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Uncertainty Analysis of the Water Balance Technique for Measuring Seepage from Animal Waste Lagoons

Department of Agronomy, Throckmorton Hall, Kansas State Univ., Manhattan, KS 66506

View larger version (42K): [in a new window]   Fig. 1. Diagram of the equipment used to measure the lagoon water balance. Not to scale.

View larger version (23K): [in a new window]   Fig. 2. Change in depth and evaporation from four animal waste lagoons during water balance experiments. A description of the lagoons is given in Table 1.

View larger version (26K): [in a new window]   Fig. 3. Effect of wind speed on the standard deviation (SD) of measurements from a float-based water level recorder. The SD was computed every 30 min from samples collected every 10 s. Data were collected for 45 d at Swine Lagoon 2 (see Table 1).

View larger version (42K): [in a new window]   Fig. 4. Fluctuations in recorded waste depth during a 3-d period at a plastic-lined swine waste lagoon. Because seepage was zero, the change in depth should equal evaporation. Shown are (a) change in depth as detected by the waste level recorder (30-min averages) and the evaporation rate predicted by Eq. [3], (b) deviations between the recorded waste depth and modeled evaporation, and (c) wind speed and wind direction.

View larger version (47K): [in a new window]   Fig. 5. Fraction of uncertainty contributed by each variable in the evaporation equation (Eq. [3]). Data are from the same 5-d water balance tests described in Table 1.

View larger version (26K): [in a new window]   Fig. 6. Uncertainty in the hourly estimates of evaporation plotted against evaporation rate. Data are from an experiment at Swine Lagoon 1 (Table 1) conducted between Day of Year (DOY) 157 and 161, 2000. Variation among measurement days was caused by differences in average daily wind speed.

View larger version (35K): [in a new window]   Fig. 7. The apparent seepage rate as calculated at different times following the start of a water balance test. Individual plots correspond to the same sites depicted in Fig. 2 and Table 1.

View larger version (18K): [in a new window]   Fig. 8. Uncertainty in the overall seepage estimate as a function of average evaporation rate. Data were integrated over measurement periods for each of the water balance tests described in Table 1. The uncertainty of the input variables was set using two scenarios, typical and best, as described in Table 2.