1. Guoquan (Bob) Wang University of Houston
Current Land Subsidence in the Houston Metropolitan Area, Texas, Derived from GPS Observations ( )
Guoquan (Bob) Wang
University of Houston
With contributions from graduate students: Timothy J. Kearns, Jiangbo Yu, Linqiang Yang, Xueyi Jia, and Jianjun Jiang

2. Outline GPS Geodesy Infrastructure in the Houston area
Public available GPS stations (Hardware)
Stable Houston Reference Frame (SHRF) (Firmware)
Single-receiver phase ambiguity resolved GIPSY PPP resolution (software)
Current subsidence mapping ( )
Scientific Questions:
(1) Is there deep seated (or fault-controlled) subsidence in the Houston area?
(2) When will the current subsidence stop?

3. Historic Subsidence in Houston
3 m within 30 years, 10 cm/year
(USGS, Coplin and Galloway, 2009)
(USGS, Kasmarek et al., 2009)
6 m
Historic Subsidence in Houston
USGS

4. Houston Ship Channel Area

5. Geodesy Infrastructure: Permanent GPS Stations
Harris-Galveston Subsidence District (70+)
Texas Department of Transportation 15+
83 GPS +11 Extensometers
City of Houston, others

6. HoustonNet NSF MRI: 40 GPS; UH: 10 GPS
Subsidence, faulting, and salt dome uplift
Hurricane intensity forecasting
Civil engineering community---buildings, bridges, dams, sea walls

7. Geodesy Infrastructure: The Stable Houston Reference Frame
Helmert Transformation
7 years:
Wang et al., 2013

8. 14-Parameter Similarity Transformation
Translation along the respective axis (in meters)
Differential Scaling of the respective axis (ppb)
Counterclockwise Rotations (in radians)

9. 14-Transformation Parameters
Unit
IGS08 to SHRF
t0 = 2012
IGS08 to NAD83(2011)
t0 = 1997*
Tx(t0) cm
Ty(t0)
Tz(t0)
Rx(t0)
mas
Ry(t0)
Rz(t0)
s(t0)
ppb
dTx
cm/year
dTy
dTz
dRx
mas/year
dRy
dRz ds
ppb/year
NGS
*Pearson and Snay (2013), Table 7

10. No-linear subsidence rate
18 Years
Jersey Village
Spatial and temporal variation of subsidence

11. Ground Deformation at Closely-Spaced (4 km) GPS Sites

12. Recent Subsidence Mapping (2005-2012)
85 years
6 m
83 GPS +11 Extensometers

13. Maximum subsidence rate <=2.5 cm/year
< 5 mm/year
7 years:

14. Aquifer Profile: Chicot + Evangeline
3600 ft
USGS

15. Subsidence---pumping (??%)+ faulting (??%)
Question 1: Is there deep-seated (fault-controlled) subsidence in the Houston-Galveston area?
Gulf Coast Geology and faults
Subsidence vs. Faulting
Subsidence---pumping (??%)+ faulting (??%)
Ortega, 2013

16. USGS Borehole Extensometers
Compaction meter
USGS
13 extensometers at 11 sites
40 years: 1974—2013

17. Addicks Borehole Extensometer (-549 m)

18. Co-Located GPS and Extensometer Monitoring Site (ADKS)
+15 years
Wang et al., 2014

19. Wang et al., 2014 Journal of Surveying Engineering
18 years
40 years
Drought of 2011
Drought of 2005
Conclusion: The compaction measurements from the long-term extensometers are reliable and the accuracy is about a few millimeters.
Wang et al., 2014 Journal of Surveying Engineering

20. Co-located GPS and Extensometer Sites
ADKS(-549 m)
NETP (-591 m)
LKHU (-661 m)
22 years
Conclusion: Compacted aquifers are limited to above -600 m

21. Clear Lake—Jonson Space Center Sites
Clear lake Deep Borehole (-936 m)
Clear lake Shallow Borehole (-530 m)
Jonson Space Center(-235 m)
50m
2.5 km
37 years
Conclusion: No compaction below -530 m

22. -530 m
USGS, 2009
Conclusion: Only partial of the Evangeline aquifer had been compacted!

23. Coastal Subsidence: Galveston vs. New Orleans
4 mm/year
It appears no considerable tectonic subsidence occurs currently in the Houston-Galveston area.

24. UH Coastal Center “Vertical” GPS Array
-1 ft
-10 ft
-20 ft
-30 ft
Borehole GPS

25. Question 2: When will the subsidence cease?
38 years
Conclusion: It took 20 years ( ) to halt the subsidence in the southeast part.

26. 38 years
Conclusion: =2025

27. Summary
The ground water and aquifer systems respond slowly to human actions. It took almost two decades (1980s and 1990s) to halt the subsidence in the south-east part of the Houston metropolitan area. Therefore, a long-term perspective is needed to manage groundwater resources and control land subsidence.
The spatial and temporal variation of subsidence could be very considerable!
subsidence=f(x,y,z t)
The groundwater regulations implemented by the HGSD are very successful in reducing subsidence rate in the Houston area. Currently, there is no considerable deep-seated or fault-controlled subsidence in the Houston-Galveston area. Current aquifer compaction is limited to about -530m.
Thank you!

28. Stable: v=0