#1: [26-Jan-02] (incomplete)

10-Jun-2002 -- I ran across this web site in an issue of Arc User magazine. I decided to check out the page and see if there were any confluences left in Alabama. I read the attempt by Rob Buckman, and knew the area sounded familiar, having worked as a forester in that area for many years. Now I work as the GIS manager for that same company. I decided to see where this confluence was exactly, so I entered the point into our GIS system, and there it was, on land that our company manages, and better yet, land that I had visited many times in the past. Since I had at my disposal very detailed maps and recent aerial photography of the area, I knew I would have a much easier time than Mr. Buckman did in locating the confluence.

On June 5, 2002, I set out with two of my co-workers, Rodney Smith and Robert Aldridge. The location is about 45 minutes away from our office. Since I knew the location well, all we brought was an aerial photo (good for locating unmapped roads and trails), our GPS units, and a digital camera. The area is a Loblolly pine plantation that was planted in 1982, and had been thinned a few years ago. Based on my experience and Mr. Buckman’s observation of the thickness of the thorny underbrush (he was right), we each put on a pair of snake proof chaps. These are heavy duty Cordura nylon (2 layers) chaps that cover your entire leg. They work great for snakes, but mostly they keep your legs from being shredded by blackberries and briars. Rodney and I also carried a long walking stick to clear away the blackberries (they work much better than a machete). As it turns out, we found a small road that led us to within 0.1 miles north of the confluence, and as luck would have it, an old skidder trail led directly from this point in the direction of the confluence. This definitely would make the task easier. We were able to easily walk very near the confluence without fighting a wall of underbrush. Once we got near the confluence and had to move away from the skidder trail, things got a little more difficult.

To navigate to the confluence, we used a Garmin GPS 12, and we also brought along a Leica GS 50 GPS with real time differential correction. We navigated to the confluence with the Garmin. It was located about 50 ft or so from the skidder trail. We recorded this position with our GS 50 and thought we were pretty close. When we got back to our office and checked the point, we were approximately 75 feet from the confluence. We knew we could do better than that, so we planned another trip for the 10th of June. This time we relied on our GS 50 for navigation, but brought along the Garmin for comparison. Using the Leica GPS unit, we measured a differentially corrected position within 7.75 feet (2.36) meters of the actual confluence. Comparing the Garmin to the Leica , we saw approximately 35 to 40 feet of error in the Garmin.