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Ridgefield National Wildlife Refuge Draft Comprehensive Conservation Plan and Environmental Assessment
Dikes, Irrigation, and Water Control Structures
Bachelor Island Unit. The wetland system on Bachelor Island was largely redesigned in 1998. New
wetlands were created, select wetland basins were expanded, and several steep banked wetlands were
re-contoured. Additional improvements were made to the water delivery and control systems
including two new intake pumps, buried delivery pipes, delivery valves, and water control structures.
There are 21 wetland basins on Bachelor Island with water management potential, including water
control structures and water delivery capability. At full capacity, the refuge could manage nearly 400
acres of wetlands on Bachelor Island. Realistically, the Columbia River’s water level, seasonal
rainfall, and soil characteristics of each wetland basin dictate the overall acreage of wetlands
managed on Bachelor Island. Most wetland basins on Bachelor Island collect water from seasonal
rainfall, with approximately 250 acres of wetlands by mid-winter. Active irrigation of wetlands on
Bachelor Island is reserved for select wetlands with proven water retention capabilities. All Bachelor
Island wetlands drain with the island’s natural topography to the north, eventually feeding to a
common drainage pond equipped with a series of expulsion pumps.
Carty Unit. The Carty Unit is part of the Columbia River floodplain with no water management.
Roth Unit. The Roth Unit is part of the Columbia River floodplain with no water management.
Ridgeport Dairy Unit. Wetland improvements were initiated on the Ridgeport Dairy Unit in 1998
with the re-contouring and disking of the Hillocks, Fingers, and Dusky marshes. The water system
was improved with the installation of a pump station, delivery pipes, valves, and water control
structures on the marshes. The three marshes (or basins) represent the managed wetlands of the
Ridgeport Dairy Unit, designed with water delivery structures and dewatering infrastructure to
regulate water levels.
Campbell Lake has a water control structure on its south end that facilitates drainage for the Hillocks
and Fingers marshes, but this structure is not intended to manage levels within Campbell Lake.
Campbell Lake is still a floodplain wetland with direct connection to the Columbia River via
Campbell Slough. Post Office Lake has partial water management capabilities in that it has a water
control structure on its drain. Water delivery to the lake could be achieved by routing water through
Dusky Marsh. The inefficiencies of this delivery mechanism coupled with the size of Post Office
Lake make this water delivery option tenuous. Post Office Lake is additionally fitted with a
‘duckbill’ tide gate to prevent floodwater from backfilling into the basin and fish entrapment within
the wetland.
River ‘S’ Unit. The River ‘S’ Unit is generally sloping from south to north. Water is expelled from
the unit by pumps on the north end. Water intake is achieved through three pumps at two pumping
stations. Both pump stations take water from Bachelor Slough. Tides impact operation of both
pump stations limiting water availability during low tides. The northern pump station supplies a
network of pipes and valves designed to either independently deliver water to four wetlands or to
supplement water delivery to the main fill ditch. The southern pump station directly fills the main
fill ditch. Water delivered to the main fill ditch gravity feeds into Bower Slough. When filled,
Bower Slough serves as the water reservoir for filling most of the wetlands of River ‘S’ Unit.
Earthen dikes and ditches from Bower Slough fitted with water control structures supply water to the
wetland network.
Chapter 5. Refuge Facilities and Public Use Programs 5-5