South Woods Geology and Ecology

Together with Hamlin Park the South Woods comprise what is the largest block of coniferous dominated forestland left between the Lake Washington ship canal and the north King County line. These properties also lie within the Thornton Creek Watershed near the headwaters of a tributary to the north branch of Thornton Creek known as Hamlin Creek. One of the geologic characteristics of the upper Hamlin creek watershed is deep sandy soils. Because of this, this sub-watershed of Thornton Creek has tremendous capacity for infiltration of surface water into the ground.

One of the benefits of retaining the South Woods as open space is peak flow reduction. Studies have shown that up to 50% of the rainfall in our area is trapped and released back into the atmosphere through evapotranspiration in a coniferous dominated forest. The area has deep deposits of sandy soils which results in a tremendous capacity for infiltration of surface water into the ground. This was confirmed while on a recent tour of the area with a state legislator, a Shoreline councilmember and two biologists with the state Department of Fish and Wildlife. We visited several outfall pipes where the record rains of recent weeks produced much storm water from these pipes into the ravines that flow through Hamlin Park. Following the trail of sediment carried by the water out of the ravines into the flat bowl within the park, we saw where it temporarily pooled, then percolated into the ground. What began as storm water will eventually enter Thornton Creek as groundwater; clean, cool and regulated. Not only does this also help reduce peak flows, it also helps to maintain base flows in the creek for fish during the critical summer months.