WSP11716

• File Number: 8507
• Description: Rio Grande Project
• State: CO
• Basin: Rio Grande
• Date: 7/1/1997
• Title: Water Management Study: Upper Rio Grande Basin part 1
• Water Supply Pro - Doc Type: Report/Study

j~

\fl
~~~l

Major Physical, Legal, and Institutional Characteristics

tt:-
,j

,~ -~J

~~

Residents of the valley responded in the 1920s and 1930s, primarily through
the establishment of the Middle Rio Grande Conservancy District (MRGCD),
to reduce flooding, alleviate waterlogging, and increase irrigated acreage.
MRGCD's development of drainage canals quickly eliminated large wetland
areas, leaving only narrow strips of aquatic habitats as refugia for water-
dependent species. Habitat concentration was exacerbated by the con-
struction oflevees and other flood-control structures to force the river to
remain in a single channel. The construction of upstream dams to control
flooding has further restricted the pulsations of alternating flooding and
drought so critical to the bosque. The current stand of dominant cotton-
woods traces back to the valley's last big flood, in 1941, when flows up to
25,000 cubic feet per second (cfs) caused widespread inundation and allowed
seedlings to germinate and establish themselves. The construction ofCochiti
Dam, in 1975, together with development within and restriction of the
floodplain has ended the potential for similar flooding and, hence, for
regeneration of cottonwoods.

,~)
;~,'
"
"..

;;",,'

~'
:i!

;,>,

;.,

The current bosque ecosystem retains little of its historical character.' It
exists as a narrow strip along the valley's river bed and canals rather than
being distributed throughout the floodplain. Much of it has no hydrological
connection to the river and is expected to experience profound change as the
current dominant cottonwoods mature and expire faster than replacements
materialize. This change will be exacerbated by the spread of exotics, such
as saltcedar and Russian olive. Detachment of the forest from the river's
influence undoubtedly will have many ecological effects, including an
increase of wildfires, but many ofthese, such as the effects on the abundance
and diversity of species, remain unclear.

'.
/,.;

)

~-,
,-

2. Surface Water

~i

The Basin falls within a transitional climatic zone, receiving precipitation
from both the Gulf of Mexico and the Pacific (Bullard and Wells 1992). The
climate is semiarid upstream of the Albuquerque area and arid downstream.
Most of the surface water in the Basin comes from snowmelt in the San Juan
and Sangre de Cristo Mountains of southern Colorado and northern

1 Evaluations of the wild and scenic character of different stretches of the river provide a
rough indicator of the extent to which the ecosystem has been modified. Of the 1,000 miles of
river in the Basin, only the first 50 miles of the river in New Mexico have been designated as a
federal wild and scenic river and the Bureau of Land Management has identified the last
25 miles in Colorado as suitable for such designation.

l~ :2883 3