| Constructed wetlands in the Malheur - helping nature work miracles |
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Written by Weisha Mize, Oregon Department of Agriculture
Wetlands provide a number of environmental benefits, beginning with water filtration – removing agriculturally-related sediment, nutrients, bacteria and chemicals from irrigation return flows. However, when you farm and flood irrigate in the Malheur basin, a good wetland can be hard to find. The ground there is silty, often with hard pan underlying the thin layer of top soil. Hydric soils are limited. In short, in eastern Oregon, there are very few natural wetlands and limited natural runoff filtration. Let’s face it, folks, it’s a desert out there. Yet much of the lands in Malheur County have been in agricultural production - onions, sugar beets, potatoes, sweet corn, even alfalfa hay and seed – for over a century. Agricultural crops require water, and that means irrigation.
Irrigation in much of Malheur County is done today as it’s been done since the area was first put into agricultural production – by overland flooding. Some water comes directly from streams, but much of it comes from storage facilities constructed to collect and release precious irrigation water. One such facility is the Owhyee Reservoir. At the time of its construction (1928-1939), the Owyhee dam was the largest concrete structure in the world, with a total capacity of 1,120,000 acre-feet (active 715,200 acre-feet), of which 100,000 acre-feet is assigned to flood control.
Three Oregon irrigation districts (Owyhee, Vale Oregon, and Warm Springs), an Oregon irrigation company (Owyhee Ditch Co.) and a Idaho distribution board (South Board of Control) furnish primary irrigation water out of the Owyhee project to 3000 producers farming over 105,000 acres lying along the west side of the Snake River in eastern Oregon and southwestern Idaho. An additional 13,000 acres are furnished supplemental irrigation water.
Of the supplied water utilized in flood irrigation, only about half is taken up by the crops to which it is applied. The remaining 50% is nutrient and sediment-laden return flows, carrying increasing concentrations of phosphorus, nitrogen, E. coli bacteria and between eight and ten tons per acre of top soil overland, into the next ditch, onto successive crop lands and ultimately into the Malheur and Snake rivers. The levels of sediment, nutrients and chemicals hitting the river far exceeded any water quality standards for the Malheur – initial samples showed pollutants at levels five times greater than the water quality standards. Total Maximum Daily Loads (TMDLs) for the Malheur basin have not yet been established.
While sprinkler irrigation is often considered more efficient than flooding, it’s also more costly, often prohibitively so. Converting from flood to sprinkler through the natural Resources Conservation Service’s (NRCS) Environmental Quality Incentives Program (EQIP) costs about $1000/acre. Add to that the approximately $50,000 per mile required to bring in the 3-phase electricity needed to operate pumps and center pivot systems, and it’s easy to understand why it often takes years to make that conversion, and why so many farmers continue to flood irrigate – and water quality in Malheur County is slow to improve. And so the question remained: what can we do to start treating agricultural water quality now?
A new idea - innovative and effective
Enter landowner Dale Luther and the idea of constructed wetlands. Mr. Luther farms 250 flood-irrigated acres near Ontario. Mr. Luther’s land is essentially at the bottom of a portion of the Warm Springs Irrigation District’s (WSID) delivery and drain system, and he ‘hosts’ a WSID drain canal which collects the runoff from his lands and 850 acres of his neighbors’ lands. Those heavily loaded return flows once returned to the Malheur after flowing through an abandoned river channel, made into a slough by a beaver colony. A modicum of sediment and phosphorus filtration was provided by the slough. Some years ago, however, the irrigation district channelized the drain canal, bypassing the slough in an effort to get water moving more quickly and efficiently through the district’s system. Consequently, those return flows were running directly into the Malheur River, carrying its sediment, E. Coli, nitrate and phosphorus load with it. Mr. Luther wanted to regain the wildlife habitat lost, to eliminate and control the noxious weeds that had moved in, and to regain – and enhance – the filtration benefits previously provided by the beaver-created slough.
With the assistance of the Malheur County Soil and Water Conservation District (SWCD) and partners the Luther Constructed Wetlands project was initiated in 2000. A team of soil scientists and engineers from NRCS, a wetland ecologist (Idaho Agricultural Research Service), and wildlife consultant (Oregon Department of Fish & Wildlife) were organized, with funding provided through the Oregon Watershed Enhancement Board and Idaho Power. The design for the project was innovative – five constructed ponds (cells), each with a specific filtration objective and unique design features, covering 12.8 acres and capable of filtering the agricultural drain water from Mr. Luther’s 850 acres.
Once an old corral and branding area filled with pepperweed and whitetop, the 12.8 acre site selected parallels the drain and the Malheur River, a perfect candidate for constructed wetlands as well as for weed control. The project team worked with the local watermaster and the Oregon Water Resources Department to obtain a waste water storage permit, and construction began in earnest.
