Groundwater Level Change Management on Control of Land Subsidence Supported by Borehole Extensometer Compaction Measurements in the Houston-Galveston Region, Texas

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.

Land subsidence contributions to relative sea level rise at tide gauge Galveston Pier 21, Texas

“…The ASLR 7,13,14 is equivalent to eustatic sea level rise (SLR) 15,16 or global-mean geocentric SLR 2 and attributed to global warming. In this paper it is assumed that LS 7,13,14,17 includes two components LS BR and LS nBR , where LS BR is subsidence contributed from bedrock systems or non-compacting strata owing to tectonic subsidence (TS) [18][19][20] and creep of bedrock systems (SC BR ) 21 ; and LS nBR is subsidence contributed from the compaction of susceptible (compressible, non-bedrock) aquifer systems owing to primary compaction (SPC) caused by subsurface fluid withdrawal [22][23][24][25][26][27] and creep of these aquifer systems (SC nBR ) [28][29][30] . Thus, RSLR = ASLR + LS, where LS = LS BR + LS nBR ; LS BR = TS + SC BR ; and LS nBR = SPC + SC nBR (see Table 1).…”

The Secondary Consolidation (Creep) due to Geohistorical Overburden Pressure in the Houston-Galveston Region, Texas

“…In other words, the changing value ofṡ s over the t period is negligible and can be ignored. This negligibly variable rate is called a pseudo-constant rate of secondary consolidation (Liu et al, 2019). For example, if a period ( t) is considered to be 10 years, 990,1990, and 9990 years are needed for specified subsidence rate decrease percentages of 1.0 %, 0.5 %, and 0.1 %, respectively.…”

“…Equation (4) (Liu et al, 2019) is employed to analyze extensometer-measured compaction rate for the three components in response to groundwater level changes in aquifers. Three distinct compaction characteristics for the three components must be correctly applied in this analysis: inelastic compaction rateṡ p−v(t) is 10 to over 100 times larger than elastic compaction rateṡ p−e(t) when groundwater levels are lower than preconsolidation pressure head (Epstein, 1987;Hanson, 1989;Helm, 1978;Liu and Helm, 2008;Sneed and Galloway, 2000); elastic compaction rateṡ p−e(t) can be negative (land rebounding) while inelastic compaction rateṡ p−v(t) decreases rapidly but is never negative when groundwater is recovering; and secondary compaction rateṡ s(t) does not change in response to changes in groundwater levels.…”

“…Hydraulic properties of the Chicot aquifer do not differ appreciably from the hydrogeologically similar Evangeline aquifer, but can be differentiated on the basis of hydraulic conductivity. The transmissivity of the Chicot aquifer ranges from 915 to 7625 m 2 d −1 and the transmissivity of the Evangeline aquifer ranges from 915 to 4575 m 2 d −1 (Meyer and Carr, 1979). The geologic units that make up the Chicot aquifer outcrop and extend inland from the Gulf of Mexico and terminates at the most northern updip limit of these units.…”

Coupled Stress-Dependent Groundwater Flow-Deformation Model to Predict Land Subsidence in Basins with Highly Compressible Deposits

“…The subscript st denotes steady state condition. Equation (5) implies that at each spatial location in the aquifer system, aquifer sedimentary materials move with the velocity equal to the difference between specific discharges of steady flow and transient flow at time, t, in that location. The concept of the potential function for irrotational incompressible bulk flow can be utilized to express Equation (5) in the form of a hydraulic head, as follows [28]:…”