On May 27 at about 3:55 in the afternoon, a longtime Ellicott City, Md., resident noticed water from a rain event starting to pool up against a curb. He called the city to express concern because he’d been through floods before, like the one July 30, 2016 that killed at least two people and wrecked homes and businesses, mostly along its Main Street.
At 4:26 what was reported as water pooling up against a curb had turned into a full-blown flood emergency, just like the one 2016 flood, this one elevated cars on Main Street and killed a National Guardsman.
In between the two floods, Howard County, Md., partnered with the National Weather Service and the Department of Homeland Security Science and Technology Directorate (DHS-ST) on a project to deploy sensors in the watershed. The sensors will give officials data on how rain events affect rivers and tributaries in the area and how best to alert residents.
But Mother Nature didn’t wait until all the projects were complete and the May flooding event had residents wondering what the county had been doing.
“The projects were going through the design phase and most of them were set up for construction for next spring and summer,” said Phil Nichols, assistant chief administrative officer for the county. “There are a lot of variables that need to be worked out before the construction phase, and 22 months is not a lot of time to get the work done.”
The project will deploy 48 stream gauges at 16 sites in the watershed. The three gauges at each site will be from separate vendors to develop an affective, low-cost gauge. The gauges typically cost between $10,000 and $20,000 each, but DHS is hopeful of getting the cost down to under $1,000 each.
Not only are the current gauges expensive, they are difficult to maintain and use. The new sensors are solar powered and use a pressure transducer (which converts pressure into an analog signal) to measure the depth of the water and communicate through radio signals.
The sensors will have to be strategically located because of the nature of the flooding. “One of the unusual things about these flash flooding events that have 1,000-year intensity is that they can be very narrow in where that rain falls,” said Brian Cleary, an engineer with the county stormwater management team. “Even if we have a rain gauge in the vicinity, it may not give us exactly the amount of rain that’s falling in the areas that impact the streams directly.”
“It’s not just putting the sensors at the place that’s going to absorb the flow, you have to have them upland from the flow as well,” said David Alexander, chief geospatial scientist and Flood Apex program director for DHS-ST. “It’s creating a new gauge network for Ellicott.”
That was part of the thinking behind increasing the number of sensors. The county currently has one state gauge.
The first phase of the project will be to distribute the sensors along the tributaries to measure how they respond to different rain events. The second phase will be to gain a better understanding of approaching weather. “A lot of times the National Weather Service will give you a huge swath of where they think these storms may be, but we don’t know exactly where,” Cleary said.
The third phase will be the notification process. As the county learned with the last two floods, there’s no time to get it wrong, but the decision to evacuate has to be made quickly.
The DHS Apex program began in 2015 at the behest of FEMA, which was interested in developing new technologies that would facilitate resiliency in communities across the nation.
Some of the important keys to this project were that it should aim to reduce fatalities, reduce uninsured losses, improve mitigation investment decisions, and improve data to better drive analytics around decision-making.
“We asked, ‘If we’re trying to reduce fatalities, where can we introduce technology that either detects or notifies those at risk and hope that they take appropriate actions?”’ Alexander said. “Current weather forecasting practices can’t be as precise, and warnings come late,” he said.
Alexander said the program will monitor areas prone to flash flooding but also areas with the threat of traditional flooding around critical infrastructure, such as dams and roadways. Charlotte, N.C., Norfolk, Va., the state of North Carolina and the state of Kentucky are also participants.
Ellicott City, as well as other jurisdictions around the country, has been experiencing more flash flooding in recent years that causes death and devastation. That was a key to their partnering with DHS.
Alexander said the sensors in most jurisdictions would be deployed beginning in August and the project will run from six months to a year.