OCR Text |
Show 71 Lieutenant Bergland began his survey. He bas examined tbe general course of tbe river for a distance of 326 miles, and caused sections to be made near the mouth of tbe Virgin and Gamp Mobave. Observations were made at Liverpool Landing and about Fort Yuma, with profiles from Fort Yuma westward to the depressed area near Indian Wells, and. from Algodones to tbe westward, in vicinity of tbe bed of New River, so called. The volume of water measured at Stone's Ferry, near the mouth of tbe Virgin, was found to be, in August, 1875, approximately 18,410 cubic feet per second, or sufficient in amount to irrigate 3,682,000 acres, assuming one cubic foot per second for each 200 acres. At Gamp Mohave in September the flowage was 8, t> 80 cubic feet per second, or sufficient at the assumed rate for the irrigation of an area of 1,736,000 acres. At Fort Yuma in March, 1876, the volume of water was found to be7,658 cubic feet per second, sufficient for the irrigation of 1,531,600 acres. The estimate of the volume of water necessary for the irrigation of a single acre for one crop, ( one two- hundredth part of a cubic foot per second, used 200 days,) is taken from the report of the commissioners, Messrs. Alexander, Mendell, and Davidson, upon the irrigation of the Sun Joaquin and Tulare Valleys of California. By assuming the increased area of the cross- sections of the river at high water as shown by the section made at Stone's Ferry, the velocity of discharge remaining the same as that noted as the mean velocity at that point in August, the increase of the volume of discharge would be 31,439 cubic feet per second, making the total volume of discharge nearly 49,849 cubic feet per second, or a little less than three times the volume observed in tbe middle part of the heated season. Gould this amount be utilized upon ordinarily compact soil, which, however, is partially impracticable, approximately 10, COO,- 000 acres of land could, by its instrumentality, be brought under cultivation. The increase of discharge upon the assumption of a mean velocity at high water, the same as that observed in September at Gamp Mohave, would give 34,274 cubic feet at that point; because of the large area of bottom- lands overflowed at high stages, the velocity would be increased bat slightly. At Fort Yuma the increase, on account of estimating with increase of cross- sections of the river at these points, as shown by cross- section, assuming an unchanged mean velocity, would be 14,244 cubic feet, giving nearly a double volume of flow, while at Gamp Mohave it is tripled, and at Stone's Ferry nearly doubled. Lieutenant Michler, while engaged upon the Mexican Boundary- Survey in the winter of 1854-' 55, estimated the volume of discharge at the Nora FROM MEMORANDA OF LIEUTENANT BERGLAND.- At Stone's Ferry and Fort Tama it is seen that the increase in discharge corresponding to the observed high- water marks is about doable that of the measured discharge, while the increase at Camp Mohave is three times that of the measured discharge. As the highest observed water- marks given at the three places do not belong to the same year, no direct comparisons can be made as to the increase in discharge, but it is. highly probable that the large approximate increase at Camp Mohave is nearer the true increase than that at the other places, since at Camp MoHave the velocity would not be greatly augmented, while at Stone's Ferry there must be a considerable inorease in the mean velocity due to the rise. This increase of velocity would be less at Fort Yuma, since a portion flows outside the sections, bat it would be much greater than at Camp Mohave. Fort Yuma, Cat, March 20,1876.- Area 2,726.5 square feet. Width 461 feet. Hydraulic radius or mean depth 5.85 feet. Mean velocity 2.809 feet per second. Discharge 7,658.74 cubic feet per second. High- water mark of 1862 above surface of river 10.19 feet. Increase of area of section at high water, 5,059 square feet. It is to be noted that when the water reaches high- water mark of 1862 the bottom- lands are more or less flooded, and all the water does not pass through the section. The- high-wsjter. marks given are the highest observed at each place. Increase in discharges |