Landform Analysis, Vol. 4: 109-117 (2003)

Structural control on drainage network orientationan example from the Loucka drainage basin,

SE margin of the Bohemian Massif (S Moravia, Czech Rep.)

Zdenek Macka

Masaryk University in BmoFactI/I)' of Science. Institute of GeographyKoi/(;fska 2. 6lJ 37 Brno. Czech Rep.

LAAbstract: This paper discusses the relationship between geological structure and drainage networkorientation at both a mesa-scale and local scale. The Loutka Basin, located at the SE margin of theBohemian Massif (5 Moravia, Czech Rep.), has been selected as the model region for these studies.In the LouCka Basin, the bedrock comprises the metamorphic TO<:ks of the Moldanubil,:um Group. whil;:hare arranged in elongated bands and lenses and arc: fractured with the dense network of faults. Thereis no extensive: cover of unconsolidated younger sediment' in the basin, nor any deep weathering regolilh.In thcsc respects. the gcological selling is extrcmely favourable for the quantification of Slructuralfeatures and their correlation with drainage orientation. The degree of correspondence between thedirection of drainage network segments and the orienlation of such structural features as faults,mylonite lones, thrust-fronts and rock linealions was invesligaled in five study areas. The third-orderstreams are lhose most influenced by structure. The higher the order of stream segment, the weaker thecorrelation. and the more importantlhe overall indination of the terrain as a controlliog faelor in Slreamflow oricntation. However, lhere is a strong structural control of firsl order streams in the peripheryof thc Basin. The structural control of stream flow direction in the Loufka Basin. which is built up withPrccambrian metamorphic rocks, varics bctween 30-50% of the rectified channel length; the upper limitis considered to be the maximum conditioned by a local very high density of various linear structuralelem<:nts.

Key word.'" drainage network, direction of stream flow, geological structure, the Bohemian Massif.S Moravia

Introduction

One of the many ways of analysing drainageevolution is by determination of streamflow ori­entation. However, while the direction of stream­flow is the key to understanding the way in whicha drainage network comes to fill the space avail­able lO it, very little auention seems to have beenpaid 10 Ihis topic. Typical dendritic patterns showa tendency to equal (random) distribution of flowdirections (Morisaw3, 1985). However, variationsfrom this may result from an initial surface slopeor geological structure. Thus, when analysing theevolution of a drainage network, it is usuallypresumed that the network, during its expansioninto the space available, gradually adjusts its

course to the underlying structure. A variety ofstructural features is presented in the literature asthe controls of flow direction: joints, faults, in­clined sedimentary strata and fold axes.

The relative influence of any particular struc­tural feature is also dependent on the scale atwhich the study of flow orientation is conduct­ed. Further, the scale chosen also determines themethodology which is to be applied. At the mega·and macro-scales, a good correlation between thecomposition of drainage networks and joint sys­tems and fault lines generated by neotectonicstress fields (both of regional and global extent)is usually to be found. In contrast, at lower scales,joint systems arc controlled by more local influ·cnces (Summerfield, 1991). The influence of both

109

Zdenek Matka Structural control on drainage network orientation ...

of the Bohemian-Moravian highlandclose to the European Continentaldivide. In its middle reaches, it runsacross gently undulating surface,part of which is clearly planated.Close to its confluence with theSvralka, it enters an area of highrelief coincident with the dissectedmarginal flexure of the BohemianMassif. For the purposes of thisstudy, five study areas were select­ed in the Loucka Basin. In these, therelationship of stream now directionto fault traces, mylonite zones,thrust fronts and rock lineations wasinvestigated (Fig. 2). The particularareas represent the following geo­morphological regions:- the summit part of the Bohemian­Moravian highland (area I and 2),- flat relief of planation surface(arca 3).- strongly dissecled marginal flex­ure of the Bohemian Massif (area 4),- lectonically defonned planationsurface which is partly dissected bydeep V-shaped valleys (area 5).

The principal criterion for adopt­ing any of the areas was the gener­ally unimodal nature of structuraldetails (which tbus made them ame­nable to quantification).

