Stormwater Management in Howard County, MD

In Howard County, Maryland, we get an average of 44 inches of rainfall a year and 24 inches of snow. According to the National Weather Service, precipitation levels overall have been increasing in the mid-Atlantic region for the past 10 years so we can probably look forward to getting even more rain in the future.

That’s where stormwater management comes in.

In this article, we answer some of the most common questions about stormwater, stormwater runoff, and stormwater management in Howard County, including your responsibilities as a property owner or manager.

If you’re looking for information about the various types of stormwater management facilities in use in Howard County, including the features, benefits, and drawbacks of each, you’ll find that in our article on Types of Stormwaproactive stormwater maintenance programs

For information about maintenance and repairs of stormwater management facilities, see our article on that topic here.

What is stormwater?

Ideally, all of the precipitation we receive will quickly infiltrate into the ground to recharge groundwater. And in natural areas, such as forests, it does just that – we typically see about 18 inches per hour of infiltration in forested areas (as opposed to lawns, where water infiltrates at just 2 inches per hour).

But in built-up areas, such as much of Howard County, the land is covered with impervious surfaces like pavement and buildings. Impervious means just that – water cannot pass through it to infiltrate into the ground.

Water that cannot infiltrate the surface still has to go somewhere. It finds the easiest path by flowing over paved areas, ground, and roofs; through gutters, pipes, and storm drains; and into the nearest waterway, such as streams, rivers, and the Chesapeake Bay.

All of the water that flows along surfaces after a rainfall or snowmelt is stormwater.

What is stormwater runoff?

Runoff is stormwater that flows across surfaces after a rainfall or snowmelt. As more precipitation falls and/or is channeled into storm drain systems, the flowing water volume increases and picks up speed.

Along the way, the water becomes polluted by surface substances like oil, grease, trash, pesticides, or fertilizers, which are then carried into our streams, lakes, ponds, and rivers. Most of the stormwater runoff from roads, driveways, rooftops, and parking lots is not treated before it reaches our waterways.

DID YOU KNOW? Urban stormwater runoff is the only major source of pollution that is increasing.

red bench flooded by stormwater

Why is stormwater runoff a problem?

Runoff from impermeable surfaces causes three major issues: flooding, erosion, and pollution.

Flooding and Flash Floods

Overdevelopment throughout Howard County has replaced natural areas with impervious surfaces, such as roads, buildings, and parking lots. Because water cannot infiltrate these surfaces, it builds up in low-lying areas, leading to flooding, and flows more quickly than it would across permeable surfaces, leading to flash floods. Many of us remember the flash floods that hit Ellicott City in 2016 and 2018, devastating our historic district.


Erosion is caused by fast-flowing stormwater that undermines paved areas and building foundations, washes away landscaping, and damages streams. Depending on the degree of erosion, it can cause significant damage to property, as well as to habitat essential for local wildlife.

The video below shows a good explanation from Montgomery County of the importance of our streams and how stormwater erosion destroys them and surrounding properties.


Common pollutants often found in stormwater runoff include:

  • Sediment (e.g., from construction sites, exposed landscape areas, streambanks)
  • Pesticides/fertilizers (these are frequently applied in excess on home and commercial landscapes, gardens, nurseries, agricultural fields, golf courses, etc.)
  • Trash and debris (e.g., from roads, sidewalks, parking lots, parks, plazas)
  • Liquid pollutants (e.g., oil, antifreeze, gasoline, soapy water from car washing)
  • Pet waste that has been left on the ground (Howard County Animal Control laws require that owners pick it up but we all know that doesn’t always happen…)
  • Salt and sand from winter weather road treatments

All of these pollutants end up in our waterways, killing untold numbers of marine and land animals and poisoning plants.

How much stormwater runoff does your property generate?

The volume of water coming off impervious surfaces during a rainfall event is far greater than many of us expect. One inch of rain that falls over 1 square feet of impervious surface creates .6 gallons of water.

So, for example, a 50,000 sqft commercial development would generate 155,843 gallons of runoff during a ½” rainstorm. That’s a lot of water! (and we frequently get storms with more than ½” of rain)

To see how much water comes off your property, use this handy rainfall calculator from the U.S. Geological Survey.

How can you prevent stormwater runoff?

The best way to prevent stormwater runoff is to manage it by installing and maintaining a stormwater management facility on your property.

a beautiful stormwater retention pond

A stormwater retention pond (a type of stormwater retention facility) doesn’t have to be ugly!

What is a stormwater management facility?

Think of a stormwater management “facility” as anything that facilitates the management of stormwater. This can involve anything from landscaping and environmental site design to large-scale infrastructure projects and underground stormwater storage systems.

Generally speaking, a stormwater management facility is designed to do one or more of the following:

  1. Control flooding
  2. Control erosion
  3. Control pollution
  4. Recharge groundwater

The end result is that these facilities protect public health and our environment.

What kind of stormwater management facility is best?

Stormwater management isn’t a one-size-fits-all approach. Instead, we recommend looking at your property as part of a larger system that includes:

You may find that a combination of practices is more effective and/or budget-friendly than any one practice in isolation.

Local Ordinances & Regulations

Howard County, like surrounding counties, has ordinances and regulations intended to control stormwater runoff and protect the overall health of the Chesapeake Bay watershed area.

These regulations cover various sections of the Howard County Code, including:

Sec. 18.914 – Maintenance is of paramount importance for our clients throughout the County. Generally speaking, the property owner or manager is legally responsible for ensuring that the property’s stormwater management facilities are properly maintained and function as designed.

The County inspects most facilities every three years to ensure that they’re fully compliant with all rules and requirements (see Sec. 18.912 – Inspection). To stay compliant, it’s important to schedule regular maintenance with a company recognized by the Howard County DPW Bureau of Environmental Services as a Contractor for both aboveground and underground stormwater management facility maintenance. 

In Summary

It’s important to understand what stormwater is, where it comes from, where it goes to, and the impact it has on water quality in our watershed. Uncontrolled stormwater runoff:

  • causes flooding,
  • contaminates our ecosystem with pollutants,
  • erodes precious wildlife habitats, and
  • damages property.

Proper stormwater management directs rainwater and snowmelt into a stormwater management facility where the water is stored before being slowly released into nearby waterways. This allows sediment and pollutants to settle out, and reduces the speed and volume of water flowing across surfaces. The end result is improved water quality, reduced erosion, and prevention of flash floods. That’s a result we can all get behind!

If you’re interested in a stormwater management program from a DPW Bureau of Environmental Services approved contractor, give eos Outdoor Services a call at 410-648-9783. We provide proactive stormwater maintenance programs and repairs to stormwater management facilities to ensure all systems are fully functional and operating according to their design, and to efficiently help you meet requirements for water quantity and quality.


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