Maintenance work to take place at Rio Vista Falls

Maintenance work will take place at Rio Vista Falls to address instream structures and bank improvements, the City of San Marcos recently announced.

The city said underwater voids and undercuts have formed in the bank and instream structures throughout the Rio Vista Falls area and require maintenance.

“The undercutting of large boulders on some of the banks as well as some of the instream structures had reached a point where they needed to be addressed,” City of San Marcos Senior Engineer Greg Schwarz said. “Due to the heavy usage of the area, the city wanted to perform the maintenance during the off-season when public usage is much less.”

The Rio Vista Falls area was reconfigured from a single dam into three sets of rapids, outline pool area and decorative boulders in 2006. According to the city, no maintenance has been done to the area since its original construction. Additionally, the city said strong currents and three major flooding events have impacted the structures since their installation.

The work planned for the area will consist of repairing voids, undercutting and deepening the foundation toe of the bank and instream structures. The city added that a protective layer of rock armoring will be installed around the foundation.

Work on the project begins in October and is expected to be completed by March 2022. Schwarz said the project will include several key stages. The first stage will include securing the site with temporary chain link construction fencing and rope connected safety buoys within the river to prevent the public from entering the construction area. Next, erosion control measures will be installed to prevent sediment from entering the river.

The next stage will include dewatering the river near Rio Vista Falls, which will include the erection of dewatering elements. Schwarz said the contractor and federally permitted biologists will work together to remove and relocate aquatic fauna, including the endangered fountain darter, and to drain the construction area. Additionally, the federally and state protected Texas Wild Rice will be removed, housed and replanted near its original location prior to construction.

For dewatering, Schwarz said there are two existing 4-foot diameter pipes located underground that were installed with the 2006 Rio Vista Falls project that will be used to divert river flow.

“These existing pipes are located along the east bank and begin at the dam area and terminate just upstream of the Cheatham Street bridge,” Schwarz said. “Pipe extensions will be installed to extend the diverted flow to the downstream side of the Cheatham Street bridge. A rock gabion splash pad will be installed where the pipes discharge into the river to protect against erosion. A coffer dam will be installed at the Cheatham Street bridge to prevent backwater from the river from entering the construction site.”

Following dewatering, key stages of the project include the construction of the repairs, reintroduction of river flow back into Rio Vista Falls and the construction’s completion.

In order to protect the river's ecosystem, Schwarz said all necessary federal and state permits have been obtained for the project, include permits from the U.S. Army Corps of Engineers, U.S. Fish and Wildlife Service, Texas Parks and Wildlife Department, Texas Commission on Environmental Quality and Texas Historical Commission. He also said several measures will be taken to protect the ecosystem, including erosion control measures; sweeping the river to remove and relocate native aquatic fauna; removal, housing and replanting of any Texas Wild Rice found within the project area; pumping out an accumulated groundwater to prevent harm to endangered fountain darters; and a turbidity curtain will be installed in the river downstream of construction to capture suspended sediment produced during construction.

Schwarz also said Texas Wild Rice downstream of construction will be monitored, river water samples will be taken downstream to ensure effectiveness of sediment control measures, non-toxic hydraulic fluid will be used in construction machinery and protocols have been established to prevent contamination of the river with oil and gasoline from construction equipment.

When the project is complete, Schwarz said minor changes will be noticed, including a new rock terraced and accessible east bank, a rock edged west bank from the most downstream instream structure to Cheatham Street bridge to protect against erosion of the west bank from river currents, and relocation of two submerged boulders outside the high velocity flow path produce by the dam chute.

“Since the maintenance work is mostly below the water level, resident’s will not notice much of a difference,” Schwarz said. “Residents can expect a more robust system of protection against river currents and future floods.”

The $970,000 project, which was awarded to Austin Filter Systems, Inc. Construction, will take three to five months to complete.