Stormwater Management Facilities: Maintenance Issues & Repairs

The goal of the Stormwater Management Department within the Howard County Bureau of Environmental Services is to improve and manage the quality and quantity of water that originates in, falls onto, or passes through the county on its way to the Chesapeake Bay. One of the ways they do that is by monitoring and maintaining public and private stormwater management facilities. That means the property owner is responsible for stormwater management facility maintenance and repairs.

In this article we cover:

  • your responsibilities as a property owner in Howard County for maintenance of your stormwater management facility,
  • the different types of stormwater management structures,
  • maintenance issues and areas to focus on for each type of facility, and
  • why a quick fix will often cost you more (and not just in repair costs!).

If you’re looking for information about stormwater management in Howard County in general, including your responsibilities as a property owner or manager, see our article on Stormwater Management in Howard County, MD.

If you’re interested in the types of stormwater management facilities used by property owners in Howard County, see our article on Types of Stormwater Management Facilities.

Your Maintenance & Repair Responsibilities

Under Howard County’s rules and permits, property owners are required to address the impacts of runoff for pollutants, flooding, erosion, and applicable groundwater issues. To meet those requirements, stormwater management facilities are designed to:

  • remove pollutants from the runoff,
  • reduce the rate or volume of flow, and
  • recharge groundwater.

After passing through a fully functional stormwater management facility, cleaner runoff can be safely discharged. Usually, water is discharged into:

  • a nearby stream,
  • the ground (as groundwater recharge),
  • a municipal storm sewer system,
  • a combined sewer overflow, or
  • an area located at a lower elevation.

Why is the maintenance and repair of these facilities important?

The water discharged by stormwater management facilities enters our groundwater, streams, and bodies of water. If contaminants remain in the stormwater runoff, it affects the overall health of our entire watershed area.

How often should maintenance activities be completed?

The Stormwater Management Division of the Department of Public Works Bureau of Environmental Services inspect stormwater facilities throughout Howard County. Inspectors visit each stormwater management facility every 3 years to confirm that it’s in compliance with County regulations.

Regular inspections and maintenance are required to keep stormwater management facilities operating as designed and to remain compliant with all the applicable rules and requirements.

To prevent fines and large repair bills, we strongly recommend setting up an ongoing maintenance plan for your facility. This will ensure all systems are operating as designed and are efficiently helping you meet requirements for water quantity and quality.

Preventive & Corrective Maintenance

Preventive actions are regular maintenance tasks intended to keep the BMP in good working order. Corrective actions are more likely to occur incidentally in response to any problems discovered during an inspection.

For example, typical preventive maintenance could include:

  • Removing trash and other debris
  • Removing any buildup of sediment and other materials that may clog forebays, inlets, outlets, and remaining structures
  • Taking care of vegetation (mowing grass, clearing brush, removing dead vegetation)
  • Removing and containing unwanted/invasive plant material from the facility
  • Regularly replacing sand, gravel, and other media
  • Loosening compacted soil
  • Maintaining bioretention areas
  • And more

Corrective actions / repairs might include:

  • Repairing structural damage to basin banks, racks, inlet or outlet structures, riprap aprons
  • Repairing any erosion or animal burrows in and around the facility
  • Re-establishing, cleaning, and repairing any rip rap stones or gabion stones in the outlets, inlets, and dams
  • Replacing or repairing the structural components of the facility to restore them to good working order
  • Backfilling channelized area(s) to repair and prevent erosion damage
  • Restoring vegetation

This is by no means a complete list! Maintenance activities could involve more (or less) work and frequency, depending on the type of facility and variations in its design. For example, the sand layer of a sand filter or infiltration basin should generally be replaced at least once every two years. But if it’s located in an area having high solids loading, you may need to replace the sand more often.

Four Types of Stormwater Management Facilities

For maintenance purposes, we classify each stormwater BMP as one of four general types:

  • Dry Basins
  • Wet Basins
  • Vegetative
  • Underground

You can read more about each type, including the specific structures, in our articles on types of stormwater management facilities in Howard County.

