Physical Geography of North-Eastern Belgium - the Boom Clay Outcrop and Subcrop Zone

EXTERNAL REPORT SCK•CEN-ER-202 12/Kbe/P-2

Physical geography of north-eastern Belgium - the Boom Clay outcrop and subcrop zone

Koen Beerten and Bertrand Leterme

SCK•CEN Contract: CO-90-08-2214-00 NIRAS/ONDRAF contract: CCHO 2009- 0940000 Research Plan Geosynthesis

November, 2012

SCK•CEN PAS Boeretang 200 BE-2400 Mol Belgium

EXTERNAL REPORT OF THE BELGIAN NUCLEAR RESEARCH CENTRE SCK•CEN-ER-202 12/Kbe/P-2

Physical geography of north-eastern Belgium - the Boom Clay outcrop and subcrop zone

Koen Beerten and Bertrand Leterme

SCK•CEN Contract: CO-90-08-2214-00 NIRAS/ONDRAF contract: CCHO 2009- 0940000 Research Plan Geosynthesis

January, 2012 Status: Unclassified ISSN 1782-2335

SCK•CEN Boeretang 200 BE-2400 Mol Belgium

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Abstract The Boom Clay and Ypresian clays are considered in Belgium as potential host rocks for geological disposal of high-level and/or long-lived radioactive waste. A good description and understanding of the relationship between surface variables, as there are the geomorphology, hydrography, vegetation, soils, land-use and hydrology, is needed to evaluate the past evolution and assess the future evolution of the surface environment. Changing climatic conditions (glacials and interglacials), global sea-level variations and tectonic movements (uplift and subsidence) may cause the surface environment to change profoundly during the next 1 Ma. In this report we describe the characteristics of the surface environment of the Boom Clay outcrop and subcrop zone. Starting from the present status, the palaeogeographical and palaeohydrological evolution of the Campine area is described in the framework of the Quaternary geological history of the area. Finally, an overview of possible future conditions of the surface environment is given, based on the integration of the palaeorecord and available modeling studies.

Table of Contents Abstract ...... 5 1 Introduction ...... 7 2 General geographical characteristics ...... 8 3 Geomorphology and orohydrography ...... 10 4 Soil associations, land cover and vegetation ...... 12 5 Climate and meteorology ...... 14 6 Hydrology ...... 19 6.1 Flanders ...... 19 6.2 Nete catchment ...... 21 7 Quaternary landscape development and evolution ...... 23 7.1 Introduction ...... 23 7.2 Climatic evolution ...... 24 7.2.1 Global climate evolution during the Quaternary ...... 24 7.2.2 Permafrost conditions in NW-Europe ...... 27 7.3 Quaternary tectonic evolution of NE-Belgium ...... 28 7.4 Quaternary geological and geomorphological development ...... 32 7.4.1 General ...... 32 7.4.2 The Flemish Valley ...... 36 7.4.3 River terraces and burial history ...... 38 8 Future evolution ...... 39 8.1 Timeframe 0-10 ka AP ...... 40 8.1.1 Global warming without marine transgression ...... 40 8.1.2 Global warming with marine transgression ...... 42 8.2 Timeframe 10-50 ka AP ...... 45 8.3 Timeframe 50-170 ka AP ...... 46 8.4 Timeframe 170-400 ka AP ...... 46 8.5 Timeframe 400 ka to 1 Ma AP ...... 47 9 Integration of the present status, and past and future evolution of the surface environment in the Campine area ...... 49 10 References ...... 53

1 Introduction High-level and long-lived radioactive waste (B&C waste) is a major radiological hazard to man and environment. ONDRAF/NIRAS, the Belgian agency for radwaste management entitled to find a solution for this problem, currently investigates the safety and feasibility of geological disposal in poorly indurated plastic clays such as the Boom Clay and Ypresian clays. The Boom Clay is a thick and relatively homogeneous clay layer that is found in the outcrop and subcrop of a large part of north-eastern Belgium. Its thickness varies between several tens (outcrop) to more than 100 m (subcrop) while its top reaches depths of up to 200 m and more in the Campine area. The Geosynthesis project launched by ONDRAF/NIRAS in 2009 aims at bringing together all 'geological' data that demonstrate and underpin the safety and feasibility of geological disposal of category B&C waste in Boom Clay. Geological data include the geology of north-eastern Belgium, the geology of the Boom Clay, its relevant properties, the regional hydrogeological system, and the geography of north-eastern Belgium. The scope of the Geosynthesis report covers the entire Boom Clay outcrop and subcrop zone, which roughly speaking coincides with an area tentatively denoted northeastern Belgium, and/or the Campine region

The earth's surface is a complex interface where atmosphere, hydrosphere, geosphere and biosphere processes interfere. In the framework of safety studies for nuclear waste disposal, the upper boundary condition governs the infiltration of precipitation (recharge) that will eventually reach deep repositories in geological layers. Similarly, discharge of groundwater eventually proceeds through soil layers into the surface environment including lakes, rivers and seepage zones. The earth's surface is also the place where biosphere receptors live and interfere with the hydrosphere and geosphere. It is clear that a solid and reliable safety analysis needs to consider aspects of the surface environment, here grouped under the name 'physical geography'. On the long-term, the surface environment will undergo important changes. With respect to a geological waste repository, the potential impact of the changing environment on the safety of such a repository should be considered. During the timeframe considered in the Geosynthesis project (up to one million years), the climate will change, as will the vegetation, soils, topography and hydrology. In this paper, the physical geography of the Boom Clay outcrop and subcrop zone in north-eastern Belgium is described in the light of the palaeogeographical and palaeohydrological evolution of the area and an assessment of the future evolution of the earth surface environment is presented.

2 General geographical characteristics The Campine region in northern Belgium covers about 4000 km², and is situated between the alluvial plain of the Upper Scheldt river in the west, the Meuse valley in the east and the Dijle – Demer river valleys in the south. It is a relatively flat and open area with sandy soils covering large parts of the Antwerp and Limburg provinces in Belgium and extending into the province of Northern-Brabant in the Netherlands. Within the framework of SFC1, the entire Boom Clay outcrop and subcrop zone is considered for geological disposal. Boom Clay is present in four Flemish provinces (Figure 1): the entire province of Antwerp, the northern part of the province of Limburg, and a small part of the provinces of Vlaams-Brabant and Oost- Vlaanderen. The outcrop, subcrop, thickness and depth characteristics of the clay are given elsewhere (De Craen et al., 2012a). Around 1/4th of the Belgian population is living in the area where Boom Clay is found at or below the surface, i.e. ~ 2.5 million people. Most of them (~ 1.7 million) are inhabitants of the province of Antwerp. The four largest cities within the investigation area are Antwerp (~ 483.000 inhabitants), Hasselt (~ 73.000 inhabitants), Sint-Niklaas (~ 72.000 inhabitants) and Genk (~ 65.000 inhabitants). Other cities, such as Lier, Turnhout, Herentals, Geel and Maaseik have less than 50.000 inhabitants. The Antwerp agglomeration is densely populated with peak densities of more than 3000 inhabitants per km² while this number drops down to 100-200 for several municipalities in northern Limburg. Within a distance of less than 50 km from the Boom Clay areal extent on Belgian territory, important agglomerations include those of Brussel (Brussels) and Gent (Ghent) in Belgium, and Eindhoven and Maastricht in the Netherlands (source: www.statbel.fgov.be/, consulted in January 2012).

The seaport of Antwerp has major infrastructure and houses a large variety of industries (see Denis, 1992). Important waterways to the hinterland include the Albertkanaal (to Liège) and the river Scheldt. Motorways connect Antwerp with the Netherlands (A12, E34 and E19), Brussels (E19), Ghent (E17) and Liège (E313). The E314 connects the Meuse Valley with the Leuven-Brussels area. Railway infrastructure is comparatively less well developed and is mostly of local significance. There is, however, a high-speed train connection between Brussels, Antwerp and the Netherlands. The small Deurne Airport near Antwerp serves several international destinations.

Major industrial activities can be found in Antwerp (seaport and chemical industry), Genk (Ford factory) and along the axis of the Albertkanaal and the E313 (e.g., chemical industry). Natural resources are found in the area, such as groundwater, coal, mine gas, clay and quartz sand (De Craen et al., 2012b). The amount of people working in (public) services is generally less than 50%, except in the agglomeration of Antwerp.

Given the relatively sandy soils (see below), agricultural activities are less important compared to other regions in Flanders (e.g., Haspengouw, polders, etc.). Arable land is scarce with maize being the most important crop. Grassland (meadows) can be found in all parts of the investigation area for cattle grazing. Some cultivation under glass can be found in the southeast of the province of Antwerp.

The Campine area (Kempen) is considered as an important touristic region with many natural reserves aiming at the preservation of natural and cultural landscapes, woodland, heathland

9 etc. In the Mol region many small lakes (i.e. Molse meren) can be found that are remnants of old sand extraction pits that now serve as water recreation area.

Figure 1 – Top: Administrative map of Flanders showing provinces and major cities. Boom Clay outcrop and subcrop zone is indicated by shading while the Campine region is delineated by the thick black line. Bottom: Main infrastructure in north-eastern Belgium (NGI, Brussel – 2003).

3 Geomorphology and orohydrography The presence of Boom Clay, in outcrop and subcrop, is distributed over several river basins: Schelde (Scheldt), Nete, Demer and Maas (Meuse), and small parts of the Dijle and Gentse Kanalen basins. Figure 2 shows the extent of Boom Clay in Northern Belgium, together with the orohydrography. The relief in the outcrop and subcrop zone stretches from ~ 100 m above sea level TAW1 in the southeast along the Meuse-Demer water divide, to ~ 0 m in the northwest along the river Scheldt. Two major rivers and several tributaries traverse the Boom Clay zone: the rivers Meuse and Scheldt. Relative uplift since about 2 Ma ago has forced these rivers to incise, which resulted in significant denudation of the landscape. More details on the palaeohydrological and palaeogeographical evolution of the Campine area during the Quaternary period will be given in section 7.4.

40 km Doel

Maas Mol

N Schelde Nete Kempen (Campine)

Demer Maas

Boom Clay outcrop Kempen area River Faults in base Boom Clay (dashed line) and subcrop zone (Campine) Nete basins and Quaternary deposits (thick full line)

Figure 2 – Digital terrain model (DTM) of Flanders with indication of the following elements: Boom Clay outcrop and subcrop zone, Kempen (Campine) area, river basins and faults (Boom Clay and Quaternary). Sources: Geologisch 3D Model Vlaanderen (v1.2011); AGIV (2006). Morphological units in the northern part of Belgium are shown in Figure 3 (De Moor and Pissart, 1992). The southernmost unit is the Boom Clay cuesta (ca. 25-30 m a.s.l. TAW; nr. 13). It developed in response to continuing denudation (Neogene and Quaternary) and stands out as a positive relief due to its erosion resistance. The Boom Clay cuesta has long been the interfluve between the Flemish Valley river system, draining to the east, and the 'Northern Belgian rivers', draining to the north. Note that this cuesta is subdivided into three parts, as a result of rivers cutting through the clay, notably the rivers Scheldt and Nete. As a result, the river systems north and south of the cuesta are connected.

1 The reference level in Belgium is expressed with respect to 'TAW', which stands for 'Tweede Algemene Waterpassing' (Second General Levelling). The reference is a point in Uccle with a given fixed level based on the First General Levelling, which zero level corresponds to the mean sea level of low tides in ordinary running water measured at Oostende between 1834 and 1853. The Second General Levelling was carried out by the National Geographic Institute between 1947 and 1968 and was recently repeated (1981-2000).

The northernmost geomorphological unit is another cuesta, denoted Campine Clay cuesta (30- 35 m a.s.l. TAW, nr. 2). It formed in response to continuing denudation during the last 1-2 Ma, and stands out as a positive relief as well. The most prominent morphological feature is the Campine plateau (or Kempen Plateau; nr. 5), which raises above the bordering valley systems from ca. 100 m a.s.l. in the south and ca. 40-50 m a.s.l. in the north. This plateau was formed in gravel, which explains the morphology. It is the result of denudation processes during approximately the last 1 Ma. Located in between these three well-pronounced positive reliefs, a valley system came into existence, due to erosional processes during the Quaternary. This valley system is called the Schyns-Nete depression (10-20 m a.s.l.; nr. 3) and is connected with the Flemish Valley (nr. 14). Polders are found in the west of the study region (Scheldt polders; nr. 19) and constitute the lowest part of it (approaching sea-level). The Campine plateau is bounded to the east by a relatively steep slope, giving way to the Meuse valley, ca. 50 m below (nr. 7). Smaller morphological entities are found in the southwest, with the Demer valley (nr. 10), the Hageland hills (nr. 11) and the Lummen hills (nr. 12).

40 km 1 2 19 19 N 18 3b 6 13 3 3a 17 Profile 1 14 4 5 12 16a 7 10 16 11 15 9 9 8

Units Boom Clay outcrop 1 Campine Clay cuesta 10 Demer valley and subcrop zone 2 Brasschaat glacis 11 Hageland hills 3 Nete-Schyns depression 12 Lummen hills Campine area 3a Geel ridge 13 Boom Clay cuesta (Kempen) 3b Lichtaart ridge 14 Flemish valley 4 Beringen-Diepenbeek glacis 15 Leie-Scheldt interfluve 5 Campine plateau 16 Coastal plain-Leie interfluve 6 Gerdingen-Bocholt plain 16a Izenberghe plateau 7 Meuse valley 17 Coastal dunes 8 Herve plateau 18 Coastal plain 9 Large hilly interfluve 19 Scheldt polders

Figure 3 – Morphological entities of northern Belgium (De Moor and Pissart, 1992) plotted on the DTM Flanders (AGIV, 2006). Boom Clay outcrop and subcrop zone (hatch) and Campine area (Kempen; dashed line) are also indicated. See Figure 4 for profile 1 and 2.

