Researchers say irrigation doesn't deplete groundwater and surface water levels in Michigan

CADILLAC — For over a decade, growers with Midwest Water Steward have collaborated with experts from Tritium Inc. to monitor groundwater and surface water levels across Michigan.

Since they began, the researchers have installed 220 monitoring wells to measure the impact irrigation wells on farm fields have on those water levels.

Based on the data they’ve collected, the researchers say irrigation isn’t depleting groundwater and surface water levels in Michigan. They have also created different models to predict future impact and have found similar results.

This research is attempting to show flaws in Michigan’s Water Withdrawal Assessment Tool, which is used by growers looking to install irrigation wells. It is a screening tool used to predict how wells will impact the groundwater or surface water levels in the area where they want to install.

Tritium Inc. hydrogeologist Todd Feenstra said the state’s model is over-predicting the depletion of water levels and preventing some growers from installing irrigation wells needed for crops or livestock.

If this continues, Feenstra said it could reach a breaking point when the wrong group of growers are told they can’t install any more wells and asked to share with others.

“The major blow-up is going to happen when the model (Michigan’s Water Withdrawal Assessment Tool) says there’s no more water in this watershed and someone tries to put another withdraw in,” he said.

Feenstra said they are working with growers across Michigan to collect as much data as they can to support their research. He said the monitor wells are installed within 200 feet of the irrigation well and go to the same depth.

This depth is between 125 to 150 feet into the ground, on average.

In Northern Michigan, he said they have wells installed in Cadillac, at several dairy farms in Lake City and Dutchman Tree Farms. They also work with a variety of crop and livestock farmers across the state.

Feenstra said they use pressure transducers installed inside the monitoring wells to collect data on the water levels and temperature every 15 minutes. The equipment is hung on a kevlar cable so it’s stable and doesn’t stretch.

The pressure transducers are accurate to about plus or minus a quarter of an inch. The water temperature is measured to see if an irrigation well is pulling water from a nearby water system like a stream or lake.

Since groundwater maintains a consistent temperature (around 52 to 54 degrees Fahrenheit), Feenstra said they would see a rise in temperature if water was being drawn from a stream.

An analysis of the data collected can be used to come up with how fast the water moves through the system and how much water is stored in it. The data is also used to find trends like seasonal changes and build or verify models used to predict future trends.

“If someone were to build a model, we can verify whether their model actually represents what’s out there because we have the data to do it with,” Feenstra said. “That’s a huge, huge step.”

One thing Feenstra and his team have found is the groundwater levels are tied to precipitation. He said many people assume the levels are flat and stable, but instead the levels vary.

For deeper, confined aquifers where groundwater is found, he said the variation is between one to three feet. For shallow, unconfined ones, he said those vary between three and five feet due to natural seasonal variation.

This correlation between the water levels and precipitation was evident from 2012 to 2020. In 2012, Feenstra said there was a drought that caused the water levels to drop around a foot compared to where they were when the monitoring wells were installed.

Between 2012 and 2018, he said the water levels were pretty stable, with a little variation. From 2018 to 2020, he said the state had three wet years in a row that caused the water levels to go up.

Based on their findings, Feenstra said there’s no question in his mind precipitation is the primary driver of the water levels found in groundwater and surface water systems.

When it comes to seasonal variations, Feenstra said they found the water levels were usually at their highest in May before the growing season begins. This was because of melting snow and frost coming out of the ground.

During the growing season between May and October, Feenstra said there was a trend of declining groundwater levels. The water levels then started going back up again during the fall and winter months.

Though the groundwater levels go down during the growing season, Feenstra said the levels recover quickly. For example, if a farmer ran their irrigation system for 24 hours before shutting it off, Feenstra said the levels recovered within 24 hours.

“It’s a mirror, so it goes down during the pumping then it recovers within that same amount of time,” he said. “The key takeaway on that is you’re not seeing declining water levels in either the groundwater system or the surface water system.”

Another big thing Feenstra said they found when an irrigation well was pumping at a high rate, the impact didn’t go out very far. He said the impact was maybe a couple of hundred feet.

With all the data collected since 2009, Feenstar said the big takeaway is groundwater and surface systems are higher than they were back then and irrigation systems aren’t depleting and drying water systems up.

This is also supported by how long the irrigation season is in Michigan. Feenstra said the season is only 90 days and on average, growers are only irrigating one out of every three days.

