Erosion Stability of Dgr Potential Sites

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00 Final report 25/2015/ENG

EROSION STABILITY OF DGR POTENTIAL SITES

Authors: Tomáš Hroch, Tomáš Pačes et al.

Czech Geological Survey

Prague, November 2015

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EROSION STABILITY OF DGR POTENTIAL SITES

Team of authors: Tomáš Hroch

Tomáš Pačes

Jan Hošek

Daniel Nývlt

Jiří Šebesta

Petra Hejtmánková

Report number: Erosion Stability of DGR Potential Sites SÚRAO TZ 25/2015/ENG

Content 1 Introduction ...... 8 2 Expert Report of T. Hroch ...... 10 2.1 Introduction ...... 10 2.2 Erosion and denudation processes and their control factors ...... 10 2.3 Determination of rates of erosion and denudation ...... 13 2.4 The rate of erosion in the Bohemian Massif ...... 13 2.5 Geomorphological analysis ...... 14 2.6 Geomorphological characteristics of potential DGR sites ...... 17 2.6.1 Březový potok ...... 17 2.7 Čertovka ...... 17 2.7.1 Čihadlo ...... 22 2.7.2 Horka ...... 22 2.7.3 Hrádek ...... 26 2.7.4 Magdalena ...... 26 2.7.5 Kraví hora ...... 29 2.8 Prognosis of morphological development of individual potential DGR sites ...... 29 2.8.1 Březový potok ...... 29 2.8.2 Čertovka ...... 29 2.8.3 Čihadlo ...... 30 2.8.4 Horka ...... 30 2.8.5 Magdalena ...... 31 2.8.6 Kraví Hora ...... 31 2.9 Summary ...... 31 3 Expert Report of T. Pačes ...... 34 3.1 Introduction ...... 34 3.2 Denudation rates in different geomorphological and climatic conditions ...... 36 3.3 The rate of erosion in the Bohemian Massif ...... 43 3.4 Effect of glaciation on the rate of erosion in the Bohemian Massif ...... 49 3.5 Influence of terrain slopes on erosion in the surveyed localities ...... 50 3.6 Conclusions...... 53 4 References ...... 55

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List of illustrations: Fig. 1 The ideal profile of a balanced watercourse gradient curve. (http://thebritishgeographer.weebly.com)...... 11 Fig. 2 Gradient curve change and distribution of prevailing fluvial processes in the river system due to the vertical movements of the Earth's crust (Leeder 1999) ...... 12 Obr. 3 Reaction of the river system to erosion base fall (http://www.gly.uga.edu)...... 12 Fig. 4 Geomorphological scheme of the Březový potok area ...... 19 Fig. 5 Geomorphological scheme of the Čertovka area ...... 20 Fig. 6 Geomorphological scheme of the Čihadlo area ...... 21 Fig. 7 Geomorphological scheme of the Horka area ...... 24 Fig. 8 Geomorphological scheme of the Hradek area ...... 25 Fig. 9 Geomorphological scheme of the Magdalena area ...... 27 Fig. 10 Geomorphological scheme of the Kraví Hora area ...... 28 Tab. 4 Denudation rate in New Mexico calculated from data of Waren and Cook (1973) ...... 37 Fig. 11 Distribution of denudation values; the red column shows the geometric mean, the green column shows the median, and the yellow column shows the arithmetic mean...... 39 Fig. 12 Rate of erosion in the catchment area of the world's rivers and smaller watercourses (Burbank, 2002) ...... 40 Fig. 13 Rate of erosion derived from accumulation of the cosmogenic isotope 10Be in various types of landscape and depending on terrain slope (Portenga and Bierman 2011)...... 41 Fig. 14 Rate of erosion derived from accumulation of the cosmogenic isotope 10Be depending on rock type, climate zone, and tectonic activity (according to Portenga and Bierman 2011) ...... 42 Fig. 15 Rate of erosion in glaciated areas, and rates of erosion caused by fluvial systems ..42 (Burbank, 2002)...... 42 Fig. 17 Small catchment area (usually 0.5 - 3 km2) used to measure the mass balance of the chemical element“i"; Measured inputs: P – Precipitation, A - Anthropogenic inputs (fertilising, liming, and other artificial inputs) Source: W - Wethering (release of the element by weathering of rocks); outputs: B - Biological fixation of the element in harvested organic matter (tree felling, harvesting crops), R - Runoff of the element in the solution, M - Mechanical erosion (removal of the element in suspended solids)...... 45 Tab. 8 Rates of erosion and denudation in small catchment areas of the Bohemian-Moravian Highlands and the Ore Mountains (Pačes, 1985) ...... 48

List of tables: Tab. 1 Legend with the main allocated geomorphological forms at DGR sites: ...... 15 Tab. 2 Average erosion rates according to various authors. Literary sources in Kukal (1983). ……………………………………………………………………………………………………36 Tab. 3 Denudation extent in the UK, calculated from data from Kirkby (1967) ...... 37 Tab. 5 Erosion rates calculated from data on accumulation and decay of cosmogenic isotopes 10Be and 26Al and by the use of complementary methods ...... 38

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Tab. 7 The average advance of denudation in the Elbe related to the profile in Litoměřice assuming the density of the weathered rock of 2,650 kg.m-1 (Pačes, 1985) ...... 47 Tab. 9 The rate of weathering, erosion, and denudation in two small catchments in the Ore Mountains and in the Behemian-Moravian Highland in the periods from 1978 to 1995 and from 1990 to 1995 (Melega, 1998)...... 48 Tab. 10 Estimated thickness of permafrost in the Upper Vistula Pleniglacial in the Czech Republic according to Balojev, Čápicina, and Czudek (Czudek, 2005) ...... 49 Tab. 11 Gradient distribution in the surveyed sites ...... 51

List of abbreviations:

A.S.L. Above See Level BP Before Present ČHMI Czech Hydrometeorological Institute DEM Digital Elevation Model DGR Deep Geological Repository EUVN European Vertical GPS Reference Network RAWRA Radioactive Waste Repository Authority

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Abstract Evaluation of erosion stability for areas selected for sites of deep geological repository for the next 100 thousand years is based on literature review and interpretation of available published data, as well as unpublished data by two independent experts leading to evaluation of erosion stability. The evaluation focused on the definition of the main factors controlling erosional processes, the evaluation of geomorphological setting of selected areas based on remote sensing methods. An evaluation of mass balance and geochemical data has been included. Predictions of geomorphological changes for two climate scenarios have been done. Also human impact, influence of glacier processes and impact of permafrost has been evaluated.

Keywords Denudation, erosion, neotectonics, geomorphological setting, mass balance, permafrost

Abstrakt Tato zpráva se zabývá zhodnocením erozní stability území vytipovaných lokalit hlubinného úložiště jaderného odpadu po dobu budoucích minimálně 100 000 let. Analýza je založená na rešerši a interpretaci dostupné publikované literatury i nepublikovaných dat a geomorfologické interpretaci dvěma nezávislými experty. Vyhodnocení zahrnuje definici hlavních faktorů erozních a denudačních procesů, rešerši dat a základního zhodnocení geomorfologické charakteristiky území na základě distančních dat. Byly provedeny predikce budoucího možného morfologického vývoje pro dva limitní klimatické scénáře. Zhodnocen byl také vliv lidské činnosti, glacigenních procesů a vzniku permafrostu.

Klíčová slova Denudace, eroze, neotektonika, geomorfologická pozice, hmotová bilance, permafrost

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1 Introduction

This report was prepared within the SURAO project "Research support for deep repository safety evaluation” which is part of preparations of the deep geological repository of radioactive waste (hereinafter referred to as DGR). The aim of the project is to obtain data, models, arguments, and other information needed to evaluate potential sites for the DGR location in terms of its long-term safety. A tender which took place in July 2014 led to a four- year contract with the ÚJV Řež, a. s. and its subcontractors: Czech Geological Survey, Czech Technical University in Prague, Technical University of Liberec, Institute of Geonics AS CR, and ARCADIS CZ a.s., Progeo, s.r.o., Chemcomex Praha, a.s., and Centrum výzkumu Řež, s.r.o. on providing research support for long-term safety assessments in the following areas: i. Behaviour of spent nuclear fuel and radioactive waste that are unacceptable to the near-surface storage in a DGR; ii. Behaviour of SNF disposal canisters (SC) and radioactive waste in a DGR; iii. Behaviour of buffer, backfilling, and other construction materials in a DGR; iv. Disposal borehole solutions and their effect on the surrounding geological environment; v. Behaviour of the geological environment; vi. Transport of radionuclides from the repository; vii. Other characteristics of the sites potentially affecting the safety of the repository.

The aim of the Erosion Stability sub-project is to evaluate various scenarios of relief changes with respect to erosion and denudation processes in the next 100,000 years in the sites with potential prospective radioactive waste DGRs in the Czech Republic and evaluation of erosion stability of selected DGR sites. The primary objective of the report was to perform a literature search and present the data from the available literature, as well as unpublished data and results of geomorphological on- site analyses. The research was carried out by two independent experts. The aim is to fulfil the project’s goal, i.e. to evaluate the erosion stability of the locations selected as prospective DGR sites. Each of the experts based their evaluation on different assumptions: 1) Erosion occurs selectively, the intensity of erosion and denudation processes can be dramatically different depending on local conditions, 2) differences in geomorphology and current rates of erosion between the different areas can be reliably detected, differences in the speeds of future changes can only estimate from a geological analogy. The differences will be much larger than the differences that we see from the current data. The intensity of erosion and denudation processes depends on many factors the parameters of which change over time. On longer time scales, these are especially endogenous factors (uplift and tectonic processes in general) and exogenous factors. The local parameters can also have a significant influence. These parameters include lithology of rocks in the area, declivity, vegetation cover density, etc. The study is based both on literature research on the general geomorphological evolution of the DGR potential sites, including impacts of erosion and denudation processes, and a geomorphological analysis of the area around DGR. The

8 Report number: Erosion Stability of DGR Potential Sites SÚRAO TZ 25/2015/ENG later allows interpreting the origin and genesis of various geomorphological features and geodynamic processes taking place on them and categorising the sub-geomorphological forms on the basis of intensity of erosion processes. The authors also assessed geochemical data and data on mass balance of selected catchment areas. Data interpretations served as input data for evaluation of future geomorphological changes in seven sites selected as potential DGRs over at least 100,000 years. Each author used different approach: T. Hroch used the assumption that geomorphological characteristics of an area are the result of a long-term influence of exogenous factors on the Earth's surface and the assumption that it is possible to employ geomorphological analysis for near-future predictions of morphological developments. T. Pačes worked mainly with the average data for the entire catchment area and with the assumption that the spread of the values of the erosion rate due to different climatic, morphological, and geological conditions can be estimated for the current conditions in the various areas of interest, yet it is not scientifically possible to identify the erosion rate differences in these areas for the next 100,000 years.

