AUSTIN (KXAN) – Questions are emerging over whether the Austin region has any better way to predict how severe the next major flood will be.
“The only technology that was available, washed away. So we should put ourselves in a position where that doesn’t happen in the future,” Travis County Judge Sam Biscoe told KXAN Investigator Robert Maxwell.
Early on the morning of Oct. 31, two United States Geological Survey (USGS) water height gauges stopped working. One at Twin Creeks near Buda was under five feet of water, according to City of Austin Watershed Protection officials, rendering it useless and impossible to get to for repairs.
A second gauge at U.S. Highway 183 at Onion Creek, near to where the most damaging floods would happen, went offline hours later. But at least it remained above the rising waters.
Timeline via text message
Text messages between USGS crews and City of Austin staff working at the region’s Emergency Operations Center show crews were able to begin work on restoring the broken Hwy. 183 gauge by 6:13 a.m. That was nearly 3.5 hours after USGS data shows it went offline at 2:49 a.m. It was repaired by 8:20 a.m. according to text messages.
But from 6:13 a.m. onward, the USGS was profoundly aware the City of Austin and the National Weather Service still needed a constant flow of information showing how quickly Onion Creek was rising in order to dispatch emergency and rescue crews to flooding neighborhoods.
“We’ve never had a measurement that high. It has never been that high,” recalled USGS hydrologic technician Milton Sunvison during a recent visit to the Hwy. 183 span over Onion Creek. Far below, twisted branches and debris still littered the mostly dry stream bed that had been a torrent days earlier.
“When you’re in a flood, you don’t have time to troubleshoot and say ‘hey what’s going on here?’” said Sunvison. He’s been measuring USGS gauges since the early 1990s.
For two hours that morning, a crew of USGS workers physically went out onto the Hwy 183 bridge, dangerously close to speeding traffic, to make manual measurements of the creek height.
They used a low tech tool called a wire weight, a small metal weight on a thin cable that is lowered to the top of the water level. At the height of the flood the metal weight was touching the top of the creek flow, just nine feet from the bridge itself, at a record-setting 41 feet. Onion Creek’s normal flow is about five feet according to USGS data on the WaterWatch section of its website.
The USGS texted or emailed data every 15 minutes, even after the Hwy. 183 gauge was deemed fixed.
Another crew actually went out in a small boat, moored it in a relatively calm spot to take sonar-like readings to show Onion Creek’s depth and to record how fast the water was flowing. Earlier in the day on Oct. 31, USGS staff said an unmanned boat was unusable due to the power of the current in the middle of the creek.
But what about next time? Such low tech heroics are being praised by Watershed Protection engineers at the City of Austin. But they admit they were blind for those three early morning hours from 3-6 a.m. in their ability to make predictions on how fast the waters of Onion Creek were rising, as well as the volumes of water rushing through the watershed.
(When Onion Creek crested, cubic foot-per-second measurements put the volume of water at 125,000 cfs – picture 9,300 full (100 gallon) bathtubs worth of water moving through one spot – every second.)
The city’s Flood Early Warning System combines that real-time data with computer models of rainfall amounts, ground water saturation levels, weather forecast numbers and historic data from the watershed in question.
But its managers say even predictions are not a precise science. Weather systems can move at the last minute, and storms can dump more or less than the expected rainfall over one area.
For example, if the storm system that passed over the Onion Creek watershed had instead moved 10 miles north, fewer homes and businesses might have flooded.
“We just don’t know how much it’s going to rise,” said Kevin Shunk with the City of Austin’s Watershed Protection Department. “We can’t predict 41 feet or 40.2 feet without the data for the models to do the predictions.”
Shunk said once a storm arrives, the only defense against being completely helpless, is a good, real-time offense: boots on the ground:
“It’s not a helpless feeling because you can’t give a prediction, because we have people there (such as Austin Fire Department crews) doing as much as they can right at that moment,” he said.
Managers at the region’s Emergency Operations Center are compiling a report into the response to the Oct. 31 floods. It’s due out before the end of the year or early in 2014. Along with improvements to police, fire, EMS and other first responders’ protocols, the report may lay out recommendations along the line of Judge Biscoe’s questions – that public money be invested into more stream gauges.
Last week at Travis County Commissioners’ Court, EOC coordinator Pete Baldwin said he supports adding stream gauges to smaller tributaries of Onion Creek. He pointed out when it backed up, the smaller streams also flooded, causing a safety risk for nearby homeowners.
Right now, those people have no warning system other than hearing about flooding nearby.