URBANIZATION + MINED PEAT BOGS: A RECIPE FOR FLOODING AND AN OPPORTUNITY FOR URBAN FLOODPLAIN MANAGEMENT IN SHORELINE, WA:

Ronald Bog is a 6-acre excavated wetland pond within an 8-acre park, in the upper North Fork Thornton Creek watershed in Shoreline, a bedroom community north of Seattle. Ronald Bog was originally a large 134-acre open cranberry marsh. Logging and clear cutting of the area in the late 1880’s cleared the way for development of this area north of Seattle. Rural and agricultural land dominated the area until the 1940s. Peat mining in the 1950s required the clearing of the vegetative cover and ditching to lower the water table. As a result, the ditch system contributed to surface water flow, where there was a limited one prior to development. The channel draining Ronald Bog, now called North Fork Thornton Creek, was likely created during the initial mining of the bog. Peat mining created an on-site pond of 11 acres. Housing development in the mid 1960s on the south end of the bog and the construction of Interstate 5 reduced the bog to its current size of 6 acres.

As a result of the wetland filling and increased urbanization of this upper watershed, the residential neighborhood south of the bog has experienced residential flooding at least 4 times in the past 25 years, flooding up to 20 homes. Many efforts to address the flooding in this area have ranged from removing the outlet pipe and creating an open channel, expanding the wetland, pumping the bog during a flood, or constructing a large flood wall/levee.

In the past two years, the City has addressed this urban flooding problem from a holistic floodplain management approach that is cost effective and well supported by the community: risk reduction through capital projects (i.e. a replacement pipe and short floodwall), emergency preparedness and effective communication for the neighborhood (i.e. an early warning system and neighborhood emergency management plan), and FEMA floodplain mapping which will reduce flood risk through the development code and communicate risk to neighborhoods.