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2 Expert Report of T. Hroch

2.1 Introduction

The study is based on the assumption that erosion and denudation are selective processes and that the intensity of erosion and denudation processes can significantly vary depending on local conditions. The intensity and nature of erosion and denudation processes that took place in the past is evidenced by the geomorphological characteristics of the area. The various relief types are the result of long-term effects of exogenous and endogenous factors on the Earth's surface. The interpretation of past processes may be applied to morphological development predictions of the areas. Thus, the study is based both on literature research on the general geomorphological evolution of the DGR potential sites, including impacts of erosion and denudation processes, and a geomorphological analysis of the area around DGR. The later allows interpreting the origin and genesis of various geomorphological features and geodynamic processes taking place on them and categorising the sub-geomorphological forms on the basis of intensity of erosion processes. The interpretations then serve as input data for evaluation of future geomorphological changes in seven sites selected as potential DGRs over at least 100,000 years.

2.2 Erosion and denudation processes and their control factors

Erosion and denudation processes are the result of direct effects of exogenous factors on the Earth's surface and they represent one of the main mechanisms shaping the resulting geomorphological characteristics of the DGR potential sites in the long term. In our country, these processes are represented mainly by mechanical and chemical weathering of rocks and mechanical erosion of materials. The intensity and the predominant type of denudation processes depend on the morphology and geology of the area, climate, vegetation, and land use (e.g. Fairbridge 1968, Gaudie 2004). Thus, geomorphological character of landscape is predisposed by complex of factors and processes including: 1) lithological and structural conditions of rocks predetermining resistance of geological environment against erosion and denudation processes, presence and nature of discontinuities in the rock environment which may represent weaker zones prone to erosion processes;

2) tectonic predisposition as one of the main factors influencing the area’s topography and gradient conditions of individual catchments areas;

3) hydrological position of the area (position in the sub-catchment area related to the watershed) which is a key long-term parameter for the alluvial erosion in terms of backward erosion; 4) position and shifts of erosion base which determine the gradient conditions of the river system predetermines the intensity of erosion processes and the outreach of “head-ward erosion” crated by the valley network in the catchment area;

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5) altitude which, in our latitudes, determines the climate characteristics of the area and the possible occurrence of glacial and periglacial processes.

In terms of active agents erosion may be divided into (i) alluvial erosion (caused by running water, (ii) aeolian erosion (caused by wind), and (iii) periglacial erosion (caused by activity of an iceberg). In terms of relief creation and changes, the alluvial erosion plays the primary role in the Bohemian Massif and the effects of other factors are marginal. The intensity of alluvial erosion is mainly determined by the river system’s gradient curve in the given catchment area and the erosion base’s position. The topographic gradient of a watercourse is described by the gradient curve. This is an imaginary line connecting points on the river bed plotted in a longitudinal height profile (i.e. a kind of longitudinal elevation profile of the river bed from head to mouth). In the ideal case (, it is the steepest in the upper course and decreases towards the estuary. In this case we talk about a balanced gradient curve. However, due to inhomogeneities in the rock environment, such as varying rheology of rocks or vertical movements of the Earth's surface, water courses do not have balanced gradient curves (Fig. 2). Water courses tend to equalise the curve which is demonstrated by intense deep erosion progressing upstream from the erosion base. The erosion base is usually related to the place where the river system’s gradient decreases and represents an area where the water course shifts from the erosion mode to the accumulation mode. The relative movement of the erosion base causes changes in the gradient and in the river system’s reactions (Fig. 2). The erosion base elevation strengthens the lateral component of the head-ward erosion, its decline, on the other hand, leads to a stronger influence of deep erosion accompanied by a recess of river valleys and an advancement of head-ward erosion to the upper parts of the catchment area (Obr. 3).

Fig. 1 The ideal profile of a balanced watercourse gradient curve. (http://thebritishgeographer.weebly.com).

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Fig. 2 Gradient curve change and distribution of prevailing fluvial processes in the river system due to the vertical movements of the Earth's crust (Leeder 1999)

Obr. 3 Reaction of the river system to erosion base fall (http://www.gly.uga.edu).

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2.3 Determination of rates of erosion and denudation

There are several methods that can be used for estimation of rates of erosion and denudation processes. First, there are methods based on mass balance of elements in individual catchment areas or measurements of the dissolved material transported by river systems. Another possibility is the methods based on the difference in height levels of the preserved datable surfaces and the current erosion base levels or calculations of the speed of vertical movements of the surface. When measuring the vertical uplift of the surface we use the assumption that the uplift is compensated by erosion due to the relative decrease of the erosion base. The rate of the uplift corresponds to the rate of erosion in the long term.

The rate of the long-term deep erosion is influenced by a number of uncertainties when calculated by the above methods (irregularly lowered terrace surface due to the erosion, destruction of their bases, regional differentiation of individual tectonic uplifts, fragmentary pre-quaternary record, the issue of stratigraphic inclusion of some fluvial accumulations, etc.). Calculations of vertical movements of the Earth's surface by the use of sensitive GPS devices placed on a stable surface bring quite heterogeneous data that is greatly influenced the sensitivity of individual devices and the suitability of their location. A promising (but expensive) method is a dating by the use of 10 Be and 26 Al isotopes. The literature uses these methods to a stratigraphic inclusion of different levels of terraces from which it is possible to derive calculation of the surface erosion rate in the catchment area in the time scales of tens to hundreds of thousands of years (Blanckenburg 2005). Another possibility is to date the fluvial sediments buried under radio-isotope datable volcanic outbursts (in the Bohemian Massif it is e.g. in the Jizera catchment area), however, these possibilities have not been utilised for calculating the rate of erosion processes so far.

2.4 The rate of erosion in the Bohemian Massif

The results of measuring the speed of erosion and denudation rates reported in the literature have a wide range, which is caused by local factors that affect the intensity of erosion processes in individual areas (climate, neotectonic activity, etc.). However, different estimates of erosion rates may be caused by uncertainties in the form of various qualities and densities of the relevant data and the methodology used. The Bohemian Massif area is a tectonically stable platform; however it has been constantly elevated since the late Cretaceous period in response to the Alpine- Carpathian orogeny (Malkovský 1987; Ziegler and Dèzes 2007). There were several stages of strong tectonic uplifting (early Paleogene, Oligocene-Lower Miocene, Upper Miocene, and Pliocene-lower Pleistocene), especially on reactivated pre-alpine crust fractures in outlying mountain ranges (Šumava, Czech forest, Ore Mountains, Giant Mountains; Adamovič and Coubal 1999). The new morphostructural vaults heavily eroded which led to creation of the “planation surface” (Demek 2004). The eroded material was then transported by the river network to Paratethys, or to basins formed on the newly formed or reactivated faults (of the North and the South Bohemian Basins).

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Balatka and Kovanda (2001) reported the following values calculated on the basis of the height difference of peneplenised surfaces, preserved fluvial sediments, and the level of erosion base rate of river system sinking for the Late Cenozoic: Middle and Upper Miocene 0.02 to 0.04 mm/year; Pliocene and Lower Pleistocene 0.062 to 0.125 mm/year; middle Pleistocene 0.61 to 0.86 mm/year; Upper Pleistocene 0.02 to 0.04 mm/year. These figures do not correspond to results presented by Tyráček et al. (2004) who analysed correlation of the Elbe and Vltava terraces estimate that the average speed of the neotectonic uplift of the central part of the Bohemian Massif in the Lower Pleistocene was 0.04 mm per year and in the Middle and the Upper Pleistocene to 0.15 mm/year. Vyskočil (2001) estimates, that the rate of the Upper-Pleistocene uplift in the Great Mountains and Jeseník was 0.1 mm per year. Those estimates are burdened by considerable uncertainties stemming from a problematic stratigraphic classification of some fluvial accumulations. The applicability of biostratigraphy (Tyráček et al., 2001) or paleomagnetic analysis (Záruba et al., 1977) is rather limited in this sediment. The studies are based on modern dating methods within which isotopes 10Be and 26Al are used. Nývlt (2008) estimated the rate of surface erosion in Lusatian Highlands during the middle and upper Pleistocene to 0.025 to 0.027 mm per year. Similar rates of Pleistocene denudation processes were calculated for the southwestern edge of the Bohemian Massif (Regen) by Schaller et al. (2001) - the value range is 0.023 to 0.027 mm per year. According to Meyer et al (2010), the Rhine Massif is part of the Variscan Mountains, as well as the Czech Massif, the rate of the denudation processes was 0.029 to 0.086 mm per year. The above areas are located on the watershed (in the case of Lusatian Highlands it is the European watershed) and it can thus be assumed that reported dynamics of denudation processes will be very similar to that in the watershed of the selected DGR locations. Other data from which we can be infer the rate of denudation processes is a direct measurement with highly sensitive GPS devices. While the rate of active horizontal tectonic movements in the Czech Massif is dealt with by many studies (e.g. Schenk et al. 2004; Švábenský and Weigel 2006; Švábenský et al. 2011; 2012; Mrlina and Seidl 2008), vertical movements have not been paid much attention so far. Again, the obtained results were very heterogeneous, largely due to different sensitivities of individual equipment, their locations, or the original aims of individual studies and the specific surveyed area. A wider geographic range of this data is available in the long- term EUVN project (European Vertical GPS Reference Network). The reported figure for our area is 1.1 mm per year measured at the station located on the southeast outskirts of the CMH, which corresponds to the results from the eastern part of the Czech- Moravian Highlands where Schenková and Kottnauer (2009) reported the uplift rate of 1 mm per year. 2.5 Geomorphological analysis

The geomorphological analysis serves for interpretation of origin and evolution of the relief in the recent geological past and predictions of its further development. It is an interpretive method that studies the evolution of the relief in terms of dynamics of geodynamic processes that were or are applied during its creation. The aim of the analysis is to define and explain the genesis of each morphological form on the surface of the Earth, i.e. what processes were and are involved in its development and whether its predisposition is endogenous or

14 Report number: Erosion Stability of DGR Potential Sites SÚRAO TZ 25/2015/ENG exogenous and whether its origin was a one-off or polyphasic. The studies also deal with spatial and relative relationships with the surrounding morphological forms and structures. The geomorphological interpretation has been prepared on the basis of a digital 4th generation terrain model (4G DEM) which shows natural or man-treated ground in digital form as points in a regular grid (5 x 5 m) generated from data acquired by airborne laser scanning. There were 10 major geomorphological forms defined within the geomorphological analysis The defined basic geomorphological forms were divided both on the basis of the genesis and according to the intensity and type of denudation processes (Tab. 1).

