Drainage and Stormwater Management

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Much of our community utilizes roadside swales to convey excess stormwater to the nearest boy of water. Swales are shallow grass areas along the road which collect and convey runoff so that our homes and roads are not flooded. Swales function much differently than underground pipe systems that many residents are more familiar with. Besides conveying water, swales also act to filter and absorb water, resulting in cleaner canals and aquifers. A swale is expected to retain small amounts of water after a rainfall event. Unless the swale retains water for more than 72 hours since the last rainfall, it is considered to be functioning properly. It is not uncommon for a swale to be wet for weeks at a time during the rainy season.

Public Works has the responsibility of maintaining common drainage areas of the City including roadside swales in residential neighborhoods. Crews regularly clear blockages at inlets and remove sediment from inlet basins and pipes to insure that water can flow freely. Drainage swales are inspected each year. GPS enabled cameras are deployed across the entire city on one particular day. From those videos we are able to identify work areas for the next year.

When your home was built, engineering inspectors worked with your builder to ensure that your swale was properly constructed. Without proper maintenance, the elevation of your swale can change, causing drainage issues for you or your neighbors. It is important that you maintain your swale because an improperly maintained swale at your home may be causing problems for your neighbors several lots away even if your own drainage seems to be working fine. There are many things a homeowner can do to help maintain their swale including:

  1. Avoid over-watering and fertilization of the swale area. As the swale is the lowest part of your yard, it will naturally get moisture and nutrients which flow from the higher areas.
  2. Keep pipes and culverts open by removing sod which may be blocking the flow of water.
  3. Dethatch Floratam lawns annually in the spring to remove dead vegetation below the surface.
  4. Avoid driving in your swale, and certainly not during wet times. Ruts cause blockages in the swales.
  5. Do not pile vegetation or other debris in the swale. Do not dispose of chemicals or other pollutants in the swales.

As part of the National Pollutant Discharge Elimination System (NPDES), the City is responsible for overseeing stormwater discharge into waters of the state. The City is required to obtain permits for any activities that may introduce additional pollutants into canals or Charlotte Harbor. An integral part of our drainage system, grass swales filter out pollutants and allow water to be absorbed into the ground. To strike a balance between environmental needs and the desire of homeowners to have dry swales, a 72 hour policy has been established, which requires water to remain for 72 hours (3 days) after the last rainfall in order for the area to be declared in need of repair.

Many residents are not properly informed about this policy. They might have several inches of water in their driveway for a couple days and still be within the established policy. Other areas suffer from very high ground water tables that cause the swales to be wet virtually the entire rainy season although there is no significant blockage downstream. Before most drainage work is done, crews often investigate water usage. It is quite common for a broken sprinkler to be the root of a problem.

Some areas of the City were designed with better drainage features than others (more outfall pipes, greater slopes, etc.). Some areas of the City have soils which absorb more water. At times Public Works has taken on capital projects to improve drainage but the vast majority of our drainage work is maintenance of the existing system. Reconstruction of a drainage system after homes and driveways are built is very expensive and can only be justified if extreme flooding persists.

There are basically two main causes for drainage to worsen over time. The first is sedimentation. Particles of soil from yards, roadways, construction activity, etc. wash into the swales and deposit at points where the water slows. This is most common on the downstream side of pipes and culverts. These blockages can often be removed with a shovel. To minimize this, barren soil is discouraged and silt fence is required at construction sites.

The second and more prevalent cause for drainage problems is from thatch buildup in lawns. This is most common in Floratam lawns.  We often see layers of matted grass thatch four to six inches thick or more. This thatch develops above the soil and is virtually impenetrable to water upstream. We see that lawns that were sodded at the proper elevation a few years ago are no longer at that elevation. This is very easy to observe along the road where sod is often several inches above the pavement.  Sod is required to be installed at the elevation of the road and is checked by inspectors as part of the building permit.

Thatch may go unnoticed for years as it occurs at a slow rate. Elevation of driveways with swales in the pavement do not change and will quickly bare the evidence of standing water. Likewise, the elevation of swales for new construction are set at the design elevation and they too may hold water due to blockages downstream. Thatch is caused by over watering and over fertilizing and can be controlled by dethatching if not left unattended too long. You can read more about thatch here.

Public Works does not dethatch lawns. Generally by the time Public Works becomes involved in a drainage problem, removal of the turf and regrading is the only answer. A large excavator is sent to the location to remove the sod/soil and the area is resodded at the proper elevation again. In early 2017, enhanced swale regarding/drainage improvements were initiated throughout the City. Over 100 locations were identified during the most recent annual inspection. View the list of properties to be addressed in FY 2019. In addition, properties adjacent to those on the list may also be worked on in order to fix an overall problem.

Here's a slideshow depicting swale issues.