WEProfile 1 + 60 m

+ 40 m

Mol area

Nete Valley

+ 20 m Coastal plain

ScheldtRiver Flemish Valley Campine Plateau Valley Roer Graben 0 m

-20 m 0 km 50 km 100 km 150 km 200 km

SWProfile 2 NE + 60 m

hilly Large interfluve + 40 m Mol area Nete Valley

+ 20 m Flemish Valley

Campine Plateau

0 m

-20 m

0 km 50 km 100 km

Figure 4 – Topographic transects (red lines) through northern Belgium, as indicated by the profile lines on Figure 3. The base of the Quaternary deposits is shown in green, to facilitate the identification of depositional and erosional morphological features.

4 Soil associations, land cover and vegetation Soils in the region of interest are predominantly sandy and loamy sandy, with various degrees of wetness (wet in alluvial plains and dry on interfluves) (Figure 5) (AGIV, 1998). These soils are characterised by the presence of a well-developed humus-B or iron-B horizon (podzol soil) or by the presence of a thick anthropogenic humus-A horizon (plaggen soils), especially in the northern and eastern Campine area. They developed on sandy parent material consisting of wind-blown quartz sands (mean grain size around 150 µm) with small amounts of silt (generally less than 10%) (see references in Beerten, 2011). In the southwestern and southern part of the study area, the sand texture is replaced by sandy loam and loamy soils with a texture-B horizon, again with various degrees of saturation. Notably the soils in the Haspengouw region are very loamy. In the westernmost part, clayey soils dominate that developed on clayey parent material from the river Scheldt polders.

Figure 5 – Soil association map of Flanders (AGIV, 1998). Land cover and vegetation in the Boom Clay outcrop and subcrop area is given in Figure 6 (AGIV, 2002). Built areas are dominant in the western part (city of Antwerp), while this type of cover is more evenly distributed in other areas. Vegetation and its relationship with the landscape is discussed below, according to four characteristic regions in the Boom Clay area (Van Landuyt et al., 2006).

The western polder region is characteristically low-lying with only slight variations in relief which are a result of former encroachments by the sea (former inlets of the sea, wetlands) and the struggle of man to reclaim land from the sea (dykes and canals). The landscape is largely treeless and is dominated by meadows and pastures.

The landscape in the sandloamy region (southwest) is dominated by agriculture, especially in the higher and drier areas. In the valleys there is more grassland, most of which is in intensive agricultural use. On the drier sandy areas there are some forests and a very rare relic of heathland.

The landscape in the Haspengouw region (southeastern part of Boom Clay area) is diverse and contains forest, hedges, arable land, meadows and pastures.

Finally, in the sandy Campine region much of the former heathlands are urbanized or converted to arable land or commercial forest with non-native species such as Scots pine (Pinus sylvestris) and red oak (Quercus rubra).

40 km

Legend Built area Arable land Meadow Orchard

Deciduous forest Coniferous forest Heathland Dunes Water

Figure 6 – Land cover in northern Belgium (AGIV, 2002). Boom Clay area is delimited by black line.

5 Climate and meteorology The present-day climate in Belgium is a temperate oceanic climate. Its middle latitude position (around 50°50’ N) is characterised by the convergence of cold polar air masses with warm tropical air masses, forming the polar front zone. The two air masses are in constant conflict and each may temporarily dominate the area, but none has exclusive control. The atmospheric circulation (lows associated with the polar front) is dominated by western winds which bring humidity from the Atlantic ocean. Wind direction determines the weather by blowing different air masses: mild, humid air masses for the dominant southern to western

15 winds; unstable, cool air masses for western to northern winds. Less frequent northern to eastern or even rarer eastern to southern winds bring rather dry, cold/warm air in winter/summer (RMI, 2011). In general, summers are relatively cool and rainy, and winters are relatively mild and wet. In Trewartha’s classification of climate types (Trewartha, 1968), the temperate oceanic climate is denoted DO. In Belgium, Uccle (located near Brussels) is the reference station of weather observation. Table 1 gives the monthly average weather variables measured in the period 1981-2010 (1901-2000 for some variables).

Table 1 - Present-day climate characteristics for RMI (Royal Institute of Meteorology) Uccle station (Leterme and Mallants, 2011). Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Year Mean 3.3 3.7 6.8 9.8 13.6 16.2 18.4 18.0 14.9 11.1 6.8 3.9 10.5 temperature (°C)† Mean max. 5.7 6.6 10.4 14.2 18.1 20.6 23.0 22.6 19.0 14.7 9.5 6.1 14.2 temperature (°C)† Mean min. 0.7 0.7 3.1 5.3 9.2 11.9 14.0 13.6 10.9 7.8 4.1 1.6 6.9 temperature (°C)† Mean precip. 76.1 63.1 70.0 51.3 66.5 71.8 73.5 79.3 68.9 74.5 76.4 81.0 852.4 (mm)† Max. precip. 143.6 149.0 138.1 130.4 145.6 153.7 196.5 231.2 198.8 227.1 174.6 171.9 1088.5† (mm)‡ Min. precip. 2.6 5.9 4.2 6.0 9.3 12.1 5.9 10.4 4.7 5.2 18.8 10.0 406.4 (mm)‡ Mean number of 19.2 16.3 17.8 15.0 16.2 15.0 14.3 14.5 15.7 16.6 18.8 19.3 198.7 precip. days† Mean number of 5.2 5.9 3.2 2.4 0.0 0.0 0.0 0.0 0.0 0.0 2.4 3* 22.1 days of snowfall‡ Mean relative 86.6 82.5 78.5 72.5 73.2 74.1 74.3 75.5 80.9 84.6 88.2 88.8 80.0 humidity (%)† Mean atm. pressure at sea 1017.5 1017.4 1015.7 1014.4 1015.3 1016.6 1016.3 1015.9 1016.4 1015.2 1015.1 1016.5 1016.0 level (hPa)† Mean wind speed 4.1 3.8 3.8 3.4 3.2 3.0 2.9 2.8 3.0 3.4 3.6 3.7 3.4 (m/s)† † period 1981-2010 ‡ period 1901-2000 * period 1971-2000

In Figure 7 and Figure 8, average temperatures are given for Flanders, based on interpolation of data from individual weather stations using topography as soft data (see Leterme and Mallants, 2011 for more details).

Figure 7 - Mean temperatures in January based on BME interpolation using topography as soft data (Leterme and Mallants, 2011).

Small hot or cold spots around RMI stations resulting from the interpolation can be caused by local factors not taken into account (e.g. the effect of urbanisation). Not all spatial variability of average temperature is explained by altitude (especially for July temperatures).

Figure 9 shows the isohyets (lines of equal precipitation) for Belgium, for the period 1833- 1975. In this figure, Uccle station is located on the 800 mm isohyet, but the time period is different from that of the statistics presented in where Uccle has an average 852 mm of precipitation per year.

Figure 8 – Mean temperatures in July based on BME interpolation using topography as soft data (Leterme and Mallants, 2011).

Figure 9 – Isohyets of Flanders, based on observations for the period 1833-1975 (see references in Leterme and Mallants, 2011). Compared to the average climate described for Belgium, the Campine has a more continental character than what one would expect at this altitude and distance from the sea. It is characterised by relatively warmer summers and colder winters, hotter days and colder nights

17 compared to Uccle. This difference with the rest of the country can be explained by the coarse-grained sandy soils. The sand absorbs heat during the daytime very fast, but during the night this warmth is also radiated quickly. Table 2 gives the monthly statistics of precipitation and temperature in the Mol-Dessel area for the period 1985-2009. The mean annual precipitation (899 mm) is notably higher than what could be inferred from Figure 9. Given that the reference time periods are not the same for these two sources, one could conclude that precipitation has increased in the last 25-30 years in the Mol-Dessel area compared to the previous 150 years.

Table 2 – Present-day climate characteristics for the Mol-Dessel nuclear zone (period 1985 to 2009 except for max. and min. temperatures: 1985 to 1998) (see Leterme and Mallants, 2011). Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Year Mean precipitation 76.2 65.9 73.5 51.9 57.7 80.2 95.9 79.3 73.5 77.0 80.8 86.9 898.7 (mm) Max. precipitation 159.0 153.5 144.4 132.1 118.6 158.2 192.0 224.3 247.8 184.0 148.1 189.3 1169.4† (mm) Min. precipitation 5.4 3.8 6.8 0.0 0.0 12.5 36.6 16.6 9.1 15.8 23.7 33.3 616.4† (mm) Mean temperature 3.3 3.7 6.6 9.8 14.1 16.5 18.6 18.3 15.2 11.5 6.9 4.1 10.4 (°C) Mean max. 5.7 6.7 10.6 14.1 19.1 21.0 23.7 23.8 19.6 15.5 9.6 7.1 14.7 temperature (°C) Mean min. -0.2 -0.4 2.3 4.1 8.3 11.4 13.4 12.7 9.9 7.0 3.1 1.6 6.1 temperature (°C) † maximum/minimum over a given year

The air pressure ranges between 950 and 1050 hPa. The annual mean wind velocity in the Mol-Dessel area ranges from 2 to 7 m/s and extreme wind speeds of 23 to 30 m/s only occur every two years.

A compass card of the wind direction is shown in Figure 10. It was established on the basis of two series of measurements (Table 3) conducted at SCK•CEN (Mol) at a height of 24 m (see Leterme and Mallants, 2011).

Atmospheric stability and wind speed data, measured at Semmerzeke in Eastern Flanders are shown in Table 4.

Figure 10 – Compass card indicating the direction of the most prevailing wind direction in the surroundings of Dessel at a level of 24m (observation periods 1964-1983 and 1998-2008). The frequency per 1000 (‰) is given.

Table 3 – Annual wind rose data (see Leterme and Mallants, 2011). Sector Wind Direction Frequency [%] 1 345° - < 15° 5.54 2 15° - < 45° 5.84 3 45° - < 75° 7.99 4 75° - < 105° 6.53 5 105° - < 135° 4.42 6 135° - < 165° 7.12 7 165° - < 195° 12.90 8 195° - < 225° 17.41 9 225° - < 255° 13.63 10 255° - < 285° 7.65 11 285° - < 315° 6.15 12 315° - < 345° 4.82

Table 4 – Annual atmospheric stability and wind speed data (see Leterme and Mallants, 2011). Pasquill stability Frequency Mean wind category [%] speed [m/s] A 6.6 4.0 B 12.8 5.2 C 9.3 6.4 D 54.3 5.0 E 3.4 3.4 F 13.5 2.0 Average wind speed for all 4.6 Pasquill stability categories

Table 5 – Monthly and annual relative humidity in Kleine-Brogel (period 1999-2004; in Herentals period 2005-2009). See Leterme and Mallants (2011). Mean relative Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Year humidity (%) Kleine-Brogel 87.7 83.6 79.6 72.0 72.8 72.6 76.2 77.4 81.4 84.8 90.0 89.9 80.6 Herentals 82.4 82.6 75.7 68.0 68.0 67.8 69.8 74.2 76.1 81.3 84.6 86.6 76.4

Relative humidity in the Campine is estimated by observations from the Kleine-Brogel and Herentals stations located respectively ~25 km East and ~16 km West from the Mol-Dessel nuclear zone. Mean monthly values of Kleine-Brogel (Table 5) are very similar to the values of Uccle station (see Table 1). Mean monthly values of Herentals are somewhat lower (but the level of confidence in the data set is lower). It should be noted that the data from Kleine- Brogel and Herentals do not cover the same period, and that mean monthly values in Table 5 are calculated on 6 years (Kleine-Brogel) and 5 years (Herentals) only. Extreme precipitation amounts were estimated for the Mol-Dessel nuclear zone. Figure 11 shows the resulting intensity-duration-frequency curves. The data show, for example, that 215 mm precipitation or more over a duration of 30 days occurs every 10 years. Concerning the maximal ‘instantaneous’ rainfall intensity, it never exceeds 5 mm per minute during a few minutes.

Figure 11 – Intensity-duration-frequency curves for Mol/Dessel region, with return periods of 6 months, 2, 10, 50 and 200 years (Leterme and Mallants, 2011).

6 Hydrology

6.1 Flanders The Boom Clay zone of occurrence covers several river basins, among which the basins of the Beneden-Schelde, Nete, Demer and Meuse are the most important ones (Figure 12; AGIV, 2004). The sources of the river Scheldt are located in Saint-Quentin, France, at 95 m altitude. Its length is ca. 355 km, among which 200 km are located on Belgian territory (De Smedt, 1992). The following rivers are tributaries: Leie, Dender, Zenne, Dijle, Demer, Grote Nete and Kleine Nete. The Lower Scheldt has a gradient of 10 cm/km. A large part of the Scheldt basin (s.l.) is influenced by tides. A tidal wave penetrates the Lower Scheldt basin and Nete basin twice a day. These tidal discharges are enormous in comparison with the basal river discharges and mount up to > 2500 m3/s near the confluence of the river Scheldt and the Rupel. Average discharges are ~ 100 m³/s for the Lower Scheldt downstream the confluence with the Rupel, ~ 50 m³/s for the Rupel, ~ 25 m³/s for the Dijle-Demer system (at Zennegat) and ~ 5 m³/s for the Grote (at Hulshout) and Kleine Nete (at Grobbendonk) (Table 6). Peak discharges are several times higher than these values. Heavy winter storms, in combination

20 with high tides and strong westerlies that increase the water level in the Scheldt estuarium, may cause inundations in the Lower Scheldt basin and the Nete and Dijle basins.

Figure 12 – River basins and hydrographical network in Flanders. Navigable waterways are indicated in dark blue, other waterways in light blue. Boom Clay outcrop and subcrop zone is delimited by the red line. Data from AGIV (2004). Aquifer recharge in the investigation area between the Meuse/Scheldt watershed on the Campine Plateau in the east, the Dijle-Demer-Rupel axis in the south, and the river Scheldt in the west ranges between < 0 mm/year and > 350 mm/year, with an average value of 286 mm/year (Figure 13) (Meyus et al., 2004; De Smedt et al., 2007). Around 65% of the groundwater recharge is drained by the rivers. Drainage is highest for river segments draining the western edge of the Campine Plateau, and the small rivers north of the Campine Cuesta. Some segments of the hydrographic network contribute to groundwater recharge. These are the canals (e.g., Albertkanaal), the docks near Antwerp and the Scheldt. Some small river segments in the Nete basin also contribute to recharge; these are small valleys that have their river beds above local groundwater level.

