Kevin Baxter | Staff Reporter
SAN MARCOS – Last October, the City of San Marcos began maintenance on the in-stream structures and band improvements at Rio Vista Falls. The construction is scheduled to be complete by March 2022.
Before 2006, the Rio Vista Falls area was a single dam. That year the falls were transformed into three sets of rapids with an outlined pool area and decorative boulders. Since this construction, no maintenance has been done until October of 2021.
According to the City of San Marcos, there have been three major flooding events, along with constant strong currents, which have resulted in the formation of underwater voids or undercuts in the bank and in-stream structures. Now, many locations of the falls require maintenance to fix these issues.
The city proposed maintenance which included repairing the voids, undercutting, and deepening the foundation toe of the bank and in-stream structure, along with adding a layer of rock to protect the foundation.
“The maintenance strategy will provide a more robust system of protection against river currents and future floods,” according to the City of San Marcos.
A project bid of $970,000 was awarded to Austin Filter Systems inc. Construction.
Before the maintenance began, the city planned to dewater the river from the dam to near Cheatham Street. Also, Safeguards were put in place to protect the water quality of the river during construction.
When asked what these safeguards were, the city responded, “Erosion control measures have been installed to prevent sediment from entering the river during construction. A turbidity curtain has been installed in the river downstream of construction to capture suspended sediment that may be produced during construction.”
The city also added that non-toxic hydraulic fluid would be used in all construction machinery.
Protection of local flora and fauna was another concern of the city when planning the repair project.. The city mentioned eight separate measures that are in place. Three of which were stated above with the safeguards to protect water quality.
Other conservation measures include during the dewatering process, federally permitted biologists will sweep the river to remove and relocate native aquatic fauna including the endangered (federally/sate listed) fountain darter. Any Texas wild rice within the project area will be removed, housed, and replanted once construction is complete.
Once the site is dewatered, the construction area will accumulate small pools of water due to the migration of groundwater. Federally permitted biologists will check any small pools of water for endangered fountain darters on a daily basis and relocate any fountain darters that are found.
The accumulated groundwater within the construction site will need to be pumped out of the dewatered area. The intake for the pump is specially developed to prevent harm to endangered fountain darters. The pumped water will be directed to a filtration basin that will remove sediment before the water re-enters the river.
Texas Wild Rice downstream of construction will be monitored and any sediment that has accumulated on any strands will be fanned off.
River water samples will be taken downstream of the turbidity curtain to ensure effectiveness of sediment control measures. Protocols have been established to prevent contamination of the river with oil and gasoline from construction equipment.
Along with these measures, the city has also obtained all necessary federal and state permits for this project.
“Permitting entities include US Army Corps of Engineers, US Fish and Wildlife Service, Texas Parks and Wildlife Department, Texas Commission on Environmental Quality, and Texas Historical Commission,” said the City of San Marcos.
Updated information on all construction projects in San Marcos can be found here.