Geological Factors in Engineering

Very interestig post, but is this true:

[quote]The Houston Galveston Subsidence District was founded to correct this very issue, but parts of Houston have subsided as much as 10 ft. over the past century. [/quote]

Also, is this really true, as well?

[quote]If the district succeeds and prevents the further pumping of water from the local aquifer, Houston's only geological concerns may be global warming and rising sea levels.[/quote]

I can see the risk of pumping from wells causing subsidence, but do we really, truly know that 'global warming' will really cause a sea level rise?

Excuse the typo, but her is the link to the Harris-Galveston Subsidence District

http://www.hgsubsidence.org/

"The Harris-Galveston Subsidence District is a special purpose district created by the Texas Legislature in 1975. The District was created to provide for the regulation of groundwater withdrawal throughout Harris and Galveston counties for the purpose of preventing land subsidence, which leads to increased flooding."

USGS has the following post about rising sea levels:

http://pubs.usgs.gov/fs/fs2-00/

"As the climate has warmed following the end of a recent cold period known as the "Little Ice Age" in the 19th century, sea level has been rising about 1 to 2 millimeters per year due to the reduction in volume of ice caps, ice fields, and mountain glaciers in addition to the thermal expansion of ocean water."

It may be an overstatement that Houston's only worries will be rising sea levels. Without excess pumping of water from the local aquifers the land is still subsiding. Storm surges reek havoc and cause flooding.

I don't mean to use the term global warming as if there is any reason without a doubt that humanity has forced the process. There has just been a noticeable decline in ice volume, which can be accurately determined by stable isotope concentrations in ice cores, which in turn causes sea-levels to rise.

In short yes the sea level is rising, land in Houston has subsided over 10 ft in some places over the past century and the Harris-Galveston Subsidence District was founded in 1975 to provide for the regulation of groundwater withdrawal throughout Harris and Galveston counties for the purpose of preventing land subsidence.

It is a quite different problem than in New Orleans, where it is a fight against a huge river. The Houston area is simply not stable ground. Both were poor places to build a city. However a Dutch-style dike would work as long as there is no river to fight. If that is not feasible as a permanent cure, then Houston is and should be treated the same as NO and slowly be abandoned. It is not worth pouring money into a hole in the ground.

Amidst the problems associated with controlling the Mississippi I see a lot of similarities between these two cities. If it wasn't for subsidence, the areas protected by levees in New Orleans would not be below sea level. It's not like we pushed back the gulf to create a city. Also, if the oceans continue to rise or rise any quicker than we have seen over the past decade these metropolitan areas will most likely be the first to fall into the ocean as they have a long history of issues associated with storm surges.

Shawn - they will not fall into the ocean for a long time. They will be slowly flooded, evacuated and abandoned long before the buildings crumble. It is the areas of NO that were built on reclaimed swamp that are most in danger, not the old city. Houston apparently was built on unstable land to begin with and apparently does not have a huge river to fight. A big dike may work as a permanent solution. Nature will change the climate and sea levels without regard for Man, who all too often builds in places he should not. In the long run it will be cheaper to move and rebuild in a safer place than to spend billions, then have to abandon the places anyway in the future.

Shawn,

Good photo. The problems you mention do not affect just Houston and New Orleans. Look also at Long Beach California and the peat islands east of the San Francisco Bay. I wonder how much of the subsidence is also related to removal of oil from the formations underneath? I am sure that similar problems are occurring in many other cities in the world.

--JMM

Seems that I heard it was common practice to displace oil with water as it was pumped out, thus avoiding subsidence.

Good call on Long Beach California, I read a posts that suggested places had seen as much as 30 ft of subsidence from extracting fossil fuels. In this case they were able to use injection wells and an immiscible fluid, salt water, to increase yield rates while preventing further subsidence. In Houston, injection wells would only pollute the ground water. There is also subsiding land taking place as a natural process.

The extraction of fluids from below the ground is a major concern because of the potential for subsidence. For about a century now they have been monitoring the subsidence in the San Joaquin Valley of California due to agricultural drawdown of the aquifer. Groundwater withdrawl is one of the most common causes of subsidences in the midwestern and western states. States like California, Texas, and Florida have huge agriculture industries that demand a lot of water. Add to that the rapidly growin populations in some areas, and you create a continuous over draft problem that just increases.

Right on, RCE. When the California Aqueduct was built to transfer Feather River water to Southern California, it was made extra deep in the San Joaquin valley for this reason.

--JMM

The California Aqueduct leaks a lot actually raising groundwater along the western fringe of the San Joaquin Valley. However, in the southern half of the San Joaquin Valley, they cause subsidence because the material in that area is aeolian collapsible soils in a very dry climate. The extra water from the surface is causing the soils to collapse slowly. Much of the early water shortage issues through out the entire Central Valley, however, can be tracked back to when dams were installed and almost alway to the 20 year period immediately following WWII when there were massive transitions to irrigated agriculture. Since the 1960s, while the agricultural impacts have increased slightly, much more of the impact has fallen on the rapid growth of the municipalities with very poor long term water planning. Under most Cities in the Cnetral Valley there is a huge groundwater depression in the deeper potable aquifers where they pump water from. This deeper depression makes the subsidence worse, since it removes the support of the deeper water but allows the weight of shallower aquifers to bear down along with the soil (most shallower aquifers are polluted with salts, nitrates, etc. from agriculture, and related industries like canning, and are not cost effective or safe for drinking water sources).

All soil is fluid flowing down hill to the sea. Even land at a high elevation moves. So any one that builds near water can expect over time to have problems. The closer to water and the heavier the structure tend to sink in. I am sure this is no new revelation to the engineers that build in these areas. The water means ports, ports mean commerce, commerce means jobs. I suspect even today city planners are still allowing building permits in areas of questionable soil stability. Their only consideration is the dollars it brings to the city. So it is up to the people to educate themselves.

Doesn't the run off from cotten farms and the Agent Orange they use to defiolate the plant before harvest poision the drinking water?

Yes herbicides are an issue for surface water pollution carried in agricultural runoff. This is why the State of California is requiring surface water monitoring programs in sensitive natural waters paid for by local co-ops of farmers (if they don't want to co-op their effort a farmer can also set up a network to monitor the portions they can contribute run off too). However, you almost never see herbicides in subsurface groundwater from agriculture (sometimes they show up around localized point source where they were stored or manufactured by distributor/manufacturers). When they do show up in groundwater it is usually in water that is highly polluted with salts, nitrates and other inorganics, and has almost no beneficial use at that point. (They are, however, good from a regulatory stand point as an indicator of source of the inorganics, and can force clean up since they won't ocur naturally unlike the salt and nitrates.)

Check this Link out:

http://www.hcnonline.com/site/news.cfm?newsid=19529697&BRD=1574&PAG=461&dept_id=639299&rfi=6

Yes, herbicides are an issue for polluting groundwater and it looks like there is a proposal to introduce injection wells that would pump 350 gallons per minute of Class 1 Non-Hazardous Wastewater into a local oilfield. I guess one way to stop residents from pumping local groundwater is to pollute it and later deam it non-potable...

Define Class 1 non-hazardous waist water... Sounds like agricultural run-off to me...

http://www.texascenter.org/almanac/Waste/INDUSTRIALCH9P1.HTML

If, by chance, the government could locate the heaviest layers of salt could they drill and install some type of " wick " that would allow the water in the salt to be drawn out.

Houston should have enough heat and wind to dry out the salt bed.