'Okm

\

Methods

The drainage network was derived from topo­graphic maps at a scale of I:25,000. Both peren­nial and ephemeral streams were included. Thenetwork was then divided into segments, i.e.reaches between the source and a confluence orreaches between confluences. For each segment,the orientation and rectified length were deter­mined. according to the recommendations ofScheidegger (1979) (Fig. 3). Measurements ofstructural elements were made from geologicalmaps at a scale of I:50,000 (Czech GeologicalSurvey, 1991-1996). Lineations were groupedinto twelve 15° intervals. The preferred stream­flows were detennined from the knowledge of theorientation and relative length of drainage ele­ments and then compared with the structuraldetail. In order to express the spatial variabilityof orientation of streamflow direction, the drain­age basin was compartmentalised into a rectilin­ear grid where each cell was 10 km2 in area. In

5

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Svratkauyslalline complex

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Thbitpluton

collision of the Carpathian-Pannonian blocks withthe North European Platform. He considered thatthe southerly drainage across the BohemianMassif was a reaction to the thrusting of theEastern Alps towards ils southern margin and thecreation of the E-W trending Alpine ForedeepBasin. Certainly, the disruption of the drainageand its diversion eastwards did not occur beforelhe Karpatian period of the Miocene when thrust·ing of the Carpathian Nappes began and the NE-SW trcnding Carpathian Foredeep Basin cameinto existence. The original southerly streamflowof the area is presumably indicated by the direc­tion of the upper reaches of some of Ihe riversof western Moravia (eg. Moravska Dyje, lele­tavka. Jevisovka) and the distribution of fluvialsediments containing tcctites derived from theplume of the Ries impact structure.

The Loucka Basin lies in tbe NE part of theBohemian-Moravian highland - a large geomor·phologically distinct area which occupies a largepart of western Moravia and eastern and south­ern Bohemia. The Loucka rises at the summit part

rig. 2. Major Slrcams or thc Louth drainage basin. Sludy arcas or detail invcs­tigations orrc:lalionship belWI:i:n drainage direclion and geological structure aremarked in grey. The geological regions or me-amorphic rocks arc delineatcd.Numbers in circles indicatc major faults or the area1 Ktidlovke r.UII. 2 - mId r.ull

The structural features of the Loutka Basinare clearly expressed. The bedrock comprisescrystalline rocks which are transected by a densenetwork of fractures. The component rocks aredisposed in sub-parallel bands ·and lenses whichvary in width from 100 to 750 m; these extendin some cases, for as much as 7 km. Such a spatialconfiguration of structural detail is unique to theeaSlem margin of the Bohemian Massif. Themajor part of the basin is noored by the metamor·phic rocks of the Strazek Moldanubicum Group.In the southern part of the Basin, isolated plutonscrop OUl, while in the east, small outcrops ofmetamorphic and igneous rocks of MoravicumGroup are present (Fig. 2). The dominanl rocktypes in the Basin are orthogneisses and parag­neisses Ihough there are minor developments ofamphibolite. granulite. phyllite and granite. Tworegionally important faults cross the LouckaBasin: the Kfidlovice fault, which divides Stni:iekMoldanubicum Group into separate blocks andthe Bit~ fault which separates the MoldanubicumGroup from the Svratka Dome of MoravicumGroup (F;g. 2) (M;saf el al., 1983).

The overall tilt of the SE margin of the Bo­hemiarn Massif was initiated at least as early asthe Miocene. The uplift of the Massif was partlydue to block faulting and partly to a regional

doming along a pronounced mar­ginal flexure. The whole structureis clearly related to the geodynamicevolution of the Carpathian Nappes(Brzak, 1997). Prevailing wisdomholds that the flow SE-wards maydate as far back as the Cretaceous(Dlabac, 1976) or the Palaeogene(Dvornk, 1995) and Ihat. during thevarious transgressions and regres­sions of the sea in the CarpalhianForedeep Basin, only the length ofthe streams changed, nOl the direc­tion. Marine transgressions had tra­ditionally been ascribed to thesinking of the margin of the Bohe­mian Massif and regressions, withuplift. After each transgression, theoriginal relief was exhumed andriver valley development continuedwithin the framework of the previ­ous physiography. However,Hnidek (1997) suggested that riv-er development is based on differ­ential development of the easternmargin of the Massif during the

The study area

,••

100 km

,..,. ."\. .--:• , <. ,..

'-...~

"- '-tPo."THE BOHEMIAN • "'"

MASSIF I '.'~

..,...,.«)' IO~~j:.

/. _'" " THE WESTERN8(n'Oc'~~-' CAR'jTHIANS

'.~"','/ ..,./.,/(T 1'4 J

... ~/..<!'''' ',//, ".,"r _ ._I....._ T VIENNA

BASIN

r ....• ....