Table 6 – Discharge and drainage surface area of several rivers in the Scheldt basin. River Surface area Discharge (km2) (m3/s) Schelde (Schelle) † 19144 104.0 Rupel† 12686 47.2 Dijle-Demer 3420 25.0 (Zennegat) † Grote Nete 443 4.2 (Hulshout)‡ Kleine Nete 590 5.2 (Grobbendonk)‡ † period 1951-1986 (De Smedt, 1992) ‡ period 1988-2010 (Vandersteen et al., 2011)

Seepage zones are shown in Figure 13 (De Smedt et al., 2007). A closer look leads to the identification of several major seepage zones in the study area. These are the polders in the seaport area and south of Antwerp, the lower course of the Nete, the headwaters of the Kleine Nete, the valley of the Kleine Nete near Kasterlee, the valley of the Grote Nete near Herselt, several tributaries of the Demer and the small valleys north of the Campine Cuesta. Naturally,

21 topographical highs are characterised by relatively deep water tables, up to 20 m below the surface (Campine Plateau, Hageland hills, Lichtaart Ridge). b

Figure 13 – Recharge, river drainage, seepage and depth of water table for the 'Centraal Kempisch Systeem' (De Smedt et al., 2007). Recharge is calculated by WetSpass (grid: 250 x 250 m) (Meyus et al., 2004).

6.2 Nete catchment In open literature as well as in reports written within the framework of the category A waste project, detailed information on the water balance is available for the Nete catchment (e.g., Batelaan and De Smedt, 2007; Leterme et al., 2010; Leterme and Mallants, 2011).

Figure 14 illustrates the water budget for four different cover types under current climate conditions in the Mol/Dessel region (Leterme and Mallants, 2011). Interception is highest in coniferous forest, due to the rather thick, permanent vegetation cover. Soil evaporation is

22 lowest for the maize cover. This is mainly because in summer when most of the soil evaporation occurs, maize has the highest interception capacity and hence less precipitation is available from the soil surface for evaporation compared to other cover types.

Transpiration is higher for coniferous forest and meadow than for maize and deciduous forest. The absence of vegetation for ~200 days per year certainly explains why transpiration is lower for the maize cover.

Concerning groundwater recharge, Figure 14 shows that crop (maize) cover has the highest mean annual recharge (55% of precipitation), before deciduous forest (42%), meadow (34%) and coniferous forest (27%).

Meadow Crop (maize) Deciduous Coniferous interception (9%) (10%) (13%) (22%) (16%) soil evaporation (24%) (26%) (19%) (21%) transpiration (33%) (19%) (31%)

(55%) gw recharge (34%) (42%) (27%)

Figure 14 – Water budget (percentage of annual precipitation; P = 899 mm) for the four different land cover types, under the present climate in the Mol-Dessel area (Leterme and Mallants, 2011)

The simulations for the four land cover types produced a negligible amount of runoff. This is consistent with the presence of highly permeable soils in the study area and the relatively flat topography. Indeed, surface runoff in the Nete catchment can be assumed to originate mainly from built areas. For example, Batelaan and De Smedt (2007) found about two thirds of the total simulated runoff in the Nete catchment originating from impervious areas or open water.

When the results presented above are weighted by the actual land cover in the Nete catchment for the present-day climate, the average groundwater recharge is equal to 391 mm/y (Leterme et al., 2010). This value is ~ 100 mm/y larger than the one calculated by Batelaan and De Smedt (2007). The difference is due to the different software that was applied in both studies (HYDRUS 1-D vs. Wetspass respectively), and the degree of soil and land-use variability that

23 was introduced into the model (stylized vs. detailed respectively). Furthermore, it should be noted that the influence of the aggregation level of precipitation was not considered, neither the spatial and temporal variability of soil hydraulic properties of specific soil horizons (e.g., podzol Bh-horizon) (Leterme and Beerten, 2012; Beerten et al., 2012).

One may consider the water budget in the Nete catchment by including rivers and groundwater. River flow is assumed to consist of an addition of baseflow and direct runoff. Estimating the water budget of the Neogene aquifer using a hydrogeological model, Vandersteen et al. (2011) suggested that about 90% of the groundwater recharge goes back to the rivers as baseflow. The rest is essentially pumped for irrigation and drinking water distribution, while a very small amount goes to surface water bodies. This modelled baseflow was compared with the baseflow inferred from hydrograph analysis at two locations. The latter method gave 18% and 28% higher values of baseflow than the former method (Gedeon, 2008; see also Vandersteen et al., 2011).

7 Quaternary landscape development and evolution

7.1 Introduction Understanding future changes of earth surface systems requires thorough knowledge and identification of the causes of the evolution of the landscape during the last few millions of years. Today's landscape of the Campine region is the result of external forces acting upon the earth surface since the last marine regression ~ 2 Ma ago. The landscape has experienced significant hydrological and morphological changes due to the continuous interplay of climate change, global sea level variations and local vertical movements of the surface (uplift and/or subsidence). Changing hydrological and geomorphological processes may not only result in thickness variations of the sediment body overlying the Boom Clay, but also in different boundary conditions with regard to groundwater flow and hydrochemistry. Landscape reconstruction is the only tool to set constraints on the future evolution of surface processes because it inherently carries realistic scenarios of these processes and the effect on local earth surface systems.

Table 7 – Neogene and Quaternary chronostratigraphy of NW Europe. Based on Mangerud et al. (1982), Vandenberghe (1985) and Gibbard and Cohen (2008). Correspondence with oxygen isotope stages is given between brackets. Stage Substage Super-stage Start End System Series Subseries (NW (NW Chronozone (NW Europe) (Ma, ka) (Ma, ka) Europe) Europe) Subatlanticum 2.4 0 Subboreal 5.7 2.4 Holocene (1) Atlanticum 9.2 5.7 Boreal 10.5 9.2 Preboreal 11.5 10.5 Younger Dryas 13 11.5 Late Glacial (2) Allerød 14 13 15 14 Weichselian Late (3/2) 30 15 Late Pleniglacial Middle (3) 59 30 Early (4) 74 59

Early Glacial 116 74 (5a-5b-5c-5d) Eemian (5e) 0.13 0.12

Quaternary Quaternary Saalian 0.39 0.13 Pleistocene (6-7-8-9-10) Middle Holsteinian (11) 0.42 0.39 Elsterian (12) 0.47 0.42 0.78 0.47 Cromerian 0.88 0.78 Bavelian 1.14 0.88 Menapenian

Early Waalian Eburonian Tiglian 2.44 1.77 Pretiglian 2.58 2.44 Piacenzian 3.60 2.58 Pliocene Zanclean 5.33 3.60 Messinian 7.25 5.33 Tortonian 11.61 7.25

Serravalian 13.65 11.61

Neogene Neogene Miocene Langhian 15.97 13.65 Burdigalian 20.43 15.97 Aquitanian 23.03 20.43

Throughout this section, reference will be made to chronostratigraphical units and names and their duration. Therefore, a detailed chronostratigraphical table is given (Table 7) that covers the Neogene and Quaternary systems according to Mangerud et al. (1982), Vandenberghe (1985) and Gibbard and Cohen (2008).

7.2 Climatic evolution

7.2.1 Global climate evolution during the Quaternary The climate evolution during the Quaternary in general, and for NE-Belgium in particular, is described in De Craen et al. (2012a), and will be summarized below.

Overall, the Quaternary period is the continuation of a slow progression towards cooler conditions that initiated in the Tertiary: moderately sized ice sheets grew in the northern hemisphere (NH) by 2.4 Ma BP, i.e. slightly later than in the southern hemisphere (SH). The

25 whole period is characterized by a marked climatic instability, oscillating between warm periods and cold ice ages (Figure 15).

During the earlier part of the Quaternary (up to about 600 ka BP), the warm to cool alternations presented a dominant periodicity of approximately 41 ka. During the last 600 ka, the situation becomes more complex. The amplitude of environmental fluctuations increased, possibly reflecting the growing size of ice sheets during cold phases. In the same interval, the climate was dominated by cycles with periods of 19 ka, 23 ka, and 41 ka, superimposed on a dominant 100 ka period. Most of these periods correspond to orbital variations (Hays et al., 1976; Berger, 1977; Imbrie et al., 1984). In general, the glacial periods in the Pleistocene occurred with a mean periodicity of about 100 ka (in fact, 50 to 130 ka), and displayed a slow (70-90 ka) and uneven cooling followed by a rapid deglaciation.

Figure 15 – Global sequences (MIS = Marine Isotope Stage; LGM = Last Glacial Maximum), sea-level curve, marine oxygen isotope curve and northwestern European regional stages of the last 2.5 Ma (Hardenbol et al., 1998; Lisiecki and Raymo, 2005; Miller et al., 2005). Graph created using TimeScale Creater 5.0, available online https://engineering.purdue.edu/Stratigraphy/tscreator/index/index.php, consulted in December 2011.

Within the Quaternary period, the two last ice ages, i.e. the Weichselian ice age (or the Last Glacial Maximum, LGM), and the Saalian ice age, deserve some special attention. These can be considered as an analogue of a future ‘extreme cold situation’ and hence of importance for scenario development in the long-term safety assessment. During the Saalian glacial stage (glacial maximum around 140 ka BP), a large ice sheet originating in Scandinavia, spread across Denmark, northern Germany and the northern Netherlands, from which it covered about half of the territory (Berendsen, 1998, 2008). According to Zagwijn (1974) and Lambeck et al. (1998), the ice caps reached the Hoge Veluwe in the Netherlands, which is about 100 km north of the Campine area. The glaciation resulted in a sea level drop of 120 to 140 m, and the rivers Meuse and Rhine were forced in a western course parallel to the southern limit of the ice sheet (Zagwijn, 1974). South of the glaciated area, tundra-like conditions existed, resulting in permafrost. The ice tongues of the Saale Glacial Stage formed elongated ridges or push moraines (in which pre-glacial sediments are pushed upward). In the Netherlands, these may reach a height of more than 100 metres while the associated glacial basins may reach depths down to 150 m below current sea level (Huybrechts, 2010 and references therein). In northern Germany, similar phenomena have been recognised (van Gijssel, 1987; Kluiving, 1994; van der Wateren, 1995; Reicherter et al., 2005).

The Last Glacial Maximum (LGM) is the last ice volume culmination that took place in the 6 3 Late Weichselian: about 50x10 km of ice spread over a huge territory in the Northern Hemisphere. The Southern Hemisphere remained comparatively free of very large ice caps: mountain glaciers developed in South America and in Australia, while the Antarctica ice cap did not grow significantly. Mean global air temperature was about 4 to 6°C lower than presently, and the global sea level was lowered by almost 120 m (Clark et al., 2001), considerably modifying the landscape, in many places on Earth (for instance, the continental shelves were mostly emerged). In Northern Europe, the most important feature was undoubtedly the development of the Fennoscandian ice cap. Important to mention is that, during the Weichselian glacial stage, the extent of ice caps was more restricted than in the Saalian glacial stage: the ice cap never extended further south than Southern Denmark and Northern Germany, i.e. some 400 km north of the Campine area. Like most of Northern Europe, Belgium experienced dry, tundra-like surface conditions during the LGM, together with permanent ground freezing (i.e. permafrost). Vegetation was sparse and dominated by steppic plants. The LGM was overall characterized by a strong decrease in global forest cover, and a concomitant increase in non-forest environments (i.e. mainly steppe, tundra, desert and ice caps). Desert environments (ice or desert land) on the one hand strongly enhance the surface albedo, and on the other hand leave land surfaces highly exposed to erosional processes (frost creep, periglacial solifluction, meltwater and sediment runoff).

Our present-day climate started developing about 11 ka BP, when temperatures and sea-level rose again to values comparable to the present ones. Northwestern Europe became reforested again, first with birch and pine, later on with a mixed deciduous forest. At the same time, soils started developing and further contributed to the stabilisation of the landscape, together with a dense vegetation cover. During the last few millennia, vegetation was gradually destroyed as a result of agricultural practices, leading to enhanced erosion (fluvial and aeolian).

Between roughly 900 and 1300 AD, evidence suggests that Europe, Greenland and Asia experienced relatively warm conditions. While historical documents and other evidence

27 testify to the warmth that occurred in some regions, the geographical extent, magnitude and timing of the warmth during this period is uncertain (NRC, 2006). A wide variety of evidence supports the global existence of a "Little Ice Age" (this was not a true "ice age" since major ice sheets did not develop) between about 1500 and 1850 (NRC, 2006). Since the industrial revolution, concentrations of all the long-lived greenhouse gases have increased due to increasing emissions of greenhouse gases from human activities which may lead to enhanced global warming.

According to the IPCC (2007), warming of the climate system is unequivocal, as is now evident from observations of increases in global average air and ocean temperatures, widespread melting of snow and ice and rising global average sea level.

Figure 16 – Reconstruction of the maximum ice-sheet extent in Eurasia during the Saalian ca. 160-140 ka BP. The approximate maximum extent of any Middle-Late Quaternary glaciation is indicated by the dotted line. From Svendsen et al. (2004), cited in Huybrechts (2010).

7.2.2 Permafrost conditions in NW-Europe During the Last Glacial (Weichsel), permafrost conditions are known to have occurred in the Netherlands and northern Belgium between 74-59 ka (Early Pleniglacial), 41.5-40 ka (Hasselo Stadial), 23-19 ka (LGM) and 12.7-11.5 (Younger Dryas). Permafrost maps for these periods are discussed in Huijzer and Vandenberghe (1998), and Renssen and Vandenberghe (2003). Table 8 gives an overview of the southern margin of permafrost conditions for several cold periods during the last glacial. As can be seen, continuous or discontinuous permafrost conditions were prevailing in the Campine area during these periods (see also Beerten (2011) for a synthesis). The Early Pleniglacial and LGM were glacial periods during which continuous permafrost developed in the Campine area. The permafrost distribution in

28 northwestern Europe during the LGM is given in Figure 17. Recently performed simulations indicate that the permafrost depth during the LGM in the Mol area would not have exceeded 200 m if snow and vegetation are introduced into the model (Govaerts et al., 2011). This is somewhat deeper than previous calculations (Delisle et al., 2003) for north-central Europe where values of 125 m were obtained. These calculations also suggest that the soil below rivers at least 50 m wide remained permafrost-free for the entire Weichselian (these are the so-called taliks).

