Abstract
As much as 3.05 m of land subsidence was observed in 1979 in the Houston-Galveston region as a result primarily of inelastic compaction of aquitards in the Chicot and Evangeline aquifers between 1937 and 1979. The preconsolidation pressure heads for aquitards within these two aquifers were continuously updated in response to lowering groundwater levels, which in turn was caused by continuously increasing groundwater withdrawal rates from 0.57 to 4.28 million m3/day. This land subsidence occurred without any management of changes in groundwater levels. However, the management of recovering groundwater levels from 1979 to 2000 successfully decreased inelastic compaction from about 40 mm/yr in the early 1980s to zero around 2000 through decreasing groundwater withdrawal rates from 4.3 to 3.0 million m3/day. The inelastic consolidation that had existed for about 63 years roughly from 1937 to 2000 caused a land subsidence hazard in this region. Some rebounding of the land surface was achieved from groundwater level recovering management. It is found in this paper that subsidence of 0.08 to 8.49 mm/yr owing to a pseudo-constant secondary consolidation rate emerged or tended to emerge at 13 borehole extensometer station locations while the groundwater levels in the two aquifers were being managed. It is considered to remain stable in trend since 2000. The subsidence due to the secondary consolidation is beyond the control of any groundwater level change management schemes because it is caused by geo-historical overburden pressure on the two aquifers. The compaction measurements collected from the 13 extensometers since 1971 not only successfully corroborate the need for groundwater level change management in controlling land subsidence but also yield the first empirical findings of the occurrence of secondary consolidation subsidence in the Quaternary and Tertiary aquifer systems in the Houston-Galveston region.
Highlights
Land subsidence (LS) can be a gradual settling or sudden sinking of the Earth’s surface owing to subsurface movement of earth materials [1]
Groundwater withdrawal historical characteristics are firstly outlined in four different periods before the temporal and spatial characteristics of groundwater level change are summarized corresponding to the four periods, respectively
After primary inelastic consolidation is completed and when primary elastic consolidation rate trends to zero, the remaining compaction of an unconsolidated or semi-consolidated aquifer system measured by a borehole extensometer is considered here to be the secondary consolidation due to geo-historical overburden pressure
Summary
Land subsidence (LS) can be a gradual settling or sudden sinking of the Earth’s surface owing to subsurface movement of earth materials [1]. More than 80 percent of the subsidence in the nation is identified as a consequence of human impact on subsurface water [1,2]. Geosciences 2019, 9, 223 show the first signs of human-induced LS—initially attributed to extraction of oil and gas from the subsurface alone [3], and has been subsiding due to the combined effects of groundwater withdrawal, hydrocarbon extraction, salt dome movement, and faulting [4]. By 1979, as much as 3.05 m of LS had occurred in the Houston-Galveston area, Texas [1]. LS is of particular concern in low-lying coastal areas such as the Houston-Galveston region. The latest flood caused by Hurricane Harvey (2017) in the Houston-Galveston region (HGR) was regarded as one of the costliest disasters in the U.S history, with damage exceeding $100 billion. Subsidence has shifted the shoreline along Galveston Bay, as evidenced by the inundation of the Brownwood Subdivision associated with
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