TITLE:
Mapping of the Water Table Levels of Unconfined Aquifers Using Two Interpolation Methods
AUTHORS:
Oswaldo Augusto Filho, Wanessa Soares, Clemente Iriguay Fernandéz
KEYWORDS:
Water Table, Deterministic and Geostatistical Interpolation Methods, SPT Boreholes, Geological-Geotechnical Database
JOURNAL NAME:
Journal of Geographic Information System,
Vol.8 No.4,
August
3,
2016
ABSTRACT: The spatial prediction of the water table can be used for many applications
related to civil works (foundations, excavations) and other urban and environmental
management activities. Deterministic and geostatistical interpolation methods were
used to predict the spatial distribution of water table levels (unconfined aquifers)
of important geological formations of the Joao Pessoa City (capital of Paraiba State,
Brazil) with dense urban occupation and high demand for new civil works. The deterministic
(topo to raster) and geostatistical (ordinary kriging) interpolation methods were
evaluated using a Geographic Information System (GIS)-based investigation. The water
table levels were obtained from 276 boring logs of Standard Penetration Test (SPT) in situ investigation distributed over
the geological formations studied (an area of 59.8 km2, covering 40 districts
of the Joao Pessoa City). The Nspt values and textural characterization data are
stored for levels of 1 m depth. Some boreholes located in the area investigated
were not included in the interpolation processes in order to be compared with estimated
values (validation of the results). Maps of the water table depths were also produced
to further analyze the quality of the water table surfaces interpolated by both
methods. The phreatic surface interpolations provided satisfactory results for both
methods (RMSE = 1.8 m). The topo to raster method showed a slight general tendency
to be less affected by local values in relation to the kriging method and also has
the advantage of integrating the drainage flow system, which is a relevant aspect
for spatial models of the water table levels of unconfined aquifers. The ordinary
kriging (geostatistical method) provides a prediction surface and some measure of
the certainty or accuracy of the predictions.