Tab. 1 Legend with the main allocated geomorphological forms at DGR sites: Intensity of Predominant Geomorphological erosion type of ID Geodynamics Genetic type form factors erosion Surface + 1 Endogenous Tectonic Fault area high linear erosion 2 Endogenous Tectonic Other high Linear erosion morphological evidences of fault structures 3 Endogenous Structural Structural slope high Surface erosion Surface 4 Exogenous Denudation Erosion slope high erosion Retreating Surface 5 Exogenous Denudation escarpments high erosion 6 Exogenous Denudation Erosion valley V high Linear erosion 7 Exogenous Denudation Erosion valley U moderate Linear erosion 8 Exogenous Denudation Palaeosurface low Surface (palaeorelief) erosion 9 Exogenous Accumulative River terraces low Surface erosion According to the type of fluvial system 10 Exogenous Accumulative River floodplain low and gradient

Among the tectonic geomorphology forms with endogenous predisposing factors were included fault escarpments and other morphological evidences of fault structures. A fault escarpment are characterised by a straight or slightly curved course predisposed by the original fault plane prepared by denudation. Due to the effects of erosion and other denudation processes the geometric match of the original fault plane and the bare fault plane

15 Report number: Erosion Stability of DGR Potential Sites SÚRAO TZ 25/2015/ENG is only partial. These are often linked to other morphological evidences of fault structures which represent morphologically distinct straight or slightly curved sections of the drainage network, strong and geometrically regular changes in the drainage network, straight or curved edges of river valleys, or areas with a significant river system gradient change. Not only tectonic structures are one of the factors affecting the morphology of the DGR potential sites and vertical movements of the Earth's surface, but they also represent zones with a weakened rock environment in which erosion processes are more apparent. Structural slopes are slightly sloping geomorphological units appearing at sites with inhomogeneous geological environment predisposed by flat structures with no direct connection with the fault tectonics. In the case of sedimentary complexes, such areas generally correspond to strata surfaces of bodies with a greater resistance compared to their bedrock or upper bed, in metamorphic terrains, these slopes may correspond with metamorphic planar structures. Retreating escarpments are inclined geomorphological forms that are kept in a state of dynamic equilibrium due to the gradual removal of the weathered material that is formed on the surface. In the long-time, the gradual erosion weathering leads to creation of a receding slope. Their creation and activity is linked mainly to the arid climate. The defined slopes located in the studied areas usually separate two different levels of palaeosurface. Erosion slopes are tied to significant erosion alleys of rivers. Erosion slopes with lower gradients have developed in the peripheral parts of palaeosurface and represent their degraded edges. They may be also linked to the top parts of erosion valley slopes. Steeper slopes, on the other hand, ale linked to central bottom parts of erosion valleys. Erosion valleys are linear erosion structures created by a considerable recess of the drainage system. They have two basic forms: (i) valleys with a V-shaped cross-section with a relatively steep catchment drainage curve and prevailing fluvial deep erosion and (ii) erosion valleys with an U-shaped cross-section which are often broad and shallow linear erosion structures without significant differences between vertical sides and the bottom. Alluvial deposits are accumulated in the axis of these valleys. Erosion valley is the most common type of geomorphological forms and it is the predisposing structure for propagation of head- ward erosion. Relics of planar palaeosurfaces are important planation surfaces on which the erosion takes place to a limited extent only. On their surface there are often fossil remains of weathering the occurrence of which, however, was bound to a warm and humid climate of the pre-quaternary period. Palaeosurfaces are an important indicator of uneven intensity of erosion processes for prediction of the relief of the area in question. Their extent depends on the area’s lithology, structural predisposition, and especially on the intensity and duration of the head-ward erosion for a specific level of the erosion base. Surfaces of river terraces correspond to relics of fills of older river valleys which are located above the current erosion base. The relative height difference of the terraces and the current surface of river floodplains of the river system is an important indicator for estimating erosion in the geological history.

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2.6 Geomorphological characteristics of potential DGR sites

2.6.1 Březový potok

The Březový potok area is located in the 3rd level watershed of the brook Březový (a tributary of the Otava river - then Vltava and Labe) and the brook Myslívský (a tributary of Uslava - Berounka - Vltava - Labe) near Pačejov. The altitude of the watershed from the west is between 562 m a.s.l. (Trávníky), 605 m a.s.l. (Plesník u Pačejova), 563 m a.s.l. (Prasecký les), 569 m a.s.l .(Soudný les), 604m a.s.l. (Vrchy nad Černicemi), spot height 618 m a.s.l. (North to Nová Ves), 584 m a.s.l. (Holý vrch near Řesanice) and Čihadlo u Polánky (629 m a.s.l.) in the east. In the vicinity of the watershed - in the northwest part of the area in question there is a relic of a degraded flat palaeosurface with the altitude of around 600 m a.s.l. which continues to the piedmont palaeorelief of Šumava on the south and Brdy on the north. The paaleorelief around this level remained at a relatively resistant monolithic granodiorite massif. The more significant morphological elevations through leading the watershed between the brooks Březovský, Myslívský, and Víska mostly consist of resistant lamprophyre veins. The south-east part of the studied area lies in the catchment area of the Otava River at a lower level of the relic palaeosurface with level about 450-500 m a.s.l. and which also lies on granodiorites. From the north, the area is drained by the brooks Myslívský and Víska to the river Úslava. In this area, the brooks form a local erosion base which lies at an altitude of 475-500 m a.s.l. The erosion of the brooks Myslívský and Vísky, and other nameless streams, mainly takes place through NW-SW and NNE-SSW faults. The height difference between the average altitude of the palaeorelief and the floodplain of both watercourses is more than 100 m. From the south the area is drained into the Otava River by the brook Březový which forms a local erosion base in this area. The erosion base lies at an altitude of 435-450 m. Some parts of the brook Březový and other nameless streams have a straight NW-SW direction. These directions may correspond to the direction of the Sudeten faults. There are no significant erosion valleys along the current watercourses. This implies that the recent head-ward erosion cycles did not affect the morphological development of the area.

2.7 Čertovka

The Čertovka area (Fig. 5) is located at the 3rd level watershed between the brooks Střela and Rakovnický (tributaries of the river Berounka, then Vltava and Labe) and Blšanka (tributary to Ohře - Labe) near Jesenice. The altitude of the watershed is between 589 m a.s.l. (Jezerský vrch), 601 m a.s.l., Žebrák 620 m a.s.l., and 606 m a.s.l. (Lhotský vrch). In the vicinity of the watershed there is a planar palaeosurface relict. Its altitude is about 600 m a.s.l. and it continues to the palaeorelief of Tepelská plane which was probably created in the Tertiary era. The palaeorelief has preserved on a relatively resistant monolithic granite and granodiorite massif forming a tectonic segment south of Lubenec. The massif sinks in the north direction and denudation here has created a cuestas system with structural slopes slightly inclined to NNE direction. The palaeosurface was degraded by a denudation processes and several tors have been preserved here. The palaeosurface which was preserved at the granitic rock massif is limited at the east side by a significant fault - there is an obvious fault-slope leading in the NNE-

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SSW direction. The fault-slope limiting the eastern edge of this massif consists of a distinct morphological level with the height difference between the top and the foot of the slope of 100 metres of altitude. There are also evident short fault-slopes corresponding to faults in the NW-SE direction. The fault-slope forms the western edge of the Žihelská Basin which is infilled with paleozoic sediments and on which is a level of palaeosurface located at the altitude of 450-500 m a.s.l. At the level of 450-500 m a.s.l., the palaeorelief is affected by head-ward erosion proceeding from the catchment area of Blšanka and the brook Jesenický, which results in the creation of erosive slopes along this drainage system. Due to the lithological characteristics of this area a dense network of erosion gullies is creating. Another significant erosion slopes and valleys are tied to the river valley of Střela and its tributaries in the southwest part of the site. The bottom of the Střela’s valley has the altitude of 400 m a.s.l., which corresponds to the local erosion base. The erosion structures related to the Střela’s valley and advancing through the catchment area degrade higher level of the palaeorelief (in level 600 m a.s.l.).

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Fig. 4 Geomorphological scheme of the Březový potok area

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Fig. 5 Geomorphological scheme of the Čertovka area

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Fig. 6 Geomorphological scheme of the Čihadlo area

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2.7.1 Čihadlo

The Čihadlo area (Fig. 6) is situated in the 4th level watershed of the brook Dírenský (a tributary of the Lužnice river, Vltava and Labe), the brook Radouňský (a tributary of the river Nežárka - Lužnice - Vltava - Labe) north of Jindřichův Hradec. The watershed’s altitude rises from Nežárka over Rýdlův kopec (553 m), Mádlův kopec (586 m), Na Klenové (588 m), Cihelný vrch (608 metres), Nejdecké Čihadlo (692 m), Bukovka spot height (678 m) and Mirotím spot height (637 m). In the south the area is drained by the Kamenice river (brooks Radouňský and Lodhéřovský) and the Řečice river to the Nežárka river. Nežárka and Lužnice rivers created a local erosion base in this area. The erosion base lies at an altitude of about 450 m a.s.l. The erosion of the brooks Lodhéřovský and Radouňský mainly precedes via the NNE faults. There are 2 palaeosurface levels on the site: a higher level of about 600 m a.s.l., which has maintained a relatively resistant position and is tectonically defined by a monolithic granite massif. The more significant morphological elevation of Nejdecké Čihadlo (692 m) could be predisposed by a resistant position of granite. The lower palaeorelief level has an altitude of around 450-500 m a.s.l. and corresponds to level of the Třeboň Basin. It mainly developed on migmatites. Relics of sandy and gravely deposits probably corresponding to the youngest member of the Třeboň Basin infill (Ledenice Formation) were preserved in this level. The surface of the palaeoreliefs degrades through a selective denudation processes, yet there are several resistant cores of finely grained granite. Both palaeorelief levels are separated by significant retreating escarpments. In some locations, this escarpment has a strikingly direct NNE-SSW course, which corresponds to fault system in Třeboň Basin. Therefore, neither in these slopes a tectonic predisposition can be ruled out. In SE the massif is in contact with moldanubicum metamorphic rocks. There are no distinct tectonic constraints. The prevailing courses of the local faults have NNE and NE directions. Erosion slopes are related to the side slopes of erosional valleys of the brooks Radouňský and Dírenský. The erosion base the river system lies at the altitude of 450 m a.s.l. and corresponds to the level of the floodplain of the Nežárka river, or the Lužnice river in the Třeboň Basin.

