Quantitative Characterisation of Wellhead Coordinate Error in Alluvial Basins

A key step in tightening the basin reference frame is understanding how surveyed wellhead coordinate error propagates into the resulting root-mean-square tracer residuals. When the physical coordinates of a monitoring well are misplaced, the aquifer's diurnal and seasonal head response relative to the datum introduces a mis-calculated transit lag (Δt_lag), which shows up as a pre-fit signal in the flow model. Our field simulations show the tight coupling between positional accuracy and lag accuracy across four instrumented alluvial wells.