King CountyFor more information about this layer please see the GIS Data Catalog . Component Types-Basic biofiltration swale: A long, gently sloped, vegetated ditch designed to filter pollutants from stormwater. Grass is the most common vegetation, but wetland vegetation can be used if the soil is saturated. -Wet biofiltration swale: A variation of the basic biofiltration swale used where the longitudinal slope is slight (1 to 2 percent or less), water tables are high, or continuous low base flow is likely to result in saturated soil conditions. Under such conditions, healthy grass growth is not possible and wetland plants are used to provide the biofiltration mechanism.-Continuous inflow biofiltration swale: A biofiltration swale where water enters the swale continuously at numerous discrete inflows with no single inflow contributing more than about 10% of total swale flow.ArcGIS FeatureLayerhttps://hub.arcgis.com/datasets/2fbc1bc459e74b0094a73cfb90336396_0engKing County GIS Open DataPublicWater Quality Swale [Washington (State)--King County]Web servicesWashington (State)--King CountyWashington (State)Last Modified: 2026-01-08