Don’t Go with the Flow
Habitat Enhancing Land Management
Christine Middleton
Do areas on your property look like this—sparse vegetation and very little topsoil? Hill County soils are notoriously thin. At one time, this spot likely had lots more soil and vegetation. What happened? Hard to tell exactly, but it’s likely due to a combination of cedar clearing, overgrazing, the slope of the land, and heavy rain. Before Europeans settled in the Hill Country, it is estimated there were about twenty-two inches of topsoil. The clearing of soil-building cedar combined with overgrazing resulted in the loss of the vegetative cover holding that topsoil in place. Topsoil became detached with each heavy rain—something called rain splash. Then the loosened soil was transported by water flowing across the land. Over time, more and more of that rich upper layer was lost. Where did the soil end up? Likely at the bottom of the hill or in a nearby river or stream. But all is not hopeless for this area and others like it. There are ways landowners can stop incremental degradation and help nature by speeding up the healing process.
The Importance of Soil
Before considering erosion, let’s think about how soil forms. If you are not a farmer, avid gardener, or geologist, that’s something you’ve probably not spent a lot of time pondering. But just what is soil anyway? Soil is defined as a mixture of organic and inorganic materials that come together in a way that supports plant life. What we call soil consists of crumbled bits of rock, decomposed organic matter, and various microorganisms as well as fungi, worms, and various ground-dwelling insects. Soil takes a long time to form—up to 500 years to create just an inch of soil. And unfortunately, if there aren't enough plant roots holding the soil in place, just a few heavy rains can wash a lot of it away.
Image from ScienceFacts.net
But those plants that do take hold in caliche soils are important because they are the first step toward recovery. The organic matter left behind is essential to restarting the process of rebuilding that rich layer capable of supporting a wider variety of vegetation. As additional plants take hold, more soil is built. The richer layer that is formed allows more water to soak in. And as more water is retained for longer periods between rain showers, microorganisms essential to plant health return. This expanding plant cover means the next heavy rain shower is less likely to wash away precious newly created soil. If you want to see this process in action, find an area where there is just caliche and bushy cedars. Reach down and pick up a handful of the organic matter that has started to accumulate under those cedars. Then look under the spreading cedar branches and notice the nursery they provide for lots of other plant life beginning to return to the degraded landscape. For the facts on how our cedars (Ashe Juniper) build and hold soil, read the article Rethinking Mountain Cedar in the June 2022 Hays Humm here .
Healthy soils include lots of air spaces, allowing water to soak in more rapidly. Imagine pouring a bucket of water on a caliche slope. Very little would soak in because there aren’t many air spaces to seep into. Now imagine pouring that same bucket of water on a similar slope on your healthy land, with soil rich in organic matter and plenty of space between the grains. It is said that a 1% increase in organic matter results in the absorption of 25,000 gallons of soil water per acre. Some of that soil water will be taken up by plants and will transpire through their leaves. What remains will infiltrate further, becoming groundwater. Some of that groundwater will eventually re-emerge to replenish the flow of our creeks and rivers. And the rest will recharge the Trinity and Edwards aquifers, which many Hays County residents depend on for drinking water. See the wider good accomplished by your land’s healthy soil? It is environmentalist Aldo Leopold’s “community” quoted at the end of this article—the powerful network to which you and your land belong.
How Erosion Begins
Besides vegetation, other factors that influence the speed and severity of erosion include intensity of rain and slope. Hays County lies at the eastern edge of the Texas Hill Country, rising from 400 feet to 1,600 feet from east to west with lots of steep canyons in between. It is said that Texas is a land of perennial drought, broken by the occasional devastating flood. And it is predicted that climate change will bring both drier conditions and heavier rains to Central Texas. Runoff associated with a heavy rain travels downhill, picking up speed as it travels downhill. Combine this with thin soils, and it is easy to understand why so many of the Hays County property owners we have visited are concerned about erosion.
To understand erosion, it is important to consider how the flow of water changes as it moves down a slope. Any runoff—water that doesn’t soak in—naturally travels downhill. The steeper the slope the more speed it picks up along the way. Source: http://releeconservation.com/erosion-control/
Sheet erosion is slowly moving soil and valuable soil-building leaf litter down a gentle slope.
Often, erosion starts as sheet erosion. That term refers to an even flow of water that results in the gradual removal of soil in thin, uniform layers. With sheet erosion, the soil layer containing the most nutrients and organic matter for supporting plant life is lost. And little evidence is left behind to indicate what is happening.
Example of eroded soil forming rills
As the speed of the water increases with the slope, it starts to carve small grooves called rills. As these rills move down the slope, they might converge to form larger channels called gullies. Rills and gullies only contain water when it rains. But with each rain, the water flow picks up soil and rocks, eroding the sides of the rills and gullies, expanding their size. This erosion is more obvious than the more gradual sheet erosion, but both forms of erosion are devastating to the health of your land.
What Can Be Done?
The solution to erosion can be summed up in three words: we can slow, spread, and sink the runoff water. But before moving to the solution, our first challenge is to identify the problem. Rills and gullies are easy to spot. But where you see clear evidence in the form of rills and gullies is likely not where the problem started—it’s only where the water gained enough energy to have a visible impact. So look a little farther up the hill, and you may find subtler clues that will help you assess the situation. For instance, movement of leaf litter in sheet erosion is a clear indication that water is picking up speed as it travels downhill. One of the best times to look for evidence is just after a heavy rain. Or if you are adventurous, head out while it is still raining—but not if there is thunder and lightning, please!
Juniper log barriers slow runoff for erosion control at Blue Hole Regional Park in Wimberley, Texas.
There are lots of ways to slow runoff and stop erosion. A simple one we often recommend on HELM visits with landowners involves laying a row of logs or rocks perpendicular to the slope, i.e., following the contours of the slope. Place multiple rows as needed at various points on the hillside. Make sure there isn’t a way for water to go around. Otherwise, you might inadvertently create a new erosion problem. And after a heavy rain, check what you have done to see if minor adjustments are needed. The idea is to slow water down as it seeps through or flows over the barrier giving sediments time to settle out. As soil builds behind the barrier, vegetation will start to establish. This new vegetation will further slow the water, encouraging even more vegetative cover up the hillside. The photo shows how this was done between the Hike and Bike trail at Blue Hole Regional Park and RR3237. This picture was taken over six years ago, and the cedar logs are still there. But there is lots more vegetation. Don’t just take our word for it. Go see for yourself!
In future issues, we’ll look at more techniques for stopping erosion—such as spreading or sinking rainwater runoff. In the meantime, you might want to read about the more advanced approaches in Hill Country Alliance publications you can find at https://hillcountryalliance.org/wp-content/uploads/Hillside-Stewardship-Guide_2023.pdf
If you would like the HELM team to visit your property to help you evaluate your erosion problems and provide insights into additional land stewardship concerns you might have, go to https://beautifulhayscounty.org/helm/ and fill out our request form.
“When we see land as a community to which we belong, we may begin to use it with love and respect.”
—Aldo Leopold