Groundwatertools

Abstract

TNO Geological Survey of the Netherlands makes groundwater information available on https://www.grondwatertools.nl/grondwatertools-viewer in addition to the measured heads at https://www.dinoloket.nl/ondergrondgegevens: (1) piezometric contours and (2) time series models with precipitation and evaporation as explanatory variables. Head time series implicitly contain information about the groundwater system. This information is reflected in response of the head to precipitation. The database with ±34000 acceptable time series models throughout the Netherlands may serve many purposes. Examples are: –– Spatial patterns (1) of heads as indication of groundwater flow directions and (2) of precipitation response quantity and response time which gives information of the aquifer system, e.g. the presence of a confining layer or aquitard; –– Improvement of bad time series models using spatial correlation of the precipitation response between neighboring monitoring wells; –– Detection of changes over time (in groundwater heads only or also the groundwater system); this can be done by e.g. (1) evaluating trends in the residuals (difference between measurements and model predictions – indicative for influences not in the time series model), (2) comparing models of different periods, (3) estimating a trend as explanatory variable in the time series model; –– Determination of status: the percentile of the actual groundwater head with respect to a standardized period and frequency. The time series models allow to fill gaps or extend measurement series so calculated percentiles are comparable. The time series models and piezometric contouring of http://www.grondwatertools.nl offer valuable 4D information for management and research on groundwater heads in the Netherlands.