The size, shape and spatial position of lithofacies types (or facies architecture) in a tidal estuarine basin are complex and therefore difficult to model. The tidal currents in the basin concentrate sand-sized sediment in a branching pattern of tidal channels and fringing tidal flats. Away from the sandy tidal flats the sediment gradually changes to mud-dominated heterolithic deposits and clay. In this paper the facies analysis of a tidal estuarine basin, the Holocene Holland Tidal Basin (HHTB) is presented based on core data and Cone Penetration Tests (CPT). Four lithofacies associations are recognized: (1) tidal channel sand, (2) sand-dominated heterolithic inter-tidal flat, (3) mud-dominated heterolithic inter-channel and (4) fresh-water peat. The high data density allowed for the construction of a detailed facies architecture model in which the size, shape and spatial position of the tidal estuarine facies elements were established. The results can be used to improve the reservoir modelling in highly heterogeneous estuarine reservoir settings.

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.

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.

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.

Object-based stochastic modelling techniques are routinely employed to generate multiple realisations of the spatial distribution of sediment properties in settings where data density is insufficient to construct a unique deterministic facies architecture model. Challenge is to limit the wide range of possible outcomes of the stochastic model. Ideally, this is done by direct validation with the ‘real-world’ sediment distribution. In a reservoir setting this is impossible because of the limited data density in the wide-spaced wells. In this paper this uncertainty is overcome by using size, shape and facies distributions of tidal channel and tidal flat sand bodies in a highly data-constrained lithofacies architecture model as input for the object-based stochastic model. The lithofacies architecture model was constructed from a densely perforated (Cone Penetration Tests and cored boreholes) tidal estuarine succession of the Holocene Holland Tidal Basin in the Netherlands. The sensitivity of the stochastic model to the input parameters was analysed with the use of varying tidal channel width and thickness values and calculating the connected sand volume per well for the different scenarios. The results indicated that for a small well drainage radius the difference in drainable volumes between the narrowest and the widest channel scenarios is large, and that for a large well drainage radius the tidal channel width hardly influenced the drainable volume. The sensitivity analysis highlighted the importance of sand-dominated tidal flats in improving lateral connectivity.

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.