2.7.2 Horka

The Horka area is situated on the 5th level watershed of the river Oslava (a tributary of the Jihlava river which then falls into - Svratka - Dyje - Morava - Danube) and the brook Mlýnský (a tributary of Jihlava - Svratka - Dyje - Morava - Danube). The altitude of the watershed rises from the confluence of Jihlava and Oslava across the spot height u Smrku (491 m), Pyšelská hůrka (511 m), Na Brčích (533 m), spot height (562 m), the spot height s. Rudíkova (563 m), Bukovský vrch (600 metres), to Skalníky (632 m). This watershed lies on the crotch between the rivers Jihlava and Oslava. The surface of this watershed represents the rest of the surface palaeorelief with the altitude of around 600 m a.s.l. The palaeosurface located at the level of 550-600 m a.s.l. preserved relatively resistant monolithic granites to syenites. In the N and NE parts of the area the massif is in contact with moldanubicum metamorphites. In the southern and southeastern part of the site the paleosurface with lower level (altitudes of about 450-500 m a.s.l.) is located. The paleosurface is also developer in a monolithic granite and syenite rocks. The significant retreating escarpement separates both palaeosurface

22 Report number: Erosion Stability of DGR Potential Sites SÚRAO TZ 25/2015/ENG levels. The palaeorelief surfaces were degraded by selective denudation. Significant morphological elevations of the watershed were predisposed by positions of a more resistant quartz syenite. The area is intersected by deep erosion valleys. Local faults with NW and NE directions predominate. The surface close to tmain rivers system is affected by head erosion processes, which is apparent from steep eroded slopes and deep erosive valleys that are linked to the river Oslava and its tributaries and the brooks Klapovský and Mlýnský (in the catchment area of the river Jihlava). The bottoms of these valleys are situated at the altitude of 400 m and create a local erosion base for this area. The difference between the average altitude of the palaeorelief and the floodplain of Jihlava and Oslava is 110 metres at most. In some localities, drainage systems are prominently straight, NNE-SSW and NW-SE trending. These parts of drainage system represent morphological evidences of fault system or other discontinuities of the rocks.

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Fig. 7 Geomorphological scheme of the Horka area

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Fig. 8 Geomorphological scheme of the Hradek area

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2.7.3 Hrádek

The Hrádek is located in the catchment area of the river Jihlava (a tributary of the river Svratka which then falls into Dyje - Morava - Danube) between the tributaries Rohozná and Jedlovský. The altitude of the crotch reaches a maximum height of 761 m a.s.l. (Čeřínek). The area of watershed is characterized by relics of planar palaeosurface at the altitude of around 750 m a.s.l. (middle part) and a lower level of palaeosurface located at around 600 m a.s.l. On the left bank of the confluence with the brook Třešťský a degraded palaeorelief level has been preserved at the altitude of about 550 m a.s.l. The individual levels are separated by an extensively degraded retreating escarpents. The palaeorelief surface was affected by a selective surface denudation processes and probably also by periglacial processes. Apparently, this surface has been exposed to chemical and mechanical weathering over the whole time. The area is drained southward into the river Jihlava, which forms the local erosion base. The height difference between the average altitude of the palaeorelief and the floodplain of Jihlava is 300 m at most. The river Jihlava and its tributaries are linked to an erosion valley with adjacent erosion slopes that were affected by late head-ward erosion cycles. The drainage system has certain arrangements; especially the Rohozná valley and the brook Jedlový have been created along a NW-SE oriented fault system. Another dominant direction in which a drainage network has developed is the morphologically obvious NNW-SSW system (the Dolnohuťský brook valley, some parts of Jihlava’s river valley). The fronts of the past head-ward erosion cycles reach to this area mainly from the rivers system of Jihlava, Rohozná, and Jedlový.

2.7.4 Magdalena

The Magdalena area (Fig. 9) is located in the watershed of the brook Sedlecký (a tributary of the brook Mastník which then falls to Vltava) in the catchment area of the river Smutná (a tributary of Lužnice - Vltava - Labe) and the brook Oltyňský (a tributary of Lužnice - Vltava - Labe). The altitude of the crotch reaches a maximum height of 648 m a.s.l. (Smrčí). The entire area lies on two relics of planar palaeosurfaces at the altitude of around 600 m a.s.l. (middle part) and a lower level palaeosurface located at around 500 m as.l. The palaeorelief with the altitude of about 600 m a.s.l. is preserved on relatively resistant granite to syenite rocks of the Central-Bohemian pluton. It is being degraded by selective surface denudation processes which did not affect several resistant locations of quartz syenite. Pronounced morphological elevations on palaeoreliefs are usually predisposed by occurance of resistant granite veins and quartzites veins. The southern part of the studied area, where a lower level of palaeosurface is developed less resistant paragneisses occurs. Both levels of palaeosurface are separated by a strongly degraded retreating escarpment, located south to Jistebnice. In northern and eastern parts of the site have been identified erosive slopes that are linked to the catchment area of the brook Sedlecký. Most of the area is drained southward into the river Lužnice, which forms the local erosion basis. The height difference between the average altitude of the palaeorelief and the floodplain of Lužnice is 300 m at most. The fronts the past head-war erosion cycles reach to this area mainly from Lužnice

26 Report number: Erosion Stability of DGR Potential Sites SÚRAO TZ 25/2015/ENG catechment by the brooks Oltyňský, Kášovický, Pilský, and Vlásenický and also from the north - catchment area of the brook Sedlecký.

Fig. 9 Geomorphological scheme of the Magdalena area

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Fig. 10 Geomorphological scheme of the Kraví Hora area

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2.7.5 Kraví hora

The Kraví Hora area (Fig. 10) is located in the catchment area of the river Svratka (a tributary of the river Thaya which then falls to Morava - Danube) between tributaries Bobrůvka and Nedvědička. The altitude reaches a maximum height of 611m a.s.l. (Kraví hora). The area consists methamorphic rocks and it is drained to the south east into the river Svratka, which forms the local erosion basis. There are two palaeosurface levels in this area: about 600 m a.s.l. and a lower level with the height of 500 to 550 m a.s.l. Coherent palaeorelief surfaces were preserved in northern, northwestern, and western parts. In the remaining parts of the area the palaeorelief surfaces have been preserved to a limited extent only as relics related to crotches of significant erosion valleys. Erosion valleys are lined with steep erosion slopes, the dominant direction of the drainage system is the NNW-SSE direction. According to geological maps, this direction corresponds to the bedrock structure, yet sometimes, there is also the E-W direction. The area is heavily affected by head-war erosion penetrating the areas from the main rivers. The height differences of the preserved palaeosurfaces and the floodplain of the current watercourses of Bobrůvka and Nedvědička amount to about 220 metres. The erosion base corresponds to the level of the river Svratka’s floodplain, i.e. to the altitude of about 300 m a.s.l.

2.8 Prognosis of morphological development of individual potential DGR sites

2.8.1 Březový potok

The humid cycle scenario of the morphological development over the next 100 thousand assumes that the site will be affected mainly by alluvial erosion along the current flows. This area is not affected by the youngest cycles of head-ward erosion and therefore it is not expected that there will be a significant formation of erosion valleys along the current drainage system within the above time horizon. The arid climate scenario foresees especially the surface erosion, which, however, should not significantly affect the morphological development. Arid conditions will be accompanied by mechanical weathering of the rocks and creation of permafrost. Especially the receding slope may be affected by removal of the weathered material associated with a further recession of the slope to the north - into the area corresponding to today's higher palaeosurface level.

2.8.2 Čertovka

The elaboration of prediction for this area is quite uncertain due to the presence of apparently neotectonic structures that are linked to the western edge of the Žihel basin. In case of movement on faults there may be a significant change in morphological conditions and gradient curves of the river systems. In case of a decrease of the edge fault of the Žihelská basin, an increase of the topographic gradient and a more intense erosion will occur on the eastern edge of the higher palaeosurfacef lying on a granite massif.

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The humid climate scenario foresees mainly the deep line erosion with progradation of erosion slopes and valleys to the surface of today’s palaeoreliefs. Due to a low resistivity of the rocks a more significant drainage network progradation and occurrence of new drainage structures with potential parameters of piracy of fluvial systems may especially occur in the area consisting of paleozoic sediments. Especially the apparent faults may act as predisposing structures for propagation of erosion structures. Based on data reported in the literature (Balatka and Kovanda 2001, Tyráček et al. 2004), it is assumed that the drainage system recess will reach the first tens of metres. According to the arid climate scenario, we can count especially with the less efficient surface erosion and with mechanical weathering of the rock environment (especially on the palaeorelief surface) associated with disintegration rocks and permafrost creation.

2.8.3 Čihadlo

The uncertainty in the prediction of this area is brought by the tectonically pre-disposed structures in the NNE-SSW direction associated with retreating escarpments. In the case of movement on these fault structures, there may be a change in the morphological conditions and the gradient curves of the river catchment systems and thus in the intensity of erosion and denudation. According to the humid climate scenario, we can expect that the deep linear erosion will play the main role. This area is not affected by the youngest cycles of head-ward erosion and thus we can expect a limited creation of new linear structures only and no significant recess. Any recess will be the most significantly reflected in the valley of the brooks Radouňský and Dírná, where the most striking manifestations of head-ward erosion can be observed. The arid climate scenario expects especially the less efficient surface erosion. Mechanical weathering and disintegration of rocks and permafrost creation may occur. Escarpments could retreat towards the surface corresponding to higher level of palaeorelief.

