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Kim M. Cohen
photo portrait Kim Cohen

Kim M. Cohen PhD

visiting scholar 2003-2004

from January 2005 at:
Department of Physical Geography
Utrecht University
PO Box 80.115
3508 TC Utrecht
The Netherlands

e-mail: k.cohen@geo.uu.nl
Phone: +31 30 253 5774
Fax: +31 30 253 1145

Kim Cohen Utrecht University personal page | Kim Cohen Utrecht University staff page

Kim was in the QPG/Godwin Institute as a visiting scholar to work towards a global database on fluvial activity in the Late Glacial and Holocene. The project was funded by the Max Planck Institute for Biogeochemistry (BGC-Jena), research group Palaeoclimatology (Jena, Germany). It was part of BGC-Jena's Past Climate Sensitivity and Variability project within the German Climate Research Programme ( DEKLIM , research area Palaeoclimate Research ) and associated to the Palaeoclimate Modeling Intercomparison Project ( PMIP ). Kim has a special interest in storing and analysing Quaternary geological data (e.g. the geometrical architecture of deposits and its sedimentary properties including dating results) in computer environments (application of GIS, geostatistical and database techniques) and the linkage of architectural frameworks to chronological frameworks at drainage basin scales.

Contents

Activities

Global database of Fluvial activity in Last Glacial and Holocene

Background

Ultimately, the projects that Kim works for want to create datasets that summarise global field-evidence for Global Climate Model (GCM) evaluation purposes. The goal of his project is to make records of former river activity (as reflected by geometry, sedimentary characteristics of fluvial deposits) available for this purpose. This initiative is similar and complementary to other global datasets developed by this group, on vegetation and lake status. Within the PMIP project (focusing on 21 ka and 6 ka BP timeframes) such databases have proven extremely useful in evaluating and inter-comparing GCM simulation results.
In this first year, focus is on the development of a database that has both a bibliographical component, a site-data component and a pathway component for 21 ka BP, covering Eurasia.
Rivers / fresh water discharge / lakes are not modeled within GCM's. The outcomes of GCM's (rainfall, evaporation) may be translated into discharges, by feeding them to algorithms that model the hydrological system (e.g. HYDRA ). Such algorithms route and aggregate discharge through drainage basins along drainage networks. The project needs to provide a way of validation of such discharge simulations. A database will be created, based on available palaeogeographic reconstructions of pathways and on documented geometries of palaeo-rivers to assess palaeo-discharge. Ultimately, quantitative reconstructions of palaeo-discharges are wanted, but these are not directly (sic) recorded in a sedimentary record. Therefore, the database will store those properties that allow estimating palaeo-discharge. Furthermore, properties related to age-control and full bibliographic references will be stored. Lastly, the database-design needs to deal with sites within drainage basins that themselves vary in extent for each time-frame due to global sea-level variations.

Illustration showing position of dates in sedimentary sequence Fig. 1: Typical field data
Kim's job is to test/proof the feasibility of this ambitious concept, by designing a prototype continental drainage database, and filling it with information on selected rivers in Europe. In practice, this means identifying locations along river valleys for which width, thickness, valley gradient and channel type of subsequent depositional units are documented (Fig. 1 ). This information needs to be stored in a database format that allows assessing the stratigraphic ordinal relations (e.g. Unit A was followed by Unit D in time, Unit X is the downstream continuation of Unit Y). The database further needs to store the unit's age estimates (including the reasoning behind the age estimate) and references to the original sources of the various bits of information that together make up the database-records (Fig. 2 ).

Illustration showing the steps from sedimentary sequence mapping to paleodischarge estimation Fig. 2: Palaeo-discharge reconstruction


This way, one can systematically generate constraining estimates (minimum, maximum) for representative palaeo-discharge peaks ('channel forming' discharge, 'bankfull' discharge). Furthermore, parameters ranking their temporal relevance can be generated, i.e. the accuracy of a discharge estimate (based on a geometry that developed over a period of time, e.g. 21-15 ka BP) can be assessed for a specific moment in time (e.g. at 21 ka BP: the timeframe for which the palaeo-climate is simulated by a suite of GCM's). When this is done, one can start comparing GCM-simulated discharges to peak-discharge constraining field-evidence, and thereby evaluate model performance (Fig. 3 ).
All of this is needed to deliver a proof of concept to the modelling community, i.e. to show that rivers provide a clear enough signal to constrain models (and to convince the community to continue activities in the line of this project).

