As we attend to the immediate needs of the residents and businesses affected by this week’s flood in Ellicott City, people are asking “Why does this keep happening and what can be done to prevent it?” I attempted to address this question with a blogpost from August 3, 2016 following the last major storm.
Much planning has been done in the last two years and several major projects are being implemented. The basic issues remain. We’re going to have to consider now whether these last two storms represent a new normal and whether the plans are sufficient. As always, it’s a judgement about the extent that we’re going to battle mother nature or adjust to her ways.
Ellicott City – The Great Floods
Lower Ellicott City had been prone to flooding since it was founded. There has been at least four different major floods in recorded history in Downtown Ellicott City. So what makes it so prone?
First of all, Ellicott City sits at the confluence of the Tiber and Patapsco Rivers. This in itself moves a lot of water. Another issue is that Ellicott City sits in a shallow valley, with many of the expanding buildings and homes having to be build literally over the Tiber river. This makes water from almost all directions converge in the valley to the Tiber River before being emptied in the Patapsco. And this isn’t even the biggest issue.
The Tiber River is tiny compared to the Patapsco River. The Patapsco can carry larger amounts of water than the Tiber River can, adding to the quickness of the flooding downtown. The valley and large water confluence causes the natural watershed to be turned into a river itself. Water rushed from all directions until the larger Patapsco River can’t handle the volume. It then backs up like how a dam backs up water. This causes water levels to rise, and rise, and rise.Flooding can cause billions in damaged and can be cause by numerous things such as hurricanes or unusual rainy periods and have unfortunately caused deaths in Ellicott City.
How does latest Ellicott City storm stack up with 2016? Meteorologists weigh in
by Christina Tkacik (Baltimore Sun) May 28, 2018
The storm that hit historic Ellicott City and nearby areas Sunday is likely worse than the storm that caused flooding in 2016, according to meteorologists.
Locations around Ellicott City and Catonsville saw between 5.36 inches and 10.38 inches of rain on Sunday, said Kyle Pallozzi, a meteorologist with the National Weather Service’s Baltimore-Washington forecast office.
In the devastating storm of July 2016, Ellicott City was hit by 6.5 inches of rain, while Catonsville got 4.2 inches.
Several weather factors combined to produce Sunday’s torrential conditions, according to meteorologists: A slow-moving cold front coming from the north and east, along with slow-moving thunderstorms. In addition, multiple storms converged in the same location, a situation meteorologists call “training convection.”
“They kept regenerating and moving over the same areas,” Pallozzi said. “It was a moisture-rich environment. The storms had a lot of moisture to work with.”
The heavy rain sent the Hudson and Tiber tributaries over their banks, with the water coursing down Main Street.
A gauge in the Hudson peaked at 3.06 feet above flood stage — which was half a foot higher than the peak in 2016, Pallozzi said.
The Patapsco River, at the bottom of Main Street, peaked about 4 feet lower than it did in 2016. But a little farther downstream, at Patapsco Valley State Park, the river peaked nearly a foot higher on Sunday than it did in 2016.
In the midst of the storm, meteorologists like Chicago-based Zac Flamig used weather radar to predict how much rain was falling.
While 2016’s storm was a 50- to 75-year storm (that is, one recurring every 50 to 75 years), according to Flamig, initial rainfall estimates show that Sunday’s storm was on par with a 200-year storm — one occurring every 200 years or more.
“The best estimates that we have in real time are saying that this is a worse flood,” Flamig said.
In 2016, experts called it a “thousand-year storm,” meaning such intense rainfall is likely to occur only once every 1,000 years. However, Flamig said such models can be misleading since they overreact to small changes in flood levels.
“Because of the way we estimate them, small changes in rainfall at the extremes can have big effects,” he said.
Ellicott City gets rainfall expected only once every millennium
by Scott Dance (The Baltimore Sun) – July 31, 2016
Six and a half inches of rain dumped on Ellicott City in about two hours Saturday night, a deluge expected to occur only once every thousand years.