2.8.4 Horka

The uncertainty in the prediction of this area development is brought both by the tectonically predisposed structures that are followed by the drainage system and also by the neotectonic activity associated with the uplift of the eastern part of the Czech-Moravian Highlands (Schenková and Kottnauer 2009). This may result in an unsteady decrease of the erosion base associated with deepening of river valleys. According to the humid climate scenario, we can expect that the deep linear erosion will play the main role. This area is affected by the youngest cycles of head-ward erosion and in connection with the present uplift the eastern edge of the Bohemian-Moravian Highlands, we expect that these line erosion structures will deepen and propagate upstream into the area of today’s palaeorelief surface, especially along fault structures and the fracture system in the rock environment. If we consider the rate of uplift of the eastern part of the Czech-Moravian Highlands reported in the literature, then the recess of river valleys may reach up to tens of metres.

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The arid climate scenario expects especially the less efficient surface erosion. Creation of permafrost, mechanical weathering and disintegration of rocks may occur especially on the receding slope connected with a recess of the slope corresponding to today’s palaeosurface level.

2.8.5 Magdalena

The uncertainty in the prediction of this area is brought both by tectonically predisposed structures that are followed by the drainage system and also by the possible neotectonic activity associated with erosion base fall of the river systems draining the eastern part of the Czech-Moravian Highlands. This process results in incising of the river valleys and progradation of the head ward erosion. According to the humid climate scenario, we can expect that the deep linear erosion will play the main role. This area is affected by the youngest cycles of head ward erosion and in connection with the reported vertical movements associated with the erosion base fall, we can expect deep incising of these V-shaped river valleys of Jihlava, Rohozná, Jedlový and Třešťský and their propagation to the site corresponding to today’s palaeorelief surface, especially along the significant fault structures in NW-SE and NNW-SSE directions. If we consider the rate of uplift of the eastern part of the Czech-Moravian Highlands reported in the literature, then the recess of river valleys may reach up to tens of metres. The arid climate scenario expects especially the less efficient surface erosion. Creation of permafrost, mechanical weathering and disintegration of rocks, as well as escarpment retreat toward surface corresponding to higher level of pallaeorelief will occur.

2.8.6 Kraví Hora

The uncertainty in the prediction of this area development is brought both by the neotectonic activity associated with the uplift of the eastern part of the Czech-Moravian Highlands (Schenková and Kottnauer 2009). This may result in an unsteady decrease of the erosion base associated with incising of river valleys. According to the humid climate scenario we can expect that the deep line erosion will play the main role (it is already significant in part of the area). This incising combined with the reported potential uplift of the eastern part of the Bohemian-Moravian Highlands by the low- lying local erosion base may reach tens of metres. We can expect that the propagation of linear erosion structures will proceed to the site corresponding to today’s palaeorelief surface, especially along the discontinuities followed by today's drainage system. The arid climate scenario expects especially the less efficient surface erosion accompanied by mechanical weathering of rocks and creation of permafrost.

2.9 Summary

The assessment of the erosional stability of the area of interest is based on literature search and interpretation, as well as on unpublished data and geomorphological analysis of the area in terms of the possibility of a stable storage of nuclear waste in seven selected repositories for at least 100,000 years. Erosion and denudation are the result of a long-term action of

31 Report number: Erosion Stability of DGR Potential Sites SÚRAO TZ 25/2015/ENG exogenous agents on the Earth’s surface. However, the intensity of these factors also depends on endogenous processes to some extent. The erosional stability evaluation focused on definition and genesis of the major geomorphological features and processes involved in creation of various forms of relief, evaluation of the role of erosion factors in various genetically defined geomorphological forms, and outlining of possible limit scenarios of morphological development of the area. The arid cycle scenario must take into account that during the Pleistocene, these periods proceeded in a cold mode. As a result of this we can assume a lower influence of alluvial phenomena on incising of river valleys and, on the other hand, a more significant influence of periglacial phenomena. In this period the main role will play the mechanical weathering of rock environment associated with emergence of frost cliffs and receding slopes. The general wind erosion will be a more important aspect. Erosion rates will not be as high as in the humid cycle but it must be counted with the emergence of permafrost, which reached hundreds of metres in our geological history (e.g. Zeman and Růžičková 1995). During the arid cycle, we cannot expect a strong erosive glacial activity since none of the localities was glaciated during the Quaternary. The humid cycle scenario assumes that changes in morphology will be mainly caused by alluvial erosion accompanied by incising of erosional valleys and their upstream spreading. The value of today's deep erosion structures should reflect the range of values reported in the literature for past geological periods. We must take into account that the range of these values may vary within a wide range depending on local conditions and the neotectonic activity. Geomorphological analyses show that deep head ward erosion threatens the least the watershed areas which correspond to palaeorelief surfaces. From this perspective, the localities that will be the least affected by erosion are Březový potok and Čihadlo. Somewhat more complicated is the situation in the Čertovka area, where significant fault slopes were identified. The possible revival of these fault structures brings uncertainty in the prediction of morphological development of the area. Another negative factor of the Čertovka area is the presence of Paleozoic sediments in the Žihle Basin which are more prone to erosion due to their lithological characteristics. In terms of erosion stability, the most problematic localities appear to be those located on the eastern edge of the Bohemian-Moravian Highlands (Kraví Hora, Horka, and Hrádek) in which the effects of the current head-ward erosion are apparent. Especially the SW part of the Kraví Hora area is heavily affected by deep erosion as the local erosion base is up to 300 metres below the highest level of the preserved surface. The strong signs of deep erosion in these areas may be caused by neotectonic movements on the periphery of the Bohemian Massif which result in uneven gradient curves of river systems in the catchment areas of the Svratka and the Jihlava river. The values of the expected rate of erosion and denudation processes are burdened by considerable uncertainties consisting in the heterogeneity of data (varying data quality and consistency - e.g. a qualitative difference in the fundamental geological maps’ scales of 1:50,000 vs. 1:25,000, lack of data on the age of the surface of the Bohemian Massif). A more precise determination of the rate of erosion and prediction of the morfostructural development requires a more detailed research performed by the use of other methods:

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- Verification of tectonic structures and application of interferometric methods for detection of vertical movements of the surface - Preparation of detailed geomorphological maps by the use of the latest LIDAR data and satellite images - Tectonic and structural-geological study - Analysis of Quaternary sediments, employment of dating methods, more accurate determination of sinking river systems in the geological past for individual river basins - Analysis of weathering cover and geotechnical characteristics of rocks - Hydrological data processing and construction of gradient curves of the drainage system that affect the DGR localities.

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3 Expert Report of T. Pačes

3.1 Introduction

The aim of this study is to determine the level to which weathering of rocks and the subsequent erosion and denudation will lower the Earth's surface in the seven localities selected as geologically suitable areas for a safe disposal of radioactive waste. All these localities can be geomorphologically described and it is also possible to identify the current rates of the above exogenous geological processes in these localities. The question remains whether these processes will depend on climate change within the next 105 years, especially at the onset of the next ice age and the subsequent interglacial period. While the differences in geomorphology and the current rates of erosion in the areas can be reliably detected and documented via geomorphological analysis and monitoring of removal of the erosion material by watercourses, future rate differences can only be estimated from the geological analogy of past events. The differences will be much larger in future than the differences that we see from the current data. During the last century until today, many researchers have used different methods to determine the rate of the Earth's surface erosion. The data obtained have the ML-2.T-1 dimension (mass loss on the defined area per one unit of time). Units used in literature are g.m-2 .year-1, kg.ha-1year-1 or t.km- 2year-1. Material removal due to erosion will cause lowering of the Earth's surface by “denudation”. The rate of denudation has LT-1 dimensions; the common unit is mm.year-1. The terms of erosion and denudation are used interchangeably in several studies and thus the rate of erosion is often expressed in units of denudation. The crucial variable in a safety analysis of a repository is the rate of denudation because it expresses the rate of the Earth’s surface lowering with respect to the depth of repository. Thus we recalculate all of the data on the erosion and denudation rates to kg.m -2..(105 years) -1 and m.(105 years)-1. Using these units the relationship between erosion and denudation rates is given as follows

D=E/ (3.1) Where D is the denudation rate, E is the rate of erosion, and  is the density of the rock material removed of the Earth's surface by erosion in kg.m-3. The rate of erosion can be derived from the thickness of the weathered surfaces of historic buildings, by measuring the removal of the dissolved and suspended material by rivers, by monitoring the mass balance of elements in different sized catchment areas, by analysing of the thickness and mineralogical and chemical composition of the regolith(i.e. the weathered surface zone of rocks) , and in recent years also by measuring the production of cosmogenic isotopes in minerals. The methods suitable for the selected localities in the Czech Republic are monitoring of mass balance in small representative catchments located in the areas according to Paces (1982, 1985) and geochemical and mineralogical evaluation of the local regolith according to Goldish (1938). The application of cosmogenic isotopes will require development of appropriate isotopic laboratory and training of laboratory staff (Brown et al.,1995).

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For example, a research on weathering of cistern walls in a house from the 2nd century AD located near Rome showed that the erosion rate was 30 m per 100,000 years (Leet and Judson, 1971). Such data, however, apply to a particular place only and are results of specific climatic conditions. The average erosion rates in larger areas were derived from annual amounts of material removed by rivers of a particular drainage basin. For example, the Tiber River where the above mentioned cistern is located removes 7.5 million tons of material every year, which corresponds to the erosion rate of 17 m per 100,000 years.. Measurements of material removal by the US rivers showed that the erosion rate ranges between 4 and 17 m per 100,000 years and the average for the entire United States was 6 m per 100,000 years. The average rate of erosion in the Amazon catchment area is 4.7 m per 100,000 years in the Congo catchment area it is only 2 m per 100,000 years. The overall estimated average rate of erosion on all continents before the industrial revolution is 2.5 m per 100,000 years. This estimate, however, does not include wind and glacial erosion. However, these ways of erosion are usually much less significant than the erosion caused by rivers. Human activity increases the natural rate of erosion. In the middle of last century, the researchers estimated that the global rate of erosion increased by a factor of 2.5 (Leet and Judson 1971). It is likely that the average erosion rate in Europe will not differ much from the data for North America. It is natural that the rate of erosion will vary in individual river catchment areas. It will depend on six main factors: Terrain gradient, petrophysical properties of rocks, precipitation, temperature, and biological cover, including soil and isostatic vertical movement of the continental Earth's crust. More information about the erosion rate can be found by monitoring the mass balance of elements in small, hydrologically well-defined catchment areas (usually an area of 0.5-5 km- 2). The mass balance is defined by the following equation Weathering (gm-2.year-1) = Inputs – Outputs (3.2) Inputs include precipitation and anthropogenic inputs, e.g. fertilization and liming, outputs include removal of material dissolved in the effluent water, removal of mechanical particles in suspension, by the bottom drift, and finally the biological material removal caused by harvesting crops and lumbering timber. On the basis of monitoring inputs and outputs of lithogenic elements (Na, K, Ca, Si) it is possible to calculate the rate of mechanical and chemical weathering which corresponds to the erosion rate of the individual elements if the regolith thickness stationary. The data may be used for calculation of the rock erosion rate and then for defining the surface denudation rate (Pačes, 1985, 1986a, b). For example, a several-year monitoring of mass balance in two forested and one agricultural catchment areas on crystalline rocks of the Bohemian - Moravian Highlands showed the present rates of denudation caused by water erosion - the values were 9 m per 100,000 years in the forested catchment area with the slope of 3.8%, 14 m per 100,000 years in the forested catchment area with the slope of 13.3%, and 32 m per 100,000 years in the agricultural catchment area with the slope of 4.0% (Pačes 1986a). The fourth method to estimate the long-term erosion is the analysis of differences in the chemical and mineralogical composition of the regolith and the basement rock from which the regolith was created by weathering and material removal (Goldish 1938). This method can detect the rate of weathering of rocks over a long geological time and the result is related

