Ebey's Prairie Watershed Remediation Study Phase 1: Water Quality & Storm Flow Investigations
Water Quality Investigation
For the purposes of the Ebey's Prairie Watershed Remediation Study Project that began March 2, 2012, the Ebey's Prairie watershed has been divided into five separate basins based on topography, direction of stormwater flows, and land uses.
Primarily in agriculture
Some low-density residential development, all served by septic systems
Gradients generally run northwest to southeast, slopes are mostly slight, some significant slopes along west edge of watershed
Seasonal ponding of stormwater in fields and ditches has been an increasingly persistent problem in recent years.
County roadside ditch system along Ebey Road has inadequate slope to convey the total volume of winter flows.
Stormwater runoff from Highway 20 drains through farm fields and enters this substandard ditch system, adding to flooding of adjacent farm fields in this basin and in sub-basin 5.
Primarily ‘urban’, includes commercial development, high density housing, three schools, two mobile home parks, a nursing home, and a hospital, all served by the Town of Coupeville sewer system
This basin has by far the highest percentage of impervious surface, primarily asphalt and rooftops
Gradients generally run from north to south,
The majority of stormwater conveyance system consists of buried pipes and catch basins
Comprised of a mix of low density housing, crop and livestock production, woodlots, and horse facilities
Stormwater flow is generally from northeast to southwest and is conveyed primarily via a surface ditch network and a pipe system, both in the public road right-of-ways and on private lands in the upper part of the basin
Surface flows to enter the pipe system along Engle Road that conveys stormwater to a point near the marine outfall
This basin includes two man-made stormwater detention ponds and a natural pond, which provide some degree of flow control and treatment; also includes a constructed phytoremediation swale, which treats stormwater runoff from parking lots in adjacent areas in Sub-Basin 2
During wet conditions, the westerly end of this sub-basin experiences flooding in the lower portions of crop fields just above the inlet to the pipe system along Engle Road
Primarily agricultural land, with some wooded areas and a few houses, which are served by septic systems
Almost all of the stormwater flows are conveyed to the northwest corner of this sub-basin via a ditch and pipe network that runs north along Ebey Road
From there, stormwater is conveyed via pipelines to the ditch near the marine outfall
Several field inlets allow surface flows to enter the pipe network directly; these surface flows can be significant during rainy periods
a few homes served by septic systems
This basin has an extensive network of subsurface field drains
Excess stormwater flows from the other four sub-basins are conveyed through Sub-Basin 5, where the marine outfall is located
Many of the subsurface field drains are over fifty years old and are in varying states of disrepair, causing increasing stormwater inundation of agricultural fields in recent years
One of the goals of this study is to estimate how much of the storm flows and pollutant loads originate in this sub-basin as compared to upstream basins