New Howard County Stormwater Management Regulations: Leading the Way in Local Responses to High Intensity Storm Events

Local Spotlight

An Interview with the Howard County Department of Planning and Zoning
by Kristen E. Humphrey, MLA, Local Assistance and Training Planner

Twice in less than two years, in July 2016 and again in May 2018, catastrophic flash floods forever changed the economic and physical landscape of historic Ellicott City, located just 10 miles west of downtown Baltimore. These events were so dramatic and destructive to the former mill town that they attracted national, and even international, attention. Much has been written about the devastation, its causes, and the recovery that followed. But what about the measures taken to mitigate, if not prevent, flash floods from happening again?

Howard County is leading the state and perhaps the country in the effort to develop new, more rigorous stormwater management regulations that take into account both water quality and quantity. We spoke with Chad Edmondson, Division Chief for Development and Engineering of Howard County’s Department of Planning and Zoning, along with Kate Bollinger, Planning Supervisor and Peter Conrad, Deputy Director about the county’s efforts to take into account public health, safety, and resource management following the storms — widely viewed as the results of global climate change experienced on a local level — that necessitated addressing these issues in a whole new way.

Can you describe the events that triggered the Department of Planning and Zoning to consider changes to existing stormwater management regulations in Howard County?

After Ellicott City was devastated by two short duration, high-intensity storms in July 2016 and May 2018, Council Bill 56-2018 was introduced by Howard County Councilman John Weinstein, and co-sponsored by then Councilman Calvin Ball (now Howard County  Executive). The bill established a temporary moratorium on development in the Tiber-Hudson Watershed (aka Ellicott City Watershed) and required the Departments of Planning and Zoning and Public Works to study the floods, stormwater facilities, existing and proposed development, existing stormwater regulations, and land uses in the Ellicott City watershed.

Infrastructure, including stormwater management ponds, culverts, bridges, and stream channels were modeled within these drainage areas to determine their capacities with respect to these short duration, high-intensity storm events. The results and recommendations of these studies were presented to the County Administration, County Council, and the public.

With those recommendations as a basis, last year County Executive Calvin Ball proposed changes to the stormwater management regulations to ensure much higher standards within the Tiber Branch, as well as the nearby Plumtree watershed. As passed by the Howard County Council, Council Resolution 123 (CR-123) requires management of short duration, high-intensity storms like those that occurred in 2016 and 2018, as well as the 10-year and 100-year storms for all future development within these watersheds.

This new short duration, high-intensity storm requirement became a complementary part of the county executive’s Ellicott City Safe and Sound Plan, which focused on comprehensive and holistic flood mitigation and recovery. The Safe and Sound Plan is the blueprint to continue the repair and restoration of Ellicott City, guide innovative capital projects to increase capacity of existing stormwater management and storm drain systems, and implement a flood warning system within Ellicott City.

These regulations represent the first of their type and scope in the country. How do they differ in their approach to both water quality and quantity from traditional stormwater regulations?

Results from these moratorium studies show that within these drainage areas, standard management requirements were not enough to protect against the type of storms experienced in 2016 and 2018.  Current management requirements address modeled storm events where the rainfall intensity is distributed in a bell curve over a 24-hour period. This type of long duration storm event allows time for ponds to fill slowly and release the runoff at a controlled rate over an extended period of time before the peak of the storm is realized.  The precipitation of the 2016 and 2018 storms was so intense that the ponds and storm drains were quickly overwhelmed.

It was determined that, of the two storms, the 2016 storm caused the highest runoff in the shortest time period. This event measured 6.6” of rainfall in 3.55-hours and was selected as the model storm for future management of storms within this watershed. With the addition of this short duration, high-intensity storm management, the county’s stormwater management practices for this watershed include both long duration and short duration events while maintaining requirements to also provide the state mandated one-year, 24-hour event and water quality using small scale, filtering devices known as Environmental Site Design (ESD).

Describe the unique characteristics of the Ellicott City area (e.g., topography, nature of the watersheds, historic land use patterns) that contributed to the devastation of the storms?

The Ellicott City watershed is unique to Howard County because it covers approximately 2,300 acres and much of the buildable land was developed long before stormwater standards were required. Ellicott City was founded in 1772, with many buildings constructed in the 1800’s. The topography of the land is very steep, with well-defined granite streambeds. These steep slopes and shallow granite layers reduce the ability for the soil to absorb runoff.

Three major streams, the Tiber Branch, Hudson Branch and New Cut, funnel the storm runoff into the floodway, converge within the city, and often overflow their banks onto Main Street. Many of the buildings along Main Street are constructed directly over the stream and floodway. Runoff from even small storms reaches the streams quickly and is transported at high velocities through Ellicott City and discharged into the Patapsco River.

What are the goals and projected outcomes of the new regs? How are the unique characteristics addressed in the new regulations?