Maintenance Requirements for Different Types of Facilities

The primary objective of maintenance for stormwater management facilities is to keep the structure(s) functioning as designed. That means you have to know what type of facility you’re dealing with, design details (such as the minimum depth of sand, number of inlets, size of the outlet orifices, types of vegetation, etc.), and how it’s intended to function.

For example, detention basins, wet ponds, and constructed wetlands are all structures that control flooding. However, they operate quite differently. Some will discharge all the runoff that flows into them and then empty completely. Others will retain some depth of water after discharging runoff. Maintenance procedures and goals will obviously be somewhat different for these structures, even though they all serve the same end purpose.

The appearance of stormwater facilities can sometimes be deceiving. But getting it wrong will not only result in ineffective maintenance, it can also cause the BMP to fail.

The best way to know the type of facility you’re dealing with is to refer back to the design documents, specifically the site plans and the stormwater management design report.

Below, we break down maintenance goals and processes by the four types of stormwater management facility.

Dry Basin Maintenance

Dry basins normally have no water in them. If it hasn’t rained within the past 72 hours, we’d expect the surface on the bottom of a dry basin to be dry.

Dry basins work by holding stormwater runoff and discharging it slowly over a prolonged period of time, helping to control flooding. They also trap pollutants from runoff; while the water stays in the basin, particles and pollutants settle out of the water and sink to the bottom.

When the water reaches a certain level, it’s released from the basin (usually into a stream or storm sewer) through an outlet. Most basins also have an emergency spillway to take overflow water away from the basin during a major storm event.

As the basin dries out, pollutants stay at the soil surface while water soaks through the bottom of the basin into the subsurface layers.

Most of the runoff will usually be discharged from a dry basin within 10 to 12 hours of a rainfall event. If there’s still standing water 72 or more hours after it rains, it probably means there’s a serious problem.

Dry Basin Facilities: Maintenance Focus Areas

Standing water in a dry basin 72 hours after a rain event means:

  • the basin bottom may be clogged with sediment or impervious debris
  • the ground in the basin bottom could be compacted
  • the outlet orifice or trash racks might be clogged with debris or vegetation
  • the ground water table could be higher than it should be (or perhaps the seasonal high water table and soil properties were incorrectly determined when the basin was constructed).

All of these issues are preventable with proper maintenance. For example, the inlet of a basin should be regularly inspected and cleared of obstacles, such as vegetation, trash, and sediment so that runoff can freely flow into the basin.

It’s especially important not to compact the bottom of a dry basin. Doing so will prevent runoff from percolating down into the subsoil. Never drive heavy equipment, like trucks, tractors, and heavy mowers, into the basin at any time, including during maintenance operations.

Wet Basin Maintenance

In a wet-type stormwater management facility, the basin is always filled with collected runoff.

Stormwater runoff transports solids and pollutants into the pond where heavy particles (sediment, pollutants) settle on the pond bottom. The clean runoff is later discharged from an orifice located above the pond bottom. This type of facility can also be designed to accommodate additional water above the normal water surface level to provide temporary storage of stormwater runoff during heavy storms.

Normally, the water depth in wet basins (such as ponds and the pool area of a constructed wetlands) is around 3 to 6 feet. This provides enough space to store settled solids and reduces thermal impacts on a receiving water body.

As air temperatures increase, shallow areas also warm up, potentially leading to stagnation. In these conditions, it’s not unusual to experience mosquito problems, algal bloom, and the development of foul-smelling anaerobic conditions.

Aerating the pool areas can reduce these problems, but it’s not always possible. For example, the cells that collect water for subsurface gravel wetlands are fairly shallow and are prone to mosquito breeding and odor issues. However, it’s not possible to aerate water in the cells or wetlands because the typical aerator cannot operate in such shallow water. Therefore, it’s important to pay particular attention to any potential issues before they become a real problem.

