New research points to over reliance on managed aquifer recharge
By Mimi Ko Cruz
Managed aquifer recharge (MAR), also known as water banking, stores water to be available for use in dry years when surface water supplies are low. It’s a remarkable technology but, groundwater agencies are too reliant on it, according to research by Nicola Ulibarri, assistant professor of urban planning and public policy, and colleagues.
In their study, published this month in Water Resources Research, Ulibarri and her co-authors Nataly Escobedo Garcia, Rebecca L. Nelson, Amanda E. Cravens and Ryan J. McCarty argue that the groundwater agencies seem to be overly relying on MAR to fix their sustainability problems.
“The parts of California that we’re studying — the places that are required to come up with groundwater sustainability plans — are places that are in critical overdraft, which means that they are using more groundwater than is sustainable long term. This has led to the many problems that the state’s Sustainable Groundwater Management Act (SGMA) of 2014 aims to address, like overdraft, land subsidence and interconnected surface water,” Ulibarri explains.
She answers a few questions about her research and water management.
How is MAR an effective water management tool?
In California, many agricultural areas rely heavily on groundwater for their crops. But, if they take out the groundwater faster than it can replenish naturally, the water levels drop over time.
Think about it like a bank account. You start with some money in the bank; if every month you get a $100 deposit, but you withdraw $1,000, you will drain your bank account over time. In many places, this has meant that groundwater levels are declining rapidly, making it more expensive to drill wells and pump, drying out rivers that might be fed by groundwater, and in some cases leading to land subsidence (roughly, when the ground surface drops because the water below it has been removed).
If you wanted to keep your bank account more stable (or even increase savings over time), one solution would be to stop taking as much money out, and the other would be to put more money in. MAR is the second option. It aims to reverse declining groundwater levels by actively placing water back into groundwater storage. This can help make long-term use of groundwater more sustainable.
It's already in use in a number of places. For instance, Orange County has one of the biggest MAR operations in the world, which is why we are able to rely on groundwater for such a sizeable part of our water supply.
In places like California, where we tend to have really wet years and really dry years, MAR also is a promising tool because it can help smooth out some of the variation year to year. The idea is that in dry years, when there is not a lot of rain or snow, we should use groundwater, making sure that the economy, agriculture, etc. can keep going. Then, in wet years, when we're dealing with floods and there is plenty of surface water, to put some of that water back into groundwater (so it's there for the next dry year).
What are some of your most surprising/important findings?
In our paper, we're looking at a proposed expansion of MAR to comply with the SMGA. This act requires local groundwater agencies to propose ways to achieve “sustainability.” We find that lots of these agencies are proposing to use MAR. This isn't terribly surprising, as this technique has a lot of potential benefits.
But, we also find that many of the agencies haven't thought through all of the needed steps to actually make MAR projects work.
For instance, these projects in total are projected to cost over $1.6 billion, but most of the agencies don't have a plan yet for where that funding will come from, or at least they don't specify that source in the plan they submitted to the state. Likewise, if all of these projects are built, they will provide a large amount of possible recharge capacity, but in most places there won't be enough surface water available to fill all that capacity. This is because of a combination of water rights (in many rivers, the water is already allocated to other uses) and hydrology (in very few years is there large enough river flows to fill the need). The paper details a number of other feasibility concerns, like a lack of attention to legal considerations and land availability and the challenge of converting large areas of land to recharge basins.
Why is it necessary to look for other ways to manage water?
The groundwater agencies seem to be overly relying on MAR to fix their sustainability problems. That would be fine if the projects were actually going to be built and supply the recharge capacity that they say they will. But, our analysis suggests that isn't the case. This means that the groundwater agencies need to look for other options if they're actually going to solve the groundwater overdraft problem. Most prominently, they should look at demand reduction — the "take less money out of the bank account" option. Unfortunately, this is a much harder social and political fix.