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ARS Home » Research » Publications at this Location » Publication #70082
Title: SALT TRANSPORT IN CRACKING SOILS AND SALT PICKUP BY RUNOFF WATERS

Author
item Rhoades, James
item LESCH, S - UCR, RIVERSIDE, CA
item BURCH, S - IMPERIAL IRRIG. DIST.
item LETEY, J - UCR, RIVERSIDE, CA
item Le Mert, Robert
item SHOUSE, P - 5310-20-05
item OSTER, JIM - UCR, RIVERSIDE, CA
item O'HALLORAN, T - IMPERIAL IRRIGATION DIST.

Submitted to: Journal of Irrigation and Drainage Engineering
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/6/1996
Publication Date: N/A
Citation: N/A

Interpretive Summary: Run-off of surface drainwater is a common phenomenon from fields irrigated by gravity-flow, surface-systems. The minimization and the utilization of tailwater is a requisite to the efficient use of water resources for such systems. Tailwater is not commonly used for beneficial purposes in the Imperial Valley of California where the surface drainwater is co-mingled with the subsurface drainwater and discharged to the Salton Sea. One means of reducing runoff to the Sea is to install tailwater recovery systems whereby the water is recirculated on the same field or farm. This is being considered for implementation in the Imperial Valley. However, salinity is an old nemesis there and the farmers are concerned that salinity levels will increase unduly in their soils through the recycling of tailwater for irrigation. This study was undertaken: 1) to measure salinity in the soil and runoff water in order to obtain evidence of the extent of and the potential for salt pickup in tailwater and of the influence of soil properties in this regard and 2) to obtain information on the dynamics of salt transport in cracking and noncracking soils, so that the feasibility of tailwater recycling could be assessed more reliably. The findings showed that the potential hazard for soil salinization is greater in this Valley than what classical theory would predict because salts normally deposited in seedbeds or leached downward are reexposed to the runoff water through the phenomenon of soil-cracking and lateral flow, which is a major occurrence in the areas soils.

Technical Abstract: This study was undertaken to evaluate the potential salinity-related hazards that might result from the recycling of irrigation run-off water in the Imperial valley of California. Detailed measurements were made of the levels and distributions of salts in representative soil profiles and fields and associated tailwaters of the Valley. The findings showed that the potential hazard is greater in this Valley which is dominated by cracking-soils than what classical theory would predict. Salts that would otherwise be "isolated" in seedbeds or leached downward during irrigations are "exposed to" and picked up by the run-off water as a result of the flow of the irrigation water throughout the beds and horizontally and upward in the topsoil via the extensive, network of cracks and fractures existent in these types of soils. As a result, the pattern of salinity within the beds were one-dimensional, rather than the classical two-dimensional, salt content in the tailwater was higher and sustained over longer periods of time, and more salt was transported horizontally across the fields, resulting in increased levels of salinity in the soil with distance across the field and proportionately more salinity in the topsoil than in the lower depths of the profile.