“You’ve got a 160-day growing season, you got 90 days of irrigation season and you only have 30 days of irrigation,” he said. “That’s not a real large number.”

“So, part of it with not doing the depletion is there’s 335 days where the system is quiet and it’s not being pumped.”

In light of his research, Feenstra said there’s a lot of fear that irrigation could deplete Michigan’s water systems and cause droughts like what’s being seen in California. He said this is due to a lack of understanding about how the systems work.

With his research, he is trying to show people how it works and build trust between the public and growers.

“(Growers) are very interested in managing the resource,” he said. “They’re very interested in being good stewards of what they have and they’re very interested in staying and having their families stay in that community they’re a part of.”

“These are good people that genuinely care and they want to do a good job of both running a business, but also managing the resources that they have. That’s a key thing for them. It’s a huge thing for them, but unfortunately, that’s not the way they’re portrayed often.”

Looking at Michigan’s Water Withdrawal Assessment Tool, Feenstra said it only accounts for certain parameters and assumes other variables like the volume of water stored beneath the ground and the rate of flow of the water.

He said these numbers shouldn’t be assumed because there’s a lot of variation depending on where you are in the state. In his opinion, the tool over-predicts how much an irrigation system will deplete a water system when his data suggests otherwise.

“The problem is that the model is being used to regulate water in Michigan and there’s a lack of additional modeling or a lack of additional alternatives,” he said.

Michigan Department of Environment, Great Lakes and Energy (EGLE) Water Use Assessment Unit Supervisor Jim Milne said three models work behind the scenes to operate the tool.

These models include how a withdrawal system like a well could impact to fish populations, the stream index flow and a groundwater model to predict how much the stream flow will be depleted by a groundwater well pumping out the water.

When using the tool, Milne said a user would put in whether it’s a surface water or groundwater withdrawal. Then, they would put in information about the characteristics of the withdrawal like the pumping rate, a pumping schedule, location and the depth to the top of the well screen.

Milne said the tool will estimate what the risk is for creating an adverse resource impact from the proposed withdrawal based on four categories, A, B, C and D. If the tool puts a user in category C or D, Milne said it doesn’t pass the tool and they can’t put a withdraw in where they are proposing to.

He said the user could request a site-specific review by EGLE staff who they’ll look to see if they agree with the tool. Users could also submit their own model or data to support their proposal.

“If we can’t authorize what is proposed, then we work with the well owner to see if we can modify the proposed withdrawal,” he said. “We negotiate with the owner to see if we can authorize a modified withdrawal that’ll still meet their water needs while preventing an adverse resources impact.”

Milne said the screening tool is on the conservative side because they are trying to protect the aquatic resources of the state while balancing competing water uses. If a water system was depleted, he said it would hurt resources like the fish population.

On the flip side, Feenstra said irrigation systems help growers make their land a bit more drought-resistant and boost crop yields. On the financial side, he said land values go up if a grower can irrigate the land and decides to sell it.

If they can irrigate it, Feenstra said the grower’s crop yield goes down and their protection against drought goes down and becomes nonexistent. This ultimately hurts them financially.

To address his concerns about the Water Withdrawal Assessment Tool, Feenstra said he believes there needs to be more data to support it. He said the state itself could gather this data or partner with another organization. This would require growers and the state to work together to obtain more data.

He also said there needs to be more models specific to a given area because there are several variables in play when it comes to withdrawing from a groundwater or surface water system. These variables can vary from county to county and having one model for the entire state is unrealistic, Feenstra said.

“I don’t think that it can continue the way that it is,” he said. “Something is going to break hard, and when it breaks, it can either be ugly and then it’s a crapshoot where things fall out or it can be a cooperative effort to get to reasonable solutions.”

Milne said EGLE is always looking for ways to improve its model and has partnered with other organizations to conduct research and gather more data. However, he said there is limited funding available for additional research projects around the state.

One recommendation being made to improve the water use program is creating something called the Michigan Hydrologic Framework. Milne said this project would look to create a framework to house groundwater models around the state by pulling available data from other projects.

Another project Milne said is being worked on to creating a data management system to compile all the data into a centralized system. Going forward, he said both EGLE staff and external parties can submit data into the system to be used by anyone for their purposes.

This could lead to a model for an individual property, a county-wide one or regional one.

“The concept is there and we’ve got a request for proposals that if it hasn’t gone out already, it will go out soon for bids,” he said. “Then work on creating the project should start in the calendar year 2024.”

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