Red River Update: July 27

Predisturbance Mapping Completed

Friday, July 27, 2001. Red River Wreck team members on Friday completed mapping and data collection on exposed areas of the boat’s stern section, and began using dredges for the first time to expose buried parts of the structure.

The crew has begun taking their measured drawings of the wreck and transferring that data to scale drawings. The distinction between the two types of drawings is subtle, but critical. A measured drawing is essentially a sketch, done on site, that shows the main features and key measurements. In many cases, measured drawings are not proportioned correctly, but this can be corrected for if there are enough accurate measurements included.

Synthesizing a set of measured drawings into scale drawings, however, can be challenging. A scale drawing is a blueprint, with every single feature drawn precisely to shape and scale. If a measured drawing is incomplete, or a specific measurement is significantly off, it becomes obvious very quickly that something is wrong. It’s at this point of preparing scale drawings that gaps or holes in the data become apparent. The field school students discovered that even the most careful of them had omitted crucial measurements that will be needed to complete the scale drawings, and part of Friday was spent in recording additional information about their assigned units.

Up to this point, the Red River Project team has focused on "predisturbance" documentation of the wreck - that is, recording what is there without actually removing or relocating any material from site. It’s vital to record everything that one can before removing the sand and gravel covering the wreck, because once that process begins it can’t be undone. In that way, investigating an archaeological site is very much like studying a crime scene - you need to record everything you possibly can in place, because once you start moving things around you can’t go back and start over.

Dredging is done with pumps and hoses. A water pump on the dive barge pushes water down through a hose to the dredge head, where it passes through a sharp U-bend in the pipe and goes out through another hose that leads away from the wreck. In the head of the dredge, just below the U-bend, is a large nozzle, several inches in diameter, that draws in sand and gravel from the riverbed, which then mixes with the outflow and is carried off the site. The dredge uses the Bernoulli effect, in which a fluid moving at high speed exerts less pressure than a stationary fluid. The fast-moving water above the nozzle literally pulls sand and sediment up the pipe. (This is the same effect that allows an airplane to fly; the shape of the wing causes air passing over it to move faster than the air below it. The higher-pressure air below literally pushes the wing up, and with it the rest of the airplane.) Divers clear away sediment by brushing or fanning it into the nozzle. When done correctly, this is a relatively gentle way of clearing sand away from a wreck and exposing more of the structure. Very small, light artifacts or bits of material may get inadvertently drawn up into the dredge, so all the outflow from the dredge is run through fine screens and sorted by hand.

This update is sponsored by the PAST Foundation and the Oklahoma Historical Society. It may be freely redistributed without modification for non-commercial purposes.

Unloading gear from the vans in the morning. . .	. . . and more gear. . .	. . . and still more gear.	Dr. Bill Breece of Orange Coast College takes a turn at the sift barge. The screen catches any small artifacts that might inadvertently be drawn into the dredge.