More than 4.5 inches fell within one hour, from 7:30 p.m. to 8:30 p.m., according to a Howard County rain gauge.
The massive burst of precipitation sent a wave of floodwaters cascading down the hillsides in the historic downtown where it turned into a wall of water smashing down Main Street, sweeping cars downhill, sending restaurant-goers scurrying for higher ground and carving away the road and sidewalks, leaving behind massive sinkholes.
The Patapsco River rose 14 feet from about 7:20 p.m. to 9 p.m., according to the weather service.
Based on records for a gauge five miles away in Woodstock, there is a less than 0.1 percent chance of such intense rainfall happening in any given year, Elliott said — making this a once-in-1,000-years storm.
Why Does Ellicott City, Maryland Keep Flooding?
by The Weather Channel
Howard County plans more Ellicott City flood control projects
by Pamela Wood (Baltimore Sun), July 26, 2017
Howard County is drawing up plans for new projects aimed at slowing and controlling stormwater in streams that flow through Ellicott City’s historic district — the same streams that swelled into a deadly and damaging flood nearly one year ago.
Four projects announced Wednesday will cost an estimated $18 million, with the county hoping to get financial help from the state and federal governments.
In the months since the flood, the county has completed other infrastructure projects. In addition to shoring up streets and sidewalks, crews rebuilt stream channels and retaining walls.
Kittleman said the projects announced Wednesday represent a next step in long-term improvements to control the flow of water in the area.
“These projects will allow us to retain more water in the upper reaches of the watershed and they will improve the way we move water downhill,” he said. “Basically, making water less likely to back up and flood the streets and our homes.”
Three of the projects involve creating vast “dry ponds” along streams to hold water during major storms so the water doesn’t rush into the stream channel. One dry pond will be upstream from Main Street on New Cut Branch, another on Tiber Branch and a third upstream on Hudson Branch near routes 29 and 40.
The fourth project involves replacing some of the pipes and culverts that carry parts of Hudson Branch along Frederick Road toward the historic district. That project includes adding a second pipe in one area to help carry additional water flow.
County officials have begun designing the projects and hope to begin construction within a year. The timing will depend on the amount of funding the county receives from the state and federal governments.
The county is also working on a master plan for the Ellicott City area, which will be added to the county’s overall master plan guiding future growth and development.
Draft Ellicott City Watershed Master Plan
Howard County Planning and Zoning, March 22, 2018
Following the [August 2016] flood, the overarching goal was to return Ellicott City to normalcy as quickly and affordably as possible. During the recovery phase, Howard County effectively worked to stabilize Ellicott City and repaired and replaced damaged infrastructure; in some cases in a utilitarian fashion (i.e., asphalt was poured on damaged sidewalk areas instead of concrete or brick replacement).
Howard County launched its master plan process for Ellicott City and its watershed on May 31st, 2017. The master plan process will help define a comprehensive community-driven vision for rebuilding a stronger and more resilient Ellicott City. The master plan will take a fresh and creative look at potential long term flood solutions and strategies.
It will also incorporate a watershed plan in a way that many traditional master plans do not. Ellicott City’s unique topography, hydrology, road network, and mill town heritage will require a tailored, well-planned roadmap for long-term rebuilding.
Maryland Flood Highlights Need for Climate Change Planning
by Becky Hammer (NRDC) – August 1, 2016
This weekend, a historic flash-flooding event killed two people and caused massive destruction in Ellicott City, Maryland. The town received more than 6 inches of rain over the span of two hours. According to the National Weather Service, an event like this should statistically happen only once every 1,000 years, based on historical data.
But because of climate change, extreme events like this one are happening more frequently, and scientists expect that trend to continue into the future. Our past experiences with floods are no longer a reliable indicator of our present or future risk.
So why is Maryland not comprehensively accounting for climate change in its new plan to protect its communities—like Ellicott City—from future natural disasters?