Ellicott City Flood and Flooding [An update from 2016]

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.

Modified
Tiber River watershed, adapted from Google Maps

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.

Feet of water flowing through Ellicott City, Maryland. (Photo/Max Robinson, accuweather.com)

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.

Photo/Kim Hairston (The Baltimore Sun)

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.

http://www.baltimoresun.com/news/weather/bs-md-weather-storm-2016-story.html

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.

Ellicott City July 30, by Josh Zimmerman
Ellicott City July 30 (Photo by Josh Zimmerman)

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.

http://www.baltimoresun.com/news/weather/weather-blog/bal-wx-ellicott-city-gets-rainfall-expected-only-once-every-few-hundred-years-20160731-story.html

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.

from Presentation at the Ellicott City Watershed Master Plan Public Meeting, March 2018

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.

http://www.baltimoresun.com/news/maryland/howard/bs-md-flood-mitigation-projects-20170726-story.html

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.

Summary of Draft Ellicott City Watershed Master Plan, March 22, 2018

https://www.howardcountymd.gov/Departments/Planning-and-Zoning/Community-Planning/Community-Plans/EC-Master-Plan

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?

https://www.nrdc.org/experts/becky-hammer/maryland-flood-highlights-need-climate-change-planning

Featured image at top of post

http://www.mdhistoricdistrict.com/wp-content/uploads/2010/01/EllicottCityFloodGauge-1024×682.jpg

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The Ellicott City Flood and Flooding

This post was updated May 28, 2018. CLICK HERE.

As we mourn the deaths of two people, the torment inflicted on residents and businesses, and the loss we feel as a community from the July 30th flood, planning has begun for the city’s restoration.

Ellicott City has a long history of flooding, and each time has recovered better than before. Short-term planning needs to consider long-term requirements for improved flood mitigation. Significant work has already been done to understand the challenges and identify the work to be done. As we consider next steps, let’s step back and get a better understanding of the big picture.

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.

Modified
Tiber River watershed, adapted from Google Maps
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.

https://www.geocaching.com/geocache/GC68XNV_ellicott-city-the-great-floods

Ellicott City gets rainfall expected only once every millennium

Ellicott City July 30, by Josh Zimmerman
Ellicott City July 30 (Photo by Josh Zimmerman)

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.
http://www.baltimoresun.com/news/weather/weather-blog/bal-wx-ellicott-city-gets-rainfall-expected-only-once-every-few-hundred-years-20160731-story.html

Tropical Storm Agnes, June 21 – 23, 1972

Flooded Main Street Ellicott City from Agnes. (Photo by Mike Hartley)
Flooded Main Street Ellicott City from Agnes (Photo by Mike Hartley)

Tropical storm Agnes struck the area with nine inches of rain causing flash floods all over the county. Massive flooding caused at least 3 deaths and bodies were still being found days later. Extensive personal and government property damage occurred as well as the complete flooding of Elkridge and Ellicott City, which had to be evacuated in the middle of the night by boat.

(The Patapsco River crested at 14.5 ft with a flood volume of 80,600 cubic feet per second.) Several commercial enterprises including trucking firms, paper producers, chemical plants, and others were completely washed away along the Patapsco River.

Howard County became what was called a “veritable island” as bridges were washed away on the Patapsco and Patuxent Rivers. This disaster was so complete that the financial damage could not be estimated in some instances due to the total removal of all traces of property. Many businesses simply did not attempt to reopen.

http://www.howardcountymd.gov/LinkClick.aspx?fileticket=7aKPRMqP_gs%3d&portalid=0

Howard County Flood Mitigation Plan, Department of Public Works (Sept. 6, 2010)

In Howard County, the flood origins consist of riverine flooding from the tributaries of the Patuxent River bordering Prince George’s and Montgomery Counties to the southwest and the Patapsco River bordering Carroll and Baltimore County to the north and northeast, as well as many streams and rivers in between. These include the Little Patuxent River, the Middle Patuxent River, Cattail Creek, Deep Run, Dorsey Run, Bonnie Branch, Plumtree Branch, Guilford Branch, Hammond Branch, Clyde’s Branch, Tiber-Hudson Branch, and many others (Figure 1.2).