The goal of the new stormwater regulations is to mitigate the increase of peak stormwater flow from new development to address the widest range of storm events that Ellicott City may experience.  These requirements, in conjunction with other components of the Safe and Sound Plan, such as flood storage and conveyance capital projects (for example, drainage improvement to culverts and bridges to increase capacity), are all designed to make Ellicott City a safer and more resilient place to live, shop, and work.

How will the changes benefit the county’s diverse communities?

Together with the other Safe and Sound Plan initiatives, these new stormwater requirements will help achieve the county’s goals of mitigating flooding, preparing for a changing climate, ensuring public safety, protecting Ellicott City’s historic charm, and supporting property and business owners. The depth of flooding and water velocity will be greatly reduced to the maximum depth of a 100-year storm modeled to be one foot in Lower Main Street and water velocity reduced to less than a fifth of the velocities experienced in these storms on lower Main Street.

How long were plans for the changes in the works, from initial concept until the present? When did the regulations go into effect?

The investigation into regulation changes began with the introduction of Council Bill-56 by Councilman John Weinstein, and then Councilman Calvin Ball (now County Executive). Research into the events continued until October 7, 2019, with the adoption of CR-123, which implemented these new stormwater regulations.  During that time period, all development plan review and permitting within the drainage area was stopped. With the approval of CR-123, all plans that were stopped and any future plans were subject to these new regulations.

Watershed modeling for Ellicott City by the Department of Public Works began shortly after the 2016 storm event. Public Works began evaluating possible locations for stormwater management devices such as ponds to reduce runoff along the three contributing streams. Public Works and their consultant, engineering firm McCormick Taylor, are still working on design and permitting for the construction of several stormwater and conveyance improvements.

Who are/were the key partners (community groups, non-profit organizations, local, and state agencies) involved in this effort? Is there a lead group?

While the Howard County government led the effort to adopt regulations for high-intensity, short-duration storms, this effort was preceded by several years of community input on flooding in Ellicott City. In 2015, the county created a temporary community group called the Flood Workgroup. After the 2016 flood, many members of the Flood Workgroup also served on the Ellicott City Recovery Community Advisory Group (CAG). Then in 2017, a Master Plan Advisory Team was formed to serve as a sounding board throughout the Ellicott City watershed master planning effort, which is still underway (with a reconstituted Master Plan Advisory Team formed in 2019).

The members of each of these groups, along with the general public and other stakeholders, provided input on resiliency and flood mitigation. Through a series of community workshops and an online portal, the county collected several hundred comments and ideas. Among these many comments were requests for strengthened stormwater requirements to better manage peak flow during flash flood events.

How has the state, and MDE in particular, assisted?

The Maryland Department of Environment (MDE) was very helpful in expediting in-stream, emergency permitting. Representatives from MDE were on site for evaluation and allowed in-stream clean-up measures to begin immediately. MDE continues to expedite review and permitting for future drainage and management projects currently in design. Howard County communicated with MDE as the new stormwater regulations were developed, and MDE provided supportive consultation.

What impacts/changes do you foresee as a result of the new regs?

Results of the new regulations will require large scale stormwater practices such as ponds and underground storage pipes to be installed in conjunction with the water quality environmental site design (ESD) practices on all future development sites. These large facilities will reduce the stormwater impacts to both the watersheds as well as adjacent and downstream property owners. Together with the storage and conveyance projects in the Safe and Sound plan, the depth of flooding and water velocity will be greatly reduced.

What have been the largest hurdles to overcome in the process of affecting these changes?

The largest hurdles to overcome were the technical and public communications aspects of the initiative. The Departments of Planning and Zoning and Public Works responded to the research required in CB56-2018 while the rebuilding of public and private infrastructure was underway in the town. Modeling of the storms and design of the new regulations were completed during the pressure of the development moratorium. Residents and property owners were devastated twice in two years by these events and needed to understand how the multiple responses (including new stormwater regulations) implemented by the county would address their concerns and reduce the impacts from future storm events.

What lessons learned would you share with other communities/stakeholders seeking to embark on a similar path?

Ellicott City is a unique town built in the 1800’s within a granite valley, with steep slopes, and homes and businesses constructed in and over the floodplain.  Given that the drainage area to this floodway is more than 2,300 acres, the town has been flooded by hurricanes and flash floods many times in the past 200 years.  Much of the development within this drainage area was constructed prior to stormwater management requirements and design methods were created.

For those areas of development constructed during the current stormwater management era, the effects of development in a drainage area similar to this should take a holistic approach and consider effects beyond the borders of individual developments. This holistic approach should also be used for conveyance of runoff downstream. Standard accepted management practices just might not be enough.

For more information regarding Howard County’s new stormwater management regulations, please contact: Chad Edmondson, Engineering Division Chief, Howard County Department of Planning and Zoning at or (410) 313-2350.

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