Private Stormwater Maintenance Program


Maintenance Program

The City of Bainbridge Island (COBI) works with local property owners to ensure that all private stormwater systems receive routine inspection (at least once per year) and maintenance. This helps these systems to function as they were designed and to prevent flooding, erosion and water quality degradation.

Understanding Your Stormwater System

Typical stormwater systems consist of some combination of roof drains, underground pipes, catch basins, swales, culverts, ditches, oil/water separators, and manmade retention, detention, infiltration vaults and ponds.

Retention and detention facilities prevent flooding and reduce contamination by temporarily storing stormwater in ponds or underground vaults with control structures. These facilities slow the rate of runoff and also allow suspended contaminants to settle out or be removed before the water enters our creeks and lakes.

Low-impact development (LID) facilities strives to mimic pre-developed infiltration, filtration, storage, evaporation, and transpiration of water into the groundwater below.

Stormwater Maintenance Tools

Stormwater System Inspection Process

Private stormwater systems must be inspected on a regular basis, at least per year:

  • Annually, the COBI will notify property owners by letter when it is time for their next stormwater system inspection.
  • Upon notification, the property owner will be responsible for completing the inspection and any necessary maintenance. Property owners must submit the Certificate of Inspection (PDF) once the inspection has been completed.
  • If maintenance is required, you will need to fill out and submit a Certificate of Completion (PDF) when the work is finished
  • COBI will perform verification inspections on a certain percentage of private facilities to ensure proper inspection and maintenance.

Maintaining Your Stormwater System

Prevent materials that are stored outside from leaking, draining, spilling or being dumped into the stormwater system. Keeping contaminants out of your stormwater system may reduce the disposal costs for materials cleaned from your system.

Check out COBI's maintenance requirements for typical stormwater facilities and/or Ecology Stormwater Manual Vol V Runoff Treatment BMPs - Maintenance Standards for Drainage Facilities (PDF). Typical stormwater system maintenance requirements might include: 

  • Cleaning contaminated sediment and liquids from detention ponds
  • Underground pipes
  • Catch basins
  • Manholes or repairing control structures

Cost of Maintenance

Maintenance costs depend on both the type and the condition of the existing system. The cost for maintenance each time it is required can vary greatly due to depth, location and number of structures.

Drainage Maintenance Service

If your stormwater system requires maintenance, we will provide you with a list of local firms that provide drainage maintenance services. You can also download a list of firms: Firms Providing Drainage Maintenance Service (PDF).

Certificate of Completion

The Certificate of Completion (PDF) should be filled out by you or your contractor. Please include all maintenance that has been performed on your system since the date it was inspected by the City. If you hired a contractor to perform the maintenance, have them sign the form as well.

Submit the completed form to:

City of Bainbridge Island
NPDES Permit Coordinator - Public Works
280 Madison Avenue N
Bainbridge Island, WA 98110

Other Helpful Information

Questions? Please call Marilyn Guthrie at 206-780-3724 or Christian Berg at 206-780-3784. You may also email Marilyn Guthrie.