courtesy The Western Producer
What are we going to do when our new well runs dry? Dig a deeper one. What are we going to do when that one runs dry? Drill deeper again and ask why the wells keep running dry.
The prairie moisture cycle has been disrupted. Nobody disputes that point. But how badly is it disrupted and can it be fixed? Nobody knows, says John Pomeroy, director at the Centre for Hydrology at the University of Saskatchewan. Prairie people know they have to go progressively deeper with their wells and as they do, the water is often lower quality than their previous well. “Most shallow surface aquifers once had very good quality water, but very little storage capacity,” said Pomeroy. Small storage limits the ability to recharge and available water is used quickly.
“These shallow aquifers are connected to the surface so they experience the same rain and drought cycles we experience. They get their water from the moisture cycle, which goes up and down, wet and dry.”
As the Prairies required more water for irrigation, livestock and municipal purposes, shallow wells ran dry and were abandoned in favour of deeper wells.
“There’s much more water underground than on the surface or in the shallow aquifers. Nobody knows how much,” Pomeroy said. “But the flow rate in the deep aquifers is extremely slow and it’s mostly very poor quality. There are a few areas with high quality deep water, such as the Assiniboine Delta Aquifer, but most deep water isn’t suitable for agriculture or people. A lot of that water was laid down in pre-glacial times, so it’s old. The older it is, the more dissolved solids it has. It can’t be used for anything.”
Pomeroy said it’s easy to see how shallow wells and their high quality water were pumped dry. The water was needed. But other land management factors affect the situation.
Recharging ground water on the Prairies is different from other places, Pomeroy said. Because these shallow aquifers are small, they recharge quickly from potholes and sloughs. Conversely, they also respond quick- ly to drought or having their recharge sources cut off. “Recharge absolutely depends on sloughs and potholes. You need water standing for a period of time to force it through that thick till layer. Sloughs are mainly filled by snow- melt runoff. Snow is the primary source of water for our prairie water tables. Summer rainfall that runs into the sloughs generally evaporates before it has a chance to recharge the water table.”
Pomeroy said a cool rainy summer will recharge some of the water tables but with 70 percent of prairie sloughs and potholes now drained, every remaining acre of surface water is vital. “Every time we drain another pot- hole, we lose one more source of snowmelt water for our shallow aquifers and recharge for those shal- lower wells. There’s another problem with the remaining sloughs. We’re not putting as much snowmelt runoff into those sloughs as we did 20 years ago.”
Farmers and researchers agree that water is the limiting factor on all types of agricultural production on the Prairies. With a limited amount of water most years, the industry has geared itself to maximum use of that precious resource.