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INTRODUCTION With ever-increasing demands being placed on the water supplies available in Colorado, im- proved efficiency of use is a necessity. Many research and development activities are now aimed at this problem. For example, consider current efforts in (a) the desalting of brackish water, (b) the reduction of evaporation from water surfaces and from high water table areas supporting low- benefit vegetation, (c) the increase of run-off from treated watershed areas, (ct) the development and storage of water underground. and (e) the reduction of seepage losses }rom canals and reservoirs. Many state and federal agencies. private companies and water districts. and universities and colleges, including Colorado State University. are engaged in these activities. This progress report summarizes the research and development work accomplished dur- ing 1961 at Colorado State University in regard to the use of Colorado clays for sealing canals and reservoirs. This project, commonly called the Colorado State University Bentonite Project, has two general objectives: (a) to inventory the clay resource (including bentonite) of Colorado, and (b) to develop methods of utilizing the local clays in sealing canals and reservoirs in Colorado. Thus, two important justifications for this state-funded work are (a) new industry development, and (b) conservation of water. The major project activities were started in July 1960 and are scheduled for completion by July 1963. This, therefore, is a report of progress to the half-way point in the investigations. Since the investigations are not complete at this time, we welcome review comments, sugges- tions, corrections, or additions to this report. In some respects, this is a rough draft outline of the final report. Please, therefore, if you can possibly spare the time, jot down comments as you read this report and send them to us. Pencil notes will be acceptable and greatly appreciated. THE SEEPAGE PROBLEM Seepage loss from canals and reservoirs is surprisingly great in Colorado, and a serious prob- lem. During the current investigations, some 100 canals and 50 ponds have been examined. The canal losses were found to range from 100 per cent (or total loss) in some systems late in the summer to one outstanding minimum of less than 3 per cent in 8 miles of canal. The pond losses ranged from as high as total loss over-night to a minimum of about I-inch per day drop in water level. Seepage loss into leaky bed and bank materials obviously is not the only source of loss but undoubtedly the major source--especially in the high loss cases. It is true that the seepage water is not physically destroyed, and undoubtedly some of the loss water returns to the main river channel; but this water after loss is seldom available for use by those who store, divert or pay for it. With favorable groundwater reservoir conditions, recovery of seep- age loss water may be feasible, but usually not with- out additional expenditures for equipment and power. In many instances, the seepage water may flood and damage land in its return flow path to the river, part of it may be used and transpired by swamp and other non-crop plants, part of it may evaporate directly from seep-flooded areas, and almost invariably it will pick up an additional load of dis- solved salts. One promising potential benefit of seepage in Colorado relates to the possibilities of planned groundwater recharge operations based on a seep- age loss from infiltration facilities, including canals and reservoirs. The various teclmical and legal problems involved in this possibility are now under study at Colorado State University. In considering all aspects of the seepage loss problem in Colorado, it is estimated that the direct and indirect losses are as follows: Assumed annual irrigation diversions ..... Assumed canal and reservoir seepage loss Annual loss of irrigation water Estimated value of loss water ...... Estimated indirect or seep- damage losses Total estimates losses 10,000,000 AF 25 ~o 2,500,000 AF $5,000,000/yr $5.000,000/yr $iO,OOO,OOO/yr As to future prospects, it is likely that the present trend toward an increase in seepage losses will continue. This trend is attributed to the gradual elimination of sediment or mud from irriga- tion water by construction of upstream reservoirs. It is a common observation in areas such as below John Martin Reservoir near Lamar, Colorado that clear water will seep from canals and irrigated fields at faster rates than muddy water. Another important factor relates to the increasing amounts of sewage in irrigation waters in Colorado. The typical J1foaming" waters, now evident in canals below some Colorado towns, seem to seep away at faster rates than the previous lInon-foaming" water supplies. 1054