Table 8 – Latitudes of southern margins of discontinuous and continuous permafrost in NW Europe for several cold glacial phases (Mol is situated at 51°N latitude). Note that this is a compilation of many data, including proxies that were found in northern Belgium (Campine area) and the Dutch-Belgian border area (From Renssen and Vandenberghe, 2003).

Cold phase Lat. discont. PF Lat. cont. PF

Younger Dryas (12.7-11.5 ka) 50°N 55°N

LGM (23-19 ka) 45°N? 50°N

Hasselo stadial (41.5-40 ka) 50°N 55°N

Early Pleniglacial (74-59 ka) 45°N? 50°N

Figure 17 – Map of permafrost limits in NW Europe for the phase of maximum cold (24-21 ka ago). The thick full line marks the position of the British and Fennoscandinavian ice sheets, the thick dashed line marks the boundary between continuous and discontinuous permafrost, and the thin dashed line marks the position of the coastline. From Renssen and Vandeberghe (2003).

7.3 Quaternary tectonic evolution of NE-Belgium A large part of the Campine area is located outside the Roer Valley Rift system, a major fault- bounded subsidence zone that has been highly active since the Oligocene. The bordering faults are believed to be reactivated Variscan or even Caledonian faults, and thus constitute a fundamental weakness zone in the earth's crust. The system is subdivided in several blocks, from SW to NE the Campine Block, the Roer Valley Graben, the Peel Block and the Venlo Block (Figure 19). The south-western border of the Roer Valley Graben is a complex fault zone, called the Feldbiss Fault Zone, located about 25 km east of the Mol-Dessel area. Recent

(Quaternary) movements along the faults that resulted in the formation of steep escarpments are clearly visible in the landscape (Figure 18). A famous example is the Bree escarpment showing a vertical offset of more than 20 m since deposition of the Main Terrace deposits of the River Meuse (Beerten et al., 1999). Along this fault a cumulative displacement of 4 m spread out over 5 individual faulting events during the last ~ 140 ka is documented (Vanneste et al., 2001).

Figure 18 - Digital elevation model of the Bree fault scarp in NE Belgium, interpolated from 1/10,000-scale topographic maps of the Belgian National Geographical Institute. Contour interval is 1.25 m. The location of excavated trenches is indicated. BFS = Bree fault scarp, HFS = Heerlerheide fault scarp. Figure 3 from Vanneste et al. (2001).

Together with the adjacent Poppel and Reusel faults, the Rauw fault is responsible for the vertical offset of the Boom Clay top by more than 100 m (Gullentops and Vandenberghe, 1995). The most recent movement along the Rauw fault is believed to have occurred in between deposition of the Mol Sands (ca. 2.5 Ma), and the Weichselian LGM (ca. 20 ka), and is in the order (cumulative) of 10 m (references in Beerten, 2010). Circumstantial evidence indicates that the Rauw fault was active during deposition of the Lommel Sands which are part of the Main Terrace deposits of Rhine and Meuse, roughly between ca. 1 Ma and 0.7 Ma ago (Gullentops et al., 2001).

Figure 19 – Instrumental seismicity in the Roer Valley Graben and surrounding areas. The Boom Clay subcrop zone in Belgium is delimited by the red line, while the Rauw-Poppel fault system is indicated by a thick black ellipse. The major faults that border the Roer Valley Graben in the southwest are indicated as GBF (Grote Brogel fault), RF (Reppel fault), BF (Bocholt fault), FF (Feldbiss fault) and HF (Heerlerheide fault). Also shown are the various tectonic blocks of the Roer Valley Rift System (in capital letters): Brabant Massif, Eastern Campine Block, South Limburg Block, Roer Valley Graben, Erft Block, Peel Block, Venlo Graben and Krefeld Block. Figure modified from Vanneste et al. (2001).

Figure 20 – Subsidence curves in the Dutch part of the Roer Valley Rift System for the last 2.5 Ma (van Balen et al., 2005). CB = Campine Block, PB = Peel Block, RVG = Roer Valley Graben (i.e. the central part of the rift system).

Figure 21 – Patterns of uplift south of the Campine area (van Balen et al., 2000; van Balen et al., 2005). Absolute uplift since the early Middle Pleistocene (ca. 700 ka) is given in meters. The Mol-Dessel area is indicated by the blue star symbol. Within the Roer Valley Graben, the cumulative subsidence during the Quaternary period amounts up to 250 m in the central part (Figure 20). Outside the Roer Valley Graben, notably in the area south of the Campine Block uplift has been the most common tectonic feature during the last few millions of years. Patterns of uplift south of the Campine area are shown in Figure 21. This can be deduced from, e.g., the river Meuse terrace staircase, showing Early and Middle Pleistocene levels at elevated altitudes up to between 100-200 m above the current floodplain. An important and well documented feature in the Northern Ardennes and Eifel is the post-early Middle Pleistocene uplift phase. This uplift phase may have affected the central and northeastern part of the Campine area as well (references in Beerten, 2010). The pattern, magnitude and cause of this uplift phase are currently debated. According to van Balen et al. (2000), uplift of 50 m in the Maastricht area (see Figure 21) is probably caused by a combination of larger-scale geodynamic processes, namely intraplate compression, mantle upwelling and volcanism, and rift shoulder uplift in response to rifting in the Roer Valley Rift System and the Lower Rhine Embayment. This view is challenged by Demoulin and Hallot (2009) who argue that the uplift phase is restricted to the area south of Maastricht and attribute 50 m of incision of the river Meuse to a supra-regional (isostatic?) or global (sea- level) relative uplift. Indeed, river incision of 50 m and more during the last 0.8-1.2 Ma is recognized all over the world and is thought to have been the result of a combination of surface uplift (Bridgland and Westaway, 2008) and the overall climatic deterioration during the Early-Middle Pleistocene transition (Gibbard and Lewin, 2009).

Relative sea-level rise reconstructions for Late Glacial to Middle Holocene times testify to the occurrence of anomalous high non-linear subsidence rates along the southern North Sea coasts while the deglaciated Scottish and Norwegian coasts show strong uplift. Geophysical

32 models explain these anomalous uplift and subsidence patterns by invoking uplift of the foreland area during ice build up in the Late Middle and Late Pleniglacial in a zone around the ice-margin, as a consequence of simultaneous crustal compression below the Scandinavian and British ice-sheets (e.g., Peltier, 2004; Steffen, 2006; see Figure 22). The most recent glacio-hydro-isostacy models indicate an area of maximal uplift of 5-10 metres along the Rhine in the Netherlands during the Late Pleniglacial, relative to central Germany and central France. Glacio-isostacy therefore is to be considered an extra external control to the fluvial system. It may have contributed to enhanced fluvial incision and deposition in the Campine area. It should be noted, however, that vertical isostatic movements are cyclic, i.e. uplift is followed by subsidence such that the net effect on the landscape may be limited.

SCK-KB10-40

Figure 22 – Predictions of forebulge warping at 21 ka by the current generation of glacio-hydro isostacy models. The location of the Campine region is indicated. Left panel shows output from the Peltier (2004) ICE5G-VM2 model (topography at 21 ka minus topography at 0 ka). Right panel shows output from Steffen (2006) using the same timeframes. Note that the figure on the left is plotted as elevation above contemporary MSL and the figure on the right is plotted as elevation compared to present topography. Contour intervals are however equal and both models predict relative upwarping amounts along in the Campine area of ca. 5 m relative to the North Sea area. Figure taken from Busschers et al. (2007).

7.4 Quaternary geological and geomorphological development

7.4.1 General The post-marine hydrographical evolution of the Campine area started with the final retreat of the sea during the Neogene. Marine conditions in the area, that is now covered by the Nete basin, are known to have occurred during deposition of the Diest Formation (11.7-7.5 Ma), Kasterlee Formation (7.5-5.3 Ma), the Mol, Poederlee and Brasschaat Formations (3.6-2.8 Ma), and the Kempen Group (2.2-1.7 Ma) (Vandenberghe et al., 2004; Louwye et al., 2007) (chronostratigraphy given in (Table 7). The outcrop areas of these deposits are relatively well- known, but reconstruction of former shorelines remains hypothetical. It is clear that the development of the hydrographic network in the area is diachronous: successive shorelines would systematically occur further to the north due to a global sea-level drop and/or tectonic

33 uplift of the area. This implies that the southern part of the Nete basin, beyond the southern limit of the 'Kasterlee sea', is experiencing full continental conditions probably already since 7 Ma, while the northern part, close to the limit of the 'Kempen sea', is experiencing such conditions only since the end of the Tiglian C5, 1.7 Ma ago (age control from Kasse and Bohncke, 2001). More important however is that during this period a south-north river network was developing, consequent to the east-west trending coastline (Figure 23). Around 2.5 Ma ago (Plio-Pleistocene boundary), the North Sea coastline was located in the northern Campine area where mainly peri-marine sediments were deposited (Campine Clay). The hydrography was relatively simple, with rivers flowing consequently from south to north while draining the hinterland that was characterised by a subdued relief. Most likely, these rivers were not incised deeply into the substrate. The situation may have been somewhat different further to the south in the upstream regions of these consequent rivers where continental conditions were prevailing already for a much longer time.

During the Early Pleistocene, major rivers such as the Scheldt and Meuse were depositing sediments that are preserved as river terraces nowadays due to relative uplift in the area south of the Boom Clay outcrop and subcrop zone. In general, however, the geomorphological evolution of northern Belgium is characterised by erosion since then. Around 1 Ma ago, tectonic activity in the Roer Valley Rift System along the Rauw fault forced the Rhine to flow over the Campine Block, the westernmost unit of this system. Simultaneously, the river Meuse was building up a massive alluvial sheet, consisting of sand and later of gravel. These deposits of the Rhine and Meuse were strongly erosion resistant such that they stand out as a positive relief today, known as the Kempen (Campine) Plateau. Strong tectonic activity in the deepest parts of the Roer Valley Graben allowed the Meuse and Rhine to deposit several tens of meters of sediment. Early Middle Pleistocene uplift (~ 750 ka BP) forced the Rhine to shift its course again to the east, while the Meuse started to incise and form the rather narrow Meuse Valley.

Figure 23 – Evolution of the river network in NW Europe from the Tiglian to the Saalian, according to Gibbard (1988; http://www.qpg.geog.cam.ac.uk/research/projects/nweurorivers/). The south to north direction of the Belgian rivers is diverted to the west as a result of the formation of the English Channel following catastrophic discharge of the Elsterian proglacial lake. See text for further explanation.

Figure 24 – Proglacial lake in the southern North Sea basin during the Elsterian glaciation (MIS 12; 450 ka). Also shown is the extent of the ice sheet during MIS 12 (one ice sheet over Europe and Britain) and the LGM (shaded areas within the large ice sheet), and large Western European rivers (a = Fleuve Manche or offshore river system; b = ice-marginal river; c = Rhine; d = Meuse; e = Thames); copy from Fig. 1 in Toucanne et al. (2009).

From the Middle Pleistocene onwards, the hydrographical network was gradually changing. Precise age control is lacking, but somewhere in the Middle Pleistocene (probably around the Early to Middle Pleistocene transition, 0.78 Ma ago) the coastline took a NNE-SSW direction (as is the case nowadays) due to the 'opening' of the English Channel (Vandenberghe and De Smedt, 1979). More recent studies (Gibbard, 2007; Gupta et al., 2007; Toucanne et al., 2009) link the opening of the English Channel to the catastrophic drainage of a large proglacial lake during marine isotope stage 12 (MIS 12), ca. 450 ka ago (Elsterian) (Figure 24). As a consequence, a westward component was superimposed onto the hydrographical network. In those areas where the river network was incising into the Diest sands, this east-west component became accentuated because of the gradually exposed Diest sand ridges that were lined-up parallel to the former ENE-WSW trending coastline. Finally, the Boom Clay took over the role of erosion resistant formation. The 450 ka event triggered the formation of the Flemish Valley, probably in different steps, with extensions towards the south and the east. Low altitude terraces, up to 20 m above the current floodplain, can be found along the river Scheldt, Zenne, Dijle etc. In the Nete basin, several planation surfaces have been recognised at different altitudes. These are interpreted as cryopediments: they were formed during periglacial conditions. The western edge of the Kempen Plateau is also considered a cryopediment connected with the development of the N-S oriented river network that gradually disappeared after OIS 12. Deep incisions are also known from the river Nete, where a deep fossilised gully, more than 10 m below the current surface, has been recognised on geoelectrical soundings near the village of Westerlo. The incision is believed to be Early Weichselian in age.

During the last glacial, again important changes took place in the configuration of the river basins. The river Scheldt, formerly flowing to the north(west), was diverted to the east and forced to break through the Boom Clay cuesta to follow its present course. The same process occurred in the Nete basin, where the hydrological connection to the west was replaced by a more south-westerly course, also breaking through the Boom Clay cuesta. Many of these stream divergences are thought to be caused by dry climatic conditions, together with massive sediment input into the valley systems by aeolian processes.

The vast majority of Quaternary fluvial deposits in Flanders are cold-climate braided river deposits from low sea-level episodes (Figure 25). Localised river terrace deposits from the Scheldt are preserved in the western part of Flanders. Thick and continuous coarse grained deposits from the Meuse can be found on top of the Kempen Plateau and in the Meuse valley. Towards the north, these deposits are interfingering with Early Pleistocene deposits from the river Rhine.

