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Title: Soil Water and Shallow Groundwater Relations in an Agricultural Hillslope

Author
item Logsdon, Sally
item SCHILLING, KEITH - IOWA GEOLOGIC SURVEY

Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: 12/14/2007
Publication Date: 12/14/2007
Citation: Logsdon, S.D., Schilling, K.E. 2007. Soil Water and Shallow Groundwater Relations in an Agricultural Hillslope. American Geophysical Union (AGU) Annual Meeting abstracts. Available: http://www.agu.org/meetings/fm07/waisfm07.html.

Interpretive Summary:

Technical Abstract: Shallow water tables contribute to soil water variations under rolling topography, and soil properties contribute to shallow water table fluctutations. Preferential flow through large soil pores can cause a rise in the water table with little increase in soil water except near the soil surface. Lateral groundwater flow can cause a large rise in water table at toeslope and depressional landscape positions. As plants transpire, water can move up into the root zone from the water table and wet soil below the root zone. Roots can utilize water in the capillary fringe. The purpose of this study was to interface automated measurements of soil water content and water table depth for determining the importance of drainage and upward movement. In 2006 soil water and water table depth were monitored at three positions: shoulder, backslope, and toeslope. Neutron access tubes were manually monitored to 2.3 m depth, and automated soil moisture was measured using CS616 probes installed at 0.3, 0.5, 0.7, and 0.9 m depth. Water table depths were monitored manually and automated, but the automated measurements failed during the season at two sites. In 2007, similar measurements were made at one toeslope position, but the CS616 probes were installed at nine depths and better quality automated well depth equipment was used. The 2006 data revealed little landscape position effect on soil water loss on a wetter date; however, on a dry day just before a rain, water loss was greatest for the toeslope positon and least for the shoulder position. After a period of intense rain, a rapid and significant water table rise occurred at the toeslope position but little water table rise occurred at the other landscape positions. The rapid toeslope water table rise was likely caused by lateral groundwater flow whereas minor water table rise at the other positions was likely due to preferential flow since the soil had not wet up below 0.6 m. Use of automated equipment has improved our understanding of the relations of soil water to water table fluctuations in an agricultural field.