Hydraulic head and groundwater 111Cd content interpolations using empirical Bayesian kriging (EBK) and geo-adaptive neuro-fuzzy inference system (geo-ANFIS)

Headnote

ABSTRACT

In this study, hydraulic head and lnCd interpolations based on the geo-adaptive neuro-fuzzy inference system (Geo-ANFIS) and empirical Bayesian kriging (EBK) were performed for the alluvium unit of Karabağlar Polje in Muğla, Turkey. Hydraulic head measurements and ¹¹¹Cd analyses were done for 42 water wells during a snapshot campaign in April 2013. The main objective of this study was to compare GeoANFIS and EBK to interpolate hydraulic head and ¹¹¹Cd content of groundwater. Both models were applied on the same case study: alluvium of Karabağlar Polje, which covers an area of 25 km² in Muğla basin, in the southwest of Turkey. The ANFIS method (called ANFIS_XY) uses two reduced centred pre-processed inputs, which are cartesian coordinates (XY). Geo-ANFIS is tested on a 100-random-data subset of 8 data among 42, with the remaining data used to train and validate the models. ANFIS_XY and EBK were then used to interpolate hydraulic head and heavy metal distribution, on a 50 m² grid covering the study area for ANFIS_XY, while a 100 m² grid was used for EBK. Both EBK- and ANFIS_XY-simulated hydraulic head and ¹¹¹Cd distributions exhibit realistic patterns, with RMSE < 9 m and RMSE < 8 µg/L, respectively. In conclusion, EBK can be considered as a better interpolation method than ANFIS_XY for both parameters.

Keywords: ANFIS, EBK, interpolation, hydraulic head, metal, ¹¹¹Cd, alluvium, Muğla

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INTRODUCTION

Earth scientists (hydrologists, geologists, biogeochemists, etc.) are interested in understanding the behaviour of hydrosystems (Kurtulus et al., 2011; Flipo et al., 2012). Usually they first do experiments/observations in the field at specific locations and then try to distribute these observations/measurements both in space and time using modelling techniques that are based on abstractions. As part of the hydrosystem, aquifer systems play a decisive role in its behaviour and act as a reservoir. Metals and metalloids in these kinds of reservoirs might be assessed as pollutants according to their abundance. In the case of using polluted water stored in reservoirs for domestic, industrial or irrigational purposes, harmful side effects will most likely be encountered. Recent studies have shown that groundwater heavy metal contamination often cannot be detected, especially in cities...