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fig. I. Location of the Lou~ka drainagc basin within thc tcrritory of Czcch Rep.and its position within the Bohcmian Massir

neoteetonie and older stress fields on streamflowdevelopment at the macro-scale is discussed inthe papers of Scheidegger (1979, 1980, 1981).Joint control of streamflow development at meso­scale was studied by Aghassy (1970) and Kos­mowska-Suffczyitska (1998), and at the locallevel by Bannister (1980) and Bi! (2000).

Clearly, the possible influence of geologicalstructure on streamflow direction is best studiedin basins where there is an absence of weather­ing mantles and sedimentary fills, and, in theserespects, the Loucka Basin, an important right­bank tributary of the middle course of the Svrat­ka, is ideal. The Svratka drains a large area of theSE corner of the Bohcmian Massif. The Louckais one of many rivers which drain the south-eastmargin of the Bohemian Massif in south-eastcrndirection towards the Carpathian Foredeep Basin;it may be regarded as a consequent stream, i.e.one which follows the general SE tilt of themargin of the Massif (Fig. 1). The aim of thispaper is to determine to what extent is this COIl­

sequent course of the Loucka has been affectedby the underlying rock structure. The analysiswas conducted at a local or mesa-scale, as defmedby the degree to which stramflow direction hasadjusted to fault traces, mylonite zones, thrustfronts and lineations of the crystalline rock base­ment of the Bohemian Massif. The paper alsoevaluates the influence of the initial surface slope.

110 III

ditioned by provcn faults. In the middle course,where the river flows SE, the valley deepens andwell-developed incised meanders are strikingfeature. Indeed, incised menders are a character­istic landform of the lower reaches of many largerrivers which drain the SE margin of the Bohemi­an Massif.

The water divide between the Loucka and theLibochtivka, the second most important river in

M1:IIIUU p.ulld I..loul ."IIlH, T"I.I >1r"~III.... lIy

r.1I11> (%) llftull"n (%) ., "XmUII I.n..nnd j%)

AREA tAll segmenlS 36.0 27.7 218 54.1External segmcnts 45.0 15.2 103 52.6

tnlernal segmentsOrder 2 28.5 12.7 48 36.3Order 3 39.6 76.7 29 84.3Order >3 8.1 50.7 38 56.3Inlernal 10lal 25.9 41.5 JJ5 55.6

AREA 2All segments 34.6 32.3 269 43.4External segments 22.6 23.4 136 31.3

Internal segmentsOrder 2 22.6 44.8 68 57.8Order 3 75.6 62.6 23 75.6Order >3 57.4 35.9 42 59.8Inlernal tOlal 52.3 45.S J33 61.2

AREA JAll segments 11.9 24.7 250 36.6External segments 9.1 28.5 J23 37.6

Internal segmcntsOrder 2 7.6 13.1 54 20.8Order 3 24.7 42.0 35 35.9Order >3 20.4 42.0 38 62.5Internal tOlal 15.4 19.9 J27 35.3

AREA 4A11 segments 27.9 23.3 2lJ 32.5External segmcnts 17.1 17.9 108 21.9

Internal scgmentsOrder 2 32.3 15.5 58 33.4Order 3 52.1 30.3 22 63.9Order >3 42.9 43.9 43 48.3Internal total 39.4 29.1 J23 43.8

AREA 5All segments 16.7 lOA 282 23.6External segments 10.8 6.7 136 15.2

Internal segmentsOrder 2 30.8 14.4 60 37.6Order 3 20.9 6.9 25 24.9Order >3 20.9 t9.8 61 37.3Internal total 25.1 15.5 146 35.5

Table I. Percentage of segments oriented parallel 10 geological stroClUrcs in the Lou.:!ka drain­age basin, SE margin of the Bohemian Massif

Structural control on drainage network orientation ...

its source, it flows south. Two shon sections thenflow E and SSE, respectively. The cast flowingsection is particularly striking; this has several

-S reaches which diverge from the east flowsat right-angled bends. Of course, this is highlysuggestive of a structural control. In this area, theLoucka parallels the Kfidlovice Fault Zone al­though the laner lies al least 5 km 10 the north.The courses of short -S valley sectors are con·

