Measuring Hurricane Rita's Storm Surge With an Experimental Sensor Network

Hurricane Rita’s path, September 22–24, 2005, and the area the sensors covered. U.S. Geological Survey.

To keep floods from becoming disasters, engineers and planners need to know how flood water arises, moves and recedes: that shapes the design of levees, dams and bridges, flood-plain boundaries, evacuation routes and land use. Storm surge from hurricanes had long been studied after the fact, from damage, debris, high-water marks and eyewitnesses. Those rarely showed when the water arrived, or the routes by which it pushed inland.

So for Hurricane Rita in September 2005, the U.S. Geological Survey tried something new: an experimental network of pressure sensors to record the timing, extent and height of the surge.

Racing the storm

In the hours before landfall, on September 22–23, crews placed sensors at 33 sites in southwestern Louisiana and southeastern Texas, along waterways and in coastal marshes from Sabine Pass, Texas, to Lafayette, Louisiana — from a few hundred feet from the coast to about 30 miles inland. Sites were chosen from surge forecasts, the location of piers and bridges, and the lie of the land.

Each sensor, housed in a metal pipe 1.25 inches wide and 18 inches long and strapped to a pier or power pole, recorded the time, temperature and pressure every 30 seconds through the storm and for days afterward. Seven sites had paired sensors for water level and air pressure; 17 recorded water level only and 9 air pressure only.

One of the sensors used to record water level and air pressure. U.S. Geological Survey.

Turning pressure into water depth

All but one sensor survived and were recovered. The water readings were corrected for changes in air pressure, and for the density of the water — salt, brackish or fresh, depending on how near the coast each sensor sat. Surveyors tied every sensor to a common elevation using temporary reference marks, tapes and GPS.

To check the data, the team compared paired sensors, nearby USGS stream gauges, the water level when each sensor was pulled out, and high-water marks. The sensors agreed with the water surface to within 0.1 foot at seven sites, and matched high-water marks rated excellent; they tended to read higher than marks rated good, fair or poor.

What the surge did

The highest water was near the coast, falling off inland toward Interstate 10. At Constance Beach, Creole and Grand Chenier, Louisiana, about 20, 48 and 54 miles east of Sabine Pass, the water peaked at more than 14 feet above the reference level. At many places it rose more than 5 feet an hour. Near Interstate 10, river flows added to the surge.

Water level and air pressure at a site in Cameron, Louisiana. U.S. Geological Survey.

Interpolated between sensors and laid over an elevation model, the readings show the flood wave moving inland along Louisiana Highway 82 in the early hours of September 24. Maps of how long water stood, when it arrived and left, and how deep it got could help explain how surges work and guide sturdier building. The USGS suggested future networks might also measure salinity and send data in real time to emergency managers.

Sources

• U.S. Geological Survey, "Monitoring Inland Storm Surge and Flooding from Hurricane Rita," Fact Sheet; rewritten in hubnx's own words. Figures from the fact sheet; the data are in USGS Data Series 220.