Piezometry mapping accuracy based on elevation extracted from various spatial data sources

摘要

Any hydrogeological conceptual model of an aquifer requires a piezometric map to enable defining flow direction, hydraulic gradient, groundwater recharge and discharge zones. Thus, the piezometric head calculation requires an accurate assessment of the elevation and the depth to water in monitoring wells. The main concern of aquifer managers remains the elevation estimate with a satisfactory accuracy, particularly in developing countries, where a lack of well surveying data is frequently encountered. A solution to this situation may be found in the use of digital elevation models (DEMs). In the present paper, a methodology to extract well elevations from DEMs based on datasets from Shuttle Radar Topography Mission (SRTM), Google Earth and digitized topographic map is presented. Statistical analyses of the elevations derived from a topographic field survey and the relative DEMs and piezometric map comparisons are used to assess the elevation accuracy. The DEM generated from the topographic map (TopoDEM) resulted in the closest match to the surveyed one with a correlation coefficient of 0.98 and a root mean square error of 0.76. The elevation from SRTM and Google Earth DEMs lead to an underestimation of the piezometry with the poorest performance from Google Earth DEM.