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to C C'! - C, C. the south side of the river, and is far superior to the quality of Little Colorado River water. However, the Geological Survey report points out that if the wells on the north side of the river are improperly cased there is danger of their being contaminated with salt water from for- mations overlying the Coconino sandstone. Water Requirements 25. Due to lack of other data, the consumptive use ~or the Joseph City area was estimated by the Lowry-Johnson method.!/ which relates consumptive use to total heat units as measured by day-degrees above freezing temperature during the growing season. The consumptive use was estimated to be 2.63 acre-feet per acre. Making allowance for winter consumptive use, effective precipitation, excess application and waste, and canal and lateral losses, the diversion demand was estimated to be 3.84 acre-feet per acre. On the basis of 800 acres, slightly in excess of the 777 acres actually under irrigation, the annual diversion requirements of the area are estimated to be 3,070 acre-feet for a full water supply. Quality of Water 26. The quality of Little Colorado River water reaching Penzance Dam, like the quantity, is related to the source of the water. Stream- flow originating in the mountains to the south is satisfactory for irrigation and domestic use. However, only a relatively small amount of this water reaches the Joseph City area during the irrigation season because of upstream use. Water of poor quality is contributed by the tributaries draining the Chinle and Moenkopi formations lying to the northeast and east, which are high in salt and shale materials. Much of their stream- flow results from summer and early fall rains and augments the water supply of the Joseph City area in the later part of the irrigation season. These waters nearly always contain a high percentage of sodium and usually carry a heavy load of suspended sediment, a large proportion of which is very fine material derived from shale. While only a portion of the long-term average flow comes from this source, at times it represents almost the entire flow available for irrigation in the project area. The water from the artesian wells is of much higher quality. Although it represents only a small part of the total water supply, it apparently improves the quality of river water by dilution during periods of very low flow. , :f ::.< 27. Water samples were taken intermittently for slightly more than a year from the Little Colorado River several miles below Penzance Dam. While the sampling was not adequate to permit conclusive deter- minations as to quality by time of year and by source of supply, general results are reasonably definite, Water quality, as indicated by the samples, varied widely from day to day and even within the same day. The total salt content of the water seldom exceeded the acceptable " ~:!: :.& ,;'" '. '," 1/ Transactions of the American Society of Civil Engineers, 1942. 9