CITY OF DES MOINES SHORELINE MASTER PROGRAM

Des Moines Shoreline Inventory and Characterization
WATERSHED CHARACTERIZATION
Ecosystem Wide Processes
The City of Des Moines is located in the central portion of the Puget Lowland, a distinct
geographic area, or ecoregion, based on topography, climate, land use, geology, soils, and
naturally occurring vegetation. The Puget Lowland ecoregion is an elongate topographic and
structural depression bordered by the Cascade Mountains on the east and the Olympic Mountains
on the west. The distinct topography, geology, and soils of the Puget Lowland are the result of
numerous glacial incursions into the Lowland from British Columbia during the Pleistocene
Epoch (2 million years ago to about 10,000 years). This lowland is characterized by a series of
ridges with the long axis trending in the north-south direction separate by deeply cut ravines and
broad valleys. In general, the ground surface elevation is within 500 feet of sea level. The
climate of the Puget Lowland is characterized by dry summers and mild, wet winters, with
annual precipitation between 25 and >60 inches. Prior to the arrival of European populations,
dense coniferous forests covered the Lowland. Vegetation in the Puget Lowland is dominated by
Douglas-fir forests with western hemlock and redcedar as the primary late-successional species.
Oregon white oak, Pacific madrone, big leaf maple, and red alder forests are frequent component
of the landscape. In the southern Puget Sound region grassland habitats are often associates with
oak habitats (WDNR, 2003). Other special habitats within the ecoregion include wetlands,
riparian areas, bogs and estuaries. Characteristic wildlife includes a rich diversity of birds (200
species), mammals and fish species. The City of Des Moines is characteristic of the ecoregion’s
landscape, biota, and urban alteration. The City is located on the Puget Sound shoreline and
contains characteristic areas of coniferous forest, and riparian and wetlands habitat, particularly
associated with several small streams that flow from east to west through the City. The City is
also characterized by substantial development and urbanization throughout the City’s
boundaries.
To understand shoreline processes and functions within the regulated shoreline jurisdiction, it is
useful to understand the natural, ecosystem-wide processes that contribute to the conditions
found along the shoreline and affect the natural, ecological functions occurring in the nearshore
environment 2 . Alterations that affect the larger area may affect the natural shoreline processes.
As water flow drives many ecological processes, a useful area for evaluation, smaller than the
ecoregion, is the watershed. For purposes of this report, the Des Moines area watershed is
defined as those stream basins that flow directly to Puget Sound and discharge in the shoreline
jurisdiction of the City of Des Moines. These include Des Moines Creek, Massey Creek,
McSorley Creek, Woodmont Creek, Redondo Creek, and Cold Creek drainage basins (Figure 3).
Surface and groundwater flow in the watershed is naturally controlled by climate, topography,
vegetation, soils, and geologic conditions, but is also altered by land use activities.
2 The Puget Sound “nearshore” is generally considered to be an area that runs from the top of bluffs on the land across the beach
to the point where light penetrates the Sound’s water.
Page 8 March 2005