The first cell, or wetlands pond, is a one-acre split sediment pond designed to capture the bulk of the fine sediment, together with some of the phosphates carried by the sediment load. In the Luther project, a check structure and pump were placed in the 400-yard portion of the drain canal paralleling this first pond and half of the next wetland cell. With this check dam holding back the flow collecting in the drain, all but the fine sediments drop out before the water is pumped into the first cell to begin its journey through this created wetland system.
This design also allows the WSID easy access to the first cell and to the drain channel for cleaning. The recovered soils are placed back on fields and leveled or sold for good top soil.
The second wetland cell is shallow, only a foot deep, planted with 25,000 aquatic plants such as cattails and rushes, creating a dense mat over 2.1 acres. The plants selected are a combination of colonizing and slower establishing species, working as a bio-filter to capture nitrates and some of the phosphates present in the return flows. Much of the planting labor in this wetland was done by ten inmates from the Snake River Correctional Facility.
The orthophosphate is taken up by the plants and algae in the water. Because winters are so cold (-25 F) and the canals are dry in the winter, the plant material dies and dries. From there, it either decomposes or is moved around or is taken up by the soil or burnt off and scattered across the fields. This shallow wetland can also be mowed off and scattered to increase the speed of decomposition.
The third and fourth wetlands are deeper, #3 is a 3-4’ deep and covering 3.1 acres, while #4 is a 5.4 acre pond between 6’-7’ deep, both designed specifically to treat E.Coli. Other “good” bacteria, parasites and vegetation work as a bio-filter to break down the E.Coli bacteria. The pond depths slow the flow and allow time for this work.
The larger pond was also designed to provide open water in the winter for migratory waterfowl as well as water for fish. While these two wetlands do serve their purpose well, Lance notes with some bemusement that the great flocks of pelicans and other waterfowl that took up residence shortly after the wetland project was completed have been – well, generously contributory to higher E.coli counts than the project started with! A mixed blessing, this project!
The last and smallest step in the constructed wetlands project is a shallow “catch-all,’ final polish cell, covering 1.2 acres. The outflow from this pond flows over a gravel drain and into the old ‘beaver’ slough – and at the end of its three-week journey through the wetlands, the water is clear.
Over the past two years, an estimated 310 million gallons of water have been treated through these constructed wetlands. Monthly sampling results showed an 86% reduction in nitrite/nitrates, 79% reduction in orthophosphate, 60% reduction in total phosphate, 62% reduction in E.coli, and an 88% and 81% reduction in suspended solids and turbidity, respectively.
Bonus benefits
Turning this unirrigated pepperweed patch into a viable five-cell wetland not only saw a tremendous improvement in water quality, it also attracted an abundance of wildlife, shore birds and migratory birds. Geese and ducks regularly nest in and visit the site year-round. Shorebirds not previously seen in the area have found these varied wetlands to be ideal for nesting and brood rearing; several bird-watching groups have also become regular visitors to the area. In addition, these functioning wetlands are reducing the mosquito population by as much as 90% via the resident amphibians, dragonflies, mosquito fish and swallows.
A lesson in economics and efficiency
Compared to the average $1,000/acre cost to convert to sprinkler, the Luther Wetlands Project was about $294/acre. “Bottom line,” says Lance, “we are treating 1000 acres of runoff and we accomplished that in two years. Converting to sprinkler irrigation for that same amount of acreage would require over $1 million, not including the cost to run electricity out there, and would take at least ten years. We did this for a fifth of the cost and time!”
Success breeds more successes
Two years after the Luther project was completed, the Bill Prather “3 P’s” triple-cell wetlands project was completed through OWEB. Lance reports that there are three more projects either in construction or getting approval, and each one, whether gravity fed or pumped, is treating more and more acres. For these latter projects, DEQ 319 funds were also added to the funding pool. “The economics are such that really everyone in the area who has drains and wastelands on their property could really do a wetlands project, it’s feasible.” In fact, the other irrigation districts are now looking at developing a series of wetlands using the canals and drains and creating 27 acres in ponds. Not only will these wetland ponds be large enough to provide recreational opportunities such as hunting and fishing, they will also be used for water skiing!
Designer wetlands – the way of the future
The Malheur SWCD wetlands team is ramping up its monitoring efforts to measure inflow and outflow from each individual wetland cell, analyzing each pond to see how it is treating the particular pollutant it was designed for. Armed with this detailed information, as new wetlands projects are installed the team will be able to customize wetland cell design and treat the particular problem or problems each landowner is working with.
In addition, the team is beginning to measure temperature and flow. Lance notes that the Malheur is in the first groundwater nitrate area and the Luther project is in the middle of it, so it’s important to learn what sort of nitrate is going in to the ground and what sort of recharge and groundwater storage is occurring in the area that might be affected or improved by filtration through these created wetlands.
To learn more about designing, funding and constructing wetlands, contact Lance Phillips at Malheur SWCD, 541 889-2588 ext 114, lance.phillips@or.nacdnet.net.
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