A detailed reconstruction of the alluvial architecture of the Coevorden gas Field (Tubbergen Formation, Upper Carboniferous), which is located in the northeastern part of the Netherlands, is presented. This reconstruction is based on well logs, cross-sections and paleogeographic maps. Sedimentological analysis of a 93 m long core allowed to refine the interpretation of the depositional environment. Accurate width determinations are necessary to correctly correlate fluvial sandbodies and reconstruct alluvial architecture. Without using sedimentological information, sandbody width is likely to be overestimated. A method developed by Bridge and Tye (2000) was used to calculate the width of one sandstone body from cross-set thicknesses. On the basis of this calculation and the paleogeographic reconstructions, it may be stated that on average the width of the channel belts we studied in the Coevorden field does not exceed 4 km. Moreover, our paleogeographic reconstructions, which point to a northwestern direction of paleoflow, are in accordance with earlier observations from the study area. The Tubbergen Formation and time-equivalent sediments in Germany are reviewed briefly to put the Coevorden Field in a regional context. The thickness of the Tubbergen Formation is ∼450 m in our study area. In the adjacent German area, time-equivalent sedimentary sequences reach higher thicknesses. This may be attributed to tectonic movements along the Gronau Fault zone and the coming into existence of the Ems Low, of which the Coevorden Field is the westernmost part.

Over the past 80 years, the Rhine-Meuse delta has been mapped extensively by drilling boreholes. These maps are compared with a new detailed digital elevation map of the Netherlands (AHN) that became available in 2004 and is based on very accurate, (sub-decimeter) laser-altimetry data. Examples show, that existing maps can be significantly improved. However, field checks remain a necessity. Therefore, the AHN-data need to be confronted with existing borehole descriptions using a GIS. Geomorphological analysis and geological interpretation of surface elevation patterns now enable us to map larger areas, in greater detail, with greater accuracy, and much faster. It is argued that detailed (≥1 : 50,000) geological mapping of the Netherlands should be resumed, combining the databases of Utrecht University, the National Geological Survey and Alterra.

The Holocene Rhine-Meuse delta is formed under the influence of sea-level rise, tectonics, and variations in discharge and sediment supply. This paper aims to determine the relative importance of these external controls to improve our understanding of the evolution of the Rhine-Meuse fluvio-deltaic system. To do this, the geological and lithological composition of the fluvio-deltaic wedge has to be known in detail, both in space and time. This study presents five cross-valley sections in the Holocene Rhine-Meuse delta, based on almost 2000 shallow borings. Over 130 14C dates provide detailed time control and are used to draw time lines in the sections. Distinct spatio-temporal trends in the composition of the Holocene fluvio-deltaic wedge were found. In the upstream delta, the Holocene succession is characterised by stacked channel belts encased in clastic flood basin deposits through which several palaeo-A-horizon levels are traceable. In a downstream direction, the fluvio-deltaic wedge thickens from 3 to 7 m. The Holocene succession in the downstream cross sections formed from <8000 cal yr BP onwards and is characterised by single channel belts encased in organic flood basin deposits. The main part of the organic beds accumulated between 6000 and 3000 cal yr BP. After 3000 cal yr BP, clastic deposition dominated throughout the delta, indicating an increase in the area of clastic sedimentation. The Holocene fluvio-deltaic wedge is subdivided into three segments based on the relative importance of eustatic sea-level rise, subsidence, and upstream controls (discharge and sediment supply). Before 5000 cal yr BP, eustatic sea-level rise controlled the build-up of the wedge. After eustatic sea-level rise ceased, subsidence was dominant from 5000 to 3000 cal yr BP. From 3000 cal yr BP onwards, increased sediment supply and discharge from the hinterland controlled the formation of the fluvio-deltaic wedge. A significant part of the present-day Rhine-Meuse fluvio-deltaic wedge aggraded after eustatic sea-level rise ceased. We therefore conclude that external controls other than eustatic sea-level rise were also of major importance for the formation of the fluvio-deltaic wedge. Because this is probably true for other aggrading fluvial systems at continental margins as well, all external controls should be addressed to when interpreting (ancient) fluvio-deltaic successions.

Management of the Dutch embanked floodplains is of crucial interest in the light of a likely increase of extreme floods. One of the issues is a gradual decrease of floodwater accommodation space as a result of overbank deposition of mud and sand during floods. To address this issue, sediment deposits of an undisturbed embanked floodplain near Winssen along the river Waal were studied using ground-penetrating radar (GPR). A number of radar facies units were recognized. Boreholes were used to relate radar facies units to sedimentary facies and to determine radar velocity. The GPR groundwave is affected by differences in moisture and texture of the top layer and probably interferes with the first subsurface reflector. The architectural elements recognized in the GPR transects confirm earlier reported insights on human-influenced river behaviour. This is testified in the development of sand bars during flood regimes that are probably more widespread than previously established.

Floodplain topography and related hydraulic patterns of overbank flow constitute a major control on the amounts and patterns of sediment deposition on floodplains. We studied the differences in sediment deposition at two scales along two river branches of the lower River Rhine in the Netherlands: the Waal and IJssel River. Human alterations like levelling and embankment construction have severely impacted the floodplains along the Waal River branch (average discharge: 1500 m3·s‒1), whereas the relatively wide floodplains along the IJssel River (average discharge: 250 m3·s‒1) still exhibit their characteristic ridge-and-swale topography and natural levees. We found that, in general, the amounts of sediment deposited sediment decreases with increasing distance to the sediment source. Clay and organic matter content generally increase with decreasing floodplain elevation. These trends are, however, far less pronounced in the Waal River floodplains than in the IJssel River floodplains. Sediment deposited on the IJssel River floodplains also contains significantly more sand than the sediment deposited on the Waal River floodplains, probably because of the absence of minor embankments along the IJssel River and its higher sinuosity. Furthermore, during inundation the individual Waal River floodplains receive more sediment per unit area than the IJssel River floodplains. At the scale of the river branch, however, the conveyance losses in the Waal River are less than in the IJssel River, because of the larger surface area of the floodplains along the IJssel River relative to its water and sediment discharge during flood events. This discrepancy stresses that both the individual floodplain sections and the total river branch should be taken into account when studying the role of overbank deposition as part of a river’s sediment budget.

Shortly after the river Rhine enters the Netherlands, it bifurcates into three branches. A predefined, fixed discharge distribution over the bifurcation points is vital, since the dikes are designed with a predefined distribution in mind. Recent observations show that the discharge distribution that is anticipated at design discharge conditions differs from the predefined one. One of the goals of the national program Room for the River is therefore to restore the discharge distribution. To control the hydraulic processes during flood events, the construction of two adaptable spillways in the direct neighbourhood of the bifurcation points is proposed as a possible solution. The spillways are capable of maintaining the proper discharge distribution. They can also act as regulators during the construction phase of the flood managements plans of the project Room for the River. Hence, the discharge ratio and thus the water levels are such that the safety-standards are not violated. The morphological consequences are most probably very small, provided that strong erosion during flood events can be prevented and the autonomous bed degradation stays within reasonable limits.