Many of our water management practices are designed to move water downstream as quickly as possible. It may be more effective to keep water in place, for use when it’s needed
The reality of living on the Canadian Prairies is that you are likely going to have too much water when you don’t need it and not enough when you do.
That’s largely because 80 to 90 per cent of surface water received on the Prairies comes from snowmelt. Managing that water effectively is the main focus of the Watershed Systems Research Program (WSRP).
The WSRP is a $1.25 million, five-year program based at the University of Manitoba. It was established by the Government of Manitoba in response to recommendations by the Clean Environment Commission and the Lake Winnipeg Stewardship Board. Its goals are to enhance the quality and use of water resources in Lake Winnipeg and its watershed.
The Lake Winnipeg watershed is the second largest in Canada, covering almost one million square miles and spanning four provinces and four U.S. states via the Winnipeg, Red, Assiniboine and Saskatchewan rivers. Over 50 per cent of the watershed is agricultural land supporting a $20 billion per year agricultural industry. It is the Red River Watershed that contributes most (73 per cent) of the phosphorus entering Lake Winnipeg. Of this phosphorus, 30 per cent comes from Manitoba sources; 43 per cent of that is rural.
“Simply due to its prevalence, agricultural land is a major contributor to runoff leading to flooding and to nutrient losses leading to eutrophication and algae blooms,” says Dr. David Lobb, senior research chair of the WSRP. “Farm, municipal and provincial drainage structures have greatly affected this contribution.”
In the case of phosphorus, although the agricultural losses are low on a per acre basis, the concentrations in the runoff water are high — 200 to 1,000 parts per billion (ppb) — making them a significant contributor to algae growth, which forms at levels of just 20 to 50 ppb and can significantly affect water quality.
To improve overall water quality throughout Manitoba, including its lake systems, runoff must be managed in a way that provides better benefits both to agriculture and the landscape. Natural wetlands, pot holes and sloughs on agricultural land act as sponges, absorbing large amounts of snow melt runoff. With the additional ecological benefits they provide, such as erosion prevention, improvements in water quality and wildlife habitat, conserving them is probably one of the first and best water management strategies. But as natural wetlands continue to be drained for various reasons, the effects of both normal and extreme runoff events continue to be felt more acutely.
Even though we must accept the inevitability of extreme events, it is possible to employ a water management strategy, says Lobb, which retains and reuses most of the water and nutrients resulting from runoff and rainfall events in most years. Lobb and his colleagues are proposing Drainage-Retention-Irrigation systems in conjunction with Capture-Recovery-Reuse systems for nutrient management which can operate locally on a farm scale and also at a community and regional scale.
Existing drainage systems are designed to convey runoff from farm fields downstream as fast as possible, treating water as a nuisance or waste. More effective systems might incorporate one or all of the following options, says Lobb:
Option 1. Back-Flood Dams or berms: These would be similar to a waffle design, a system that was developed in North Dakota for flood control. Fields bounded by raised roads, ditches and wetlands are used as temporary water storage areas to store flood waters and slowly release them after water levels have peaked.
More appropriately designed for agricultural production, the back-flood areas would use existing low lying areas of fields where flooding is more likely to occur naturally and enhance their water storage capacity by building berms around them to retain more snowmelt runoff.
Option 2. Ditches and Retention Ponds: “Existing ditches are designed to convey runoff and have little capacity to store runoff, even temporarily,” says Lobb. “The design of existing ditches does not provide for filtering and capture of nutrients by vegetation, and they do not provide for the harvesting of vegetation for nutrient recovery.”
Expanding the existing networks of ditches to help retain larger amounts of runoff would be effective as well as channelling them into retention ponds — perhaps expanding existing natural ponds or potholes — to create or enhance wetland areas, which retain snowmelt runoff early in the season for later release or re-use.
In a study of five best management practices (BMPs) in the Tobacco Creek watershed from 2006-08, researchers found that phosphorus export was reduced by 38 per cent and phosphorus concentration by 32 per cent. The management practices studied were nutrient management, riparian zone and grassed waterway management, grazing restrictions and perennial forage conversion. Researchers found that between one to two-thirds of the phosphorus reductions were attributed to the incorporation of a holding pond, below a beef cattle overwintering feedlot, which covered just one per cent of the area and held four per cent of the total runoff.
The advantages of these drainage systems is the delay of water release to reduce downstream effects, and retention not just of the water resource on the land for irrigation or livestock watering purposes, but also retention of nutrients like phosphorus, which could potentially be recaptured and reused.
“We are not realizing all of the potential benefits of the limited water which is available,” says Lobb. “There is a need for new and innovative approaches to water management systems on agricultural lands.” †