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000172 SECTION I INTRODUCTION " The matter of canal and stream losses in Colorado has long been a sub- ject of great interest to irrigators, to state water administrators, municipal officials, and others, and has been the objective of numerous field and office studies since the early days of the development of the State. Seepage runs have been made on many of the major irrigation ditches in the State at one time or another, and most irrigation companies have ditch loss estimates which the ditch rider uses in distributing water to the users. Ditch officials real ize that the percentage of ditch loss varies greatly, depending upon the amount of water being carried in the ditch, though they often apply a flat per- centage for the sake of convenience and because of somewhat I imited basic data. Generally when the amount of water being carried in the ditch drops to low levels, the ditch loss percentage rises to a high value. With lower amounts of water in the ditch, the technique of sectional ization of the ditch for admini- stration purposes is used. From the early beginning of irrigation in Colorado when reservoirs were first constructed, rivers and streams have been used to transport water from the reservoir to ditch headgates many miles below the reservoir. More re- cently the wide use of exchanges from One ditch to another has meant more use of natural streams and rivers for transportation of decreed water. Historically, stream losses have been estimated and appropriate charges n~de to those trans. porting the water, and while it was known that these losses were only generally rough estimates, it was realized that there was nothing better to use. f:. On some of the streams of the State of Colorado, substantial effort has been made to help define stream losses and travel times, and the most notable of this work has been on the Arkansas River and the Cache la Poudre. Mean- while, however, other rivers, such as the Colorado, have had almost no work done, and only rough guesses exist relative to travel times and transit losses. . Following the drouth of the mid-1950's, unit costs of water have been rising steadily throughout the State with the most notable increases occurring on the eastern slope of Colorado where most of the State's urban development has occurred and where the most intense farm land irrigation takes place. The ccn- struction of large transmountain diversion projects and the construction of large reservoirs in the stream headwaters has created more dependence on natural streams and rivers for transportation purposes. This increase in the amount of water transported in natural waterways, coupled with the higher unit prices for water, has brought to bear more pressure for more accurate and dependable estimates of travel time and transit loss. It is clear, even to the layman, that the transportation downstream of 50,000 acre-feet of water using a transit loss estimate which is only two percent off can result in an overcharge or an undercharge of 1,000 acre-feet of water. With water being worth perhaps $10 an acre-foot, this could represent a $10,000 error. This can affect repayment capabil ities for particular projects. Perhaps more important than the monetary aspect, however, is the potential adverse effect upon owners of vested water rights where an under estimation of two percent would mean that 1,000 acre-feet was being taken from the natural waters available for distri- bution to them for use by those transporting water.