Lake Charlotte Detailed Contour Mapping Project
Completed December 2012, posted July 2013
In early 2012 I decided to commit to the very large project of mapping the depth of the bottom of Lake Charlotte. There were two reasons for this, one being that I had become concerned with the large volume of sediment being deposited on the Mac Bayou delta from the Trinity River through the Cut – I’ve watched the delta transition from a sand bar with a few grasses growing from it to an island with trees on the verge of merging with the mainland to the northwest of it; the other reason was simply that it would be a really cool thing to have accomplished.
I purchased a Humminbird Fishfinder 325, which combines a sonar depthfinder with GPS, with the ability to save results to an SD card (I also added a portable battery to power it). I fixed the sonar transducer to the base of a rod that I could mount to the side of my 17’ Wenonah Prism canoe, with the transducer immersed about 6 inches below the surface. I also purchased a copy of DrDepth software to handle merging the Humminbird depth and GPS data into a contour map of the lake bottom.
Between July and October of 2012 I made 16 trips to Lake Charlotte, crisscrossing the lake east-to-west and north-to south, recording depth throughout. Some regions I surveyed more finely than others, depending on my level of interest; the bulk of the lake was surveyed at about 500’ intervals. This is summarized in the image below (darker color indicates deeper depth). Each trip took about 4-5 hours on the water, plus another couple hours of commute.
Following each trip, I recorded a copy of the official lake gage depth for that day, from which I obtained a good estimate of the depth at the time I was on the lake surveying. There were no major floods on the Trinity during the duration of the survey (which would have dumped additional sediment), so the depths measured provide a good snapshot. Once the surveying was completed, I used DrDepth to align all the depth transects and assemble a very detailed contour map of the lake bottom, referenced to sea level, including a bit of Mud Lake. The contours are at 6 inch intervals. I saved the contours as a *.kml file which can be viewed in Google Earth or Google Maps. Here’s an overview:
The map is not ideal. There are some false contours in the region between Lake Charlotte and Mud Lake. The Lake Charlotte was only about 3 feet deep throughout the duration of the survey (at times when the Trinity floods it becomes MUCH deeper), and the lake bottom is nearly flat, so a lot of the fine squiggles in the bottom contours are artifacts of the procedure used by DrDepth to create smooth contours. Nevertheless, the overall trends are quite clear. The Mac delta has nearly merged with the western shore of the bayou, and a new delta is forming to the east of the old. This makes very clear the large amount of sediment accumulating from Mac Bayou, perhaps adding impetus to plans to seal the Cut from the Trinity River.
Finally, here is the KMZ file itself:Google Earth KMZ data. You'll need to install Google Earth on your computer (it's free) to view this.