Heron Dam

Heron Dam is a storage dam Rio Arriba County, in northern New Mexico in the southwestern United States, just north of the El Vado Dam. It is owned and operated by the United States Bureau of Reclamation. The dam is about 9 miles west of the town of Tierra Amarilla.

Construction
The dam was built as part of the San Juan–Chama Project, which transfers water from the San Juan River basin through the 12.8 mi Azotea Tunnel under the Continental Divide into Willow Creek, where it is stored in Heron Reservoir as part of the Colorado River Storage Project. The dam is located on Willow Creek near the creek's confluence with the Rio Chama. Construction was completed in 1971. The outlet works at El Vado Dam, just downstream from Heron Dam, were enlarged as part of the San Juan-Chama Project so releases from Heron Reservoir could pass unimpeded through the dam. The capacity of the El Vado outlet works was increased to pass 6600 ft3 per second.

Structure
The reservoir lies at an elevation of 7192 ft above sea level. The earthfill dam is 1221 ft long and 276 ft high. Heron Dike, one mile northwest of the dam, helps contain the reservoir. It has a concrete crest spillway with an open chute with a discharge capacity of 600 ft3 per second. The dam's outlet works include an intake structure, 10 ft diameter concrete-lined upstream tunnel, gate chamber, 11 ft modified horseshoe concrete-lined downstream tunnel, and a stilling basin. The discharge capacity is 4160 ft3 per second at a reservoir elevation of 7190.8 ft.

When filled, the reservoir covers 5905 acre. The maximum safe storage capacity is 401000 acre.ft. Downstream channel capacity is about 6000 ft3 per second.

Operations
The dam was built strictly for storage and delivery of San Juan-Chama Project water for municipal, domestic, industrial, recreation, irrigation, and fish and wildlife purposes. The water is diverted to New Mexico as agreed under the Colorado River and Upper Colorado River Compacts. The amount of water diverted each year, and the way in which it is used, are subject to well-defined agreements. Flows of "native" or "natural" water from Willow Creek and from the Rio Chama upstream of the dam are measured and bypassed through the reservoir.

The dam provides up to 5000 acre.ft of San Juan-Chama water annually to maintain the recreation pool at Cochiti Reservoir. The dam can supply about 96200 acre.ft of San Juan-Chama water annually to users with reasonable certainty. There is no carry-over provision: contractors must take delivery of their water by December 31. This means that contractors such as the City of Albuquerque or the Middle Rio Grande Conservancy District often withdraw their water and arrange to store it in downstream reservoirs such as El Vado, Abiquiu, Jemez Canyon (by exchange), and Elephant Butte.