MEASURING EVAPORATION AND SEEPAGE LOSSES FROM LAGOONS USED TO CONTAIN ANIMALWASTE

Abstract

Seepage (S) from animal-waste lagoons was estimated using a water balance approach by measuring changes in waste level (i.e., depth) ( D) and evaporation (E) over brief periods (e.g., 6 days) when all other inflow and outflow were precluded. Data were collected at commercial swine and cattle feedlots in southwestern Kansas. Precision waste level recorders, floating evaporation pans, and meteorological models were used to measure each lagooni¯s water balance. Different strategies for calculating evaporation and seepage were compared. Initial work at a 2.5-ha plastic-lined lagoon (S = 0, E 5.1 mm di©1) showed that evaporation over 6- to 11-day periods could be measured to within i¾0.5 mm di©1 with floating evaporation pans using a pan coefficient of 0.81. A bulk-transfer evaporation model, which incorporated realtime measurements of lagoon surface temperature, predicted evaporation to within 6% when using a transfer coefficient of 2.8 i? 10i©3. Evaporation models that did not include surface temperature resulted in significant errors (e.g., > 50%) under certain environmental conditions. The water balance of a soil-lined, cattle-feedlot lagoon over an 11-day period was: D = 2.1; E = 1.9, and S = 0.2, all in mm di©1. Additional work over a 6-day period at a soil-lined, swine-waste lagoon resulted in a water balance of: D = 5.4; E = 4.5, and S = 0.9, all in mm di©1. Data suggest that seepage from lagoons can be determined to within i¾0.5 mm di©1 by making precision water balance measurements over short periods (5 to 10 days), if evaporation is less than 6 mm di©1.