A watershed, or drainage basin, is a land area that drains into a stream; the watershed for a major river may encompass a number of smaller watersheds that ultimately combine at a common point (U.S. Environmental Protection Agency). Each drainage basin is separated topographically from adjacent basins by a geographical barrier, such as a ridge or hill, which is known as a water divide.
To begin to understand how drainage basins work, it is important to understand the basic topography of the land. On the map to the left, it is clear that the basins topographically converge at a few common points--Lake Washington and the Sammamish River. They are the two largest waterbodies that Kenmore's watersheds flow into, and the mouth of the river is located right in the middle of the city. In Northern Kenmore (North of SR 522), the vast majority of the natural water flows south, eventually making its way into the lake or the river. In Southern Kenmore (South of SR 522), most of the surface water flows north or northwest flowing into the river or lake. A small portion of the surface water in flows into Kirkland's Juanita Creek Watershed to the south.
Most of the smaller streams and tributaries are extensions of the larger water bodies carved into the land over time. The water follows gravity and always make its way downhill, or downstream. Over time, the precipitation and subsequent land development created the stream pathways we see today. Due to Kenmore's precarious location at the downstream end of several large drainage basins it is very susceptible to flooding. The stormwater system was built to help convey the water to where it was always meant to go.
The storm water system is also gravity fed to mimic the natural tendency of the water. The basins are a mixture of free-flowing/open-channel creeks and the man-made stormwater infrastructure. Their characteristics and land-use percentages can be found on their “Basin Report Cards”