Report number: Erosion Stability of DGR Potential Sites SÚRAO TZ 25/2015/ENG to a specific mineralogically and chemically defined weathered profile which was created by weathering of the basement rock. Finally, over the last 20 years have been published results of measurements of cosmogonic isotopes 10Be and 26Al which are created by solar radiation incident on the Earth's surface (Brown et al. 1995, Portenga and Bierman 2011). These results in combination with half-life of these isotopes were used for deriving of the erosion rates that are discussed below.

3.2 Denudation rates in different geomorphological and climatic conditions

The thickness of the surface layer removed in 100 thousand year can be calculated from data on erosion rates published by various authors. These thicknesses are summarized in Tab. 2.

Tab. 2 Average erosion rates according to various authors. Literary sources in Kukal (1983). 100,000 years metres Kuenen, 1950 13 Lopatin, 1952 5 Gilluly, 1955 12.6 Pechinov, 1959 9.7 Fournier, 1960 23.2 Schumm, 1963 8.2 Holman, 1968 7.5 Jansen, Pinter, 1974 10.6 Europe Mechanical 4.3 erosion Garrels, Mackenzie, 1971 Chemical 3.15 erosion Overall erosion 7.45

The thicknesses range from 5 to 23 metres per 100 thousand years. The average thickness of the layer removed by chemical and mechanical erosion in Europe is 7.45 metres in 100 thousand years. However, the erosion rates may significantly vary depending on the morphology of the terrain. For example, Kirkby (1967) provided the speeds of slope, channel, and surface

Report number: Erosion Stability of DGR Potential Sites SÚRAO TZ 25/2015/ENG erosion in the Deugh basin in the UK. Tab. 3 shows the published values recalculated to the thickness of the rock removed during 100 thousand years.

Tab. 3 Denudation extent in the UK, calculated from data from Kirkby (1967) Type of erosion Slope Linear Sheet cm.year-1 0,077 0,017 0,003 Years Thickness of removed rocks in metres 100,000 77 17 3

Another example of different erosion rates depending on the morphology of the terrain was presented by Waren and Cook (1973). These erosion rates were measured in New Mexico (Tab. 4).

Tab. 4 Denudation rate in New Mexico calculated from data of Waren and Cook (1973)

Total Sheet Linear Slope

Years Metres

100,000 2020 14.2 29 1976

However, such high rates of slope erosion correspond to landslides and are considered extreme in this case. Large differences in erosion rates are shown in the data obtained by measurement and interpretation of cosmogenic isotopes (Tab. 5)

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Tab. 5 Erosion rates calculated from data on accumulation and decay of cosmogenic isotopes 10Be and 26Al and by the use of complementary methods Locality Catchment area Method Denudation Reference (m in 100,000 years) Australia Fanning 10Be 1.847 Croke, J. et al. (2015) Burdekin 162.2 Croke, J. et al. (2015) Burkina Scale of Remote sensing 0.2 Grimaud, J-L. et Faso and morphology al. (2015) Southwestern Burkina Faso Himalaya Namche Barwa Thermo- 30 to 500, the average Tu, Ji-Yao et al.

s Peak chronological data value 170 (2015) Tibet Qionghai Lake 82 to 182 Chen, N. et al.

watershed, (2015) (anthropogenic southeastern influence) Tibetan Plateau, Calabria Suila Massif 10Be, morphology 80 and 40 (unclear Scarciglia, F.

units) (2015) Brazil The upper 10Be the average value of Pupim, F. et

watershed of the 0.57, max. 2.83 al.(2015) Paraguay river Italian Zielbach 10Be 14 to 265, the average Savi, S. et al. Alps catchment value 77 (2014) Puerto Luquillo 10Be, balance 4.3; 7.5 Brown, E.T., et Rico Experimental al. (1995). Forest USA North America Before civilisation 0.8; Reusser, L. et

on the slopes 95 al. (2015) Summary drainage area 21.8, median 5.4 Portenga E.V. of the and Bierman data till P.R. (2011) 2011 Summary outcrops ,.2, median 0.54 Portenga E.V. of the and BiermanP.R data till (2011) 2011 California Feather River river sediments >25; 1.5 Attal, M. et al.

Report number: Erosion Stability of DGR Potential Sites SÚRAO TZ 25/2015/ENG

canyon (2015)

10Be, 26Al 5.1 Ciner, A. et al.

(2015) Andean river channels in 0.3 to 20 Pupim, F. et

valley the Andes al.(2015) Andean 6 to 40 Vanacker, V. et

valley al.(2015) Taiwan Landslides 265 to 517 Chen, Yi-chin et

al.(2015) Appalachi mountain ridges 10Be 0.9±0.1 Portega, E.W. et an Mnt. al. (2013) Himalaya Western Bhutan 10Be, 26Al 38.8±2.2 Portenga, E.W.

s et al. (2015) Himalaya Western Bhutan 10Be, 26Al 95.6±16 Portenga, E.W.

s et al. (2015) Himalaya Western Bhutan 10Be, 26Al 70±6.2 Portenga, E.W.

s et al. (2015)

The denudation thicknesses from Tab. 4 are shown in the chart in Fig. 11.

Denudation rates derived from the data on cosmogenic isotopes

met 1,000.0 res/ 100 100.0 tho usa 10 , 0 nd year 1 , 0 s

0 , 1 1 3 5 7 9 11 13 15 17 19 21 23 25 27 29 31 33 35 37 Data registration number

Fig. 11 Distribution of denudation values; the red column shows the geometric mean, the green column shows the median, and the yellow column shows the arithmetic mean.

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The figure shows that the range of the denudation values is nearly 4 orders of magnitude, depending on location. The lowest values correspond to outcrops of rocks in the lowlands; the highest values correspond to denudation in the Himalayas. Mean values are highlighted in colour. The approximately linear course of the semi-logarithmic scale implies that this is a log – normal distribution. Therefore, the geometric mean at the seventeenth position, i.e. 14 m in 100 thousand years, corresponds best to the mean value of this data set.

Fig. 12 shows erosion rates measured in catchment areas of 280 rivers and smaller waterways worldwide. These results imply that the erosion rate increases with decreasing catchment area. The erosion rates in smaller catchment areas that correspond to the areas of interest range between 0.1 to 5 mm.year-1. This corresponds to denudation of 10-500 metres in 100 thousand years. The high rates, however, decrease by two orders of magnitude with increasing size of the drainage area.

Fig. 12 Rate of erosion in the catchment area of the world's rivers and smaller watercourses (Burbank, 2002)

The rate of erosion depends mainly on the terrain gradient. This is documented by the chart in Fig. 13. The chart shows the data obtained by measuring activity of 10Be in quartz from terrains with different gradients. The chart shows the rates in metres per one million years. They range from approximately 1 to 50 metres in 100 thousand years with the gradient of 0- 30°.

Report number: Erosion Stability of DGR Potential Sites SÚRAO TZ 25/2015/ENG

Fig. 13 Rate of erosion derived from accumulation of the cosmogenic isotope 10Be in various types of landscape and depending on terrain slope (Portenga and Bierman 2011).

Fig. 14 shows the erosion rate variability in relation to the type of rock, the climatic zone, and the tectonic activity. The top charts in this figure show the rates of erosion on outcrops of rocks, the bottom charts show the rates in basins. t The erosion rate in the basins is one order of magnitude higher than in the bare rocks. There is a large variance in the data sets. The lowest rate of erosion had outcrops of magmatic rocks - on average only about 0.5 m per 100 thousand years with the rise of 1 m per 100 thousand years. In the basins the rock-type is not so decisive and erosion is almost one order of magnitude larger - about 7 m per 100 thousand years. An interesting finding was also the difference in the rate of erosion in the polar climatic zone where the rate is the smallest in rock outcrops and largest in basin areas. The variability of erosion rates in different climatic zones is large. The differences in the rate of erosion in tectonically active and inactive regions show that the erosion is larger in the active areas.

Report number: Erosion Stability of DGR Potential Sites SÚRAO TZ 25/2015/ENG

Fig. 14 Rate of erosion derived from accumulation of the cosmogenic isotope 10Be depending on rock type, climate zone, and tectonic activity (according to Portenga and Bierman 2011)

Finally, we should also take into account the erosion caused by glaciers with regard to the next ice age. The differences in glacial erosion and the erosion caused by rivers can be clearly seen in Fig. 15.

Fig. 15 Rate of erosion in glaciated areas, and rates of erosion caused by fluvial systems (Burbank, 2002).

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While the rate of glacial erosion reaches 1 to 90 mm per year (100 to 9,000 metres in 100 thousand years), the river erosion rate is 0.02 to 9 mm per year (2 to 90 metres in 100 thousand years). The overview of literature data shows that the range of erosion rates and the resulting surface denudations is several orders of magnitude - from tenths to one thousand metres per 100 thousand years. The extremely fast erosion is caused by landslides in the high mountains and by glacial erosion. The low erosion was calculated for outcrops of magmatic rocks with a low surface slope. In temperate climates the erosion rates usually range from 5 to 12 m per 100 thousand years. The geometric mean of erosion rates determined by measuring the activity of isotopes 10Be and 26Al was 14 m per 100 thousand years.

