Comparison of specific-yield estimates for calculating evapotranspiration from diurnal groundwater-level fluctuations

Gribovszki, Zoltán

Comparison of specific-yield estimates for calculating evapotranspiration from diurnal groundwater-level fluctuations | Comparaison de valeurs estimées de porosité efficace pour calculer l’évapo-transpiration à partir de fluctuations piézométriques diurnes Comparación de estimaciones de rendimiento específico para calcular la evapotranspiración a partir de las fluctuaciones diurnas del nivel del agua subterránea 对单位出水量估算值进行对比,进而根据白天地下水位波动计算蒸发蒸腾量 Comparação de estimativas de rendimento especifico para o cálculo da evapotranspiração a partir de flutuações diurnas do nível da água subterrânea

2018

Gribovszki, Zoltán

Methods that use diurnal groundwater-level fluctuations are commonly used for shallow water-table environments to estimate evapotranspiration (ET) and recharge. The key element needed to obtain reliable estimates is the specific yield (Sy), a soil-water storage parameter that depends on unsaturated soil-moisture and water-table fluxes, among others. Soil-moisture profile measurement down to the water table, along with water-table-depth measurements, can provide a good opportunity to calculate Sy values even on a sub-daily scale. These values were compared with Sy estimates derived by traditional techniques, and it was found that slug-test-based Sy values gave the most similar results in a sandy soil environment. Therefore, slug-test methods, which are relatively cheap and require little time, were most suited to estimate Sy using diurnal fluctuations. The reason for this is that the timeframe of the slug-test measurement is very similar to the dynamic of the diurnal signal. The dynamic characteristic of Sy was also analyzed on a sub-daily scale (depending mostly on the speed of drainage from the soil profile) and a remarkable difference was found in Sy with respect to the rate of change of the water table. When comparing constant and sub-daily (dynamic) Sy values for ET estimation, the sub-daily Sy application yielded higher correlation, but only a slightly smaller deviation from the control ET method, compared with the usage of constant Sy.

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