Illustration showing the parallel aproaches of model and field-based reconstruction allowing intercomparisson Fig. 3: Field - model intercomparisson

Project activities in 2003-2004

A database prototype was set up and filled with data on the middle and lower reaches of the rivers Meuse and Rhine. These rivers were used as a familiar starting point when designing the initial prototype for the database. We expanded this with surrounding rivers with comparably-sized drainage basins, thereby covering NW Europe (Rhine, Meuse, Loire, Rhône, Seine, Weser). Palaeodischarge estimates (modal peak discharges) for these rivers were produced for the LGM and Late Glacial.
The database in principle allows for systematic evaluation of climate model output versus field-evidence for selected time frames over continental scales. The approach also is a strong test of the internal consistency of local fluvial reconstructions over larger stretches of river.
A project report has been produced and delivered to co-workers within the bigger climate model evaluation projects. It is expected to become online-on-request via PMIP's site in the near future. We are currently (January 2005) still deciding on how to continue this project.
Kim keeps looking for more locations along the middle-lower valley reaches of major European rivers, for which the following parameters can be aggregated:
1. The number of geomorphological/geological channel units
that are generally identified within a middle-lower valley reach of the river, spanning the last 50.000 years. Usually there are 3-6 identified units, e.g. "Pleniglacial river bed/terrace", "Tardiglacial river bed/terrace", Early-Middle Holocene river bed, Modern (historic) river.
2. For each of these units, we need estimates of
o Channel bed (terrace) palaeo-width [ e.g. 6.5 – 6.8 km ]
 o Channel bed (terrace-deposit) thickness [ e.g. 4 – 5 m ]
 o Channel bed longitudinal slope (valley-gradient) [ e.g. 0.28-0.33 m/km ]
 o Channel type [ e.g. 'braided' ]
Surely, site specific studies on palaeo-hydrology use much more detailed information,
but for a prototype-database aiming at continental scale coverage, the above are the essentials.
3. For each of these units, we need estimates of
o The age of abandonment of this deposit
o The duration of formation of the deposit
o The reasoning behind the age of the deposits [ e.g. direct dating, stratigraphic correlation, morphological analogue ]
4. Bibliographic references to the original data-sources on which this record is based.

Publications

This webpage serves as a project outline summary. The results of the pilot-project described above are further document in:

Cohen, K.M. (2004) Global Continental Drainage project report: A database on field records of rivers of the last 50 ka, for palaeo-discharge estimation and GCM intercomparison. Palaeoclimatology group, Max Planck Institute for Biogeochemistry, Jena, Germany / PMIP-2 Paleoclimate Modelling Intercomparison Project Phase II / DEKLIM project Past Climate Sensitivity and Variability Project. 86 pp.

The project as such was not actively continued.
Elements of the proposed approach have found continuation in the setup of a database for the Lower Rhine system:

Cohen, K.M., Wallinga, J., Busschers, F.S., Hoek, W.Z., Kasse, C., Jones, A., Rhodes, E., Macklin, M.G., Benito, G. (2009) Regional database of Lower Rhine OSL dates in sedimentary context: Can we unravel preservation and sampling bias from climatic depositional overprints? 27th Meeting of the International Association of Sedimentologists, Alghero, Sardinia, Italy. Oral presentation.

1999-2003 work in the Rhine-Meuse delta (the Netherlands)

GIS-based palaeoenvironmental reconstruction

From 1998 on Kim worked on the late Quaternary of the Rhine-Meuse delta (the Netherlands) at the Physical Geography department of Utrecht University. From 1998-2001, he worked with colleages Berendsen & Stouthamer, to implement their palaeo-geographic reconstruction of Holocene distributary channel belts in a GIS. This GIS was then used to cross-check the reconstruction and to produce a geological map and a series of 16 palaeo-geographical maps of the Rhine-Meuse delta , published as poster-sized coloured maps by Berendsen & Stouthamer (2001, Add. 1 & 2).

