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<br />water in the San Luis VaHey. It is interesting to
<br />note that this condition still exists, and regardless
<br />of the snow supply many of the ditches are without
<br />water by July 1st; even in 1941 with about I million
<br />acre-feet mnoff at the Del Norte gaging station,
<br />ditches in District No. 20 went on appmpdation
<br />basis on July 23rd, with the result that some areas
<br />were short of water for proper maturing of crops.
<br />The amount of water decreed to each ditch is, in
<br />most cases, far greater than the firm" supply, and
<br />the aggregate amount of water adjudicated to various
<br />claimants thmughout the vaHey is far in excess of
<br />the quantity discharged by the streams, even dudng
<br />good water years.
<br />The moderately small reservoirs constructed
<br />mostly during the 1905-1915 period to supplement
<br />the streams of the vaHey have helped in a meager
<br />way but are far short in total capacity to store suf-
<br />ficient water during the good years to carryover to
<br />the dry years. The San Luis VaHey is greatly in need
<br />of Some 400,000 to 500,000 acre-feet of additional
<br />storage to assure better river regulatio~.
<br />It seemS apparent that the study of the needs fm
<br />a larger storage unit on the upper Rio Grande indi-
<br />cates that little new water would be made available
<br />by additional storage. The records show gradual
<br />depletion for the past 25 years of the mean annual
<br />flow at the Del N orte Station, the No. I index sta-
<br />tion on the upper Rio Grande. Fwm the pedod 1890-
<br />1948, the mean annual flow was 699,000 acre-feet,
<br />for the period 1925.1948 mean annual flow was
<br />642,000 acre-feet; and for the last 5-year pedod,
<br />1950-1954, the mean was 478,200 acre-feet.
<br />The foHowing tabulation breaks down the mean
<br />annual discharge of the Rio Grande at the Del Norte
<br />Station in 5-yeaf periods, starting in 1911 and
<br />ending in 1954, in 1,OOO-acre-feet units.
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<br />Period
<br />
<br />Mean Annual
<br />Discharge
<br />(1,000 Acre-Feet)
<br />
<br />1911 to 1915 Inc.
<br />1916 to 1920
<br />1921 to 1925
<br />1926 to 1930
<br />1931 to 1935
<br />1936 to 1940
<br />1941 to 1945
<br />1946 to 1950
<br />1911 to 1950
<br />1928 to 1937
<br />1950 to 1954
<br />Fm the Conejos River
<br />1928 to 1937
<br />1950 to 1954
<br />
<br />782.7
<br />825.2
<br />860.1
<br />752.2
<br />551. 0
<br />542.2
<br />754.5 "
<br />666.0
<br />716.7
<br />593.1
<br />478.2
<br />
<br />349.2
<br />272.8
<br />
<br />It is interesting to note that the period 1950-1954
<br />"shows the lowest mean annual discharge of any
<br />previous 5-year period on record.
<br />Ri ver regulation has been mentioned. The working
<br />out of river regulation in actual practice would be-
<br />come complicated, but it seems apparent that Some-
<br />thing of this nature must be evolved-even if this
<br />means coordinating the management of our surface
<br />and underground water supplies.
<br />The Bureau of Reclamation has made an extensive
<br />study of land classification, soils formation, etc.,
<br />under the Rio Grande Division of the San Luis Valley
<br />Pwject, to be served by the pwposed Wagon Wheel
<br />Gap Reservoir, coveting some 275,000 acres. The"
<br />reports indicate that, at the time the study was
<br />made, more than half of the irdgated land was sub-
<br />irrigated.
<br />Subirrigation is possible, due to the rather shallow
<br />sandy topsoil and the coarse subsoil; the system
<br />has been quite successful when the spring runoff is
<br />sufficient. Large diversions are made in the spring
<br />to bring the ground water close to the' surface, or
<br />what is locally known to "bdng up the sub." The
<br />water table is raised so that it makes contact with
<br />the lower part of the topsoil, the water reaching the
<br />roots of the crops by capillarity. Water is run in
<br />the fields in ditches spaced 50 to 80 feet apart to
<br />maintain the proper relation between the ground
<br />water and the surface of the soil.
<br />The extended dry petiod of the past 5 years with
<br />subsequent pumping, necessary for crop production,
<br />has all but ellminated this economical and pw-
<br />ducti ve type of irrigation.
<br />With a brief look at the Bureau study one leams
<br />that the valley generally has rather a shallow sandy
<br />loam topsoil from 12 to 20 inches in thickness,
<br />undedain with sandy gravel of rather great depth.
<br />This condition exists, as stated, quite generally
<br />over the valley floor, except along the river and
<br />small streams and creeks of relative low elevation,
<br />where the land shows a texture of loam or heavier
<br />soil 4 feet or more in depth. These areas were once
<br />largely used as native pasture and meadow, but
<br />during the past 3S to 40 years considerable acreage
<br />has been converted to cultivated cmps.
<br />The San Luis Valley now has a cultivated area of
<br />appmximately 650,000 acres of valuable pwductivity,
<br />with a total valley floor area of about 6 times the
<br />cultivated area or about 4 million acres. Much of
<br />this marginal land is fertile and well adapted for
<br />crop production except for lack of water.
<br />A feature that cannot. be overlooked is the native
<br />vegetative cover on much of the vacant land, with
<br />rather heavy growths of salt grass, chico, grease-
<br />wood, willow, and cottonwood trees along the streams.
<br />By use of the many effective chemicals available
<br />today, the battle against willow, especiaHy along
<br />ditch dghts-of-way and other wasteland, is exten-
<br />sive and most successful.
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