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OGJ173 2 The need for better transit loss estimates cannot be argued. The need for more dependable travel time estimates, while perhaps not so pressing, is also important for proper water administration because if a recipient headgate is opened at the wrong time to divert the water which was transported down river for its headgate, a hole can easily be created in the stream hydrograph repre- senting natural water taken which is due someone else with a vested water right for natural river water. On the other hand, if the headgate is opened too late, the opposite effect occurs, and the recipient headgate will miss some of the transported water. While it would appear that diverting at the receiving head- gate at the right time would be rather simple, it is not easy to observe a "slug" of water in a major river where, for instance, 100 cfs might be trans- ported in a natural river flowing 2,000 cfs. The more frequent the transpor- tation of transmountain storage water in natural rivers, the more necessary it will be to be able to predict both the arrival and the ending of the "slug"; furthermore, the rate of arrival bears a direct relationship to the rate at which the water should be removed from the stream. In particular, the Frying- pan-Arkansas Project may release "slugs" of water that may amount to less than five percent of the water in the river. In this case, the change in the stream hydrograph can probably not be detected with present measuring techniques. ARKANSAS RIVER ;'1" Many years ago it became evident on the Arkansas River that travel time - transit loss estimates of a degree better than that for other Colorado rivers was necessary. This was a result of the construction of the Twin lakes trans. mountain diversion project and the construction of two other large reservoirs, Sugar loaf and Clear Creek ReservoIrs. Detailed studies were done On the Arkansas River by former State Engineer M. C. Hinderlider in the 1920's and 1930's. These estimates were used for many years and have always been COn- sidered reasonable, even though questions have been raised over the years as to their accuracy. With the advent of the Fryingpan-Arkansas Project, which wi 11 further uti I ize the Arkansas River as a transportation route, the matter of travel time and transit losses is again receiving significant attention. Even though the construction of the Pueblo Reservoir will probably reduce the necessity of more' accurate and comprehensive travel time determinations, the knowledge of the hydraul ic characteristics of the river upstream of Pueblo Reservoir will be useful. On the other hand, more accurate determinations of travel time downstream of the Pueblo Reservoir will take On a new degree of Importance. Needless to say, transit losses will play an important role in the operation of the Fryingpan-Arkansas Project, both to protect the project and to protect owners of vested water rights. ,. This study which is reported upon here is a prel iminary study. It is recognized that the accurate determination of travel time and transit losses will be a subject for continuing study over many years because of the hydro- logic vagaries which exist in a natural stream and its basin and the continu- ing change of the hydrologic regime of the river. After the transit losses are dependably estimated to within a few percent, the need will still exist for a higher degree of accuracy. It is bel ieved that the need for more accurate travel time - transit loss determination on the Arkansas River is only a forerunner of the needs which will arise on the other rivers of the State. For instance, sales of Green Mountain water on the Colorado River to users at Grand Valley may Soon