During warm interglacials (Holsteinian, Eemian, Holocene) estuarine and marine sedimentation resumed in some parts, testifying to important marine transgressions in the southern North Sea basin (Vandenberghe et al., 2004). Middle and Late Pleistocene estuarine sediments are preserved in the Ijzer basin, the Flemish Valley and the Scheldt estuary. The widespread occurrence of aeolian deposits, coversands in the north and loess in the south, suggests that during some intervals, climatic conditions were very dry. Most aeolian deposits are Weichselian in age, although older sediments can be found as well, especially in the loess area (Gullentops et al., 2001).

Figure 25 – Quaternary geological map of Flanders, based on Bogemans (2005). Star symbol gives the location of the Mol-Dessel nuclear zone. The Campine Plateau clearly stands out by its red (Meuse deposits) and dark green (Rhine deposits) colour. Younger Meuse deposits are indicated in grey. Purple: Kempen Group substrate overlain by cover sand. Light green: (buried) fluvial deposits. Blue: interstratified fluvial and estuarine deposits. Hatching: recent estuarine deposits. Yellow: coversand. Orange: loess.

7.4.2 The Flemish Valley The Flemish Valley is defined as a broad and relatively deep depression below current sea- level that formed as a result of fluvial erosion during sea-level lowstands (Tavernier, 1946; Tavernier and De Moor, 1974) (Figure 26). At present, it is completely filled up with sediment. The deepest parts are situated in the Ghent area and along the coastline, where it reaches depths below – 15 m, down to – 30 m. Extensions of the Flemish Valley can be found to the south and the east of the Ghent area. The evolution of the Flemish Valley during the Quaternary has been described differently, according to various authors. The age of the Flemish Valley has been assigned to the Cromerian (Paepe et al., 1981) and, alternatively, as a result of polycyclic development during the Holsteinian, Saalian, Eemian and Weichselian (De Moor, 1963). The southern and eastern extensions or branches are thought to have been developed first in the Saalian, but the deepest incisions are attributed to the Eemian and Weichselian (Bogemans, 1993). In Figure 27, a schematic topographical transect is shown from the Campine down to the deepest part of the North Sea off the Belgian coast. This transect more or less crosses the eastern and central Scheldt basin, and thus gives an indication of the general gradient that fluvial systems such as the Nete follow. Additionally shown in the figure is the projected depth of the Flemish Valley, including its eastern branch up to the town of Westerlo. As can be seen, there is a strong gradient just off the current coastline, down to the bottom of the southern North Sea, with the presence of a wide submerged valley. This valley has developed in response to consecutive sea level lowstands posterior to 450 ka when a huge offshore fluvial system drained the bottom of the North Sea, and/or the catastrophic drainage of proglacial lakes. The projected Flemish Valley can be identified as a subsequent hanging valley of this wide offshore valley system. With its present altitude of -30 m to -40 m, this offshore valley bottom seems to have served as the baseline for fluvial development in the Scheldt basin. This base level itself, now set at approximately - 30 m, may be subject to downcutting given the fact that sea level lowstands may be as low as

-120 m, as occurred during the last glacial maximum. Erosion processes would then again be triggered by fluvial erosion from the huge offshore river system that would flow through the southern North Sea and the English Channel to the Atlantic coast, fed by large European rivers and possibly also glacial meltwater.

As can be seen in Figure 26, the Flemish Valley has developed in subsequent position to the Boom Clay cuesta. This observation has already been described by, e.g., Vandenberghe & De Smedt (1979), and is attributed to the erosion resistance of the consolidated and very cohesive Boom Clay relative to the under- and overlying Tertiary sands (note that dipping layers appear adjacent to each other on a geological map). This means that the Boom Clay outcrop zone effectively hampers fluvial erosion and expansion of the Flemish Valley to the north. Here, we introduce the concept of the self-protecting role of Boom Clay against erosion. During the Pleistocene, two rivers succeeded in breaking through the Boom Clay cuesta: the rivers Nete and Scheldt. This resulted in c. 30 m of localized linear erosion.

Figure 26 – Map with base of Quaternary deposits in Flanders (): areas with base > 0 m in greyscale (between 0-150 m) and < 0 m in color scale (between -40 m and 0 m). The Boom Clay outcrop and subcrop zone is indicated by the red line, while major Quaternary faults are white coloured. The Flemish Valley can be defined as the zone in the western part of Belgium with Quaternary deposits below sea-level. Note that in the deepest parts of the Roer Valley Graben, the base of the Quaternary deposits is also below 0 m (east of the major faults). Source: Geologisch 3D Model Vlaanderen (v1.2011).

current topography Campine Plateau 60 Pleistocene Flemish Valley Response to past glacial sea level lowstand 40

Mol reference site 20 England North Sea

current interglacial sea level 0 progressive downcutting to new base level during future glacial -20 sea level lowstand (below -30 m)

-40 sea level (meters abovealtitude current TAW) 300 200 100 0 distance (km)

Figure 27 – General topography of eastern and central Scheldt basin down to floor of North Sea, along an east-west profile from the Campine area to the coast of England. Also shown is the projected depth of the presumed valley floor of the fluvial Flemish Valley system, at discrete locations (bathymetry based on Google Ocean). Projected valley floor of the Flemish Valley system is based on the Quaternary geological map of Flanders, map sheets 16 (Lier), 23 (Mechelen), 24 (Aarschot), 13 (Brugge), 14 (Lokeren) and 15 (Antwerpen) (Source: www.dov.vlaanderen.be).

7.4.3 River terraces and burial history River terraces of different ages can be found on different altitudes, and they reflect the erosional history within the basins. Terraces in south-western Belgium and the Maastricht area, well beyond the southern limit of the Boom Clay outcrop zone, give a clear indication on the relief intensity that developed during the Miocene and Pliocene on the one hand, and during the Quaternary on the other (Gullentops et al., 2001; van den Berg and van Hoof, 2001; Westaway, 2001). Around the Plio-Pleistocene transition, the relief intensity would have been around 60-70 m between the highest interfluvia of Miocene age and valley floors, whereas another 80-120 m of erosion were added to this during the Quaternary. The top of Miocene residual hills is now at altitudes between ca. 150 m (Scheldt) and 200 m (Meuse) above present-day floodplains. Note that maximum incision in the Scheldt basin is below sea- level, witnessed by the presence of terrace levels within the Flemish Valley. Other fluvial records in Belgium are poorly documented especially with regard to available age control. A first indication might be the altitude difference between the height of Diestian hills and present-day valley floor altitudes, which is ca. 60-70 m in the case of the Dijle river near Leuven, and ca. 40 m in the case of the Demer river near Lummen. This value is much lower

39 than the one recorded for the Scheldt and Meuse. Analogous to the latter river systems, about 2/3th of the amount of erosion would have occurred during the Quaternary.

Plio-Pleistocene burial graphs for different regions within the Campine area are shown in Figure 28. The curves follow the relative vertical movement of a point that was at a relative altitude of 0 m a.s.l. 5 Ma ago, when deposition of the Kasterlee and Kattendijk Formations is thought to have started (Vandenberghe et al., 2004). Between ca. 5 Ma and 2.5 Ma ago, the entire Campine region was characterized by steady-state and/or subsidence patterns. The most dynamic region in that time window is the Roer Valley Graben, showing substantial subsidence. Other regions show intermittent phases of subsidence and equilibrium. Around 2 Ma ago, the first clear erosion phases become visible, possibly as a combined effect from uplift, sea-level drop and reduced landscape stability. The first pulse is visible in the western Campine area between ca. 2 and 1 Ma ago. During the last 1 Ma, the central Campine area is thought to have been experiencing large-scale erosion and denudation. This for instance has led to the removal of ~ 30 m of sediment in the Mol area. Overall, with respect to the burial and erosional history during the last 5 Ma, the Campine area can be subdivided into two distinct zones. One zone is characterized by rather shallow burial, usually less than 50 m, and intermittent erosional phases. This region encompasses the western, central and eastern Campine (Campine Block or Kempen Plateau). The other zone is characteristic for its consistent burial and subsidence behavior during the last 5 Ma and comprises the northern Campine area, and the Roer Valley Graben.

Time BP (Ma) 543210 0

-50

-100

-150

Depth (m) Depth -275 Central Campine (Mol area) Western Campine (Kruibeke area) -300 Northern Campine (Poppel area) Campine Plateau (Hechtel area) Roer Valley Graben (Maaseik area)

Figure 28 – Plio-Pleistocene burial history of the Campine area (this report; compilation of data from Geologisch 3D Model Vlaanderen (v1.2011)).

8 Future evolution Climate modelling (BIOCLIM 2001) suggests a long and warm interglacial for the next 50- 170 ka after present (AP), depending on the CO2 scenario used, with possibly marine inundations in the Campine area (Fichefet et al., 2007). Cold climatic conditions are not

40 expected before 50 ka AP, while the return to typical Quaternary glacial-interglacial cycles (100 ka cycles) with permafrost development is expected for the period after 400 ka AP. An ice-sheet advance over northern Belgium is not expected before 1 Ma AP (Huybrechts, 2010) but cannot be ruled out neither in that timeframe. Climatic changes and tectonic movements together will largely determine the evolution of individual components of the physical geographical system, such as the orohydrography, soils, vegetation and hydrology. The impact of human activities will not be considered in this work. The assessment of the future evolution of the surface environment will proceed according to different timeframes that are based on relevant periods from climate modelling (BIOCLIM 2001) and specific requirements from the viewpoint of performance assessment (thermal phase up to 10 ka AP; see De Craen et al., 2012a).

Changes in the surface environment will be evaluated, given maximum conceivable uplift and subsidence rates of 0.1 mm/year (see references in Beerten, 2010). This equals 1 m of vertical movement in 10.000 years (10 ka). These values are conservative values given the fact that they are derived from areas with a different tectonic setting (Ardennes and central Roer Valley Graben) south and north of the central Campine area where uplift and subsidence rates respectively are much higher (see section 7.3).

8.1 Timeframe 0-10 ka AP Tectonics are not considered in this timeframe given the very limited amount of potential vertical movement. Global warming is expected to occur, with or without a marine transgression.

8.1.1 Global warming without marine transgression Various studies regard global warming in Northwestern Europe as a transition from a temperate (present-day) to a subtropical climate (Leterme et al., 2010; BIOCLIM, 2004). Average temperatures are expected to increase by several degrees as a result of anthropogenic greenhouse gas emissions (possibly between + 1.1°C and + 6.4°C by the end of the 21st century already; IPCC, 2007). Due to the long residence time of CO2 in the atmosphere, the impact of human activities on global climate is likely to be maintained for several centuries and millennia. In addition, rainfall seasonality is expected to increase (drier in summer and wetter in winter). The behaviour of rivers is now relatively well understood in typical warm- cold-warm transitions as did occur during the Late Quaternary (Vandenberghe, 2008). These processes, however, are not applicable to the global warming scenario, the effects of which are discussed here. The typical incision phases recorded at the end of the last glacial period, and the transition to the next warm period are the result of major climatic changes, i.e., a transition from a periglacial to a temperate climate. In fact, the landscape in the Campine area has proven relatively stable during the present interglacial (Holocene), mainly as a result of the dense vegetation cover. The density of the cover, and the type of vegetation is not expected to change significantly with a temperature increase of several degrees, and slight to moderate changes in precipitation (BIOCLIM, 2004). It is therefore assumed that landscape stability will largely remain unchanged (Figure 29). Instead, human activities and changes in land use could have more impact on the landscape than global warming itself.

Figure 29 - Present-day landscape and subsurface geology of the upstream parts of the Kleine and Grote Nete basins (view is to the NE). Dark green colours refer to areas with mainly forest, while light green colours are used for meadow, arable land etc. This present-day stable situation is thought to be representative for a future warm climate without marine transgression. View towards the north-east.

Simulations in BIOCLIM (2004) suggest reduced summer precipitation and slight to moderate increases in winter precipitation. Runoff may increase during winter, which may lead to changes in the river system. Amplitude and wavelength of meanders may increase together with fluvial erosion. Overbank events may increase in number. In summer, stream and river flow will be reduced, with some smaller streams becoming ephemeral. In general, however, fluvial incision would not exceed 1 m per 10 ka on average. Global sea level rise of a few metres would result in inundation of low-lying farmland (Scheldt polders) and would force the base level for erosion to rise.

Although considerable variability exists in the scenarios of future climate, simulations for Northern Europe and Belgium suggest reduced summer precipitation and slight to moderate increase in winter precipitation (BIOCLIM, 2004; Ozer et al., 2008). Runoff may increase during winter, which may lead to changes in the river system. Amplitude and wavelength of natural meanders may increase together with fluvial erosion. Overbank events may increase in

42 number. In summer, stream and river flow will be reduced, with some smaller streams becoming ephemeral. In general, however, fluvial incision would not exceed 1 m per 10 ka on average. Global sea level rise of a few metres would result in inundation of low-lying farmland (Lower Scheldt basin) and would force the base level for erosion to rise. The exact amplitude of global sea level rise in the next 10 ka highly depends on the hypothesis of a meltdown of the Greenland or Antarctica ice caps. However, estimates of equilibrium global average sea level rise above pre-industrial levels due only to thermal expansion range from 0.4 to 3.7 m, depending on the gas emissions scenario and the resultant temperature rise (IPCC, 2007). Using climatic analogue stations, Leterme et al. (2012) found an increase of groundwater recharge on grassland by 3% for a 5% increase of annual precipitation. According to recently obtained LOVECLIM simulations (Loutre et al., 2010), infiltration rates (i.e. the water available for infiltration) may well increase, thereby enhancing groundwater recharge. In the case of warm and dry summers, the groundwater pumping rate may increase and lower the groundwater table significantly. It is expected that the situation will be restored during winter and spring. BIOCLIM (2004) suggests that groundwater resources would be less than at present and that regional water levels would be lowered, inducing a downslope shift of spring lines. In the central Campine region, the water table may be 0.25 m lower during very dry summers, relative to 'normal' summers (Labat, 2008).

Generally, chemical weathering will be enhanced and will produce a rather thick regolith with poor mineralogy. In vegetated areas, podzolisation processes will continue and may be responsible for the formation of thick eluvial and enriched (organic C and Fe/Al) horizons.

