How seasonally shifting irrigation practices can make an impact
Changes in Water Availability
In recent decades Teton County Idaho’s aquifer has been in decline: on average well depths have dropped roughly 25 feet, and up to 55 feet in some localized areas. This decline has affected the entire Teton Valley community. Agricultural and residential wells have gone dry and the Cities of Driggs and Victor are concerned about protecting their local source of water. For irrigators, the problems are exacerbated by earlier calls from downstream holders of senior water rights. With the aquifer in decline, surface water flows are also impacted in the Teton River which impairs fishing, wetland habitat and overall riparian health.
The reasons for the change in water availability are varied, but three key factors seem to be driving it; changes in snowpack, demand and irrigation.
Snowpack
Recent drought and rising temperatures mean more of the Teton’s spring moisture comes as rain rather than snow, leading to earlier runoffs and less water available in the summer, when both agricultural users and the ecosystem need it the most.
Demand
Increased number of residential wells, which draw out groundwater without replacing it. At the same time, many of the senior water rights in the Teton River system lie downstream in the Eastern Snake River Plain around Idaho Falls and Rexburg. As those users deal with increased demand for water, they have made earlier calls for water in headwater basins like Teton Valley.
Irrigation
Most of Teton Valley’s agricultural producers have switched from flood irrigation to sprinkler systems which reduce water use, improve crop production, and decrease labor costs. From the perspectives of both water conservation and production, this is a positive change. However, an unforeseen consequence is that the extra water used in flood irrigation no longer seeps into the ground, and less water emerges into local riparian systems later in the summer.
Returning water to the aquifer
Hydrology is the science of water. It studies the properties, distribution, and circulation of water on and below the Earth's surface and in the atmosphere. It includes creeks, rivers, springs, wetlands, groundwater, precipitation (rain and snow), evaporation, seepage and movement in and out of the system by human activity such as irrigation and wells.
The unique hydrology of the Teton Valley means that ground and surface water are closely linked. This connection allows irrigators to store surface water into the aquifer through recharge and have that water return to the Teton River later in the summer.
Summer water is more valuable than early-season spring water
The goal of the Teton Water User’s Association (TWUA) is to convert abundant cheap snowmelt runoff water into scarce valuable summer water.
The seepage into the ground that occurs during irrigation and through unlined irrigation canals is known as incidental recharge. Once in the aquifer, this water travels slower than water on the surface, delaying its delivery into local streams by an estimated 1-3 months, depending on location.
The shallow aquifer acts like an underground reservoir, storing abundant, cheap spring water and turning it into scarce, valuable summer water, which can then provide downstream producers with increased water availability for irrigation, feed wetlands and streams, and boost the water table.