Since 2000 the GIS database has proved to be useful in many projects by third parties (e.g. to produce indicative maps of archeological value and in prospecting studies for new railways and highways). Kim has continued to manage this GIS at the Utrecht department of Physical Geography during his time as a PhD student (1999-2003).

Snapshots from the Rhine-Meuse delta GIS

Rhine-Meuse delta Holocene geological channel belt map
Rhine Meuse delta Holocene animated channel belt palaeogeography
Geological - geomorphological map (fragment) Palaeogeographic maps (same area)
Holocene delta distributaries colored by their age of abandonment. Result of GIS implementation of reconstruction by Berendsen & Stouthamer (2000, 2001).
Depicted are 5 out of 16 maps that were created using the same GIS-data as were used for the map to the left. Timeframes shown: 10,000 - 7,000 - 6,500 - 6,000 - 5,500 ka BP (14C ages)
Green: 7-4 ka BP. Yellow: 4-2 ka BP. Red: 2 ka BP-present (all 14C ages)
Orange: active channel belts. Green: abandoned channel belts
Lighter tones: later eroded/reworked parts. Darker tones: preserved parts.
(c) Berendsen & Stouthamer 2000, 2001 ; Rhine-Meuse Delta Studies, Dept. of Physical Geography, Utrecht University.
Post-processing by KartLab Map and Cartography services ;
Faculty of Geosciences , Utrecht University.

Quantifying Late-glacial - Holocene differential subsidence

In his PhD project "Neotectonics in the central Netherlands fluvial district", Kim used the fluvial sedimentary record of the last 15,000 years to quantify subsidence in the central Netherlands (Roer Valley Graben, Peel Boundary Faultzone). The project was carried out at the dept. of Physical Geography, Utrecht University and was supported by a NWO-ALW grant. Daily supervisor and co-promotor was dr. H.J.A. Berendsen, Promotors were Prof. dr. E.A. Koster and Prof. dr. S.A.P.L. Cloetingh (VU Amsterdam). The resultant thesis has a full-colour map of the central Rhine-Meuse delta and a cross-section covering all Rhine and Meuse channel belts since the last glacial maximum. These maps were created using the earlier developed GIS and provide a partial update of the larger maps published in 2001.
Although the geological/geomorphological evolution of the Rhine-Meuse system since the Last Glacial Maximum (~21 ka BP) are known in great detail, the effects of neotectonics in the Rhine-Meuse delta had only been recognised recently. The PhD-research brought new evidence on the spatially and temporally non-linear rates of differential subsidence in the central Netherlands. Late-Glacial- and Holocene-active faults were identified and mapped from the fluvial deposits. Deformation was quantified from deformations of gradient lines, in two ways: (1) by analysing longitudinal profiles of abandoned channel belts and (2) by geostatistically reconstructed palaeo-groundwater surfaces from basal-peat radiocarbon dates. Syn-depositional effects of active differential subsidence to active fluvio-deltaic deposition were identified, and were used to further constrain differential subsidence in time and space. The thesis' results strongly support a forebulge hypothesis: the Late-Glacial – Holocene Rhine-Meuse delta appears to be located on the southern flank of a collapsing Weichselian forebulge in the North Sea basin, related to Scandinavian and British ice-sheets.

