Author
 |
Daniel, John |
|
Submitted to: Proceedings of the Ogallala Aquifer - Steps to Sustainability
Publication Type: Proceedings Publication Acceptance Date: 10/30/1999 Publication Date: N/A Citation: N/A Interpretive Summary: Animal waste in the Texas High Plains is sometimes contained in shallow depressions called playas. Cracks formed in the depression floor during dry periods allow downward movement of surface water. If feedlots contribute enough water to keep the playa floor wet then cracks and fractures cannot form, thus restricting or eliminating surface water flow through cracks. This paper describes the lake surface area in selected playas with and without feedlots during wet and dry periods, and 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-impacted 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 usually maintain enough water in them to reduce ground surface desiccation and crack formation, and restrict downward flow 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 can be zones of active recharge to the Ogallala Aquifer. Groundwater recharge estimates to the Ogallala Aquifer are calculated using hydraulic properties of playas which are not used as waste emanagement sites. A concern is raised whether these hydraulic properties of playas not associated with feedlots are valid to estimate groundwater recharge from feedlot-impacted playas. The objective of this paper is to provide evidence to show that hydrology is different for feedlot- impacted playas, and therefore, hydraulic properties are different for feedlot and non-feedlot playas. Historical precipitation data was examined to delineate extended wet and dry periods for Texas High Plains. Lake boundaries of seven feedlot-impacted playas and seven non-impacted playas were compared using LANDSAT Thematic Mapper (TM) band 7 (2.08 to 2.35, um) satellite data. 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 a sizable surface area of standing water in both the dry and wet periods. These results indicate that the playas associated with beef feedlots behave different hydrologically, and consequently are hydraulically different and should be considered different for hydrologic modeling and recharge estimate calculations. |
