Littlebrook Creek Culvert Replacement

Abstract

Littlebrook Creek is a tributary of Thornton Creek, located in North Seattle. Under NE 120th Street, between NE 35th Ave and 36th Ave, there is a culvert that runs perpendicular under the street that is collapsing. This culvert is also a barrier to salmon passage during spawning season because the culvert invert is too high above the creek bottom on the downstream side. A new long-term solution needs to be installed, otherwise the culvert could fail, causing NE 120th Street to collapse which would result in the damming of the stream and pooling of water from the stream potentially overflowing into neighbors’ yards. This project will consist of designing a replacement culvert. It will include removing the asphalt road, excavating soil, and removing the current thirty-inch concrete culvert in order for a sustainable replacement to be installed. The creek will have to continue to flow throughout construction which means that water will have to be dammed upstream of NE 120th Street and the water pumped across the street and released downstream, allowing for a dry construction area. Measures will need to be taken to prevent debris from construction contaminating the stream. Through diverting the water from upstream to downstream it will help with contamination prevention. Construction must also take place in the window of time that will not impede salmon migration.