Finite element method in estimation of lag time of rainfall recharge to Holocene groundwater aquifer in Hung Yen province

Abstract

In the Red River delta, Holocene aquifer has main recharge from rainfall and irrigation. The recharge is much dependent upon the unsaturation-saturation condition of the semipermeable layer covering the aquifer. The paper presents the analysis of moisture transfer in this covering semipermeable layer to estimate the lag time of rainfall recharge to the Holocene aquifer in Hung Yen province in the Red River delta. A finite element modeling had been developed and applied for this purpose. The lag time results have been based on the condition that the degree of saturation of 90% or more is representative for saturation water movement, and therefore the rainfall is actually recharging the aquifer via saturated flow through the covering semipermeable layer. The lag time is 3 days for continuous wet condition from the rainfall if the thickness of the semipermeable layer is 2m, and 5.5 days if the thickness is 3m. For consecutive wet day and dry day condition the lag time is 4 days if the thickness is 2m and 13 days if the thickness is 3m. Therefore, the duration of rainfall for recharge estimation for the study area would be up to about two weeks.

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