The three reservoirs that operate in the Rio Chama watershed are collectively used for water storage and the control of flooding and river sediment. The Heron and El Vado reservoirs are used mainly for storage while Abiquiu Dam is used to control water supply delivery, flooding and sediment (USBR, 2017). This reservoir system is used as a collaborative operation between the U.S. Bureau of Reclamation and the U.S. Army Corps of Engineers to deliver San Juan-Chama Project water to its owners, to pass natural flows downstream in a controlled manner and to protect local acequia irrigation systems, homeowners and towns from flooding. Each dam operates under strict guidelines dictated by use requirements for the Middle Rio Grande Conservancy District (MRGCD), requests and designations made by the Office of the State Engineer (or Secretary of the Interior), and the Rio Grande Compact. For instance, only imported water from the San Juan-Chama (SJC) project may be stored in the Heron Reservoir. A total of 180,000 acre-feet of native Rio Grande water can be stored in El Vado. The general flow plan for the Abiquiu Dam is to send down the natural Rio Chama river flows up to an operating capacity of 1,800 cfs (USBR, 2017). The flow is controlled below Abiquiu Dam to protect the downstream acequias from damage to their diversion structures. Regulations such as these govern the operations of river water in Rio Chama watershed and may be difficult to change or modify without bringing multiple parties into agreement.
Figure 1. Rio Chama Monthly Reservoir Storage.
Reservoir storage data has been collected for the past ten years from the USGS website database. The data was then averaged to look for both monthly and annual patterns. By studying an average year of reservoir storage, or the 10-year monthly averages with regards to capacity storage, it is easy to see the operating patterns of each dam. Both Heron and El Vado accumulate springtime runoff from both local snowmelt and San Juan-Chama Project water while Abiquiu Dam’s capacity remains relatively stable as its main operation is flood control. As Heron is only allowed to store San Juan-Chama water, its storage increases later in the summer.
Storage data was also averaged for each of the previous ten years in addition to available data for the current year. The averages for all three dams show a decline in storage around the year 2013. This is most likely due to a very dry year for precipitation in northern New Mexico and Colorado, however, more data and information would need to be collected to confirm this. What is most interesting is the subsequent rise in Heron storage, which. A further study using evaporation estimates may also prove to be useful in better understanding storage patterns. There is no doubt that evaporative losses will be a concern as climate change continues to affect water supply in the Southwest.