Central Rhine-Meuse delta: detailed mapping of alluvial architecture

The cross-section below is based on boreholes (fieldwork 1999-2001 and archived descriptions dd. 1980-1998), geomorphological mapping and radiocarbon dating. The fragment on this webpage shows ~12 km. Full section is ~22 km long and spans the full width of the Saalian-Weichselian palaeovalley and onlapping Holocene delta-plain. Note incised level of Late Weichselian and early Holocene age and overlying aggrading level of middle-late Holocene deltaic aggradation. This section is upstream of the present Rhine-Meuse confluence, and approximately at the Rhine-Meuse confluence during the Last Glacial Maximum 21,000 year BP ago. The S-N section covers the polder in between the present delta-distributaries river Maas (Meuse, South = left) and river Waal (a Rhine branch, North = right). The Waal channel carries 2/3 of the Rhine discharge (i.e. 2/3 of ~2200 cumecs Mean Annual Flow, 2/3 of up to 15,000 cumecs during extreme discharge peaks).
crosssection Rhine Meuse delta LGM Rhine-Meuse confluence

Fragment of Addendum 2 to Ph.D.-thesis (c) Cohen, 2003 . A full version is for download via Utrecht University library (as a PDF) .

Cross-section legend

icon of pdf document
full description in Cohen, 2003 : Ch. 5		 brown:
 Floodbasin peats, gyttjas and strongly humic clays of Holocene age: Distal floodbasins and residual channels
pink:
 Eolian sand of latest Weichselian Lateglacial age: Younger Dryas inland source-bordering dunes.
 green : Fluvial clays of Holocene age: Distal floodbasins, distal crevasse-splays .
purple:
Clays with admixed sand of Weichselian Lateglacial and early Holocene age: Floodplain overbank areas .
 green-
yellow:
Fluvial sandy and silty clays of Holocene age: Proximal floodbasin levees, crevasse-channels and -splays .
reddish-
orange:		 Gravels and gravelly sands of Weichselian Pleniglacial and Lateglacial age: Burried terraces and incised channel belts.
 yellow:
Fluvial sands of Holocene age: Channel belts of Meuse (left) and Rhine (right) .

Publications

Selected publications related to the 1999-2003 work described above:

Berendsen & Stouthamer (2001) Palaeogeographic development of the Rhine-Meuse delta, The Netherlands. Assen: Van Gorcum 268 pp + addendums. ISBN: 90 232 369 5. Containing:Berendsen, H.J.A., K.M. Cohen, E. Stouthamer (2001) Maps and cross-sections. p. 49-55.

Berendsen, H.J.A, K.M. Cohen & E. Stouthamer (2007). The use of GIS in reconstructing the Holocene paleogeography of the Rhine-Meuse delta, The Netherlands. Int. J. of GIS, 21, 589-602.

Cohen, K.M. (2003) Differential subsidence within a coastal prism. PhD-thesis. Dept. Physical Geography, Utrecht University. Published as: Netherlands Geographical Studies 316 176 pp. ISSN: 0169-4839.

Cohen, K.M. (2005) 3D geostatistical interpolation and geological interpretation of palaeo-groundwater rise within a Holocene coastal prism. In: L. Giosan, J.P. Bhattacharya (eds). River Deltas - Concepts, models, and examples. SEPM Special Publication 83, p. 341-364.

Cohen, K.M., E. Stouthamer, H.J.A. Berendsen (2002) Fluvial deposits as a record for neotectonic activity in the Rhine-Meuse delta, the Netherlands. Geologie & Mijnbouw / Netherlands Journal of Geosciences 81 (3-4), 389-405.

Cohen, K.M., M.J.P. Gouw, J.P. Holten (2005) Fluvio-deltaic floodbasin deposits recording differential subsidence within a coastal prism (central Rhine-Meuse delta, the Netherlands). Chapter 11 in: Blum, M.D., S.B. Marriott & S.F. Leclair, eds. (2003), Fluvial Sedimentology VII. Special Publication 35, International Association of Sedimentologists. Blackwell Scientific.

Current activities (2005 - present)

An up to date overview of activities (2005-2008: Post doc; 2009 - present: Assistant Professor Utrecht University)

See Kim Cohen - Utrecht University and Kim Cohen - Utrecht University for current projects.

Miscellaneous

Allier hydrograph at Moulins
Discharge data of the river Allier at Moulins (central France) related to M.Sc.-thesis (1998, Physical Geography, Utrecht University). MS-Excel graph, created in 1998 for Antoine Wilbers.