Water in the San Luis Valley has long been a challenging and at times divisive subject, as its management is difficult. Over appropriation is the key cause, meaning there are more water rights than there is actual water. Water users want to use all of the water they hold rights to, but often cannot because of dry conditions and water restrictions. One of the most helpful solutions for this issue is water augmentation.

Augmentation, in simple terms, is the act of mitigating injury to senior water rights, caused by a junior water right. It is a way of ensuring equitable access to water and allowing people with varying water needs to be able to use this limited resource. Because water is managed through the lens of the prior appropriation system in the state of Colorado, water rights are appropriated by water users through a priority system- first in time, first in right. The first people who file for a water right are the first who are able to use the water, and the following priorities are served in succession. There are situations where people need access to water but hold priorities that are junior and therefore aren’t served or don’t have any water rights at all. This is a case where water augmentation can be helpful.

Augmentation plans allow out of priority water rights holders to put water to beneficial use, so long as a replacement supply of water is available and utilized to prevent injury to senior water rights. The plans specify exactly how much water will be used by the augmented user, how the injury will be calculated, and how impacts to senior water rights will be accounted for and replaced.

The injury caused by the augmented water use can be replaced by a number of means. A common method is to store water decreed for the beneficial use of augmentation in reservoirs and release that water into the river to mitigate the impact, or depletion, caused by out of priority water uses. Replacement water can come from any legal means, so augmentation practices can vary widely.

Augmentation has been an effective approach to stretching a limited and valuable resource farther. This is helpful as it gives junior priority water rights holders, or new members of communities who may be building a home or business, a chance to still put water to beneficial use, it allows development and progress to continue, while ensuring impacts to senior water users are offset.

Augmentation plans are utilized for a wide range of water uses and situations across Colorado. In the San Luis Valley, there are numerous small, private augmentation plans as well as regional augmentation plans managed by the San Luis Valley Water Conservancy District, Conejos Water Conservancy District, and the Groundwater Management Subdistricts. These entities most commonly augment new domestic or commercial wells or existing wells that are subject to the Rules Governing the use of Groundwater in Division 3.

Across the valley, augmentation is employed to remedy impacts to streams caused by well pumping. Augmentation water is either left in streams if it is native to the basin, diverted through trans-basin ditches and stored in reservoirs, or exchanged into reservoirs to be used later. Throughout the year, streamflow’s in the Conejos River and Rio Grande are bolstered by the addition of water to offset injury caused by well pumping or out of priority surface water diversions. Further, the confined and unconfined aquifers can be augmented. By releasing water from reservoirs and diverting it through canals and into recharge pits, the impact of well pumping on groundwater is augmented.

In Costilla County, the Trinchera Groundwater Management Subdistrict has been taking big steps and using a multi-pronged approach to effectively manage a very limited water source. To comply with the groundwater rules, subdistricts are charged with two main requirements: mitigate impacts to streams caused by well pumping and ensure sustainable aquifers are maintained. Because hydrologic conditions vary across the valley, each subdistrict is working through different challenges in complying with the rules.

In the Trinchera Subdistrict, surface water is not abundant, and groundwater is a major water supply. In order to mitigate injury to local streams, the subdistrict dried up 1,300 acres of irrigated land, which was previously irrigated with groundwater. Three associated wells became augmentation wells, which means that the roughly 2,600-acre feet of consumptive use water that was formerly used to grow crops is now being pumped into which is being used specifically to offset depletions in the lower reach of the Rio Grande.

Along with the use of augmentation wells, the subdistrict also has been employing forbearance agreements on both the Rio Grande and Conejos, utilizing pools in Beaver Reservoir and water rights from the Taos Valley #3 for aquifer recharge, and exchanging water with Subdistrict #3 (Conejos subdistrict).

Finally, to maintain a sustainable aquifer the Trinchera Subdistrict has developed a system to gauge current conditions and determined how much water can responsibly be pumped in those conditions. It is known as the *Composite Water Head Metric (link attached below). This metric is divided into four tiers, each one specifying the consumptive use limits for the conditions in each tier. Each successive tier has more restrictive pumping limits, with the first having hardly any limitations, and the fourth completely limiting pumping. This year, the subdistrict fell into tier three conditions, therefore the groundwater users in the subdistrict reduced pumping by 46%, with 3,000-acre feet set aside for augmentation of injury to the Rio Grande, and 13,500-acre feet left for use by irrigators. Each farm has a pumping allocation based on their percentage of pumping. With these established restrictions and recharge occurring, the plan strives to prevent injury to the aquifer and improve conditions therein. The subdistrict’s president Monty Smith is confident in this plan. “I’m proud of the fact that we have a direct way of limiting pumping, in order to take care of our aquifer,” he said. With this in place, the subdistrict plans to reach a point of sustainability and improvement for the aquifer.

Using all of these tools, the subdistrict has managed, even during dry years, to continue irrigation while also maintaining a healthy, sustainable aquifer and satisfying the requirement to replace their injury to stream systems

Moving forward, the subdistrict plans to seek more long-term, wet water solutions. They hope to find and create solutions that are more focused on surface water and move toward using less groundwater wherever possible. Monty Smith stated “We’d like to get to where we are self-sufficient, to where we can do all of our replacement with actual wet water to lessen the amount of forbearance agreements we have to depend on. The sooner we can replace our depletions with wet water, the better off we’ll all be.” With self-sufficiency and groundwater health as priorities, the subdistrict continues forward. Thinking outside the box and looking at creative, new solutions will be the Trinchera Groundwater Management Subdistrict’s future, and the future of the Rio Grande Basin as a whole.

Article by Peyton Valentine