A river landscape transformed
SARA says trees need to be removed to restore habitat, stop flooding
On the banks of the San Antonio River on the South Side, near the Hot Wells park and VFW Boulevard, a tractor is shredding trees and leaving mulch in its wake.
It chomps them up quickly and spits out wooden pieces, layering a portion of the river slope before moving on to the next trunk. So far, yards of trees have been reduced to mulch, while the bank on the other side of the river is completely cleared.
Before the tractors, this area looked like a little forest, with trees and shrubs so dense in parts that passersby could make out the river only through occasional cracks in the vegetation. Residents nearby loved the leafy additions to the river and how the shade made the path there accessible in the summer heat.
But in October, much to the shock of locals, the San Antonio River Authority began removing trees to create a grassland prairie as part of the Mission Reach Ecosystem Restoration and Recreation Project. The process, which takes months, is intended to restore habitat and, more importantly, prevent floods.
Floodplain models produced by the Federal Emergency Management Agency in 2017 predict which types of habitats would best prevent flooding in San Antonio. Habitats along the San Antonio River range from dense woodlands to grasslands. Near Hot Wells, the models called for an area with far fewer trees.
“What we’ve done with the Mission Reach restoration project is create a healthy ecosystem and manage flood control as best we can equally,” said Steven Schauer, director for external communications at the river authority. “Flood control, however, does take priority, and in some areas, trees and shrubs can
negatively impact the floodplain. … It’s really about finding the perfect balance.”
Trees on the bank
Before the Mission Reach restoration project began in 2008, the river looked more like a drainage ditch. Nonnative grass sloped to a winding channel with no recreational paths.
San Antonio’s native ecosystem consists of grasslands, with dense forest areas and live oaks to the north and prairie land in central Bexar County.
To restore the land to how it was, Bexar County, the city of San Antonio and SARA worked together on the improvements, which were overseen by the Army Corps of Engineers. The priorities — in order — were flood control, restoration and recreation.
When SARA began to rip up the trees by Hot Wells, however, many residents were mortified. After watching the trees slowly grow since the restoration began nearly a decade ago, the immediate reaction was devastation and confusion.
Justin Parr, who often uses the trail for recreation, was frustrated by what he felt was an “inhuman” approach to the tree removal. While he understood the importance of floodplain data, he wished the process had been done with a human touch, such as cutting down the trees by hand and leaving some up. Heavy machinery, he worries, can cause the soil to become compacted, which can harm future growth.
SARA said the tractors were needed to shred the trees, creating mulch nutrients for the future grasslands.
“All the wildlife is gone, all the trees are gone,” Parr said. “It’s like your happiness is gone with it. It’s like the drainage ditch again.”
Meanwhile, he expressed concern about the plastic weed guard fabric and drip irritation tubing from the earlier tree planting, which he says is being chopped up in the process. He’s also concerned that wildlife, such as turtles, are being harmed in the process.
When it rains, Parr said, much of the material will be swept into the river. He said he’s found small pieces of plastic from drip irritation floating downstream.
Schauer said that while a SARA trash team collects large pieces of plastic that they see and removes them from the brush, smaller bits might be missed.
But for SARA, this process is necessary.
Near Hot Wells, the trees — or stems, as SARA calls them — can worsen flood conditions along the river by widening the floodplain, causing water to accumulate on the bank instead of flowing downstream. Grassland gives the water room to move, preventing the river from rising during a storm. While some trees can remain to hold the river shoulder in place, most need to go.
Denser vegetation in a river channel results in greater “hydraulic roughness,” said Brian Laub, assistant professor in the environmental science and ecology department at the University of Texas at San Antonio.
That means water flows more slowly, he said.
“It tends to back up that water and hold it a little longer and increase flood levels,” Laub said.
Restoring native grassland as a means of flood control isn’t necessary in other parts of the riverbank, where woody vegetation is less threatening, Schauer said. It depends on the floodplain map.
Change in plans
Creating grassland along the river wasn’t always the plan. Originally, Parr said, the goal had always been trees. SARA had planted 22,000 thousand for the restoration project, including some in the Hot Wells location.
“Now they’re coming back and saying it’s planned to be a grassland,” he said. “No one ever told us that could change or would change so suddenly.”
But during the restoration project’s early stages, the floodplain map showed a different outlook for the bank.
“The original floodplain map, from 2008, didn’t require the same flood controls that the current map does,” said Kristen Hansen, manager of SARA’S Watershed and Parks Operations Department. “When new data comes on board, like the 2017 floodplain map, we are required to use it. And the new map found that the bank (by VFW and Hot Wells) could only handle very few trees during a flood, not all the trees that either we planted or came up on their own.”
About 90 percent of the trees being removed during the current effort are ones not planted by SARA, referred to as volunteer trees. Before the work at Hot Wells, SARA also removed trees farther south between VFW and Southeast Military. Next year, it plans to remove trees north of the current spot.
Dense vegetation can have many benefits for a river’s ecosystem, such as providing shade to keep water cooler and adding nutrients from organic material such as leaves, Laub said. But vegetated grassland can also provide similar benefits. Grassland can prevent banks from eroding and add its own nutrients to the river.
After the trees are removed, SARA will plant native seeds throughout the bank, which the tree mulch will help fertilize. Already, the area that was converted to grassland last year looks like a wild prairie.
“In a year’s time, this place (by Hot Wells) won’t look so ripped up,” Hansen. said “It’ll be all green and lush, with native plants and flowers.”