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Keeping the perfect amount of water in reservoir is the job of three
inlet valves which operate with a float system demonstrated by Gary
Smith, Sequim Prairie Tri Irrigation Association member. |
Living in the shadow of the Olympic Mountains, Sequim Prairie
farmers receive roughly 11 inches of rain annually and depend upon the Dungeness
River for their irrigation needs.
In 2005, Washington suffered through drought conditions brought on from lack of
winter snows, causing many rivers to have minimal summer stream flows.
The concern for water flow in the Dungeness River – and conservation – motivated
the Sequim Prairie Tri Irrigation Association (SPTIA) to upgrade their
irrigation system from an open ditch method of delivering water to a modern,
high pressure pipeline system.
"Keeping more water in the Dungeness River was our objective in switching to a
pipeline system," says Gary Smith, SPTIA member. "The drought situation did not
meet minimum flow requirement for salmon habitat in the river," he says.
The SPTIA Reservoir Project consists of 11 landowners, including both commercial
agricultural producers and residential owners, with more than 670 acres to
irrigate.
"Landowners were tired of watching good water being wasted with an open-ditch
irrigation system," says Mr. Smith. "It required constant maintenance,
high-labor, and allowed far too much wasted water, with high energy costs
running the pumps," he says.
To upgrade the irrigation system SPTIA needed technical and financial assistance
from local conservation partners.
"This water conservation project was funded by the Washington State Salmon
Recovery Funding Board, Washington State Irrigation Efficiencies Funds, and the
Clallam Conservation District," says Mr. Smith. "The USDA-Natural Resources
Conservation Service (NRCS) provided the engineering design."
"This is a complicated project. Fortunately, we have the expertise to handle the
design," says Leigh Nelson, NRCS State Irrigation Engineer. "We were able to
provide the engineering design through our Conservation Technical Assistance (CTA)
program," he says.
According to Nelson, CTA is a voluntary program that provides
technical assistance supported by science-based technology to help people
conserve, maintain, and improve their natural resources. "NRCS provides CTA
assistance to landowners, communities, conservation districts, and tribes," he
says.
The old irrigation system consisted of approximately 18,000 feet of open ditches
with 11 pumps to convey water across the project area.
"The problem with an open ditch irrigation system is evaporation, seepage, and
maintenance," says Nelson. "The pumping plants used by the individual landowners
require extra water to ensure adequate supply to the pumps," he says.
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All the water needs for the Sequim Prairie
Tri Irrigation Association begins at this inlet structure where Leigh
Nelson, NRCS State Irrigation Engineer, and Gary Smith, calculate the flow
of water entering the first stage of the irrigation system. |
"Modern irrigation equipment will provide more water to the
land efficiently with very low maintenance costs, especially compared to
controlling the open-ditch system," says Mr. Smith. "Cleaning debris out of
five miles of ditches is a hassle," he says.
The high-pressure irrigation design works in three stages to ensure the most
efficient and effective system. First, water is diverted from the Dungeness
River and enters an existing 3-mile long supply ditch where an inlet was
available for the reservoir project. Water then flows into the storage
reservoir. In the final stage, a pumping plant located below the reservoir,
pressurizes the system and supplies water to the landowners.
According to Nelson, the reservoir makes better use of the water by
minimizing tail water loss and allowing for variations in pumping by the
landowners. "The system is designed for all users to operate at one time
with constant pressure, without continually adjusting flows diverted from
the river," he says.
"The reservoir can hold 4.1 million gallons of water which is enough water
to fill 137,000 standard size bathtubs," says Mr. Smith. "An 18 inch pipe
from reservoir to pumping plant can handle 7.8 cfs (cubic feet per second)
or 3,500 gallons a minute," he says.
"The pumps were designed to maintain a set pressure in the system by varying
the speed of the motors," says Nelson. "The flows will vary based on
cropping, climate, precipitation, and management practices," he says.
"Twenty-thousand feet of pipe connect to the pumping house," says Mr. Smith,
"to irrigate our crops: alfalfa, grass, hay, barley, cauliflower and red
beets for seed, lavender, and raspberries."
To handle overflows from the water inlet structure, an outlet was
incorporated into the design allowing excess water to run into an adjacent
wetland then flow into Sequim Bay.
"A high density, 18-inch pipe handles overflow to the wetland," says Nelson.
"To limit the disturbance to the surrounding environment, the pipe was laid
on the surface," he says.
Flow meter stations at the head of the irrigation/overflow site and at the
reservoir monitor water levels while a computer keeps logs of both readings
(cfs of water and height at reservoir).
The true test of the pressurized system will come during the peak of
irrigation season, July and August. The season begins April 15 and runs 154
days until September 15.
"In the first month the irrigation system has been on-line, we have saved
half of the water we would have used in previous years," says Mr. Smith.
Conserving water in the Dungeness River for salmon habitat was SPTIA’s major
focus in upgrading the irrigation system with the added bonus of using water
more efficiently and effectively saving them time and money.
"Everything is working well and is still under warranty," says Mr. Smith.
"It is a great design." A design made possible through NRCS’ conservation
technical assistance.
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