The surface of the eastern margin of theBohemian Massif slopes gently E and SE, as doesits drainage which is therefore presumed to beconsequent. The Loucka follows such a coursedownstream from its middle reaches but, in itsupper course, there are significant deviations fromthis general trend. For a distance of 15 km from

The analysis of orientationof streamnow directionin the Loucka drainage basin

was related to geological structure. In study areaI, the relationship of streamflow direction to faulttraces and zones ofmylonite was investigated. Inareas 2, 3 and 4, to fault traces and rock linea­tions; and in area 5, to fault traces and the oldthrust front oUhe Moldanubicum Group. Wherethe structural features are not unimodal and inareas which lack a statistically·reliable number oflineations, quantitative analysis of any relation­ship between streamflow direction and structureis difficult at the meso·scale. This is especiallythe case for area 5, which is why the reliabilityof the conclusions is suspected here.

Fig. 4. The preferred onentalion of channel network segmenlsin grid cells with an area 10 km~. Grid cells with similarslream channel OTlentation were grouped and regions wilbuniform drainage direction were delimited. Segments of allordcrs were used for the calculation of lhe preferred streamchannel orientation in the grid cell. Numbcl"l' in cells indi­cate the relevant classes of stream ehannd orientation: I .0-15°1180 195°,2 ... 15.1 - 30°/195.1 ~ 210°. elC.

I

8 I 10 11,

6 8 7 8-

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7 9 6 6 7 11

11 9 9 6 8 9 I 11......... """""11 I

I

7 9 I 4 8 8 4

9 6 61

10 10 5-11 9 9 9 7

II-- /--'

'­-......._....~

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---- Perennial stream

------0 Ephemeral stream

each of these a display of all stream order deter­minations was used 10 calculate preferred stream­flow direction in each part of the network. Whereadjacent cells showed the same patterns, thesewere grouped into regions; it is assumed that eachregion was probably conditioned by tbe same,unique set of controlling factors (Fig. 4).

The percentage ratcs of drainage elementsoriented parallel with geological lincations wasindependently calculated for all five study areas(Table I). Orientation data for both strearnflowand structural elcmcnts wcrc ploncd as rose di­agrams (Fig. 5). The data was then re-ploned inrespect of external segments (first order streams),internal segments (streams of second and higherorders) and jointly for streams of all orders. Thiswas so as to examine whether or not stream order

Fig. 3. An example ofchannclllctwork rectificatiun procedure.All segments of channel network in the Loutka drainagebasin were converted inw straight lines ill 1his manner.Rectified orientation and length of segments were thenmeasured

ldenek Milcka

112 IS - l.uIdform 113

Zdemlk Macka Structural control on drainage network orientation ...

(Svatei hora elevation, Deblin highland, Libo­cbuvka depression). Evidently, the higher orderstream directions are independent of geologicalstructure; in many cases, stream orientation ishighly oblique or even perpendicular to the dom­inant structures in the basement.

,Svati bon /elevation ,//'

...., /........ ,,/....__....

s

N

,

Fig. 6: The map of hypothetical initial surface on which the development of channel network in the Lou~ka drainage~as~n began. T~e s~rfaee was reconstructed on the basis of summit level allitude detc:nnination. NumbeI1i al the linesmdlcate elevation In m a.s.l.

Oi!l!!'lO_iZ_""._.=""!i5i;;;; ~1~O~"""""""""",,,,~I? km

levels in the evolution of the drainage, both ofwhich have been a considerable influence on floworientation: firstly, a general tilting of the SEmargin of the Bohemian Massif mainly towardsthe SE. though locally to the SSE, followed byregional tectonic elevations and depressions

Inlemal segments

Front ofa thruSt

/ Rock lineations

upper course of the Libochuvka are presumablyexplained by the post-tilting tectonic highs andlows wbich have warped the original surface(Fig. 6). The fonn of original surface was recon­structed by contouring the summit level surface,using the technique of Clark (1966). It is conclud­ed that the skeleton of the modem drainage sys­telll evolved on this initial slope and was then re­modelled during incision into the underlyingbasement, its course there being detcnnined bylinear belts of weakness, such as fault zones. Thusit seems reasonable to postulate two hierarchical

Extemal segments

the basin, is unusual. Both channels run 5ub­parallel until close to their confiuence. Up to thelatter, each course is J 1.5 km long and the iner­fiuyc is about 1.5 km wide. However. the drain­age divide lies much closer to the Libochuvka,which has very few left bank tributaries. In thewestern part of the basin, the drainage is in aconverse, i.e. northerly direction. Such a direc­tion is followed by both the Libochiivka and someof its tributaries, including the Lucni creek, animportant right bank tributary of the Upper Louc­ka. These seemingly anomalous features of the

Fig. S. Rose dIagrams sho.....ing segment orientation and orienlation of geological struetuTes in five study areas in the loucla drainagebasin. Orientation of intcmal, c}[lemal and all segments and orientation of faults and rock lineations are depicted

AREA 4

AREA 3

AREAS

All segments

AREA2

AREA I

114IS' liS

Zdentlk Macka Structural control on drainage network orientation ...

