WSP03653 - Laserfiche WebLink

Home Browse Search

000003 Mid-Summer 1999 Progress Report Identification and Solution of WATERLOGGING AND SALINITY PROBLEMS IN THE ARKANSAS RIVER VALLEY, COLORADO Timothy K. Gates anll John W. Laballie, Principal Investigators Civil Engineering Depaliment, Colorallo State University The Problems at Hand Salinity and drainage ptoblems usually appeat in intensively-irrigated alluvial valleys within a few decades to a few hundred years of the commencement of large-scale irrigation, Soonet or latet, tl,e artificially high rate of application of watet to land exceeds the natural rate of dtainage. the water table rises. and artificial drainage is needed to regain an acceptable water and salt balance, In the lowet Arkansas river valley in Colorado, irrigated since tlle I 870s, saline high waler tables began to appear in the early part of tlle twentielll century. Installation of subsurface dtains in the 1930s seemed to assuage the problems for awhile, Howevet, watet tables began to rise again in tlle late 1970s, Watts and Lindner- Lundsford (1992) suggested that tlle blanle be placed on increased diversions from the river for irrigation application and associated reduction in groundwater pumping, Indeed, the operations of the John Martin and Pueblo reselVoirs have drastically changed the river. Flushing from floods was substantially reduced and controlled releases were made from the reselVoirs, This allowed yeat-round. or at least prolonged, supplies of water CO lIle canals on lIle pedmeter of the valley. Lower velocities in the dver have caused the river channel to widen, sediments to deposit on the bed, and the river level to rise, Recent investigations by the principal investigatots of water levels in the reach of the Arkansas river upstream of John Martin reservoir indicate an increasing trend since about 1989. TIle overall rise in the river level (of about 0,6 m) may have significantly reduced the gradient that drives drainage flows from the irrigated land to the river. Since 1991, irrigation water supplies from snow pack and rainfall have been far above average. Many of tile large supply canals in the area have diverted more water in each of the last three years than in lIleir 100+ year histodes and have increased seepage throughout the basin, Also, in response to the recent Kansas-Colotado court ruling, groundwatet pumping in the valley, which selVes to reduce water table levels, has diminished" These factors contribute to a growing body of evidence tllat the irrigated lands of the lower Arkansas are subjected to influences tllat are elevating the severity of waterlogging and saliluzation, At a time when conjectute about the main causes and prognosis of the problems is growing, some people feel that conditions already have reached a crisis stage, Infotmal and anecdotal evidence abounds: salt crus ling on soil surfaces, seepage and wet spots in selected fields, stunled growth of crops, and reduced crop yields, Such losses threaten the economic wellbeing of tile rural communities in the valley and, by extension, diminish the agricultural base of the state, Until recently, however, scientific investigations of tile problems have been sparse. Furthennote, studies often are limited in their scopes and piecemeal in their approaches, failing to provide a cohetent understanding of the extent and severity of tile problems. Project Objectives There is an acute need to place the diagnosis of salinity and waterlogging problems in tile Arkansas valley on a sound scientific footing. Furthennore, beyond the need to accucately describe the problems for fanners and for stale and regional agencies, a reliable database is needed to help prescribe the best possible solutions through the use of advanced computer simulation models, These issues are being addressed by Colorado State University through a suile of projects that come under the major heading of "Identification and Solution of Waterlogging and Salinity Problems in the Lower Arkansas River Valley, Colorado", This work is funded by the Colorado Agricultural Expetiment Station, the United Slates Bureau of Reclamation (USSR). the Colorado Water Resources Research Institute, the United States Geological Survey, and the Colorado Slate Soil Conservation Board Cooperating agencies include the