8.1.2 Global warming with marine transgression It is important to note that we will consider a full marine inundation of the Boom Clay outcrop and subcrop zone, starting from a gradually rising sea-level (Figure 30). In first instance, rising sea-level is thought to bring about several changes, first transforming the low- lying areas in a coastal zone (Figure 31). A sea-level rise of 20 m for instance will bring the coastline as close as several km from Mol while a 3 m-rise will already cause inundation of the lower parts of the Scheldt basin. The central Campine area will evolve in a broad embayment, bounded by the Campine Cuesta in the north, the gentle slopes of the Campine Plateau in the east and the slightly elevated Hageland area in the south.

Figure 30 – Indicative land-water distribution in the southern North Sea basin with rising sea-level (from internet source http://flood.firetree.net/, consulted in October 2011). Symbol marks location of Mol-Dessel nuclear zone. Note that melting of all ice on earth will cause a sea-level rise of about 60 m (references in De Craen et al., 2012a).

Figure 31 – Transgressive and prograding marine depositional environments. The Nete basin may become fully submerged during marine transgression. From Mathijs (2009) and references therein.

As a consequence of a marine transgression, a marine abrasion surface will be formed due to coastal erosion processes. During the transgression, the pre-existing topography with distinct highs and lows will be flattened out, in particular if the transgressed surface consists of unconsolidated sediments as is the case in the Campine area (Figure 32). However, marine erosion is limited and considered to be within several meters only. The broad and deep 'Diestian' gully in the Hageland type area, now filled with sands of the Diest Formation, has been originally interpreted by Gullentops (1957 and 1963) as being the result of marine erosion due to strong coast-parallel currents during the opening of the Strait of Dover (not to be confused with the re-opening of the Strait of Dover during the Elsterian, OIS 12), similar to the current situation along the Belgian coast. However this is not a valid comparison for a future transgression over the Mol area, the scientific basis for this statement being discussed in Vandenberghe et al. (1998). Indeed, in the first place a future transgression of the North Sea over the Campine area can be expected to result in a more open embayment type geography, rather than a funnel shaped basin, given the present general low relief in the area. Furthermore, the present day Flemish sand bars in the North Sea are not deeply eroding into the substrate below (references in Vandenberghe et al., 1998). In fact, the 'Diestian' gully is more likely the result of an important drop of the base level for erosion as a result of relative uplift of the land combined with a major sea level drop (Vandenberghe et al., 1998) while global warming on the contrary will result in a sea level rise rather than in a base level fall.

Figure 32 - Landscape and subsurface geology of the upstream parts of the Kleine and Grote Nete basins with sea level rising to ~ +30 m (view is to the NE). Dark green colours refer to areas with mainly forest, yellow colours are sandy beaches. View towards the north-east.

During a marine transgression, estuarine and marine sedimentation will resume in large parts of the Boom Clay area. The concept is given in Figure 33, where the transition from a fluvial environment to an estuarine environment and eventually a marine environment is depicted relative to the rising sea-level for the Mol-Dessel area. It is likely that the Mol-Dessel area itself will only experience full marine conditions (not estuarine conditions) in a shallow sea, leading to deposition of fine sands (compare with Kasterlee and Poederlee Formations; Vandenberghe et al., 2004).

Figure 33 – Inundation of incised river system and associated sedimentary environments and deposits (modified from Mathijs, 2010). This scheme is for a tide dominated estuary that may develop in the Nete basin following a marine transgression. Sea levels are indicated (on the right) as well as two reference points in the basin itself, i.e., the Kleine Nete valley near Lichtaart and the interfluvium between the Kleine and Grote Nete near Mol-Dessel. The sequence boundary is the current morphology of the area.

8.2 Timeframe 10-50 ka AP Future climate projections, even the most conservative, do not foresee major changes towards colder climates within this timeframe (see references in De Craen, 2012a). Therefore, it is expected that either of the two scenarios described for the timeframe between 0-10 ka AP will persist, or will alternate with a climate that is comparable to the present one. Tectonic movements in the order of 5 m may lift up the earth surface, or may cause the surface to sink, such that erosional processes become more important or less important respectively. It will also influence the position of the coastline. It is anticipated that the vegetation density remains more or less the same. Ongoing soil formation processes may further transform the mostly sandy substrate into podzol soils with thick leached and deep accumulation horizons

(Thompson, 1981). Pronounced argillic horizons may develop on glauconite-rich parent material (Diest and Kattendijk Formations; to a lesser extent also the Kasterlee and Poederlee Formations) that are typical for the Campine area (van Ranst and De Coninck, 1983). These may significantly alter the hydrological characteristics of the unsaturated zone. Fault reactivation in the eastern part of the Campine area will likely produce morphologically visible fault steps in the landscape.

8.3 Timeframe 50-170 ka AP Within this timeframe, relatively warm conditions are expected to dominate the climatic sequence. Climate changes will occur, but cold conditions with a significant sea-level lowering are not expected. The effect of erosion as a result of a limited global sea level drop may further be enhanced by uplift, or counterbalanced by subsidence of the Campine area. At maximum rates of 10 m in 100 ka, the area may have experienced almost 20 m of uplift or subsidence by 170 ka AP. For changes in hydrology and vegetation see previous paragraph.

8.4 Timeframe 170-400 ka AP Within this timeframe, the first cold climatic conditions will likely appear in the investigation area. A cold climate in the Campine region without permafrost development may be identical to a subarctic (BIOCLIM, 2004) and a boreal (Leterme et al., 2010) climate (subarctic and boreal are synonyms). The main features of such a climate are lower temperatures, a lower amount of precipitation, different precipitation (more snow) and a seasonally frozen ground. Furthermore, several climatic cycles likely will occur that are comparable to the glacial- interglacial cycles that the Boom Clay outcrop and subcrop area has experienced during the Quaternary period. Together with tectonic movements, this may lead to rather complex scenarios. The full timeframe between today and 400 ka AP may already see 4 glacial cycles, the intensity of which will depend on future greenhouse gas emissions (see references and discussion in BIOCLIM, 2001).

The baseline for erosion will be lowered drastically due to a sea-level drop. It is thought that the dry North Sea valley bottom at ~ 30-40 m below sea-level will be the limit, resulting in potential erosion of ~ 60 m in the upper reaches of the Kleine Nete basin and ~ 30-40 m near the river Scheldt estuary (Beerten, 2010). Denudation of interfluvia and fluvial erosion may be enhanced because of the increased importance of frost weathering and increased erosivity of precipitation (i.e., snowmelt on a frozen substrate in spring). The hydrographical network may show the appearance of braided rivers. Recharge conditions may be less favourable as a result of reduced infiltration rates (Leterme and Mallants, 2011). Vegetation density is likely to remain unchanged, although the type of vegetation will drastically change: coniferous forest will be the dominant landscape element. As a result, soil formation processes on a sandy soil, such as podzolisation, will likely to continue.

Estuarine conditions that may have developed during the previous timeframes may significantly alter the soil associations and surficial geology of the Campine area. Deposition of estuarine clays will likely change the hydrology and vegetation after the marine regression

47 that follows from the global sea level drop. Recharge may completely change and runoff may increase drastically and enhance fluvial incision.

Even though cold climatic conditions will likely occur during this timeframe, it is expected that they will alternate with warmer interglacial conditions. Sea level rise following a sea- level lowstand may cause the incised valleys to fill up again with marine and/or estuarine sediments. Given the duration of this timeframe, perhaps one or two climatic cycles may occur.

8.5 Timeframe 400 ka to 1 Ma AP Glacial-interglacial cycles will continue, and permafrost development during strong glaciations becomes very likely during this timeframe. In general, the amplitude of conditions described for the previous timeframe will increase; within a time span of 1 Ma, not less than 10 glacial-interglacial cycles may be expected. A cold climate in the Campine region with permafrost development may be identical to an arctic (BIOCLIM, 2004) or a tundra (Leterme et al., 2010) climate. The main features of such a climate are lower temperatures (mean annual temperature below -4°C), a lower amount of precipitation, different precipitation (more snow) and a permanently frozen ground. It is assumed that there is no direct or indirect influence from expanding ice-sheets in northern Europe (Huybrechts, 2010).

Denudation and erosion rates will drastically increase because of a combination of frost weathering, a vulnerable active layer in summer and peak runoff on a frozen and barren underground. Landscape development will be characterised by important slope retreat due to cryopedimentation (Figure 34). Peak discharge will cause periodical activation of braided river systems that will show alternations of deposition and erosion. The maximum amount of erosion is constrained by the altitude of the dry North Sea bottom at ~30-40 m below current sea-level. A total number of 10 sea-level lowstands may cause the relief in the Campine area to be lowered by 35 m in the west (Scheldt area), and more than 60 m in the east (Nete area). Glacio-isostacy may trigger climate-induced uplift of 5-10 m.

In the presence of water, cryosols will develop that are characterised by cryoturbated horizons, frost heave, thermal cracking, ice segregation and patterned ground microrelief (IUSS Working Group WRB, 2007). Vegetation is usually reduced to sparsely to densely vegetated tundra.

Depending on the degree of permafrost development, the hydrological system at the surface may become largely independent from the remaining subsurface groundwater system. A dense network of runoff channels towards larger braided river systems may be expected to develop.

Warm/cold transitions are known to produce very unstable conditions at the earth's surface (see references and discussion in Beerten, 2010). During a warm-cold transition, deep fluvial incisions are to be expected that are followed by massive sediment input from denudating interfluves and retreating slopes. Some of this material will be transferred to the coastline which is located near the Gulf of Biscay. During successive cycles, such large scale incision

48 and denudation will continue in different steps, until the altitude of valley floors reach the level within which sea level is fluctuating. From then onwards, incision during warm/cold transitions is counterbalanced by deposition during the next interglacial period of high sea level.

The characteristics of the earth surface during successive glacial-interglacial cycles will shift from a stable landscape with dense vegetation, thick soils, meandering rivers and sufficient connection between the surface and subsurface hydrological system during interglacials to a generally instable landscape with less vegetation, weakly developed (frozen) soils, braided river systems arranged in a dense network, strong erosion phenomena and temporarily isolated surface hydrological systems during glacial stages. Note that the landscape will become draped by a thin cover of aeolian material (sand or silt) during some intervals of a glacial stage.

Vertical movements may modify this pattern because they influence the potential energy of fluvial processes and the relative position of the baseline for denudation and erosion. At estimated maximum uplift rates of 1 m in 10 ka, the maximum total amount of erosion in the Campine area after ca. 1 Ma may be more than 100 m. An equal amount of subsidence will generate the opposite effect and may even cause marine transgressions during a cold climate.

Ice-sheet development in Flanders has a low probability but is not impossible. If it occurs, the landscape will be completely covered with ice, and another type of erosion process, i.e. glacial erosion, will start playing a determining role in landscape development. A range of surficial deformation processes may then be responsible for the erosion of several 100 m of sediment in the Campine area (Huybrechts, 2010).

Figure 34 - Landscape and subsurface geology of the upstream part of the Kleine Nete basin during a cold climate with permafrost, after several glacial-interglacial cycles (posterior to 400 ka AP). Brown areas refer to tundra vegetation with few or no trees at all while yellow colours refer to sandy plains (plateaus and fluvial braided plains). As a result of fluvial erosion (R), terraces will be formed (T), while slope retreat (S) and cryopedimentation (P) will further widen the braided river plains and cause large-scale denudation. Note that some valleys are cut down below present sea level, a situation similar to the core area of the Flemish Valley during the Late Pleistocene. The Campine Cuesta and Campine Plateau remain relatively stable due to the erosion resistant composition (cohesive clay and gravel respectively). Permafrost depth may be ca. 200 m on average, but will be significantly less in the valleys. View towards the north-east.

9 Integration of the present status, and past and future evolution of the surface environment in the Campine area The present-day geographical characteristics of the Campine area, and more precisely the Boom Clay outcrop and subcrop area, are relatively diverse. The present landscape varies from low-lying polders in the west, characterized by clayey substrates underneath arable land and built areas (Antwerp agglomeration), resulting in hydrologically 'wet' conditions with important seepage zones. Canals and the river Scheldt contribute to groundwater recharge. Towards the east, the relief intensity increases gradually, culminating at the Campine Plateau (up to ~ 90 m a.s.l.) in the southeast. The eastern part of the Boom Clay subcrop zone is characterized by sandy soils with profile development (podzols) that become increasingly dry in eastern direction. Unlike the western part, this area is covered with abundant pine forest, meadows and heathland, while built areas and arable land are less abundant. The unsaturated zone extends up to 10 m depth on the Campine plateau and is characterized by groundwater recharge processes. The north-eastern Campine area is one of the driest areas in Belgium,

50 with less than 700 mm precipitation per year on average. Across this west-east gradient, soils become loamy to the south and sandy to the north, with concomitant changes in vegetation and hydrology (i.e., increasing amount of heathland and pine forest, and increasing infiltration of precipitation towards the north). The most important rivers draining the Boom Clay subcrop zone are the Scheldt and the Kleine and Grote Nete. The rivers Meuse and the Demer-Dijle fluvial system actually form the eastern and southern limit of the Boom Clay outcrop/subcrop zone respectively. Except for the river Meuse, these fluvial systems are partly influenced by tidal processes in their lower reaches. In the Nete basin, most discharge is due to baseflow while runoff is rather limited. The palaeogeographical evolution of the Campine area during the Quaternary is characterized by important stream divergences, relative uplift and erosion. Tectonic uplift of the Campine Plateau forced the river Meuse to incise into the substrate while stable phases are witnessed by the deposition of fluvial deposits that are preserved as river terraces nowadays. To the west of the Campine Plateau, erosional processes shaped the Nete basin and the Lower Scheldt basin as a result of combined uplift and gradual sea-level drop. The Campine Plateau being covered by coarse fluvial deposits from the Early and Middle Pleistocene, was and still is protected from erosion. The same holds true for the Campine Cuesta, that stands out as a positive relief as a result of the cohesive and erosion resistant clay substrate. Burial graphs covering the last few million years from different locations in the Boom Clay subcrop zone reflect processes of subsidence, uplift, sea level variations and climate change in relation to the erodibility of the substrate. Continuous burial during the Quaternary as a result of subsidence is observed for the northern Campine area, near the Dutch border, and for the Roer Valley Graben. Burial graphs for the Campine Plateau, coinciding with the Campine Block as a tectonic unit, do not show important erosional phases during the last several million years. This is due to the protecting cover consisting of coarse fluvial deposits. The area that is now occupied by the Lower Scheldt and the Nete basin has experienced erosion (up to 30 m) during the last 2 Ma. The formation and development of the Flemish Valley, that probably started around 450 ka BP at the earliest as a result of a sudden baseline drop down to -30 m a.s.l., has mainly been limited to the area south of the Boom Clay outcrop zone in Belgium. This is due to the erosion resistance of the clay, forcing the eastern extension of the valley system to erode the softer sediment south of it. However, some incisions into the Boom Clay outcrop did occur in the past, as witnessed by the rivers Nete and Scheldt that cut through the Boom Clay cuesta and thus erode the softer Neogene sediments overlying the deeper subcropping Boom Clay. Renewed base level lowering might cause reactivation and headward expansion of the now filled-up valley system. The future evolution of the surface environment in the Boom Clay outcrop and subcrop zone will mainly be the result of the response of the terrestrial system to changing climatic conditions and internal geodynamics (uplift/subsidence). During the first 50 ka AP, it is likely that vegetation density and landscape stability remains overall the same, with topographical changes of less than 5 m. However, there might be significant changes in hydrology as a result of changing climatic conditions, with more runoff and river peak discharge. Major hydrological changes will occur in the case of a marine transgression.

