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, , ' , , I .. . . ,~' " ".' ~\'1; ~ "~ ..~~;, ~:\.. _ S: SAN LUIS VALLEY PROJECT, COLORADO PRELIMINARY EVALIlAfiON OF RESTORATION OF CHANNELS OF THE RIO GRANDE AND ITS TRIBUTARIES IN THE SAN LUIS VALLEY OF COLORADO Irrigation in the San Luis Valley was begun in the ear~ 1850's, but it was not until about, 1880 that extensive development occurred. Then in the decade 1880~90, accelerated activity resulted in most of the large canal systems and otber irrigation works tbat exist today. This development great~ cbanged tbe regimen of flows of tbe Rio Grande and its tributaries. During tbe past eigbt decades, the cbannel of tbe Rio Grande, in adjusting to the smaller residual flows, bas general~ deteriorated into a braided, ill-defined water course. The same phenomena has also occurred, to a somewhat lesser extent, to tbe channels ,of tbe Conejos and San Antonio Rivers. The channels of the smaller tributaries, La Jara, AlamOsa, and Rock Creeks have been similar~ affected by reduced flows and farming and ranching practices. The limited water supp~ of the Rio Grande is used and reused so many times that essential~ no flow from the Upper Rio Grande Basin escapes past Fort Quitman, Texas. The limited supp~ is allocated to international use by the United States and the Republic of Mexico under the terms of 'the Convention of 1906. The residual United States supply is further allocated among the States of Colorado, New Mexico, and Texas by the Rio Grande Compact. The State of ColoradO has been attempting to make its Rio Grande Compact deliveries to the downstream States on a dai~ basis. The trans- mission of the larger flows throug~the present deteriorated channels of restricted capacity has resulted in large overflows throughout the flood plains of the Rio Grande, the Conejos River and the San Antonio River with the resultant high, nonbeneficial transmission losses. The overflow in the Rio Grande flood plain has also restricted the discharge of the smaller tributaries and drains, causing additional overflow and loss of water. Such diminution of the meager water supply is not a local problem as it adverse~ ,affects all of the water users in the Upper Rio Grande Basin. The problem of channel deterioration is not unique to the Colorado portion of the Rio Grande Basin. It has been a stead~~ developing problem throUghout the Upper Rio Grande Basin which has occurred more slow~ in Colorado because of different hydrologic and ecologic conditions and the light sediment loads transported by the headwater flows. It has been nec- essary to restore extensive reaches of the Rio Grande channel. Such work was accomplished from Fort-Quitman upstream to Caballo Dam by the International Boundary and Water Commission. In the Middle Rio Grande Valley, the Rio Grande has been channelized northward 'from the Narrows of Elephant Butte Reservoir to the mouth of White Rock Canyon some 50 miles above Albuquerque. This work was accomplished by the cooperative efforts of the Bureau of Reclamation, the Corps of Engineers, the State of New Mexico, and the Middle Rio Grande Con- servancy District. 1