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<br />Report to the USDI, Bureau of Reclamation <br />from Colorado State University Cooperative Extension <br /> <br />tv <br />to <br />CJ1 <br />C.il <br /> <br />Background <br /> <br />Surge irrigation has the reputation of cutting down deep <br />percolation, and providing uniform irrigation application in a <br />furrow-irrigated field. Irrigation by use of furrows is by far the <br />largest practice in a surface irrigation system. <br /> <br />surge irrigation has been recognized for its ability to enhance <br />water advance across a field. The principle involves switching <br />irrigation water between two sets of furrows accomplished by use of <br />a suitable valve or gate and operated by a motorized controller. <br />The controller is battery operated and continuously re-charged by <br />the solar panel and is relatively maintenance free. The first <br />application of water advances down the furrow to a certain distance <br />before it is switched over to the alternate side. The number of <br />times of alternating the water from one side to the other is <br />dependent upon the soil type, length of irrigation run and the <br />amount of water available. To simplify the operation, the operator' <br />either needs to know from his past experience how much time it took <br />to reach the end of the field under normal stream flow used or the <br />length of the furrow. The time taken to advance the furrow stream <br />to the end of the furrow is also known as "out time." Depending on <br />the manufacturer, the out time or the length of furrow can be used <br />to set the controller, which will calculate the initial alternating <br />times called the "advance cycles" based on a computer. program <br />already provided in the controller. When the advance cycles are <br />complete, the water should reach the end of the furrows and the <br />"out time" is complete. The "out time" may be adjusted by making <br />midstream change for some controllers in case the advance is <br />complete earlier than the time entered at the start. In others the <br />canned program number to use may have to be altered. At the end of <br />the advance cycles, the irrigation must continue to provide "soak <br />time" to wet the rootzone uniformly. The cycles are now shorter to <br />avoid excess run-off or "tail water." Soak cycle has to continue <br />until the required inches or depth of water is applied to fill the <br />rootzone and the depth of application is normally calculated prior <br />to the start of irrigation by taking into account the total flow, <br />acreage, root depth and soil moisture depletion or E.T. of the <br />crop. On-the-spot checking of the depth of wetting may be made by <br />pushing a rod or a ball-probe into the soil. When required depth <br />of wetting is achieved the irrigation may be stopped. <br /> <br />Several theories exist as to why surge irrigation works. The most <br />accepted version is that the water may continue to penetrate the <br />soil even after the irrigation water is removed; which results in <br />some .soil "sealing" by breaking of some capillary flow and <br />compacting .of the soil particles. The infiltration rate changes <br />from 'intrinsic' rate to a 'basic rate' faster. The hydraulics of <br />the furrow changes to a smoother surface. Hence, there is less <br />penetrating during the subsequent "surge" of water and there is <br />more water available to move faster down the furrow. Thus the <br />depth penetrated in the wetted ground progressively becomes <br /> <br />2 <br />