Silence card 2014/2017 optimistic (m-mv)

The map, based on the helicopter measurements of 2014 and 2017, gives an optimistic estimate of the depth of the sweet and brackish groundwater boundary in metres relative to ground level. Taking into account the uncertainty of the measurements, two versions of the silver map were drawn up: 1. A conservative estimate of the depth of the boundary area assuming a 96 % probability of finding fresh groundwater above this boundary. 2. An optimistic estimate of the depth of the boundary area assuming a 89 % probability of finding fresh groundwater above this boundary. Freshwater means conductivity of less than 2000 µS/cm. It is appropriate to consult both border areas in order to estimate the distribution of freshly brackish water at a given location. In addition, data points are available (‘silver card_2014/2017_helicopter measurements’) to identify where effectively measured and interpolated. The data points are on flight lines where a vertical profile is visible, reflecting salinity, bulk resistivity, lithology and stratigraphy. The boundaries between sweet and vomiting (optimistic and conservative) and between brackish and salt groundwater are visible on the profiles. The limit between brackish and salt groundwater is defined as 25000 µS/cm. Due to construction and other obstacles, certain areas within the coastal and polder area could not be measured. For these areas, the salinage map of 1974 can be traced back.