THE Rio Grande Basin, which encompasses the San Luis Valley, is a massive area constituting roughly 8,000 square miles, with a culture and economy primarily centered around agriculture. Since its early settlement, the inhabitants of the Valley have used water supplies from various sources available to develop agriculture. With generally dry conditions, irrigation is a critical component of agriculture in the area, with around 523,000 irrigated acres. Irrigation practices have changed and developed drastically over time, yet some aspects have remained the same since its early use.
Today, irrigation in the basin is done mainly in one of two ways: flood irrigation or sprinkler irrigation. There are various ways of flood irrigating, as well as different types of sprinkler irrigation. For much of the Valley’s early history, flood irrigation was the main method. Flood irrigation can be done in a few different ways, but overall the concept is the same. Water from a river or well is diverted from a ditch and flooded across land, either in open meadows or across fields with dikes to direct the water down the land. Some irrigators divert the water by damming it and digging a “check” into the ditch bank, which is a small opening where the dammed water can flood out. Other farmers use siphon tubes that are positioned along the ditch bank that draw the water out to irrigate the land. Flood irrigation is around 40 to 55 percent efficient.
Sprinkler irrigation in the basin is done mainly with center pivot systems, as well as some wheel line sprinkler systems. With center pivot irrigation (sometimes called circle irrigation), the irrigation equipment rotates in a large circular shape, with sprinkler nozzles that irrigate crops. Center pivot irrigation is very efficient and uses less water to produce a large number of crops. The other type of sprinkler used for irrigation in the basin is the wheel line, which is a long sprinkler system that is run by a central motor, with pipes with sprinkler spickets and wheels that extend outward on either side of the motor. Every so often these sprinklers are moved across the land as one section is irrigated. These are less common, however, and are often used on smaller plots of land. Sprinkler irrigation is roughly 65 to 85 percent efficient.
Irrigation uses different water sources. The two primary water sources are surface water and groundwater. Surface water is the water that comes from snowmelt runoff, and is the water found in the rivers and streams that feed into the basin. This water is appropriated through water rights and is delivered to water users based on their position in the priority system. The other water source is groundwater. This is water stored below ground in either the confined or unconfined aquifer. This water is pumped out of the ground and used for irrigation.
Groundwater use is administered with its own set of rules. Well owners are allowed to pump under these conditions: their wells are adjudicated for irrigation, the subdistrict to which they belong is meeting sustainability requirements, and if they pay river depletions. Sustainability requirements are determined by aquifer conditions. If the aquifer is too low, there can be pumping restrictions and, in some cases, pumping can be stopped altogether.
Irrigation in the basin has progressed over the years due in large part to the hydrological changes in the basin. With less snowpack and dryer conditions, a rising need to make water use more efficient has led to the shift from flood irrigation to the use of sprinklers. As technology has changed and expanded, farmers have been provided more options. There are pros and cons. Flood irrigation returns more water to the ground, which keeps subsurface water levels higher. Flood irrigation, however, is more labor intensive and much less efficient than sprinkler irrigation. By applying less water, a farmer can typically grow more and better crops with a center pivot. Sprinkler irrigation is much more efficient but does not return as much water to the ground. Additionally, setting up and running center pivot systems can be much more costly than flood irrigation.
There is a need for efficiency in water management with dry conditions and a limited water supply. Looking to the future, it is important that water users implement efficient and effective irrigation practices. This will benefit economies, production, and the water resource availability. Water administrators in the basin are making great efforts to ensure the water resources are being managed efficiently and properly, for irrigation, recreation, environment, and compact needs.
This article was brought to you by the Rio Grande Basin Roundtable. The roundtable meets the second Tuesday of the month. If we are in-person, we are meeting at the Rio Grande Water Conservation District, 8805 Independence Way, Alamosa, CO 81101. Due to Covid restrictions we are also offering a Zoom option. We welcome your attendance but encourage checking the Roundtable website at www.RGBRT.org prior to the meeting to see if an in-person option is available.