Land subsidence and aquifer compaction in Montgomery County, Texas, U.S.: 2000–2020

Abstract

Groundwater-withdrawal-induced land subsidence has been a big concern in Montgomery County, Texas, U.S. since the 2000s. As of 2020, approximately half of the entire county is experiencing subsidence over 5 mm/year. This study aims to investigate ongoing land subsidence in Montgomery County using groundwater-level, extensometer, and GPS datasets. According to this study, land subsidence in Montgomery County since the mid-2000s is primarily contributed by sediment compaction in the Evangeline and Jasper aquifers; the compaction of Jasper aquifer contributes approximately one-third of the land subsidence since the mid-2000s; the pre-consolidation heads of the Chicot, Evangeline, and Jasper aquifers in Montgomery County are close to each other, approximately 15–25 m below mean sea level; the virgin-compaction/head-decline ratio is approximately 1:250 in the Evangeline aquifer and 1:800 in the Jasper aquifer in central and southern Montgomery County. As of 2020, the Jasper groundwater-level altitude is approximately 20–40 m below the pre-consolidation head in the central and southern Montgomery County; the Evangeline groundwater-level altitude is about 40–60 m below the pre-consolidation head. Land subsidence will continue to occur as long as the groundwater-level altitude in either the Evangeline or the Jasper aquifer remains below the pre-consolidation head.

New Preconsolidation Heads Following the Long‐Term Hydraulic‐Head Decline and Recovery in Houston, Texas

“…According to our investigations in the southeast portion of the Houston area, the inelastic compaction primarily occurred within 600 m below the land surface (Yu et al 2014). Long‐term groundwater level data illustrated in our previous studies (Wang et al 2021; Zhou et al 2021) and this study indicate that the groundwater levels in the upper Chicot (approximately within the top 150 m) were relatively stable, independent of the groundwater‐level changes in the lower Chicot. The upper Chicot behaves as an unconfined aquifer that has the water table as its upper boundary.…”

“…The preconsolidation head is a critical parameter for understanding the relationship between groundwater withdrawals and land subsidence. Preconsolidation heads in the Houston region have been investigated recently by several researchers (e.g., Kearns et al 2015; Amentini 2017; Wang et al 2021). Those investigations were not able to distinguish the preconsolidation head occurred before human pumping and the newly finalized preconsolidation head following the long‐term hydraulic head decline and recovery.…”