3.3 The rate of erosion in the Bohemian Massif

Erosion in the Bohemian Massif is measured with respect to soil loss. Fig. 16 shows a map of soil erosion calculated by the Research Institute for Soil and Water Conservation. Extreme rates of erosion are considered the values above 7.5 t.km-2.year-1.

Fig. 16 Potential loss of soil in the Czech Republic by water erosion (Research Institute for Soil and WaterConservation, (http://www.vumop.cz/sites/File/Katalog_Map/20130529_katalogMap_Ohrozenost_Vodni_erozi.pdf)

Report number: Erosion Stability of DGR Potential Sites SÚRAO TZ 25/2015/ENG

The rates of soil erosion were calculated according to the Potential Exposure of Agricultural Land formula: G = R x K x L x S x C x P (3.3) where: G – average long-term soil loss (t.ha-1.year-1),

R – erosive efficiency of rain expressed by the relation of the kinetic energy and the intensity of potentially erosive rains K – soil erodibility factor expressed by the relation of the texture and structure of soil, organic matter content, and permeability of the soil profile,

L – slope length factor expressing the effect of the uninterrupted slope length on the extent of the loss caused by soil erosion,

S – slope factor expressing the effect of the slope length on the extent of the loss caused by soil erosion, C – the protective influence of vegetation expressed by the relation of vegetation development and the agricultural technology employed, P – efficiency of erosion control measures.

Data on water erosion of soil in the Czech Republic are shown in Tab. 6. The data indicate that only 18% of soils are exposed to the risk of an extreme erosion.

.Tab. 6 Water erosion risk degree in the Czech Republic (http://eroze.sweb.cz/home.htm)

Very Very Water erosion risk exposure low Low Medium High high Extreme

Soil washes [t .ha-1 . year-1] 1.5 1.6 - 3.0 3.1 - 4.5 4.6 - 6.0 6.1 - 7.5 7.5 and more and less

Percentage of agricultural 3 26 25 17 11 18 land area

The extreme value of 7.5 t.ha-1year-1 corresponds to the denudation thickness of only 2.8 cm in 100 thousand years. In contrast, the suspended solid measurements in the Elbe River (when leaving the Czech Republic) show a one order of magnitude higher erosion rate. Halířová and Stierand reported that the annual runoff of suspended solids by the Elbe River was 347 thousand tonnes in 2011. As the Elbe’s catchment area in our country is 49,933 km2, this corresponds to the erosion rate of 69.5 t.km-2.year-1. With the suspended solids density of 2,650 kg.m-3 this corresponds to the denudation of 26 cm in 100,000 years This includes the suspended solids only. The part of chemically weathered rocks is removed in

Report number: Erosion Stability of DGR Potential Sites SÚRAO TZ 25/2015/ENG the solution. Furthermore, the rate of erosion increases during periods with higher flow rates. According to the Czech Hydrometeorological Institute, the average flow rate in the river Elbe in the Ústí nad Labem profile is 293.0 m³.s-1 and the 100-year flood has a flow rate of 4,290 m³.s-1 (https://cs.wikipedia.org/wiki/Labe#cite_note-20). In such extreme runoff situations the mechanical water erosion is most intense. Therefore, it is difficult to estimate long-term volume of material exported by the Elbe river from our site on the basis of a single measurement of suspended solids. An estimate of the total erosion rate in the Bohemian Massif was based on calculation of mass balance in small catchments and in the Elbe river drainage basin. (Pačes 1982,1985). The principle of the calculation can be verbally expressed as follows: The amount of the chemical element brought into the catchment area (by precipitation, fertilizers, etc.) minus the amount taken away (runoff of groundwater and surface water and during crop harvesting or tree felling) is equal to the change in the amount of the element in the catchment area. This principle is illustrated in Fig. 17.

Fig. 17 Small catchment area (usually 0.5 - 3 km2) used to measure the mass balance of the chemical element“i"; Measured inputs: P – Precipitation, A - Anthropogenic inputs (fertilising, liming, and other artificial inputs) Source: W - Wethering (release of the element by weathering of rocks); outputs: B - Biological fixation of the element in harvested organic matter (tree felling, harvesting crops), R - Runoff of the element in the solution, M - Mechanical erosion (removal of the element in suspended solids).

The following equation applies to small catchment areas:

Wi + Pi + Ai –Ri –Mi –Bi = ∑i (3.4) The individual terms on the left side of the equation are fluxes in kg.ha-1year-1 and are explained in the caption to Fig. 17; "i" means the chemical element for which the Σi balance is calculated. A negative value of Σi means a means loss of the element in the catchment

Report number: Erosion Stability of DGR Potential Sites SÚRAO TZ 25/2015/ENG area and a positive value indicates accumulation of the element. A zero value corresponds to a steady state in the catchment area. It is possible to monitor precipitation (P), anthropogenic inputs such as fertilising, liming, and other artificial inputs (A), runoff of elements in true solution (R), and the biological fixation in the harvested organic material (B). In contrast, the release of elements by weathering of rocks (W) cannot be measured directly and the mechanical erosion (M) can only be measured by the use of expensive sedimentation tanks. The mechanical erosion cannot be practically measured by a periodical monitoring because the decisive share of mechanical erosion is attributable to a few short time intervals during the hydrological year, such as intensive melting or heavy rain, which are usually not recorded by a periodic monitoring. This drawback is solved by the model that allows for calculations of the rate of weathering of rocks and the mechanical erosion rate of regolith.

The rate of weathering of rocks,Wrock, and the rate of mechanical erosion of regolith,MRGL, is a function of the flow of elements and a dimensionless concentration of these elements in the rock, Xi,rock, and in regolith, Xi,RGL.

Wrock = Wi / Xi,rock (3.5)

Mrgl = Mi / Xi,rgl (3.6) This model is based on an assumption that the state of sodium and silicon in the catchment area is stationary. This assumption is justified by the preservation of silicon between the rock and regolith (only a negligible amount of silicon is deissolved with regard to its amount in the rock and in regolith) and sodium is practically not fixed in the sorption complex of soil, it is not significantly consumed by plants, and it is not significantly anthropogenically fed to the catchment area, so its release from the rock and its runoff are in a steady state. Under this assumption ΣNa = ΣSi = 0. By combining the two equations (3.4) for sodium and silicon (3.5) and (3.6) we obtain

Mrgl = {[(PNa + ANa – RNa – BNa) / XNa,rock] - [(PSi + ASi – RSi – BSi) / XSi,rock]} /

[(XNa,rglth /XNa,rock) – (XSi,rglth / XSi,rock)] (3.7)

The equations (3.7) are used to calculate the MNa and MSi and substitute for sodium and silicon into the stationary mass balance equation (3.4). Then we divide this by the concentration of rock and we get the overall rate of the rock’s weathering

Wrock = - (PNa + ANa – RNa – BNa – MNa) / XNa,rock = (PSi + ASi – RSi – BSi – MSi) / XSi,rock (3.8)

The regolith denudation, Dm, is then calculated by the equation

Drgl = Mrgl / rgl (3.9) and the rock’s denudation, Dh, is calculated by the equation

Drock = Wrock / rock (3.10)

Where rgl and h are densities of regolith and the rock. The calculation results are presented in Tab. 7. Since the Elbe River drains most of the Bohemian Massif, the calculated rates of erosion and the subsequent denudation represent the average values for the entire site. The chemical composition of water in the Elbe was

Report number: Erosion Stability of DGR Potential Sites SÚRAO TZ 25/2015/ENG already analysed in 1892 and thus it was possible to compare the rate of weathering in the Bohemian Massif before the significant pollution of waters and during the period of maximum pollution in 1976. The rate of denudation calculated by this model was 9 m per 100 thousand years in 1892, while in the year 1976 the rate increased to 29 m per 100 thousand years due to anthropogenic influences (Tab. 7.). These values are approximately one order of magnitude higher than the rate of denudation derived from annual measurements of suspended solids. In fact, the high rate of 1976 is lower because the calculation did not took account of the amount of material that has been brought to the Elbe river catchment area from outside, e.g. by imports of chemicals from abroad. The denudation rate of 9 m per 100 thousand years calculated before the intense industrial development in the twentieth century is higher than the rate of denudation calculated for the entire United States (6.1 m per 100 thousand years). Given that the Bohemian Massif is undergoing a cymatogeny caused by the pressure of the Alps the speed of which is about 1 mm per year i.e. 100 m per 100 thousand years (Schenk et al. 1996, 1999 and Schenk in Pačes and Mikšová ed., 2011) and acts as a watershed for Central Europe, the faster erosion of the Bohemian Massif seems to be real.

Tab. 7 The average advance of denudation in the Elbe related to the profile in Litoměřice assuming the density of the weathered rock of 2,650 kg.m-1 (Pačes, 1985)

1892 1976

Rate of erosion kg.ha-1year-1

2,500 7,650

Advance of denudation

Years Metres

100,000 9.4 28.9

During 1978-1982 a several-year monitoring of atmospheric and anthropogenic inputs and runoff and biological outputs from small catchments was performed (Pačes 1985). It was followed by a monitoring in the Ore Mountains and the Bohemian-Moravian Highlands in the years 1990 to 1995 (Melega, 1998). Tab. 8 shows the rates of erosion and the resulting denudation for 100 thousand years in four monitored catchment areas. X-0 is the forested catchment Hartvíkov (gradient 3.8%), X-8 is the forested catchment Salačova lhota (gradient 13.3%), and X-7 is the agricultural catchment Vočadlo (gradient 4.9%). All these three catchments belong to the watershed of the Trnávka River in the Bohemian-Moravian Highland. The fourth catchment is a forested catchment Vysoká Pec near Most (gradient 18%) in the Ore Mountains. In all cases the basement rock is gneiss.

Report number: Erosion Stability of DGR Potential Sites SÚRAO TZ 25/2015/ENG

Tab. 8 Rates of erosion and denudation in small catchment areas of the Bohemian-Moravian Highlands and the Ore Mountains (Pačes, 1985) Erosion Denudation metres per 100,000 kg.ha-1year1 year X-0 420 1.9 X-8 732 2.8 X-7 1700 6.4 X-14 1510 5.7

The rate of erosion and the associated denudation of the Earth's surface was calculated from data on mass balance in the X-16 catchment Jezeří, which lies next to the X-14 catchment Vysoká Pec in the Ore Mountains, and in the X-8 catchment Salačova Lhota in the Bohemian-Moravian Highland, between 1990 and 1995 (Melega, 1998). The rate of denudation was calculated using the regolith density of 2,650 kg.m-3 and the rock density of 2,700 kg.m-3 ( Tab. 9).

