By Lisa Wade, Water Resources Engineer
Colorado is home to an enormous variety of landscapes. One of the most unique river basins in Colorado is the headwaters of the Rio Grande. This basin is bounded by the San Juan and the Sangre de Cristos Mountains, which funnel water to the San Luis Valley. It is a basin of sharp contrast, with the Great Sand Dunes National Park spilling sand out of the mountains and a productive agriculture community raising crops next door.
Agriculture is the primary water user in the basin, but its use is limited by the Rio Grande Basin Compact, which divides the water of the Rio Grande among Colorado, New Mexico, and Texas. The Colorado Division 3 Engineer is charged with administering water use in Colorado so that enough water flows into New Mexico each year. The Compact has identified four stream gages that serve as “index gages.” Depending of the total annual flow volume that passes each index gage, a set amount of water must be delivered to New Mexico. To make sure that the right amount of water flows to New Mexico, the Engineer curtails, or turns off, water diversions made in Colorado. It is a tricky balancing act. The Engineer wants to maximize the beneficial use of water in Colorado, but make sure that enough water is left in the river to satisfy the rules of the Compact.
To administer the basin, the Engineer needs to know how much water will flow past the index gages. At the end of the year, that is easy to figure out based on the observations, but at that point, it is too late to deliver the water. So, how can the Division 3 Engineer know how much water will go past the index gages at the beginning of the year?
Traditionally, he uses water supply forecasts provided by the Natural Resources Conservation Service (NRCS). Riverside Technology developed a new tool that uses long-range streamflow forecasts provided by the National Weather Service (NWS) West Gulf River Forecast Center (WGRFC). The tool is built in Excel and automatically pulls down the weekly forecasts, the observed streamflow, reservoir storage, diversions, and transmountain exports and imports. The tool automatically computes a range of possible index flows and therefore, a range of possible delivery requirements. This information is summarized in tables and graphs for easy review. The tool also allows the user to provide input on how the system will be operated, so different scenarios can be examined. Jay Day, Chief Engineer, and I went to Alamosa to deliver the tool on February 9 and 10, 2015. The training and demonstration went so well, we even got our names in the local newspaper, the Valley Courier!