Offshore Pumping Impacts Onshore Groundwater Resources and Land Subsidence

• Published in: Geophysical research letters Vol. 46; no. 5; pp. 2553 - 2562
• Main Authors: Yu, Xuan, Michael, Holly A.
• Format: Journal Article
• Language: English
• Published: Washington John Wiley & Sons, Inc 16.03.2019
• Subjects: Agriculture; Aquifer systems; Aquifers; Coastal aquifers; Coastal effects; coastal groundwater resources; Coastal resources; Coastal waters; Coasts; Computer simulation; Drilling; Drinking water; Feasibility studies; geologic heterogeneity; Geological structures; Geology; Groundwater; Groundwater availability; Groundwater depletion; Groundwater discharge; Groundwater flow; Groundwater resources; Heterogeneity; Land subsidence; Mathematical models; Numerical models; Numerical simulations; Offshore; offshore drilling; Offshore drilling rigs; Offshore engineering; Offshore structures; Oil production; Petroleum production; Pumping; Salt advection; seawater intrusion; submarine groundwater discharge; Subsidence; Vulnerability; Water resources; Water use
• ISSN: 0094-8276; 1944-8007
• DOI: 10.1029/2019GL081910

Freshened groundwater exists offshore along many coastlines worldwide. Pumping of these offshore resources has been proposed for more efficient oil production as well as drinking and agriculture. Although pumping can occur tens to hundreds of kilometers offshore, these activities may threaten connected onshore aquifer systems. We conducted numerical simulations of variable‐density groundwater flow and salt transport in coastal aquifers with different geologic structure subject to offshore pumping to assess potential impacts. Results show that offshore pumping can diminish both onshore groundwater availability and submarine groundwater discharge and can cause widespread land subsidence. Heterogeneity increases water resource vulnerability relative to equivalent homogeneous and layered systems and exacerbates the magnitude of land subsidence. More continuous geologic structure causes propagation of maximum subsidence farther landward. This work suggests that coastal aquifers may be vulnerable to offshore pumping activities and that these effects should be considered in feasibility assessments for offshore drilling. Plain Language Summary Fresh groundwater extends offshore along many coastlines worldwide. These reserves may be a resource for water use on land and may also be used as a source of freshened water for more efficient offshore oil production. However, we do not know how offshore pumping of groundwater may affect water resources onshore. We investigated this question using numerical models that simulate groundwater flow and salinity in the subsurface onshore and offshore. We tested impacts of offshore pumping of groundwater for oil production. The results show that offshore pumping can deplete groundwater resources and cause land subsidence onshore, tens of kilometers away from the pumping zone. We therefore must be cautious when using offshore groundwater to minimize adverse effects on precious coastal water resources. Key Points Offshore pumping reduces fresh submarine groundwater discharge and onshore groundwater storage Geologic heterogeneity increases onshore water resources vulnerability compared to equivalent homogeneous and layered models Geologic heterogeneity propagates maximum land subsidence away from pumping location with potential for severe onshore effects