Tab. 9 The rate of weathering, erosion, and denudation in two small catchments in the Ore Mountains and in the Behemian-Moravian Highland in the periods from 1978 to 1995 and from 1990 to 1995 (Melega, 1998)

Rock weathering rate

Weathering Denudation

kg/.ha/-1year-1 m/100,000 years

X-8 1978-1982 1090 4.0

X-8 1990-1995 468 1.7

X-16 1978-1982 1864 6.9

X-16 1990-1995 1205.8 4.5

Rate of mechanical erosion of regolith

Erosion Denudation

kg.ha-1year-1 m/100,000 years

X-8 1978-1982 1332 5.0

X-8 1990-1995 569 2.2

X-16 1978-1982 2676 10.1

X-16 1990-1995 1712 6.5

The high rate of erosion of regolith in the X-16 catchment Jezeří in the Ore Mountains is caused by its high gradient (18%) and deforestation (70%). The calculated rates of

Report number: Erosion Stability of DGR Potential Sites SÚRAO TZ 25/2015/ENG denudation caused by chemical and mechanical weathering of rocks and regolith imply that the erosion rate in the years 1978 - 1982 was probably increased by acid rains which accelerated the weathering. After the reduction of acid precipitation in the years 1990 - 1995 the rate decreased. 3.4 Effect of glaciation on the rate of erosion in the Bohemian Massif

When estimating the rate of erosion and denudation it is needed to take into account that during the coming Ice Age, the Bohemian Massif will be in a periglacial zone within which permafrost will be created. Its build-up and the subsequent melting will disrupt hydrogeological and petrophysical parameters of rocks above the repository. The calculated depths of permafrost in the last Ice Age in the Pleniglacial (73 to 14,500 years BP) are summarised in Tab. 10.

Tab. 10 Estimated thickness of permafrost in the Upper Vistula Pleniglacial in the Czech Republic according to Balojev, Čápicina, and Czudek (Czudek, 2005)

Altitude Average annual Maximum m a.s.l. ground thickness surface temperature of permafrost in (oC) in peak Upper Pleniglacial

Pleniglacial

Hrušky, Dolnomoravský 172 -2 60 Trough -3 85

440 -3 120 Ml. Vožice, Vlašim Upland -5 160

Cínovec, Ore Mountains 859 -5 160 -7 230

248 -2 70 Chotětice, Vlašim Upland -4 130

Vizovice, Vizovice 394 -2- 80 Highlands 4 140

Praděd, Hrubý Jeseník 1,491 -7 220 -8 245

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Geophysical surveys in Poland (near the border with Russia and Lithuania) showed that in the Vistula glaciation in the foreground of Scandinavian glacier the thickness of permafrost was up to 520 m (Šafanda et al. 2004). According to these authors, the cause of such a thick permafrost was a very low average annual temperature of the terrain during the last glacial period (-10.3 °C) together with a low terrestrial heat flow less than 40 mW.m-2. Žák et al. (2012) estimated the depth of permafrost by analysing the isotopic composition of oxygen and carbon in cave carbonate sinters. In caves with limited ventilation in Weichselian (116 - 11.5 thousand years BP) permafrost reached a depth of at least 65 m in the lowlands. But, This method showed that the depth of permafrost in the High Tatras was at least 285 m. Zeman and Růžičková (1995) analysed the core of the borehole Blahutovice-1 which lies in the altitude of 260 m in the NW part of the Moravian Gate and found post-cryogenic textures (lenticular and retiform cryogenic texture with a 2 mm-deep frost microcracks) in fine sandy clay down to the depth of 220 m. This is probably a direct evidence of the deepest permafrost in territory of the Czech Republic in the Pleistocene. Experience from the research of hydraulic properties of crystalline rocks (Rukavičková, 2008, 2009) shows that the surface layer zone with opened fissures typically reached 150 m. These were mostly subhorizontal open cracks that occurred during freezing and melting of ground water. This depth probably corresponds to the thickness of permafrost in the last Ice Age identified by the methods presented above. If a periglacial climate will predominate in the Bohemian Massif throughout the 100 thousand- year period, the permafrost layer can be considered to be a protection layer because it will prevent the circulation of groundwater. If, however, the next Ice Age is shorter, then the rocks above the repository will be mechanically disrupted by melting and this will allow faster flow of groundwater and accelerate the erosion caused by runoff of the melt water. This means that with regard to the future glaciation that shall prevail in the next 100 thousand years and also with regard to the uplift of the Bohemian Massif it is necessary to count with the rate of erosion and the subsequent denudation of 0.5 to 30 m per 100 thousand years where the upper limit is the estimate that corresponds to the acceleration of water erosion in the subsequent interglacial and lower limit corresponds to full glaciation during the whole period of 100 thousand years.

3.5 Influence of terrain slopes on erosion in the surveyed localities

The main difference between the localities which affects the rate of erosion is the slope of the terrain. The regional distribution of slope conditions is shown in Tab. 11.

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Tab. 11 Gradient distribution in the surveyed sites

Čertovka

Slope in degrees Area in pixels % shares of indiv. categories

0-2.5 5951977 27.54

2.5 to 5 6474995 29.96

5 to 10 6027677 27.89

10 to 15 1912287 8.85

more than 15 1246707 5.78

Total 21613643 100

Magdalena

Slope in degrees Area in pixels % shares of indiv. categories

0-2.5 59201941.5 29.27

2.5 to 5 67590049 33.41

5 to 10 54561039.25 26.97

10 to 15 13550744.75 6.70

more than 15 7383002.25 3.65

Total 202286776.8 100

Kraví Hora

Sklope in degrees Area in pixels % shares of indiv. categories

0-2.5 2464137 13.58

2.5 to 5 4124367 22.73

Report number: Erosion Stability of DGR Potential Sites SÚRAO TZ 25/2015/ENG

5 to 10 5541060 30.54

10 to 15 2824027 15.57

more than 15 3188415 17.57

Total 18142006 100

Hrádek

Slope in degrees Area in pixels % shares of indiv. categories

0-2.5 44500297.2 21.56

2.5 to 5 79120667.5 38.34

5 to 10 66783862 32.36

10 to 15 11603246.5 5.62

more than 15 4352058.5 2.11

Total 206360131.7 100

Horka

Slope in degrees Area in pixels % shares of indiv. categories

0-2.5 57342141.5 27.22

2.5 to 5 67206835.7 31.90

5 to 10 53026311.2 25.17

10 to 15 17767014.2 8.43

more than 15 15301456.5 7.26

Total 210643759.1 100

Čihadlo

Slope in degrees Area in pixels % shares of indiv. categories

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0-2.5 93399482 43.31

2.5 to 5 75896252.2 35.19

5 to 10 39105861.5 18.13

10 to 15 5110592 2.37

more than 15 2138789.25 0.99

Total 215650977 100

Comparison of individual terrain slopes of sites which are considered for the future geological research to find a suitable place for a deep repository was performed by the use of weighted averages of the slopes in table 11. The slope was expressed by the median of the slope category, i.e. by the values of 1.25; 3.75; 7.5; 12.5. The value of the highest slope was 17 degrees. These slopes were weighted by the percentage share of each category in the locality. The result is a list of the localities sorted by the average slope: Čihadlo (3.7°), Magdalena (5.1°), Hrádek (5.2°), Čertovka (5.6°), Horka (5.7°), Kraví Hora (8.2°). Currently, the locality least prone to erosion is Čihadlo and most erosion-prone locality is Kraví Hora. However, in the long term and given the uncertainty in predicting climate change and biological changes in land cover, the importance of these gradient differences for predicting the rate of erosion and denuded surface thickness is not significant.

3.6 Conclusions

1. Calculations and estimates of the rate of erosion and denudation vary depending on the method of calculation. However, these differences are insignificant for performing the risk analysis due to uncertainties regarding future climate trends. 2. The rate of erosion and denudation increases by the end of glaciation and the subsequent runoff of glacial water. With regard to the future glaciation that shall prevail in the next 100 thousand years and also with regard to the uplift of the Bohemian Massif it is necessary to count with the rate of erosion and the subsequent denudation from 0.5 to 30 m per 100 thousand years where the upper limit is the estimate that corresponds to the acceleration of water erosion in the subsequent interglacial and lower limit corresponds to full glaciation during the whole period of 100 thousand years. 3. The rate of erosion and denudation is increased by human activities. In 1976, i.e. in the period of the greatest pollution, the erosion and denudation in the Bohemian Massif which is drained by the Elbe River was so fast that it would correspond to runoff of a 30 m thick layer of material in 100 thousand years. When limiting the anthropogenic influence, the

Report number: Erosion Stability of DGR Potential Sites SÚRAO TZ 25/2015/ENG

thickness could reach around 9 m per 100 thousand years. The current rate of erosion in small forested catchment areas in the Bohemian Moravian Highland and the Ore Mountains corresponds to the thickness of denudation in the range of 1.7 to 10 m per 100 thousand years. The average gradient of the terrain in these catchment areas is 3.8 to 18%. Data on erosion rates in other river basins in the Czech Republic are not available. 4. Uncertainties and inaccuracies in determining erosion rates with respect to extrapolation to 100 thousand years are so large that it is not scientifically justified to differentiate the rate of erosion and denudation in the individual sites of interest formed by granite or crystalline rocks with approximately the same morphology. 5. The differences in the present erosion rates in the sites of interest can be determined by monitoring of mass balance of elements in representative small catchments located within the sites. The differences in historical erosion rates can be determined by detail Quaternary research and mineralogical and chemical comparison of local bedrocks and their regoliths. Application of cosmogenic isotopes would require a development of special isotopic laboratory and special training of researchers. 6. Permafrost, which is likely to reach a thickness of more than 200 m in the next Ice Age, will reduce the rate of erosion because it will prevent the circulation of groundwater and its runoff. It will therefore have a protective effect. In the following interglacial period, however, melting of permafrost will create open fissures with a sub-horizontal orientation. This will result in the faster and deeper circulation of groundwater, in changes in petrophysical properties of the overlying rocks, and in accelerated erosion caused by water runoff from both the permafrost and the melting of northern continental glacier.

Report number: Erosion Stability of DGR Potential Sites SÚRAO TZ 25/2015/ENG

4 References

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