Operation and maintenance of dry swale (grass swale)
This page is in development
The most frequently cited maintenance concern for dry swales is surface soil/media and underdrain clogging caused by organic matter, fine silts, hydrocarbons, and algal matter. Common operational problems include:
- standing water;
- clogged soil/media surface;
- clogged inlet, outlet or underdrains; and
- invasive plants out-compete native vegetation.
Contents
Design phase maintenance
Implicit in the design guidance is the fact that many design elements of filtering and infiltration systems can minimize the maintenance burden and maintain pollutant removal efficiency. Key examples include:
- limiting drainage area;
- providing easy site access (REQUIRED);
- providing pretreatment (REQUIRED); and
- utilizing native plantings (see Plants for Stormwater Design).
For more information on design information for dry swales, link here.
Construction phase maintenance
Proper construction methods and sequencing play a significant role in reducing problems with operation and maintenance (O&M). In particular, with construction of filter and infiltration practices the most important action for preventing operation and maintenance difficulties is to ensure that the contributing drainage area has been fully stabilized prior to bringing the practice on line (this is a REQUIRED practice).
Inspections during construction are needed to ensure that the filter/infiltration practice is built in accordance with the approved design standards and specifications. Detailed inspection checklists should be used that include sign-offs by qualified individuals at critical stages of construction, to ensure that the contractor’s interpretation of the plan is acceptable to the professional designer. An example construction phase inspection checklist is provided below.
Dry swale construction inspection checklist.
Link to this table
To access an Excel version of form (for field use), click here.
| Project: | ||
| Location: | ||
| Site Status: | ||
| Date: | ||
| Time: | ||
| Inspector: | ||
| Construction Sequence | Satisfactory / Unsatisfactory | Comments |
|---|---|---|
| 1. Pre-Construction | ||
| Pre-construction meeting | ||
| Runoff diverted (Note type of bypass) | ||
| Facility area cleared | ||
| Soil tested for permeability | ||
| Soil tested for phosphorus content (include test method) | ||
| Verify site was not overdug | ||
| Project benchmark near site | ||
| Facility location staked out | ||
| Temporary erosion and sediment protection properly installed | ||
| 2. Excavation | ||
| Lateral slopes completely level | ||
| Soils not compacted during excavation | ||
| Longitudinal slopes within design range | ||
| Stockpile location not adjacent to excavation area and stabilized with vegetation and/ or silt fence | ||
| Verify stockpile is not causing compaction and that it is not eroding | ||
| Was underlying soil ripped or loosened | ||
| Size, location, and inverts per plans | ||
| Side slopes stable | ||
| Groundwater / bedrock verified | ||
| 3. Structural Components | ||
| Stone diaphragm installed per plans | ||
| Outlets installed pre plans | ||
| Check dams installed per plans | ||
| Underdrain installed to grade | ||
| Pretreatment devices installed per plans | ||
| Soil bed composition and texture conforms to specifications | ||
| Inlets installed per plans | ||
| Underdrain installed per plans | ||
| 4. Vegetation | ||
| For native dry swales, plants and materials ordered 6 months prior to construction | ||
| For native dry swales, construction planned to allow for adequate planting and establishment of plant community | ||
| Complies with planting specs | ||
| Topsoil complies with specs in composition and placement | ||
| Soil properly stabilized for permanent erosion control | ||
| 5. Final Inspection | ||
| Dimensions per plans | ||
| Pretreatment operational | ||
| Check dams operational | ||
| Inlet/outlet/underdrain operational | ||
| Soil/media/filter bed permeability verified | ||
| Effective stand of vegetation stabilized | ||
| Construction generated sediments removed | ||
| Contributing watershed stabilized before flow is diverted to the practice | ||
| Comments: | ||
| Actions to be taken: | ||
Post-construction operation and maintenance
Proper maintenance is critical to the successful operation of a filtration/infiltration practice. Without regular maintenance, filtration/infiltration system soil/media can become clogged, losing its ability to conduct and infiltrate water at the designed rate. This can lead to stagnant water, mosquito breeding habitat, and reduction or elimination of pollutant removal capacity.
Inspection and maintenance planning
A maintenance plan clarifying maintenance responsibilities is REQUIRED. Effective long-term operation of filtration/infiltration practices necessitates a dedicated and routine maintenance schedule with clear guidelines and schedules. Proper maintenance will not only increase the expected lifespan of the facility but will improve aesthetics and property value. Some important post-construction considerations are provided below along with RECOMMENDED maintenance standards.
- A site-specific O&M plan that includes the following considerations should be prepared by the designer prior to putting the stormwater practice into operation:
- Inspection and routine maintenance checklist (see below)
- Operating instructions for any outlet components
- Vegetation maintenance schedule