Intro
After recently completing the San Antonio River Basin earthcache, on the way home, I was thinking about where I lived. I live in Cedar Park, TX, and despite the local news constantly covering Lake Travis and the rest of the Texas Hill Country lakes, and the Colorado River, I knew that the nearest creek, Brushy Creek, drained not to the Colorado River, but to the Brazos River, before reaching the Gulf of Mexico. Upon returning home, and in looking at the LCRA website, https://hydromet.lcra.org/, I realized for the first time that virtually none of Williamson County, where I live, was part of the Colorado River basin. I also knew that the border between Williamson County and Travis County to the south was rather irregular. And well, that brings us to the earthcache
Drainage Basin
A drainage basin is any area of land where precipitation collects and drains off into a common outlet, such as into a river, bay, or other body of water. The drainage basin includes all the surface water from rain runoff, snowmelt, hail, sleet and nearby streams that run downslope towards the shared outlet, as well as the groundwater underneath the earth's surface. Drainage basins connect into other drainage basins at lower elevations in a hierarchical pattern, with smaller sub-drainage basins, which in turn drain into another common outlet
Other terms for drainage basin are catchment area, catchment basin, drainage area, river basin, water basin, and impluvium. In North America, the term watershed is commonly used to mean a drainage basin, though in other English-speaking countries, it is used only in its original sense, that of a drainage divide.
The drainage basin acts as a funnel by collecting all the water within the area covered by the basin and channelling it to a single point. Each drainage basin is separated topographically from adjacent basins by a perimeter, the drainage divide, making up a succession of higher geographical features (such as a ridge, hill or mountains) forming a barrier.
Drainage Divide
In topography, a drainage divide, water divide, divide, ridgeline, watershed, water parting or height of land is elevated terrain that separates neighboring drainage basins. On rugged land, the divide lies along topographical ridges, and may be in the form of a single range of hills or mountains, known as a dividing range. On flat terrain, especially where the ground is marshy, the divide may be harder to discern.
Continental Divide
If you are familiar with North America and the Rocky Mountains, then you have probably heard of the Continental Divide or Great Divide. This is a line running along the Rocky Mountains that separate the two drainage basins for the Atlantic and Pacific Oceans. Precipitation east of the divide will eventually find its way to the Atlantic Ocean, while precipitation west of the divide will find its way to the Pacific Ocean. Focusing on the eastern side of the divide, additional divides further separate the drainage basins for the Gulf of Mexico, the Atlantic Ocean, the St Lawrence, and the Hudson Bay in Canada.
With the drainage basis for the Gulf of Mexico, additional divides separate drainage basins for the Mississippi River (which covers approximately 40% of the United States) as well as numerous drainage basins for rivers in Texas.
Geo-political boundaries
Back to my original thoughts about why the Travis-Williamson boundary was so irregular. In doing a little research, I found that Williamson County was created in 1848 from Milam County. The original Milam County was created from a colonization grant from Mexico in 1825. The grant's boundaries followed the Navasota River, turned southwest along the San Antonio road to the divide between the Brazos and the Colorado rivers, then northwest to the Comanche Trail, and east back to the Navasota. Travis County was not part of Milam County, but part of Bastrop County, which was a separate grant. Hence, the irregular boundary between these two counties.
Questions and Analysis
For the earthcache, we’re going to look at a few small creeks. You will need to visit a few different waypoints, all within a short driving distance. Please follow the steps in order to make your observations. You will need the ability to take altitude readings, and also determine compass directions.
- Go to N 30 28.921 W 097 50.465 (posted coordinates). This should be a creek crossing on Sunchase Blvd.
- What is the altitude ?
- Is there water in the creek?
- What direction does the creek flow? What does this likely indicate about your position relative to the drainage basin for this creek?
- Drive north along Sunchase Blvd. Turn left at the intersection of Zeppelin Drive. Stop and pull to the side of the road just before the light at N 30 29.067 W 097 51.104 (Stage 2)
- What is the altitude ?
- What did you observe as you drove to this location?
- Continue through the light on Zeppelin Drive, and go to N 30 28.829 W 097 51.414 (Stage 3). You should see a drainage pond to the right
- What is the altitude ?
- What did you observe as you drove to this location?
- Is there water in the drainage pond or creek?
- What direction would water be flowing in this creek? What does this likely indicate about your position relative to the drainage basin for this creek.
- Based on the information that you obtained, do you think these two creeks are part of the same or different drainage basins, and why?
- Did you cross a drainage divide in this short trip? Where was it ?
- How does a drainage basin resemble a tree ? Explain.
- How does man affect drainage basins and the flow of water? Give a few examples.
Logging Requirements
To successfully log this earthcache, please send an e-mail or message using the links on my profile. Please indicate your geocaching id if it is not obvious. Please answer the questions 1-7 in your email or message. Each cacher should send their own answers (no group answers). Please do not put answers in your log.
Optional requirement: In your log, identify your drainage address. If you are in Texas, you can use this website: https://tpwd.maps.arcgis.com/apps/Viewer/index.html?appid=2b3604bf9ced441a98c500763b8b1048. If you are from out of state, or out of country, see if you can find a similar application (if you do, let me know and I will include it here)
For example, my drainage address is the following:
- [Sub-watershed] South Brushy Creek - Brushy Creek
- [Watershed] Turkey Creek - Brushy Creek
- [River sub-basin] San Gabriel
- [River basin] Brazos River Basin
Sources