Variogram-based approach for selection of grid size in groundwater modeling
2013
Mohammadi, Zargham
In this paper a geostatistical approach based on the variogram concept is used for decisions about the size of a grid network applicable to a groundwater model. One of the important properties of the variogram function is the range of influence, which is interpreted as a measure of similarity and correlation distance between spatial phenomena. Taking the concept of range into account, several available spatial variables of the under study aquifer were used to plot the variogram in different directions. The study area is an unconfined aquifer (Boushkan Plain in southwest Iran) with an average thickness of 50 m and area of 100 km². The variables used for computing the variogram include aquifer thickness (D), groundwater pumping rate (Q) and electrical resistivity (R) of the aquifer material. The range of influence was estimated to be 2,000, 2,500, and 2,000 m for D, Q and R, respectively. Comparisons of statistical parameters of spatial variables over a grid size ranging from 1,000 to 5,000 m were done to confirm the proposed grid size according to variogram plots. The bounded area of each cell could be considered as homogenous media according to the spatial variation of the variables used. The optimum size of the grid network was selected according to the minimum of the variance and coefficient of variation over each cell size. Results suggest a 2,500 × 2,500 m grid size for the modeling process in the studied aquifer. The results emphasize the role of variogram function in selection of grid size for the groundwater model.
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