Four Corner - Texas Water Development Board

deposited on the inside curve of a river bend, where deposition of sands and other sediments is a
result of lower river flow velocities. On the outside curve of the river's meander, erosion of the
bank occurs. A similar location was studied by the Bureau of Economic Geology about two
miles downstream near Richmond. A view of the regional topographic map shows that the BEG
study area is very analogous to the Cummings Road area. Two geologic cross sections are
presented in Appendix A (Plate A-1) which shows the that sand and gravel deposits are present
to at least 60 feet in depth. Interbedded with these sand bodies are discontinuous clay lenses
representing interchannel deposits.
Faulting
In the Texas gulf coast region, faults associated with deep-seated salt domes are common, and
many subsurface faults extend to the land surface in the Pleistocene formations. Further, growth
faults which are not directly related to a salt dome occur throughout the area. Groundwater or
hydrocarbon production and accompanying subsidence activates these faults by differential
compaction of the sediments. Active surface faults, although slow moving, will eventually
damage buildings, deform rail lines, crack and deform roadbeds and damage sewers.
The nearest fault to the project is the Clodine Fault, which crosses FM 1464 about 1500 feet
northwest of the northwest comer of the Four Comers area. The Renn Scarp is also a known
fault about one mile east-northeast of the Four Comers area. Neither the Clodine Fault or the
Renn Scarp are known to be present in the study area. A map showing the location of major
faults and in the area is presented on Plate 5, and a detailed map of the Clodine Fault, the closest
active fault near the Four Comers area is included in Appendix A. No active faults are known to
be present in the Cummings Road area.
Site reconnaissance did not reveal any evidence of active or potentially active faults in the Four
Comers or the Cummings Road areas. There is a potential for faults to become active in the
future. As further development occurs in this area, additional structures and/or pavements will
be built which are susceptible to faulting. With fewer roads and structures in these area at this
time, the likelihood of identifying an active fault is less.
Subsidence
Subdivisions and industrial sites surrounding the study areas draw down groundwater for
municipal, industrial and commercial usage; the principal cause of localized land-surface
subsidence in the study areas. Subsidence has been measured by the U.S.G.S. between 1906 and
1978 throughout the study areas. Recently, annual measurements by the Harris-Galveston
Coastal Subsidence District (HGCSD) were conducted on several extensometers located in the
Houston area. Total subsidence in the project area ranges from three feet in the Four Comers
Area to about one foot at the Cummings Road area. Copies of maps showing the regional
subsidence in Fort Bend County from the HGCSD are included in Appendix A. In the project
areas groundwater is the main source of water. Therefore, it is likely that subsidence will
continue in the area. The primary consequence of this subsidence has been the alteration of
natural drainage patterns and the revisions of floodplain designations.
Topography
Four Corners. A copy of the Clodine USGS 7.5 minute quadrangle map is included in Plate
6.1. The ground surface in most of the project area gently slopes to the southwest toward the
Brazos River. In the northern part of the area, surface runoff flows into ditches which drain into
Keegans Bayou, which eventually empties into Brays Bayou about eight miles east of the area.
Most of the area, however, drains southward through ditches and empties into Red Gully, which
eventually empties into Oyster Creek about one mile south of the area. The elevation in the
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