Measuring Gulf Coast Subsidence
by: Rod Rice, January 29, 2007 5:01:00 am
Even though there are thousands of benchmarks along the Texas coast designed to measure subsidence, petroleum geologist Arthur Berman says the benchmarks themselves have not been measured since the 1980s.
"The National Geodetic Survey's Gilbert Mitchell told me a year and a half ago that of these two-thousand benchmarks that we have in Houston, almost none of them are worth using."
If they are sinking as a group they don't tell you the whole story. Berman says it's like two people standing on the deck of a ship trying to determine if the ship is sinking by looking at each other.
"We're about the same height, and we're eyeball to eyeball so I guess there's no problem. But the ship is sinking. So, how do we know that the ship is sinking? Well, when the water comes over the deck I guess we know. But, if we're deciding if the ship is sinking by...'are you going down relative to me or am I going down relative to you'...we never know."
Recent history has shown that not knowing the amount an area is subsiding can have a devastating result. An article published last June in Nature found that some levees failed in New Orleans during Hurricane Katrina, not because they were improperly constructed, but because the area had subsided up to three feet in some places. Levees thought to be 20 feet above sea level were really 17 above sea level.
At a National Geodetic Survey meeting in Houston it was announced the Army Corps of Engineers now believes it is important to know more about subsidence along the Texas coast. So too does Senator Kaye Bailey Hutchison. She's seen to it that Texas A & M, Corpus Christ, got three quarters of a million dollars to begin to up-to-date benchmark measurements along the Texas coast. In reality, though, that is just seed money for a project that would cost millions just in the Houston area alone. Arthur Berman says millions is a fair amount of money.
"But you look at the kind of damage that places like Houston sustain every time we have a flood, the Allison storm was billions of dollars, Katrina, I don't even know what the number is but it's tens of billions of dollars. When you look at that as a possible consequence, a few million in hindsight looks like it would have been a relatively small and wise investment."
Berman believes that if the area is to mitigate and deal with the affects of subsidence, its leaders must have accurate information. He says, after all, that's exactly how we live with the threat of hurricanes.