Wet Basin Facilities: Maintenance Focus Areas

To ensure the proper functioning of wet basin facilities, focus on:

  • Maintaining the appropriate water depth for the specific type of facility
  • Removing sediment from forebays, inlets, outfalls, catch basins, etc.
  • Inspecting and rapidly remedying any problems that cause anaerobic conditions, mosquito breeding, and algal bloom, such as problems with aerators
  • Inspecting and repairing structural components that contain or direct water entering, in, and/or leaving a wet basin stormwater management facility
  • Removing debris, trash, and excessive vegetation that could block inlets, outlets, and other structures
  • Routinely cutting back, removing, replacing, and treating vegetation to maintain an aesthetically pleasing appearance
  • Installing, repairing, and inspecting safety measures to prevent the risk of drowning

Maintenance of Vegetative Type Stormwater Management Facilities

The vegetative type facility uses vegetation to intercept pollutants in runoff. Runoff flows through a densely vegetated area at a shallow water depth, approximately two inches or less. Some, such as grass swales, allow runoff to flow through. Others, such as vegetative filter strips, spread water out rather than conveying it.

Normally, the top of the vegetated area is dry. Water or ponding should not be visible within that area if it hasn’t rained in the past three days.

All vegetative type stormwater management facilities need dense coverage with healthy vegetation and without channelization of flow. Neither grass swales nor vegetative filter strips should have any ponded areas of water, spots of dead vegetation or bare soil, or areas where soil is eroding.

Vegetative Facilities: Maintenance Focus Areas

Here’s where to focus your maintenance activities for vegetative BMPs:

  • Regularly inspect the facility to ensure that it is fully drained within 72 hours after a rain event
  • Add soil or other material as needed to maintain the required separation between the groundwater table and the bottom of the swale or vegetative strip
  • Evaluate and treat plant material for pests and disease, as needed, to maintain overall health and ensure dense vegetative coverage
  • Inspect for bare patches and replant with appropriate vegetation
  • Identify and remove invasive plant species
  • Cut back or contain spreading, aggressive, or unwanted plant material for prevent clogging
  • Fill areas showing signs of erosion to help prevent channelization or concentration of flow
  • Mow turf and other vegetated areas to maintain an acceptable height
  • Remove trash, debris, or excessive sediment that may clog the outlet and/or inlet of a grass swale (to avoid water ponding)

Undergound Facility Maintenance

Underground facilities often need more frequent care to remove sediments or replace the treatment media.

A Quick Fix Isn’t Always the Best Answer

Sometimes, the obvious fix for an issue won’t really resolve the problem. For example, clearing sediment, trash, and vegetation from a clogged inlet won’t prevent flooding from recurring if the inlet itself is in bad condition. It’s equivalent to a doctor treating the symptoms rather than finding and curing the root cause of an illness.

That’s where a long-term, consistent maintenance program with measurable outcomes is required. Each stormwater management facility should have:

  • a detailed maintenance plan that’s specific to that type of facility,
  • annual inspections to identify any potential problems,
  • regular implementation of preventive and corrective actions, and
  • clear and up-to-date records of all work done.

Need a Hand?

If you’re interested in a stormwater maintenance 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 both aboveground and underground stormwater management facilities. We’ll ensure all systems are fully functional and operating according to their design, and efficiently help you meet requirements for water quantity and quality.

Specifically, our maintenance plans for stormwater management facilities include:

  • VEGETATION MANAGEMENT – We remove and/or contain any unwanted and invasive plant material from your facility, regularly mow vegetated areas, and manage growth of any other plant material to prevent clogging.
  • SEDIMENT CONTROL – We remove sediment that has built up in forebays, inlets, outfalls, swales, catch basins, and other structures to improve water flow and groundwater recharge.
  • EROSION CONTROL – We repair and remediate any erosion or unstable soil (including destabilization due to animal burrows) in and around your facility.
  • RIP-RAP & GABIONS – We repair, re-establish, and clean the rip-rap or gabion stones in all of the outlets, inlets, dams, and other structures.
  • STRUCTURAL REPAIRS – We repair or replace damaged or failing structural components, such as drainage channels, retention ponds, and inlets.
  • BIORETENTION AREA MAINTENANCE – We maintain bioretention areas to help control sediment and pollutants, prevent excessive overgrowth, and improve their appearance.

Give us a call and experience the eos difference!


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