City of Sammamish - COVID-19 (Coronavirus) Information & Resources
The City incorporated in 1999 and inherited the many neighborhoods previously constructed under the jurisdiction of King County. These older neighborhoods were developed to the standards at the time which included ditches to convey stormwater from homes and roadways to stormwater ponds.
Ditches help reduce flooding, erosion, and pollution caused by stormwater runoff from homes and the roadway. After runoff enters the ditch, some infiltrates into the ground and the rest flows into a nearby stormwater pond or natural waterbody. For ditches to function properly, they must be clean and clear so runoff can flow unobstructed to the drainage system. Culverts and ditches full of dirt can cause water to back up and potentially create flooding.
Ditches lining City roadways are in the public right-of-way. Like roadways, ditches are owned by the public and maintained by the City on their behalf. There are occasions where a Homeowner’s Association may be responsible for maintenance of the ditches and stormwater facilities in their neighborhood. This responsibility is assigned by the documents that created the subdivision and is typically noted on the map of the subdivided land on file with the King County Assessor's office.
Maintenance, repair, and replacement of culverts under access to private property is the responsibility of the property owner. Although the culvert is located within public right-of-way, the purpose of the culvert is to facilitate access by the property owner to their private property. The City cleans driveway culverts when conducting neighborhood ditch maintenance to ensure the drainage system will function properly. However, culverts should be regularly cleaned by the property owner to reduce the potential for flooding.
Ditches are most commonly replaced when development subdivides land to create new lots to build a new neighborhood. Development is required to install infrastructure to current City standards which includes piping and treating stormwater and installing roadway improvements like sidewalks. The City can pursue projects to fill in sidewalk gaps that may cause ditches to be replaced with pipes, however, this typically occurs on arterial roadways as part of a non-motorized improvement and not through local neighborhoods.
No, ditches must remain open because they are an efficient means of providing conveyance for stormwater runoff. The installation of pipe and sidewalk is a significant change to infrastructure that would increase the cost to maintain the current stormwater system.
The City conducts an annual ditch and drainage maintenance program to clean neighborhood ditches. The work includes digging out excess sediment in the ditches, cleaning culverts under roadways and driveways, and planting grass to prevent erosion. Where ditches are sloped, the City may place rock instead of grass or use other measures to prevent dirt from flowing downstream.
Grass-lined ditches filter and absorb pollutants in the runoff before the water is conveyed to a catch basin or stormwater pond. If you fill a portion of the ditch with yard debris, such as branch cuttings or grass clippings, or if you add rocks or beauty bark, it can cause flooding, damage the neighborhood stormwater pond, or add pollutants to streams and lakes.
In 2019, the City completed a ditch condition assessment following King County guidance to determine the areas requiring more immediate attention. The evaluation included criteria such as the amount and type of vegetation present, whether the vegetation requires maintenance such as mowing, and the amount of sediment blocking the culverts.
Based on these scores, neighborhoods were prioritized for maintenance. Upon selecting the neighborhood(s) for each year’s work (approximately two to four linear miles of ditch line), the neighborhood’s stormwater system is reviewed to understand the most important connections in the system. These connections are vital and work on these may include removing private pipes and re-opening ditch segments. Whenever this kind of work is deemed necessary, the City project manager will attempt to contact you prior to commencing work.