The orientation of streamflow in respectof geological structure

When the spatial distribution of areas withuniform drainage direction arc compared with theorientation of structural features (Fig. 4) andbearing in mind the form of the original slope(Fig 6), it is seen that the relationship betweenthe uniform areas and geological structures orinitial surface is negative. It is presumed, there­fore, that the spatial distribution of the uniformareas is probably the result of several controllingfactors. The association of such areas with geo­logical structure is also obscured by the inclusionof each and every datum concerning stream or­der; all segments were included in this compar­ison, regardless of rank.

Study areas I and 2 are both situated in thesummit area of the Bohemian·Moravian highland,where the structural features are generally orient­ed \V-SE. The Kfidlovice Fault runs throughboth areas. In both areas, the peaks of the struc­tural plots lie in the same interval; further, thefault traces have a minor peak in the directionperpendicular to the major, i.e. NE-SW. Studyarea 3 is situated in the sub-basins of the Libo­chuvka and the Lucni creek. The network offaults here is not so dense as it is in areas I and2; nevertheless, the rock lineations are also dom­inant in the NB-SW sector. The fault traces heresignificantly trend NNW-SSE. Study area 4 issituated in the left bank of the lower course ofthe Loutka. Here, a dense network of faults androck lineations both peak at NNW-SSE on theplots. Study area 5 is situated in the sub-basinsof the Halda and BlahoMvka in the Jinosov andDeblin highlands. Two significant structural fea­tures run across this area - the Bites Fault andthrust-front of Moldanubicum Group over Mora­vicum Group. However, they do not producemajor peaks on the structural plol.

The c1early·expressed parallelism of structuralfeatures and the coincidence of fault traces withrock lineations in study areas 1-4 should, theo­retically, produce a high degree of structuralcontrol of streamflow there. This should partic­ularly apply in areas I and 2, where exists thehighest rates of structurally·influcnced sectors. Infact, study area I is structurally controlled overmore than 50% of the length of the channelnetwork (Table I). In study areas 3 and 4, thiscontrol is much weaker, which may be explainedby the high rate of structurally controlled sectorsof the first and second order in area I and, toa lesser degree, in area 2. Within the other studyareas, the sensitivity of the first and second or-

116

der streams to structure is much weaker and theirdirections arc fashioned more so by the localslope, i.e. the valley side slopes. Area I is remark­able in respect that the preferred orientation offirst order streams along fault traces (45% of thestream lenf:,...h) compares so well with that alongrock lineations (15%). In study area 2, orienta­tion parallels both types of structural features toa comparable degree (22% along faults; 23%along rock lineations). The significant local de­pendence of first order sectors on structure mightbe explained, firstly, by the exceptionally highdensity of structural features in this area; second­ly, by the location of the area in the preferentialzone of drainage network expansion close to theEuropean Continental divide. The first orderstreams which are the agent of this expansionhave utilised for their preferential growth the linesof weakness (represented here by faults and lin­cations). The degree of structural control on theinternal sectors (streams of second and higherorders) is also fairly high in study area I, while,in area 2, the value may even exceed 60%.

The general trend in all study areas is anincrease of geological control with stream order,the maximum being reached at the third orderlevel. However, the coincidence of 4th orderstreams with meso-scale structures is weaker andthe importance of the initial slope factor increas·es proportionally.

Conclusion

Investigations concerning the relationship ofstreamflow orientation with geological structurein the Loucka Basin shows that, generally, theleast influenced flows are those of first order; lessinfluenced are the first order streams which aregoverned simply by the valley side slopes onwhich they developed. However, in certain geo­logical and geomorphological situations, there areclear exceptions to this generalisation; certainly,locally, geological control of these small streamsmay be even higher than in many streams ofhigher order. In the peripheral parts of the Basin,expansion of drainage into the available space hasobviously been easiest along lines of weaknessand, as a consequence of this, streams of the firstorder come to exhibit a high degree of adjustmentto the underlying structure.

