The panel concluded that a single gate failure resulting in a maximum flow of between 11,000 cubic-feet per second and 13,000 cubic-feet per second was the most likely scenario at each dam and that “cascading failures” of gates located at dams downstream are unlikely.
“It is the opinion of the independent expert panel that a ‘sunny day’ gate failure, i.e. a gate failure occurring during non-high-flow periods, is the critical scenario due to gates being in full upright position, elevated population at risk, and no advanced warning of the failure,” the report states. “This is deemed the most likely failure scenario … not multiple gates at one dam. The independent expert panel’s understanding … further suggests that cascading failures of gates at downstream dams would not be expected in the event of single gate failure at an upstream dam.”
In the panel’s first report, focusing on lakes and river segments between Dunlap Dam and FM 1117, it was determined that the area 900 feet upstream of the TP-3 Dam at Lake McQueeney and area 250 feet downstream should be declared a prohibited unsafe zone.
An area 800 feet upstream of the TP-4 dam near Lake Placid is now considered a prohibited unsafe zone, and an area 300 feet upstream of Son’s Island and 300 feet downstream of Hwy. 78 is now considered a restricted unsafe zone.
Downstream of the TP-4 dam, a 1,050-foot area of the Guadalupe River and Meadow Lake and a 1,200 feet area upstream of Nolte Dam are now considered prohibited unsafe zones. Elsewhere, a segment of Guadalupe River downstream of Nolte Dam up to the FM 466 crossing is now a prohibited unsafe zone, and another section of river from FM 466 to FM 1117 is now a restricted safe zone.
Based on identifiable unsafe zones, the panel prescribed new safety measures, including signage and buoys, and determined all activities on or in the water, including boating and canoeing, should be prohibited within all designated “prohibited unsafe zones.”
In addition, water activities, such as swimming, wading and tubing, are now prohibited in “restricted unsafe zones.”
The expert panel will ask for a 30-day extension to fulfill its task of establishing unsafe zones or areas unsuitable for recreational activity on four Guadalupe Valley Lakes: Lake McQueeny, Lake Placid, Meadow Lake and Lake Gonzales.
The panel is expected to make final determinations by Nov. 15 for Lake Gonzales and for an area stretching from Hwy. 80 to Gonzales CR 143.