Author
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DANIEL, JOHN |
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Submitted to: Annual Hydrology Days Conference Proceedings
Publication Type: Proceedings Publication Acceptance Date: 4/2/1998 Publication Date: N/A Citation: N/A Interpretive Summary: Playas are shallow depressions and are often used as sites of animal waste management. Playas are also zones of active groundwater recharge, possibly by downward movement of surface water through cracks and fractures formed during dry periods. If feedlots contribute enough water to keep the playa floor wet then cracks and fractures can not form, thus restricting or eliminating surface water flow through cracks. The objective of this paper is to show the lake surface area in selected playas with and without feedlots during wet and dry periods and show how feedlots affect water levels in playas. Historical precipitation data was studied to find wet and dry periods. Standing water in a playa was identified by examining LANDSAT Thematic Mapper satellite data. Lake boundaries of seven feedlot-impacting playas and seven playas without feedlots were compared. Results show that all the playas without feedlots were dry during the dry period and most had standing water in the wet period. However, all but one feedlot playa had standing water in both the dry and wet periods. Playas with feedlots could maintain enough water in them to reduce ground surface desiccation and crack formation, and restrict downward of surface water. Technical Abstract: Playas are shallow depressions, and in the Texas High Plains, are often used as sites of animal waste management of beef feedlots and dairy operations. Playas are also zones of active recharge to the Ogallala Aquifer. While the exact mechanism of groundwater recharge is unknown, desiccation cracks and fractures in a playa bottom formed during dry periods may play a role in the downward movement of surface water and potential contaminants. However, ground surface fracture formation should be limited, if feedlots contribute enough water to keep the playa floor wet; thus restricting or eliminating preferential flow through cracks. The objective of this paper is to delineate the lake surface area in selected playas with and without feedlots during periods of extended dry and wet conditions and relate how feedlots affect water levels in playas. Historical precipitation data was examined to define the extreme climatic conditions. Standing water in a playa was identified by examining LANDSAT Thematic Mapper (TM) band 7 (2.08 to 2.35 micrometer) satellite data. Lake boundaries of seven feedlot-impacting playas and seven playas without feedlots were compared. Results show that all the playas without feedlots were dry during the dry period and most had standing water in the wet period. However, all but one feedlot playa had standing water in both the dry and wet periods. Water surface area during the dry period of five of the feedlot playas was 70% to >100% compared to the wet period. Two other feedlot playas had water surface areas less than 10% for dry versus wet periods. One feedlot playa was dry during drought. Playas with feedlots could maintain enough water in them to reduce ground surface desiccation and crack formation, and restrict downward of surface water. |
