When Systems Fail

When a system fails, it can result in significant damage to buildings, property and utility infrastructure. This will also have a direct impact on the project schedule for removal and replacement of all or part of the failed system as well as to repair any resulting damage. These costs can quickly escalate, even reaching into millions of dollars on large-scale commercial or residential development projects.

Failures can occur in all types of stormwater management systems for a wide variety of reasons; however most of the failures can be assigned to one of the following failure categories:

• Maintenance, environmental, installation, related failures
• Functional or process failures related to capacity and volume
• Structural/material failures

Having a stronger understanding of the contributing factors that can lead to stormwater management system failures will lead to better system designs that are less likely to fail.

Swale/Bioswale Failures

Sink hole caused by failed stormwater system in Dalton, Ga. Photo courtesy of Dalton Utilities

Maintenance failure. Growth and maintenance of vegetation play an important role in the ongoing function of a bioswale system. Failure to properly maintain bioswales can result in failed vegetation growth and poor water conveyance, permeation, and failed treatment.

Functional failure. As with all types of stormwater management systems, swale and bioswale systems are dependent on proper planning, design and execution during all phases to ensure success. Miscalculations in any of these phases can result in the swale not functioning as intended. If the required volume or capacity is underestimated, the results would be a failure of the swale to properly manage or treat stormwater runoff.

Structural failure. Over time, erosion can strip away vital vegetation and soils of a bioswale and result in an overall breakdown of the swale itself. Ground saturation during extreme rain events can result in reduced ground permeability and increased surface water that can result in erosion as well as flooding onto roadways, walkways or other surrounding ground surfaces.

Pond System Failures

Maintenance failure. Poor ongoing maintenance is the primary cause of pond failure. Retention/detention ponds that are poorly maintained can result in unwanted algae blooms, foul odors and a build-up of trash or debris resulting in the clogging of inlet or outflow pipes as well as clogged permeable base material.

Functional failure. Treatment of stormwater primarily occurs by allowing particles to settle to the pond bottom and facilitating the uptake of pollutants, including nutrients, through the biological processes of the pond. When a pond stops functioning as designed, it can result in an overloading of the biological process within the pond. Additional treatment solutions such as aeration may then be required.

Structural failure. In addition to reduced water quality, each new rain event brings the potential for flooding and destructive erosion of surface areas surrounding the pond, creating the potential for a washout to occur. Erosion is often prevalent at concentrated inflows to ponds. Ponds that are poorly maintained or neglected also pose serious health and safety risks, particularly to children. Unfenced ponds are often mistaken for recreational water areas and result in countless unfortunate child deaths each year. Several states including Indiana and Hawaii have proposed legislation that would require perimeter barriers or fencing around retention and detention ponds in an attempt to reduce the number of injuries or deaths associated with ponds.