The Ellicott City Flood and Flooding

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