The first cold climate conditions are not expected before 170 ka AP. However, uplift of the area may cause significant fluvial erosion already before that time. Conversely, subsidence may cause (new) marine transgressions in the Campine area, even with lower global sea-level. Cold climate conditions may ultimately lead to permafrost development (glacials) that alternate with warm periods, comparable to present-day conditions (interglacials). During glacial stages, vegetation will change drastically from densely vegetated (deciduous) woodlands over boreal forest to tundra. The landscape becomes relatively unstable, giving rise to erosional processes such as river incision (terrace formation) and pedimentation. Hydrological changes include the transition to a dense network of small channels and the development of braided river plains in the valleys. During episodes of permafrost, the surface hydrology may become entirely disconnected from the groundwater system. Soils may be transformed into cryosols and disturbed by periglacial deformation processes. Recharge will be less compared to present-day conditions. The return to Quaternary glacial-interglacial cycles, which is expected to occur around 400 ka AP at the latest, will alter the surface environment considerably. It is expected that the Flemish Valley will be reactivated again, leading to renewed fluvial erosion and denudation in the Boom Clay outcrop and subcrop region. These processes may become enhanced as a result of regional and local uplift. The maximum conceivable amount of cumulative erosion and denudation after 1 Ma AP is conservatively estimated at 100-150 m for any location in the Boom Clay outcrop and subcrop zone. Within the next 1 Ma, several examples of extreme landscape changes may be considered. In terms of direct climate change response, vegetation and hydrology will change drastically during permafrost conditions, as will the topography. With continuing uplift, there is a reasonable chance that the river Meuse will be captured by the Dijle-Demer axis in the Bilzen-Maastricht area. In the case of such event, the river Meuse will occupy the eastern branch of the Flemish Valley which will give rise to a huge Meuse-Scheldt confluence area south of the city of Antwerp. Tectonic activity may result in fresh fault morphology near the southwestern border of the Roer Valley Graben. Morphologically visible fault steps are expected to occur along or east of the Feldbiss fault system. The most drastic changes, however, would be caused by an ice-sheet advance over the Campine area. This would completely change the landscape as a result of subglacial and fluvio-glacial erosion. The extent and consequences of this event are most difficult to assess, but at the same time its probability appears to be very low. Low-end scenarios, which we consider here to be those combinations of features, events and processes that would govern a marine inundation in the Campine area all have several changes in common. The pore water composition of the aquifers will gradually change from meteoric to seawater and the sedimentary overburden above the Boom Clay is likely to increase (sand and/or clay) by several meters, perhaps several tens of meters, depending on the uninterrupted duration of these conditions that may reach 100 ka and more. This timeframe is derived from warm BIOCLIM simulations that predict an almost ice-free world during the next 170 ka AP. Subsidence may further contribute to these conditions. The flow system will also change drastically with strongly reduced flow velocities and changing flow paths. High-end scenarios, which we consider here to be those combinations of features, events and processes that govern the persistence of continental conditions due to uplift, and the

52 development of cold climatic conditions, also share several characteristics. Uplift over the next 1 Ma will promote fluvial incision and denudation of interfluvia, such that the thickness of the overburden decreases. Erosion resistant landscape elements, such as the Campine Plateau, the Campine Cuesta and the Boom Clay Cuesta are expected to remain topographical highs, whereas the sands will become eroded, especially in the valleys. Reactivation and further development of the Flemish Valley during (extended) sea-level lowstands, may further enhance the overburden reduction. Strong changes in relief will also bring about changes in the configuration of recharge and discharge zones. During episodes of continuous permafrost, the groundwater system may completely become disconnected from the surface hydrology, leading to strongly reduced recharge and discharge. However, it should be noted that if an ice sheet were to advance in northwestern Europe, the groundwater system may become pressurized, such that water flow velocities increase significantly (van Weert et al., 1997). No flow conditions are thus not very likely, also in the light of the existence of taliks (unfrozen ground underneath rivers and lakes). Even if such conditions should occur, they would not last longer than several millennia in our regions, based on palaeoenvironmental reconstructions of the Weichselian (see Govaerts et al., 2011). An ice sheet advance over northern Belgium may completely change the hydrogeological system as the overburden may be deformed and/or removed (Huybrechts, 2010). Such an event is not expected but cannot be ruled out completely.

10 Conclusions The large-scale geomorphological development of the Boom Clay outcrop and subcrop zone is generally well-understood. The synthesis of Quaternary landscape evolution, in this work focussed on the specific application of waste disposal, lines up with the description of the current geomorphological and hydrographical configuration of the area of interest. Furthermore, it provides insights into the processes that might occur during the next 1 Ma, the timeframe under consideration in the long-term safety assessment of radioactive waste disposal in geological host rocks. At present, erosion estimates based on the geological archive of sea-level variations and uplift/subsidence are treated as extreme values and need further refinement for specific locations within the Boom Clay outcrop and subcrop zone from detailed geomorphological investigations. A full understanding of the future evolution of the surface environment also needs input from analogue approaches and modelling studies, e.g. with respect to the hydro(geo)logical evolution including sea water intrusion as a result of global sea level rise, permafrost development during forthcoming glacial stages and the advance of ice sheets in northwestern Europe. The evidence and reasoning presented in this paper clearly indicates that the surface environment of the Campine area will undergo significant changes during the next 1 Ma with respect to hydrological conditions. The current patterns of recharge and discharge will completely change during marine transgressions, permafrost development and ice sheet development. Uplift and erosion will change the aquifer configuration (infiltration areas) and the overburden thickness, while soil development and vegetation changes will have an impact on landscape stability and infiltration/percolation of precipitation.

11 References AGIV (Agentschap Geografische Informatie Vlaanderen), 1998. Bodemassociaties, versie 1992, schaal 1:500 000. Vlaamse Landmaatschappij.

AGIV (Agentschap Geografische Informatie Vlaanderen), 2002. Bodemgebruiksbestand, opname 2001. AGIV.

AGIV (Agentschap Geografische Informatie Vlaanderen), 2004. Vlaamse Hydrografische Atlas. Vlaamse Milieumaatschappij.

AGIV (Agentschap Geografische Informatie Vlaanderen), 2006. DHM Vlaanderen, raster, 100 m. Departement Mobiliteit en Openbare Werken en Vlaamse Milieumaatschappij.

Batelaan, O., De Smedt, F., 2007. GIS-based recharge estimations by coupling, surface- subsurface water balances. Journal of Hydrology, 337, 337-355

Beerten, K., Brabers, P., Bosch, P., Gullentops, F., 1999. The passage of the Feldbiss Bundle through the Maas Valley. Aardkundige Mededelingen, 9, 153-158.

Beerten, K., 2010. Geomorphological evolution of the Nete basin: identification of past events to assess the future evolution. External Report of the Belgian Nuclear Research Centre, Mol, Belgium. SCK•CEN-ER-137, 40 p.

Beerten, K., 2011. Permafrost in northwestern Europe during the Last Glacial. External Report of the Belgian Nuclear Research Centre, Mol, Belgium. SCK•CEN-ER-138, 24 p.

Beerten, K., Deforce, K., Mallants, D., 2012. Landscape evolution and changes in soil hydraulic properties at the decadal, centennial and millennial scale: A case study from the Campine area, northern Belgium. Catena, 95, 73-84.

Berendsen, H.J.A., 1998. De vorming van het land. Inleiding in de geologie en geomorfologie. Fysische geografie van Nederland. Assen: Van Gorcum, derde gewijzigde druk.

Berendsen, H.J.A., 2008. De vorming van het land. Inleiding in de geologie en geomorfologie. Fysische geografie van Nederland. Assen: Van Gorcum, vijfde gewijzigde druk.

Berger, A., 1977. Support for the astronomical theory of climate change. Nature, 269, pp. 44- 45.

BIOCLIM, 2001. Modelling Sequential BIOsphere systems under ClIMate change for radioactive waste disposal, Deliverable 3: Global climatic features over the next million years and recommendation for specific situations to be considered, pp.27. http://www.andra.fr/bioclim/documentation.htm BIOCLIM, 2004. Modelling Sequential BIOsphere systems under ClIMate change for radioactive waste disposal, Deliverable D10-12: Development and Application of a

Methodology for Taking Climate-Driven Environmental Change into Account in Performance Assessments, pp. 299. http://www.andra.fr/bioclim/documentation.htm Bogemans, F., 1993. Quaternary geological mapping on basis of sedimentary properties in the eastern branch of the Flemish Valley: Toelichtende Verhandeling voor de Geologische en Mijnkaarten van België, 35, 49p.

Bogemans, F., 2005. Technisch verslag bij de opmaak van de Quartairgeologische kaart van Vlaanderen. Vlaamse Overheid, Dienst Natuurlijke Rijkdommen.

Bridgland, D., Westaway, R., 2008. Climatically controlled river terrace staircases: A worldwide Quaternary phenomenon. Geomorphology, 98, 285–315.

Busschers, F.S., Kasse, C., van Balen, R.T., Vandenberghe, J., Cohen, K.M., Weerts, H.J.T., Wallinga, J., Johns, C., Cleveringa, P., Bunnik, F.P.M., 2007. Late Pleistocene evolution of the Rhine-Meuse system in the southern North Sea basin: imprints of climate change, sea- level oscillation and glacio-isostacy. Quaternary Science Reviews, 26, 3216-3248.

Clark, P.U., Mix, A.C., Bard, E., 2001. Ice sheets and sea level of the Last Glacial Maximum. EOS. Transactions of the American Geophysical Union, 82, 241 and 246-247.

Delisle, G., Caspers, G., Freund, H., 2003. Permafrost in north-central Europe during the Weichselian: how deep? In: Permafrost (Eds. Phillips, Springman and Arenson), 187-191. Swets & Zeitlinger, Lisse.

Demoulin, A., Hallot, 2009. Shape and amount of the Quaternary uplift of the western Rhenish shield and the Ardennes (western Europe). Tectonophysics, 474, 696-708

Denis, J. (Ed.), 1992. Geografie van België. Gemeentekrediet, Brussel.

De Craen, M., Beerten, K., Honty, M., Gedeon, M., 2012a. Geo-scientific evidence to support the I2 isolation function (geology & long-term evolution) as part of the Safety and Feasibility Case 1 (SFC1). External Report SCK•CEN-ER-184.

De Craen, M., Beerten, K., Gedeon, M., Vandersteen, K., 2012b. Geo-scientific evidence to support the I1 isolation function related to human actions, as part of the Safety and Feasibility Case 1 (SFC1). External Report SCK•CEN-ER-186.

De Moor, G., 1963. Bijdrage tot de kennis van de fysische landschapsvorming in Binnen- Vlaanderen. Bull. Soc. belge d’Etudes Géogr., 32, 329-433.

De Moor, G., Pissart, A., 1992. Het Reliëf. In: Geografie van België (Denis, J., Ed.). Gemeentekrediet, Brussel.

De Smedt, F., 1992. De Hydrologie. In: Geografie van België (Denis, J., Ed.). Gemeentekrediet, Brussel.

De Smedt, F., Verbeiren, B., Adem, G., 2007. Ontwikkeling van regionale modellen ten behoeve van het Vlaams Grondwater Model (VGM) in GMS/MODFLOW, Perceel 1: Centraal Kempisch Systeem. Deelrapport 3. Ministerie van de Vlaamse Gemeenschap,

Departement Leefmilieu en Infrastructuur, Administratie Milieu-, Natuur-, Land- en Waterbeheer, Afdeling Water.

Fichefet, T., Driesschaert, E., Goosse, H., Huybrechts, P., Janssens, I., Mouchet, A., Munhoven, G. 2007. Modelling the evolution of climate and sea level during the third millennium (MILMO), Scientific Support Plan for a Sustainable Development Policy, Belgian Science Policy.

Gedeon, M., 2008. Neogene Aquifer Model. External Report of the Belgian Nuclear Research Centre SCK•CEN-ER-48, 110p.

Geologisch 3D Model Vlaanderen (v1.2011). Opgemaakt door VITO in opdracht van de Vlaamse overheid, ALBON.

Gibbard, P.L., 1988. The history of the great north-west European rivers during the past three million years. Philosophical Transactions of the Royal Society of London, B318, 559-602.

Gibbard, P.L., 2007. Europe cut adrift. Nature, 448, 259-260.

