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Show REPORT OP THE CHIEF OP ENGINEERS. 291 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 au unchanged mean velocity, would be 14,214 cubic feet, giving nearly a double volume of flow, while at Camp 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 junction of the Colorado and Gila Rivers G,24fl cubic feet per second, with a velocity of o feet per .second. The estimated evaporation at Camp Mohave as given by Lieutenant Hergland, deduced from observations extending over a small interval, is a little less than H feet: this would be increased at Yiima, while at Stone's Ferry it would be similar in amount. A lake required to contain the influx of all the waters of the river at the stage mentioned near Fort Yuma, the only point near which it can be diverted, would be somewhat less than one thousand square miles. The area of depressed region (approximately) to which a channel can be cut from the river is 1,000 square miles. Hence, it appears that during the low-water stage this lake would act as a reservoir without outlet. while at a high stage the overflow at its maximum would cause a regular channel to be cut, making its own outlet to the gulf and forming along its route a series of lagoons during seasons of no llood, or the greater part of each year; but should it be possible to introduce waters from the gulf to the lake thus to be formed in the depressed area, the same would be transferred into a tidal lake with a current setting in toward the gulf by way of the conduit thus formed, receiving fivsh waters from the river and affected by the changes of the high and low-waters from the sea. No change of climate can be expected to ensue from the formation of a lake or number of lakes, aggregating the above area. The amount of evaporation from the surface would be insullieient to change noticeably the relative humidity of the surrounding atmosphere, while the prevalent winds, both from local and far-distant sources, would diffuse and disseminate the amount of moisture thus received with great rapidity. The soils along portions of the route, as shown by Dr. Loew's report, (see Appendix U <>,) are, many of them, of an arable nature, needing moisture only to be made productive. In the lower parts of the valley of the Colorado, cotton, colVee, sugar, tea, and flax could undoubtedly be grown with success, while a small change for the better in the relative humidity at local points could most likely be brought about by planting the eucalyptus, and trees of like None fhom Mkmoicanka ok LiKLTKNAXT Hkiuji.ani>.-At Stone's Ferry anil F«rt Yuuia it is seen that the increase in discharge corresponding to the observed high-water marks is about double that of the utcttMiml discharge, while the increase at Camp Mohave is 1 hree times that of tho measured discharge. As the highest observed water-marks given at tho three places do not belong to tho same year, no direct comparisons can be made as to tho 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 Moliave the velocity would iiot Wgreatly augmented, while at Stone's Ferry there must be a considerable increxso in the mean velocity due to the rise. This increase of velocity would be less at Fort Viiina, since a portion Hows outside the sections, but it would Im much greater than at C'amp Mohave. Fort Yuma, Cnl, March *», WO.-Area 2,7'2<».r» square feet. Width Ifil fe«t. Hydraulic radius or mean depth &J& feet. Mean veloeity •J.rtt'J feet per second. Dis-tharge 7,CM.7A cubic feet per second. High-water mark of IrttfcJ above surface of river 10.l'J f«.«.t. Increase of area of wet ion at high water, ."».H.V.» square feet. It is to be noted that when the watt* reaches high-water mark of l*tii the bottom-lauds are more or lesn Hooded, and all the water does not pass through the section. The high-water marks given are the highest observed at each place. Increase in discharges |