. Capillary movement of soil moisture. Soil moisture. ^ BULLETIN No. 835 Contribution from the Bureau of Public Roads THOMAS H. MacDONALD, Chief. jn-f^^<»=f«. Washington, D. C. PROFESSIONAL PAPER August 6, 1920 CAPILLARY MOVEMENT OF SOIL MOISTURE, By Walter W. McLaughlin, Finiior Irrlnntinn Engineer. CONTENTS. Pago. Object 2 Plan of experiments 2 Pate and xtont of movement of soil moisture by capillarity 13 Effect of gravity on tbe movement of soil moisture bj- capillarity 39 Evaluation of empirical curves 47 Page. Open versus covered flumes 54 Effect of temperature on soil-moisture conditi
. Capillary movement of soil moisture. Soil moisture. ^ BULLETIN No. 835 Contribution from the Bureau of Public Roads THOMAS H. MacDONALD, Chief. jn-f^^<»=f«. Washington, D. C. PROFESSIONAL PAPER August 6, 1920 CAPILLARY MOVEMENT OF SOIL MOISTURE, By Walter W. McLaughlin, Finiior Irrlnntinn Engineer. CONTENTS. Pago. Object 2 Plan of experiments 2 Pate and xtont of movement of soil moisture by capillarity 13 Effect of gravity on tbe movement of soil moisture bj- capillarity 39 Evaluation of empirical curves 47 Page. Open versus covered flumes 54 Effect of temperature on soil-moisture conditions 56 The capillary siphon 58 Capillary movement of moisture from a wet to a di-y soil 63 References 69 The irrigation engineer has long felt the need of more detailed information as to the importance of capillarity as a source of loss of water from irrigation works and the part it plays in distributing, within the soil, water applied in irrigation. It has long been recog- nized that impounding reservoirs and conveying channels lose more water than can be accounted for by direct percolation and evapora- tion. Whether this loss was the result of capillary action alone or in combination with the transpiration from plant growth along canal banks has been only a matter of conjecture. Wliere the water ap- plied to soil by irrigation goes and how it ultimately distributes itself within the soil have been questions of speculation. It has been observed that the percentage of moisture determined in the field in the usual way has not always given a true basis upon which to determine the necessity of applying water by irrigation. In some instances, the percentages of moisture determined have been above the wilting point and yet plants were wilted. This condition has caused the irrigation engineer to speculate upon the probability of the rate of movement of soil moisture from one point to another by capillarity, as well as the extent to which the moisture may move. The irrigator is alwa
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