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.

Over the last decades luminescence dating techniques have been developedthat allow earth scientists to determine the time of deposition ofsediments. In this contribution we review: 1) the development of themethodology; 2) tests of the reliability of luminescence dating onNetherlands’ sediments; and 3) geological applications of the method in theNetherlands. Our review shows that optically stimulated luminescence datingof quartz grains using the single aliquot regenerative dose method yieldsresults in agreement with independent age control for deposits ranging inage from a few years up to 125 ka. Optical dating of quartz has successfullybeen applied to sediments from a wide range of depositional environmentssuch as coastal dunes, cover sands, fluvial channel deposits, colluvialdeposits and fimic soils. These results demonstrate that optical dating is apowerful tool to explore the natural archive of the Netherlands’subsurface.

Application of the traditional lithostratigraphic framework to subdivide theMiddle- and Upper-Quaternary locally-derived fine-grained deposits in theNetherlands is problematic. Deposits of many formations cannot bedistinguished from each other based on lithological characteristics andstratigraphie position alone. To overcome this problem, we present a new,well-defined lithostratigraphy for these deposits, based on detailedresearch in the central part of the Roer Valley Graben. This area containsan up to 35 m-thick sedimentary record of Middle- and Upper-Quaternary sand,loam and peat deposits. These have mainly been formed by aeolian andsmall-scale fluvial processes and have been preserved as a result oftectonic subsidence. The traditional lithostratigraphic subdivision of thesedeposits into three formations (Eindhoven Formation, Asten Formation andTwente Formation) was based on a combination of litho-, bio- andchronostratigraphic evidence and the presumed widespread presence of ahorizon of organic-rich interglacial sediments of Eemian age. To avoidintermingling of criteria regarding lithological characteristics, genesisand age, we now incorporate all fine-grained sediments into the new BoxtelFormation. The implications for the lithostratigraphic framework in otherparts of the country are explored and discussed. Eight lithostratigraphicmembers are introduced that describe the most characteristic parts of theformation. To fully illustrate the sedimentary sequence in the Roer ValleyGraben, two new members are defined here. The Best Member incorporatesalternating floodloam deposits and sandy aeolian deposits in the lower partof the Boxtel Formation. The Liempde Member includes reworked aeolian loessand sandy loess deposits (‘Brabant loam’) that occur in the upper part ofthe sedimentary sequence.

Alluvial architecture has been subject of many studies because of theoccurrence of natural resources in ancient fluvial successions. This paperprovides an overview of the current state of research on alluvialarchitecture with special reference to Holocene fluvio-deltaic settings.Several examples from modern fluvio-deltaic areas, especially the HoloceneRhine-Meuse delta (the Netherlands) and the Lower Mississippi Valley(U.S.A.), are used to illustrate the architectural elements that can bedistinguished in fluvial successions and to show the influence of thevarious controls on alluvial architecture (base level, climate, tectonism,aggradation, avulsion, and compaction). Avulsion is regarded as a principalprocess in the formation of fluvio-deltaic sequences, because it determinesthe location and number of active channels on the floodplain. The avulsionmechanism is still subject of debate, though. A brief description of theevolution of process-based alluvial-architecture models is given. Thesemodels simulate the proportion and distribution of coarse-grained channelbelts in fine-grained overbank deposits. The major drawback of thepresent-day alluvial-architecture models is the lack of (three-dimensional)quantitative field data to test and validate them. The paper concludes withthe suggestion to collect more architectural data from natural fluvialsettings, to improve simulation of channel-belt geometry inalluvial-architecture models, and to implement new data and knowledge offluvial processes into models.

The deposits of the Rhine and the Meuse in the Netherlands alternate intheir delta in a complex way. This paper discusses a method to distinguishthe deposits of the Rhine and the Meuse based on the differences in naturalradioactivity of 40K, 238U and 232Th, andthe effect of the age of the deposits on the radiometrie signal. In total,six channel belts of the Rhine and the Meuse were selected for sampling withan approximate age of about 2000, 4000 and 6000 14C years B.P. Ofeach channel belt 5 samples of different lithology were taken: clay (C),clay leads (CL), sandy clay loam (sCL), sandy loam (sL) and sand (S). Allsamples were analysed on organic matter content, grain size, geochemistryand radioactivity of the radionuclides 40K, 238U and 232Th. The radioactivity of the sample is mainly influenced bythe grain size of the sample. Therefore, this signal is divided in partialradioactivities for three grain size fractions – clay (<16 μm), silt (16– 63 μm) and sand (>63 μm) – to make the radiometric fingerprint, whichis independent of the grain size of the sample. These fingerprints show adifference between the Rhine and the Meuse. Additionally, the radiometricsignal strongly depends on the age of the deposits. Remarkably, this trendwith age is opposite in the deposits of the Rhine and the Meuse and oppositein the clay and silt fraction. Because the radiometrie differences betweenthe samples seem more distinct than the geochemical differences, theradiometric fingerprints are more suitable to distinguish the deposits ofthe Rhine and the Meuse. A method is presented to derive the contribution ofthe Rhine and the Meuse in a deposit of unknown origin, assuming that theradiometric fingerprints found are consistent and valid for the Rhine-Meusedelta. To distinguish the deposits of the Rhine and the Meuse, both thegrain size composition and the age of the deposits have to be known.

