed by Schlumberger allowed the water managers to quickly review water level and water quality data (Figure 3), thus facilitating the management of water conservation strategies in the long term. Schlumberger recommended strategic locations of future water quality monitoring wells to detect salinity changes in the coastal aquifer and provide reliable, long-term data.
Challenge: Assess the nature and extent of the threat of saltwater intrusion into the coastal ecosystem and the public water supply in light of rapid population growth, increasing water supply demands, and sea level rise.
Solution: Design a groundwater withdrawal scenario that prevents saltwater intrusion and enables water managers to establish reliable, long-term permitting requirements.
Results: Demonstrated that saltwater intrusion is a real threat to the study area by using a GIS-based database that facilitated a quick review of water level and quality data. A long-term salinity monitoring strategy that included monitoring well locations was recommended.
