Saturday, December 11, 2010

What a Geologist Thinks About...[Original Post Date 9/15/07]

often while reading or hearing a news report on a "man vs. nature" issue, is - "Why is this happening?". From The Seattle Times, by way of WND - there is a story on serious coastal erosion problems on the northern side of Willapa Bay along the southwest Washington State Pacific Coastline (see inset map associated with the article). Though there are some explanations within the article, we realize that there may be more than one reason why this is happening.

From the Seattle Times article:

..."This two miles of shoreline at the northern confluence of the Pacific Ocean and Willapa Bay, 12 miles south of Westport, is believed to be the fastest-eroding beach on the Pacific Coast. It has lost about 65 feet a year to the sea since the late 1800s. More than 100 homes, including the entire town of North Cove, have already disappeared, many of them in the past 20 years."...

Shorelines are unquestionably active - deposition takes place in some areas, while erosion takes place in other areas. The first question would be - "Is there something humans have done to make this natural process worse?" Can we estimate how long this rate of erosion has been taking place?

Sometimes along shorelines, erosion control efforts, e.g., jetties, groins, seawalls,...may slow erosion in their intended area, while making it worse somewhere else. And it may take decades to see the results. We have to look carefully before spending additional millions of taxpayer dollars, when any "fix" may be only temporary.

One of my cousins rents a beach house every summer at St. Simons Island, GA. It didn't used to be a beach house. Up until the late 1950s/early 1960s, there used to be another row of cottages along the shoreline. The loss of this row of cottages was not the result of ongoing regional shoreline migration, but the effects of a couple of hurricanes. [Yes, before 1970, there was another "active hurricane cycle", which may have started in the 1940s.]

As for the Pacific Coast in SW Washington State:

..."George Kaminsky, a coastal engineer for the state Department of Ecology who has studied the erosion since 1993, thinks it has become "self-feeding."

Sand from the Columbia River built up a sandbar at the mouth of Willapa Bay, channeling the water flowing out of the bay straight into Cape Shoalwater. And as the cape eroded, the sand built up the sandbar even more.

Pinpointing the original trigger is difficult, Kaminsky said. But man-made jetties likely have halted a natural sand migration that could reverse the erosion."...

This local interruption of sand migration is a form of "sand starvation", i.e., a normal supply of sand might have protected the shoreline.

And though this Seattle Times article doesn't address this possibility, there could be a larger "sand starvation" issue along the coastline. This Wikipedia map shows more than 2 dozen dams in the Columbia River drainage basin (watershed). Prior to the construction of these dams, the down-river perpetual movement of sand, as "bedload" and as "suspended load" (during storms), kept an ample supply of loose sand available for distribution at the "whims" of longshore currents.

Each one of the dams on this map disrupts the normal river transport of sand, ultimately resulting in there being less sand reaching the Pacific Ocean than there was prior to the construction of the first dam. The cumulative effects of the existence of these dams (for decades) is that there is "sand starvation" along portions of the coastline.

This is a problem that takes decades to reveal itself and other than the "deep ecologist" dream of dynamiting everyone one of these dams, there is probably not an easy solution. The dams are a source of relatively clean energy and the environmental disruptions associated with building the dams has already taken place. To remove the dams (or open them permanently) would again represent a series of environmental disruptions. Besides, it would take decades for the sand supply to "resume" it pre-dam transport pattern.

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