Gibbard, P.L., Cohen, K.M., 2008. Global chronostratigraphical correlation table for the last 2.7 million years. Episodes, 31, 243-247.

Gibbard, P.L., Lewin, J., 2009. River incision and terrace formation in the Late Cenozoic of Europe. Tectonophysics, 474, 41-55.

Govaerts, J., Weetjens, E., Beerten, K., 2011. Numerical simulation of Permafrost Depth at the Mol site. External Report SCK•CEN-ER-148.

Gullentops, F., 1957. L'origine des collines du Hageland. Bull. Soc. Belge Géol., LXVI, 81- 85.

Gullentops, F., 1963. Etude de divers facies quaternaires et tertiaires dans le Nord et l'Est de la Belgique. In: 6e Congrès International de Sédimentologie, Belgique et Pays-Bas, Excursion O-P, 20 p.

Gullentops, F., Vandenberghe, N., 1995. Toelichtingen bij de geologische kaart van België, Vlaams Gewest, Kaartblad 17, Mol. Belgische Geologische Dienst.

Gullentops, F., Bogemans, F., De Moor, G., Paulissen, E., Pissart, A., 2001. Quaternary lithostratigraphic units (Belgium). Geologica Belgica, 4, 153-164.

Gupta, S., Collier, J.S., Palmer-Felgate, A., Potter, G., 2007. Catastrophic flooding origin of shelf valley systems in the English Channel. Nature, 448, 342–345.

Hardenbol, J., Thierry, J., Farley, M.B., Jacquin, Th., de Graciansky, P.-C., Vail, P.R. (with numerous contributors), 1998. Mesozoic and Cenozoic sequence chronostratigraphic framework of European basins. In: Mesozoic-Cenozoic Sequence Stratigraphy of European Basins (edited by de Graciansky, P.-C., Hardenbol, J., Jacquin, Th., and Vail, P.R.), SEPM Special Publication (Tulsa) 60, 3-13.

Hays J.D., Imbrie J., Shackleton N.J., 1976. Variations in the Earth’s orbit: pacemaker for the ice ages. Science, 194, 1121-1132.

Huijzer, B., Vandenberghe, J., 1998. Climatic reconstruction of the Weichselian Pleniglacial in northwestern and central Europe. Journal of Quaternary Science, 13, 391–417.

Huybrechts, P., 2010. Vulnerability of an underground radioactive waste repository in northern Belgium to glaciotectonic and glaciofluvial activity during the next 1 million year. Departement Geografie VUB, Report 10/01, 26 p.

Imbrie, J., Hays, J.D., Martinson, D.G., McIntyre, A., Mix, A.C., Morley, J.J., Pisias, N.G., Prell, W.L., Shackleton, N.J., 1984. The orbital theory of Pleistocene climate: support from a revised chronology of the marine δ18O record. In: Berger A., Imbrie J., Hays J.D., Kukla G. and Salzman B. (eds), Milankovitch and Climate, Reidel, pp. 269-306.

IPCC, 2007. Climate Change 2007: Synthesis Report. Contribution of Working Groups I, II and III to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change [Core Writing Team, Pachauri, R.K and Reisinger, A. (eds.)]. IPCC, Geneva, Switzerland, 104 pp.

IUSS Working Group WRB. 2007. World Reference Base for Soil Resources 2006, first update 2007. World Soil Resources Reports No. 103. FAO, Rome.

Kasse, C., Bohncke, S., 2001. Early Pleistocene fluvial and estuarine records of climate change in the southern Netherlands and northern Belgium. In: Maddy, D., Macklin, M.G. and Woodward, J.C. (eds.) River Basin Sediment Systems: Archives of Environmental Change. Balkema Publishers, Lisse, 171-193.

Kluiving, S.J., 1994. Glaciotectonics in the Itterbeck-Uelsen push moraines, Germany. Journal of Quaternary Science, 9, 235-244.

Labat, S., 2008. Piezometric Measurements at the Mol-Dessel Site. Site Characterisation for Disposal of Category A Waste. External Report of the Belgian Nuclear Research Centre SCK- CEN-ER-57, 26p.

Lambeck, K., Smither, C., Ekman, M., 1998. Tests of glacial rebound models for Fennoscandinavia based on instrumented sea- and lake-level records. Geophysical Journal International, 135, 375-387.

Leterme, B., Hooker, P., Jacques, D., Mallants, D., De Craen, M., Van den Hoof, C., 2010. Long-term climate change and consequences for near-field, geosphere and biosphere parameters. NIROND TR 2009-07E V1.

Leterme, B., Mallants, D., 2011. Simulation of evapotranspiration and groundwater recharge in the Nete catchment accounting for different land cover types and for present and future climate conditions. External report SCK•CEN-ER-192.

Leterme, B., Beerten, K., 2012. Modelling overland flow during extreme precipitation events: influence of precipitation aggregation level, soil development and climate change. Geophysical Research Abstracts 14, EGU2012-5184. EGU General Assembly 2012, Vienna. Leterme, B. Mallants, D., Jacques, D., 2012. Sensitivity of groundwater recharge using climatic analogues and HYDRUS-1D. Hydrology and Earth System Sciences, 16, 2485–2497.

Lisiecki, L. E., Raymo, M.E., 2005. A Pliocene-Pleistocene stack of 57 globally distributed benthic d18O records. Paleoceanography, 20, PA1003, 17pp.

Loutre, M.F., Crucifix, M., Berger, A., Fichefet, T., 2010. Simulation of extreme climate changes under interglacial boundary conditions for radioactive waste disposal. A study performed with the LOVECLIM model in a Belgian perspective. Scientific Report 2010/01. Georges Lemaître Centre for Earth and Climate Research (TECLIM). Université Catholique de Louvain.

Louwye, S., De Schepper, S., Laga, P., Vandenberghe, N., 2007. The Upper Miocene of the southern North Sea Basin (northern Belgium): a palaeoenvironmental and stratigraphical reconstruction using dinoflagellate cysts. Geological Magazine, 144, 33-52.

Mangerud, J., Birks., H.J.B., Jäger., K. D., 1982. Chronostratigraphical Subdivisions of the Holocene. A review. In: Chronostratigraphical Subdivision of the Holocene (Mangerud, J., Birks, H.J.B. & Jäger. K. D., Editors). Striae 16, 1-6. Uppsala.

Mathijs, M., 2009. The Quaternary geological evolution of the Belgian Continental Shelf, southern North Sea. PhD, Ghent University, 454 p.

Meyus, Y., Woldeamlak, S.T., Batelaan, O., De Smedt, F., 2004. Opbouw van een Vlaams Groundwatervoedingsmodel: Eindrapport. Rapport in opdracht van AMINAL, afdeling Water, Brussel.

Miller, K.G., Kominz, M.A., Browning, J.V., Wright, J.D., Mountain, G.S., Katz, M.E., Sugarman, P.J., Cramer, B.S., Christie-Blick, N., Pekar, S.F., 2005. The Phanerozoic record of global sea-level change. Science, 310, 1293-1298.

National Research Council (NRC), 2006. Surface Temperature Reconstructions For the Last 2,000 Years. National Academy Press, Washington, DC.

Ozer, J., Van den Eynde, D. & Ponsar, S. 2008. Evaluation of climate change impacts and adaptation responses for marine activities: CLIMAR. Trend analysis of the relative mean sea level at Oostende (Southern North Sea – Belgian coast). Report of the CLIMAR project for Belgian Federal Science Policy Office.

Paepe, R., Baeteman, C., Mortier, R., Vanhoorne, R., 1981. The marine Pleistocene sediments in the Flandrian area. Geologie en Mijnbouw, 60, 321-330.

Peltier, W.R., 2004. Global glacial isostasy and the surface of the ice-age Earth: the ICE-5G (VM2) model and GRACE. Annual Review of Earth and Planetary Sciences, 32, 111–149.

Reicherter, K, Kaiser, A., Stackebrandt, W., 2005. The post-glacial landscape evolution of the North German Basin: morphology, neotectonics and crustal deformation. International Journal of Earth Sciences, 94, 1083-1093

Renssen, H., Vandenberghe, J., 2003. Investigation of the relationship between permafrost distribution in NW Europe and extensive winter sea-ice cover in the North Atlantic Ocean during the cold phases of the Last Glaciation. Quaternary Science Reviews, 22, 209-223.

RMI, 2011. Royal Meteorological Institute of Belgium (RMI), www.meteo.be (accessed on Feb., 8th 2011).

Steffen, H., 2006. Determination of a consistent viscosity distribution in the Earth’s mantle beneath Northern and Central Europe. Published Ph.D. Thesis, Institut für Geologische Wissenschaften der Freie Universität Berlin, Germany.

Svendsen, J.I., Alexanderson, H., Astakhov, V.I., et al., 2004. Late Quaternary ice sheet history of northern Eurasia. Quaternary Science Reviews, 23, 1229-1271.

Tavernier, R., 1946. L’évolution du Bas Escaut au Pleistocène supérieur. Bull. Soc. belge de Géol., 55, 106-125.

Tavernier, R., De Moor, G., 1974. L'évolution du Bassin de l'Escaut. Centen. Soc. Géol. Belgique, 159-233, Liège.

Thompson, 1981. Podzol chronosequences on coastal dunes of eastern Australia. Nature, 291, 59-61.

Toucanne, S., Zaragosi, S., Bourillet, J.F., Gibbard, P.L., Eynaud, F., Giraudeau, J., Turon, J.L., Cremer, M., Cortijo, E., Martinez, P., Rossignol, L., 2009. A 1.2 Ma record of glaciation and fluvial discharge from the Western European Atlantic margin. Quaternary Science Reviews, 28, 2974-2981.

Trewartha, G.T., 1968. Fundamentals of Physical Geography, McGraw-Hill Co. van Balen, R.T., Houtgast, R.F., Van der Wateren, F.M., Vandenberghe, J., Bogaart, P.W., 2000. Sediment budget and tectonic evolution of the Meuse catchment in the Ardennes and the Roer Valley Rift System. Global and Planetary Change, 27, 113-129. van Balen, R.T., Houtgast, R.F., Cloetingh, S.A.P.L., 2005. Neotectonics of the Netherlands: a review. Quaternary Science Reviews, 24, 439-454. van den Berg, M.W., van Hoof, T., 2001. The Maas terrace sequence at Maastricht, SE Netherlands: evidence for 200 m of late Neogene and Quaternary surface uplift. In: Maddy, D., Macklin, M.G. & Woodward, J.C. (eds): River Basin Sediment Systems: Archives of Environmental Change, Balkema (Rotterdam): 45-86. van der Wateren, F.M., 1995. Structural Geology and Sedimentology of Push Moraines. Processes of soft sediment deformation in a glacial environment and the distribution of glaciotectonic styles. Mededelingen Rijks Geologische Dienst, 54, 1-168.

59 van Gijssel, K., 1987. A lithostratigraphic and glaciotectonic reconstruction of the Lamstedt moraine, Lower Saxony (FRG). In: van der Meer J.J.M. (ed.) Tills and glaciotectonics. Balkema, Rotterdam, 145-155.

Van Landuyt, W., Vanhecke, L., Hoste, I., 2006. Geografische factoren in de verspreiding van planten – Hoofdstuk 6. In: Atlas van de flora van Vlaanderen en het Brussels Gewest (Eds. Van Landuyt et al.), p. 83-93. Nationale Plantentuin van België en Instituut voor Bosbouw en Wildbeheer (INBO), Impressum Meise, Brussel.

Van Ranst, E., De Coninck, F., 1983. Evolution of glauconite in imperfectly drained sandy soils of the Belgian Campine. Zeitschrift für Pflanzenernährung und Bodenkunde, 146, 415- 426. van Weert, F. H. A., van Gijssel, K., Leijnse, A., Boulton, G.S., 1997. The effects of Pleistocene glaciations on the geohydrological system of Northwest Europe. Journal of Hydrology, 195, 137-159.

Vandenberghe, J., 1985. Paleoenvironment and stratigraphy during the Last Glacial in the Belgian–Dutch border region. Quaternary Research, 24, 23–38.

Vandenberghe, J., 2008. The fluvial cycle at cold-warm-cold transitions in lowland regions: A refinement of theory. Geomorphology, 98, 275-284.

Vandenberghe, J., De Smedt, P., 1979. Palaeomorphology in the eastern Scheldt basin (Central Belgium) - The dijle-demer-grote nete confluence area. Catena, 6, 73-105.

Vandenberghe, N., Laga, P., Steurbaut, E., Hardenbol, J., Vail, P.R., 1998. Tertiairy sequence stratigraphy at the southern border of the North Sea basin in Belgium. Mesozoic and Cenozoic Sequence Stratigraphy of European Basins, SEPM Special Publication, 60, 119-154.

Vandenberghe, N., Van Simaeys, S., Steurbaut, E., Jagt, J.W.M., Felder, P.J., 2004. Stratigraphic architecture of the Upper Cretaceous and Cenozoic along the southern border of the North Sea Basin in Belgium. Netherlands Journal of Geosciences, 83, 155-171.

Vandersteen, K., Gedeon, M., Mallants, D., 2011. Beschrijving van de regionale en lokale hydrologie van het oppervlaktewater met betrekking tot de site voor berging van laag- radioactief afval te Dessel. SCK•CEN ER-172, Mol, Belgium.

Vanneste, K., Verbeeck, K., Camelbeeck, T., Paulissen, E., Meghraoui, M., Renardy, F., Jongmans, D., Frechen, M., 2001. Surface-rupturing history of the Bree fault scarp, Roer Valley graben: Evidence for six events since the late Pleistocene. Journal of Seismology, 5, 329-359.

Westaway, 2001. Flow in the lower continental crust as a mechanism for the Quaternary uplift of the Rhenish Massif, north-west Europe. In: Maddy, D., Macklin, M.G. & Woodward, J.C. (eds): River Basin Sediment Systems: Archives of Environmental Change, Balkema (Rotterdam): 87-167.

Zagwijn, W.H., 1974. The Paleogeographic Evolution of The Netherlands during the Quaternary. Geologie en Mijnbouw, 53, 369-385.