Potential Flood Damage

Several conclusions can be made regarding the question of flooding vulnerability in Howard County.

  • First, given that Howard County has a number of streams and rivers that have significant floodplains and given that it contains more than 90,000 improved properties, the fact that only 198 (0.2%) are vulnerable to flooding is probably a result of strong land use regulations and the leadership and foresight to implement them (as well as a fortuitous geomorphology).
  • Second, given the potential for increased development potential plus the “flashy” nature of many of the County’s streams, the time to redouble the County’s efforts to protect its citizens from flooding is now.
  • Third, even though the County is largely flood-resistant, there are certain areas that remain very vulnerable, such as Ellicott City and Elkridge, for which there is no easy answer.
      • In the chapters that follow, a number of potential actions will be recommended. In the end, it will be incumbent upon the people of Howard County to reduce their personal vulnerability to flooding.

    https://www.howardcountymd.gov/Departments/Public-Works/Bureau-Of-Environmental-Services/Stormwater-Management/Flood-Protection

    Historic Ellicott City Flood Workgroup, Introduction

    Flooding is a major problem in the Patapsco River and Hudson/Tiber Watershed Tributaries, causing significant property damage and personal loss. There have been numerous incidents of flooding, including several recent major events.

    The Howard County Flood Mitigation Plan identifies Historic Ellicott City as an area of flood vulnerability, stating:

    “The (Old) Ellicott City area will potentially be one of the most impacted during a 100-year flood event on the Patapsco River…Nearly all structures in the area may suffer flooding damage to their buildings and contents. Many are likely to be impacted significantly or severely. In addition to flooding from the Patapsco River, the (Old) Ellicott City area is also impacted by the Tiber Hudson Branch, Cat Rock Run, Autumn Hill Branch, and New Cut Branch. There are many businesses in the (Old) Ellicott City area, making both the buildings and their valuable contents vulnerable to flooding.”

    The Howard County Executive funded approximately $2,500,000 in Fiscal Year 2016 for a first phase (Phase I) of flood mitigation projects in the Historic Ellicott City area. In conjunction with that effort, the Howard County Executive created the Historic Ellicott City Flood Workgroup through Executive Order 2015- 06. While the Workgroup will not oversee Phase I efforts, it is tasked with recommending flood mitigation solutions to be included in future efforts (Phase II).

    http://livegreenhoward.com/green/water-resources/floodplain-flood-protection/historic-ellicott-city-flood-workgroup/

    Workgroup Recommendations (Dec. 1, 2015)

    The Historic Ellicott City Flooding Workgroup is making the following recommendations to the Howard County Executive and County Council with the goal of protecting the Ellicott City Historic District by enhancing public safety and minimizing damage to properties.

    A. Structural: The Flood Workgroup has identified short and long range structural improvements to the stormwater management systems in the Ellicott City drainage area to mitigate and possibly eliminate property damage.

    B. Maintenance/Monitoring: Minimize the amount of debris that accumulates within the stream channels of the Tiber and Hudson tributaries, as well as the drainage channels that empty into the Tiber and Hudson; Monitor the channels and tributaries on a scheduled basis of four times per year.

    C. Education: In a world where climate changes are somewhat unpredictable and building developments can change the flow of stormwater in Historic Ellicott City, Howard County should reach out to developers, commercial interests, business owners and residents with the latest information about techniques to control and mitigate floodwater.

    D. Programmatic/Capacity: In order to mitigate flooding in Ellicott City, the Flood Workgroup feels that consistent and dedicated resources need to be applied to the flooding issue until measurable improvements are seen.

    E. Other

    http://livegreenhoward.com/green/water-resources/floodplain-flood-protection/historic-ellicott-city-flood-workgroup/

    Elli­cott City Clean Green and Safe Com­mit­tee

    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?

    https://www.nrdc.org/experts/becky-hammer/maryland-flood-highlights-need-climate-change-planning

    Featured image at top of post

    http://www.mdhistoricdistrict.com/wp-content/uploads/2010/01/EllicottCityFloodGauge-1024×682.jpg