The maximum structural control is usuallyreached by the streams of the third order, this istrue of all five study areas. Towards the higherorders, the influence of structure becomes weak­er and the nature of the initial slope seems to be

the overriding influence. In respect of the Lout·ka Basin, two hierarchical levels may be distin.guished. In the first, an older slope which isinclined to SE towards the Carpathian ForcdeepBasin; secondly, the superimposed later tectonicfeatures which have caused local elevation anddcpression. Evidently, these have affected thedrainage system profoundly. Quantification of therelationship between stream flow direction andstructure did not identify any particular structur.al feature as a preferred route for the drainageexpansion. Further, the measurements made didnot clearly indicate whether srreams of any par·ticular order are preferentially adjusted to anyspecific structural feature. Thc analysis suggeststhat, in those pans of the loucka Basin where theexpression of structural fearures is marked, thecontrol on drdinage is normally 30-50% of theentire dminage length. In regions which have amuch denser than average network of structuralfeatures oriented unimodally, the relationshipreaches 50% in the extreme case, though there arcsignificant dcpartures from this generalisation. Itwould be particularly instructive to supplementthese measurements at the meso- and local levelby direct structural measurements ofjoint patternsand foliation of metamorphic rocks, i.e. to repeatthe investigation at the micro-scale.

References

Aghassy, J., 1970: Jointing, drainage, and slopesin a West African epeirogenetic savanna land.scape. An"als 0/ American Geographers 60:286-298.

Bannister, E., 1980: Joint and drainage orienta­tion of S. W. Pcnnsylvania. Zeilschrift fi;r Geo­morphologie 24: 273-286.

Bil, M., 2000: Vztah orientace ficni site a struk­turnich prvku (na pfikladu povodi VsetinskeBecvy). I,,: J. Prasek (Ed.) Soucasny slav geo.

mor/ologicJrych vyzkunlu - Sbornik referaluz mezintirodniho seminafe konaneho ve dnech13.-14. dubna 2000 v NYdku. PHrodovMeckafakulta Ostravske univerzity, Ostrava: 3-6.

Brzak, M., 1996: Vybrane problemy ficni sitev povodi Jihlavy. (;asopis Moravskeho nluzea.wJdy geologicke 81: 109-120.

Clarke. J.I., 1966: Morphometry from maps. In:G.H. Dury (Ed.) Essays in geomorphology.Heinemann, London: 235-274.

Dlabat. M., 1976: eogen na jihovychodnimokraji Ceskomoravske vrchoviny. V)'zkumneprace uue 13: 1-21.

Dvofak, J., 1995: Tektonickj a morfologickyvyvoj jv. okraje ceskeho masivu pi'i podsouvanipod Karpaty. Knihovnicka ZPN 16: 15-24.

Hradek, M., 1997: PHme a nepfime antropogen­ni transformace relicfu vyvolane vystavbou aprovozem objektu energcticke soustavy Duko­vany - Dalesice. Pfirodovedny sbornik Zapa.domoravskeho nluzea v TfebiCi 25: 1-67.

Kosmowska.Suffczynska, D., 1998: Wplyw sp~­

kOli CiOSOlVych na kierunkolVosc rzeiby (noprzykladzie pQlnoc"o-wschodniego obrzeieniaGor SlVi~lokrzyskich). Uniwersytet Warszaw­ski, Warszawa: 165 pp.

Misaf, Z. el al., 1983: Geologie CSSR (Cesl..jmasiv). SPN, Praha: 333 pp.

Morisawa, M., 1985: Rivers - form and process.Longman. London: 222 pp.

Scheidcgger, A.E., 1979: Orientationsstruktur derTalanlagen in der Schweiz. Geographica Hel.vetica 34: 9-15.

Scheidegger, A.E., 1980: The orientation of val­ley trends in Ontario. Zeitschrift /iir Geomor­phologie 24: 19-30.

Scheidegger, A.E., 1981: ValIey trends in Tibet.Zeilschrijt fi;r Geomorphologie 25: 203-212.

Summerfield, M.A., 1991: Global geonlorpholo.gy - an introduclion 10 lhe study ofland/arms.Longman, Harlow: 537 pp.

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