River Management & Analysis


Surface Water Management conducts feasibility analyses, hydraulic analysis, and other river- related studies to support floodplain management, flood hazard management, flood warning systems, bank stabilization, salmon recovery, permitting, and capital improvement projects.

Developing strategic plans for flood-prone rivers is a high priority, as floods are the most prevalent natural hazard in the county. These plans are based on thorough scientific and engineering assessments of river characteristics and flood hazards. They provide sound guidance for project selection, project design, land use regulations, and other action priorities.

Planning Process

The planning process involves building a technical understanding of a river (typically through computer modeling) to fully understand the patterns of flooding and flood damage that occur, and providing a method of evaluating how proposed solutions might reduce flood damages. Cost-effective solutions can then be selected, ranging from new flood control structures to land use policies and better early warning systems.

Analysis Focus

Analyses are focused on specific topographical regions. Watersheds are large geographic areas in which all sources of water, above and below the ground, drain to a common stream or water body. They are also known as basins. Rivers are the large natural streams that empty into an ocean, lake or other body of water. Some publications define rivers to include the entire watershed that drains into them. Within the watershed are smaller areas, known as sub-basins. Sub-basins are created as portions of the basin drain into groups of minor streams.

Snohomish County, as the watershed map (PDF) shows, contains large portions of the Stillaguamish, Skagit, and Snohomish watersheds, and smaller portions of the Lake Washington and Puget Sound watersheds.

Each of these watersheds contains a number of sub-basins. A sub-basin (PDF) within the Skagit watershed, the Sauk River Sub-basin, covers a large portion of northeastern Snohomish County