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<br />First of all, "it would enable us, or let's say, would aid us, in <br />better understanding and defining the complex relationship between <br />irrigation practices and water quality variations. What again is <br />more important, such a model would enable us to predict and evaluate <br />the impact of any proposed changes in management techniques or <br />irrigation practices. This study was sponsored by the Four Corners I <br />Regional Commission and the Water Resources Division of the U. S. <br />Geological Survey in cooperation with the Colorado Water Conservation <br />Board. <br /> <br />(Slide) The area selected for study was near the city of La Junta, <br />along the Arkansas River Valley. One reason this area was selected <br />was because water quality problems relating to irrigation practices <br />were known to exist throughout this valley. The general increase in <br />dissolved solids concentration shown on this slide is a very general <br />pattern and you will see that in a few minutes when we look at the <br />stJ~yarea in more detail. <br /> <br />The study area was the ten-mile reach from La Junta to the Bent-Otero <br />...County line. Another reason why this particular area was selected <br />,'~'for study was that detailed hydrogeologic data were available from <br />'previous studies conducted in the area by the Geological Survey. <br />Furthermore, the ground water use patterns and irrigation practices <br />within this small study area are fairly typical of those throughout <br />the Arkansas River Valley, and in fact are typical of those in many <br />other similar irrigated river valleys throughout the West. <br /> <br />There are many physical (Slide) factors which affect the movement of <br />water and the changes in water quality which accompanied this water <br />movement. <br /> <br />(Slide) To illustrate the number of practices which must be considered <br />in the model and their complex interrelationships, first of all, water <br />can~e. applied to the fields, to individual fields, with surface water <br />diverted from canals or with ground water pumped through irrigation <br />wells. Now of this water which is applied to the fields. there will <br />be a certain amount of it consumed or lost to evapotranspiration. <br />Because of this 19s5 of water, any salts .or dissolved solids contained I <br />in the water applied to the fields will become more concentrated. <br />Thus, any water recharging the aquifer will be of a higher dissolved <br />solids concentration than the water which was applied to the fields. <br />Since the aquifer containing the ground' water is, at least in this <br />area, in hydraulic connection with the stream itself, any stresses <br />placed upon the aquifer, that is. any recharge to the aquifer with <br /> <br />-23- <br />