The Mema is a semi-arid region in central Mali with a rich archaeologicalheritage indicating the former existence of large urban settlements. Thearchaeological data suggest millennia of occupation history of the Mémapreceding relatively sudden abandonment by the 14th or 15th century AD.Population numbers have remained low since then and today’s human presencein the area is sparse and largely mobile. Geomorphologically, the Méma canbe characterized as a graben hosting various generations of aeolianlandforms and (presently mostly dry) interdunal channels and lakes, linkedto the neighbouring Inland Niger Delta floodplain. Given this setting, andthe variability of the Sahelian climate, climatic contributions to theregion’s sudden abandonment are likely. A geomorphological survey of theregion, and interpretation of the observed geomorphological record in termsof climatic history, aimed at providing a basis for understanding theintensive occupation and subsequent abandonment of the Méma. The results ofthis study underscore dramatic Holocene climatic variability, leading to theregion’s present geomorphological diversity, but also suggest thatneotectonic movements constitute an important additional cause of regionaldesiccation. Both may have encouraged prehistoric people to abandon the Mémaafter a long period of occupation.

The morphodynamics of the lower River Vecht, the Netherlands, and theinfluence of geomorphological setting and bank composition on meandermigration were studied by means of reconstructing the pre-channelizationlandform configuration on a scale of 1 : 25,000, using historical maps from1720, 1850 and 1890 A.D. and other data.

A downstream sequence of reaches was observed, each with a typical fluvialstyle and channel migration rate: (a) a narrow meander belt and a highlysinuous channel with intermediate migration rate, in the middle of anextensive floodbasin; (b) a wide meander belt and high rates of lateralchannel migration, especially where large meanders impinged upon valleybluffs, as part of an incised setting; (c) a low sinuosity, embanked channelwith low rates of downstream migration because of confinement by dikes,occurring in an inland delta with sandy sediments.

Local variation in meander migration rates was observed within reach B. Thiswas caused by the spatial variability of bank resistance as reflected by thewidth-depth ratio of the channel and the silt-clay ratios of deposits. Riverbanks are: 1) very erodible when consisting of channel deposits, aeoliandune deposits or when coarse fluvio-periglacial deposits occur at theirbase; 2) erodible when dominated by overbank deposits or aeolian sand sheetdeposits; 3) resistant when a plaggen-layer is exposed; and 4) veryresistant when dominated by floodbasin deposits.

These implications of meander variability enable to assess the effects ofthe rehabilitation of the meandering process.

At river bifurcations water and sediment is divided among the downstreambranches. Prediction of the sediment transport rate and division thereof atbifurcations is of utmost importance for understanding the evolution of thebifurcates for short-term management purposes and for long-term fluvialplain development. However, measured sediment transports in rivers rarelyshow a uniquely determined relation with hydrodynamic parameters. Commonly ahysteresis is observed of transport rate as a function of discharge or shearstress which cannot be explained with the standard sediment transportpredictor approach. The aim of this paper is to investigate the causes ofhysteresis at a bifurcation of the lower Rhine river, a meandering riverwith stable banks, large dunes during flood, and poorly sorted bed sediment.The hydrodynamics and bed sediment transport were measured in detail duringa discharge wave with a recurrence interval larger than 10 years.Surprisingly, the hysteresis in bedload against discharge was in theopposite direction upstream and downstream of the bifurcation. The upstreamclockwise hysteresis is caused by the lagging development of dunes duringthe flood. The counter-clockwise hysteresis downstream of the bifurcation iscaused by a combination of processes in addition to dune lagging, namely 1)formation of a scour zone upstream of the bifurcation, causing a migratingfine sediment wave, and 2) vertical bed sorting of the bed sediment by duneswith avalanching lee-sides, together leading to surface-sediment fining andincreased transport during and after the flood. These findings lead tochallenges for future morphological models, particularly for bifurcations,which will have to deal with varying discharge, sediment sorting in thechannel bed, lagging dunes and related hydraulic roughness.

In mesotidal settings the transition of a coastal plain estuary to the riveris marked by the change of a multiple ebb and flood channel configuration toa single channel system. At high river discharge fluvial processes operate,whereas in periods of low discharge the flow is complicated by a tidalcomponent and a landward intrusion of the salt wedge. These hydraulic andmorphological characteristics make the transitional zone different from the‘pure’ fluvial and estuarine environment. Inspection of published andunpublished data from a number of outcrops of Recent and Tertiary depositsof the Rhine reveals that also in a sedimentary sense a transitional zonecan be recognized. In order to separate this zone from the upstream fluvialand downstream estuarine environment a sedimentological definition of thefluvial-tidal zone is proposed being the part of river that lies between thelandward limit of observable effects of tidal-induced flow deceleration onfluvial cross-bedding at low river discharge and the most seaward occurrenceof a textural or structural fluvial signature related to the high riverstage.

A combination of geological and anthropogenic processes have rendered theU.S. Gulf Coast in general – and the Mississippi Delta in particular –extremely sensitive to coastal hazard. Thus, the Katrina disaster was not aquestion of ‘if’ but of ‘when’. This contribution outlines thegeo-environmental context of the Mississippi Delta that evolved during the20th century and set the stage for Hurricane Katrina’s devastation. Thisincludes a brief discussion of the processes responsible for coastal erosionand wetland loss, the proposed measures to combat these problems, and thepolicy decisions (or, rather, the lack thereof) made so far. A connection ismade with the 1953 storm surge that devastated the southwestern Netherlandsand had a profound impact on Dutch science and engineering by providing theimpetus for the widely known and highly praised Delta Plan, as well as forunprecedented studies of Holocene sea-level change. Whether a similar routewill be followed for the Gulf Coast is primarily dependent on the amount ofpolitical will. Results are presented of recent studies of crustal movementsin the Mississippi Delta that show surprising long-term stability of thePleistocene basement, evidence that could prove critical for decision makerswith regard to the rebuilding process. Finally, the neglect of theprecarious situation along the Gulf Coast by the federal government isviewed as a possible metaphor for current U.S. policies with respect toscience in general, and to global warming in particular.