A brief overview is given of the history of geological mapping of theHolocene Rhine-Meuse delta. The first accurate map of the delta, based onfield observations, was made by Vink (1926). The geological map of theNetherlands, scale 1 : 50,000, made by the ‘Geologische Stichting’ (1927 –1938) under the supervision of P. Tesch totally neglected Vink’s work, andwas a step backwards with regard to the mapping of the Holocene delta.Between 1940 and 1965, the Wageningen group of soil scientists produceddetailed regional soil maps, that had a strong ‘geogenetic’ component. Inthe 1960’s a revolutionary ‘profile type legend’ was introduced by theNetherlands’ Geological Survey. This allowed to map not only the outcroppingsediments, but the whole Holocene succession, which gave more insight intothe geological history. Over the past 30 years, the Rhine-Meuse delta hasbeen studied extensively by students of physical geography at UtrechtUniversity. More than 250,000 borehole descriptions, 1500 14Cdates and over 36,000 archeological artifacts with associated ages(collected by the National Service for Archaeological Heritage) haveaccumulated, resulting in the largest database of a delta in the world. Theproduction of detailed maps has been crucial to the solution of manyscientific problems. The use of GIS has greatly enhanced geological andgeomorphological mapping, and subsequently, understanding of the evolutionof the Holocene Rhine-Meuse delta. A new detailed digital elevation map ofthe Netherlands, based on very accurate laser-altimetry data, will enable usto map larger areas in greater detail, with greater accuracy, and in a muchshorter period of time.

We present new local groundwater-level rise data from two Late Glacial aeolian dunes, located near Barendrecht and Oud-Alblas in the western Rhine-Meuse delta. These data are based on AMS radiocarbon dating of terrestrial macrofossils, collected from the base of peat formed on the slopes of these dunes. This method avoids contamination of bulk peat samples by old soil carbon or younger rootlets and rhizomes, as well as the hardwater effect. The new data are used to assess the reliability of previously published groundwater-level index data based on conventional radiocarbon dating of bulk basal peat samples from the slopes of the Late Glacial aeolian dunes at Barendrecht, Hillegersberg, Bolnes and Wijngaarden, all located in the western Rhine-Meuse delta.

Comparison of the new and published groundwater-level data shows no significant systematic difference between conventionally dated bulk peat samples and AMS-dated samples of terrestrial macrofossils. The new data from the dune at Barendrecht confirm the reliability of the younger than 6600 cal yr BP age-depth data from the dunes at Hillegersberg and near Bolnes. This result supports the validity of this part of the mean sea-level (MSL) curve for the western Netherlands. Consequently, the position of the groundwater-level curve for Flevoland (central Netherlands) below this MSL curve can most likely be attributed to differential land-level movement.

The available data show that the groundwater-gradient effect in the western Rhine-Meuse delta became less than 5 cm/km after 6600 cal yr BP. Finally, temporal correlation between temporary increases in local groundwater-level rise with known shifts of river courses in the delta plain suggests, that avulsions can explain sudden local deviations from the trend in groundwater-level rise. A general conclusion of this study is that a complex relationship exists between sea level and local delta-plain water levels.