Blanco Diversion Dam

Blanco Diversion Dam is a feature of the San Juan-Chama Project, located in southern Colorado and northern New Mexico.  The purpose of the Blanco Diversion Dam is to divert water from the Rio Blanco into the Blanco Feeder Conduit, which conveys the water to the Blanco Tunnel.  The concrete-lined Blanco Tunnel then conveys the water 8.64 miles to the Little Navajo River, where the Little Oso Siphon carries it under Little Navajo River to the Oso Tunnel.  The water is then conveyed through the 5.05-mile Oso Tunnel to the Navajo River.  At the Navajo River, the Oso Siphon carries the water under the river and into the 12.8-mile long Azotea Tunnel.  At the Azotea Tunnel, it is, in turn, carried into Azotea Creek in the Rio Grande Basin.  These waters then flow down Azotea and Willow Creeks 11.78 river miles to Heron Reservoir.

 Blanco Diversion Dam spans across the Rio Blanco (or Blanco River) and consists of a concrete overflow weir, sluiceway, and headworks for the Blanco Feeder Conduit and Blanco Tunnel.  Each abutment consists of vertical concrete wing walls protected by a 2-foot thick layer of riprap on a 1-foot thick layer of sand and gravel.  The layout of Blanco Diversion Dam is almost identical to that of the Oso Diversion Dam and similar to that of the Little Oso Diversion Dam.

The spillway is a concrete overflow structure that consists of an uncontrolled, ogee crest weir and fore apron.  The spillway is ungated and has no mechanical features.  The spillway has a crest length of 50 feet at crest elevation 7867.5.  The fore apron is a slotted bucket type structure for energy dissipation.  Spillway releases from the slotted bucket discharge into a 30-foot long riprap-protected section of the river channel.  The riprap is 4 feet thick on a 1-foot thick layer of sand and gravel.

The sluiceway is located on the left side of the spillway and consists of a single 5-foot wide bay.  The sluiceway is controlled by a 5- by 17-foot radial gate with a gate sill at elevation 7854.5.

The headworks structure for the Blanco Tunnel consists of a reinforced concrete inlet structure located on the left abutment and the Blanco Feeder Conduit.  Flow enters the inlet structure through two sloping trashracked openings with inverts at elevation 7859.25.  A gap in the floor slab of the inlet structure traps sediment into a 30-inch diameter pipe before it can enter the Blanco Feeder Conduit.  The 30-inch bypass concrete pipe, controlled by a 30- by 30-inch cast iron slide gate, carries the sediment to the sluiceway.  Flow into the Blanco Feeder Conduit is controlled by either a 16- by 7-foot top seal radial gate with a gate sill at elevation 7859.5 or a 3-foot square bypass controlled by a 3- by 3-foot cast iron slide gate with an invert at elevation 7859.5.  The Blanco Feeder Conduit begins downstream of the inlet structure and consists of a 16-foot wide concrete conduit that is approximately 139 feet long and contains a modified Parshall flume.  The Blanco Feeder Conduit ends at the inlet structure for the Blanco Tunnel.

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