SOILS and THEIR GEOLOGY in the GEUL VALLEY W. Van De
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SOILS AND THEIR GEOLOGY IN THE GEUL VALLEY W.va n deWestering h CONTENTS 1. INTRODUCTION 1 2. GEOLOGY 4 2.1 Stage I 4 2.2 Stage II 4 2.3 Stage III 6 2.4 Stage IV 7 2.5 Stage V 8 3. SOIL CONDITION 9 3.1 Soils 9 3.2 Calcareous material 10 3.3 Hydrology 10 3.4 Soil map legend 11 3.5 Soil map 12 3.6Fan s 17 4. THE PRESENT LANDSCAPE 18 5. SUMMARY 20 6. SAMENVATTING 21 7. REFERENCES 24 1. INTRODUCTION Therive rGeu risesl nea rEynatte n inBelgium .I tenter sTh eNetherland snea r Cottessenan dflows int oth eMeus enea rBunde .B ythe ni tha scovere dabou t5 6 km, two-thirds of this distance being in The Netherlands (Fig. 1). From the Dutch-Belgian frontier to Mechelen it flows in a south-north direction, from Mechelent oSchi no pGeu li trun snorth-wes t andfro m Schino pGeu lt oBund e in a more westerly direction. It receives many small tributaries. Together they form an essential part ofth epleasan t South Limburg landscape (Fig.2) . By Dutch standards the Geul is a fast flowing river. The slope varies from about 7.62m/k m near Epen to 1.33m/k m near Houthem. Theaverag ei sabou t 3m/km . Itsdischarg e isver yirregular . Near Meerssen theaverag edischarg ei s Meded. Landbouwhogeschool Wageningen 80-8(1980) 1 K.j- /^""de / X boundary of HEERLEN vïf / s. Meerssen ^ ->(the river system # ' Rothem-iÇ^. Vroenhof , ^-_j., (^St.Gerlach / _^ Schaloe n f vauenDurg ^fC-Schin op Geul MAASTRICHT Genhoes/ >.Etenaken _,'' •i GERMANY AKEN BELGIUM \ HENRI-CHAPELLE FIG. 1.Th e river system of the Geul. Meded. Landbouwhogeschool Wageningen 80-8(1980) Meded. Landbouwhogeschool Wageningen 80-8(1980) about 2,3001/ s; th eminimu m discharge inrecen t yearswa s95 01/ s (September 1971),wit ha maximu m of24,2001/ si nOctobe r 1974.I nth ever ywe tperio do f December 1966th edischarg ea tValkenbur g wasabou t 65,0001/s (Information supplied byth e LimburgPubli cWork s Department). Underpresen tcondition s severefloodin g isrelativel yrare .Th elas tfloo d was inth esprin go f1974 . Ona naverag eflood s occurever ytw oyears .Th edischarg e by means ofregulation , hasbee n improved sotha t floods canb eprevente do r theirduratio nshortened .Locall ysmal larea sar emor efrequentl y flooded.Whe n floods occur in the late autumn, winter or early spring, there isusuall y little damage to agriculture, high water levels being generally of short duration. Beforeth emoder nregulatio no fth eGeu lth erive rha da natura lcharacter .Bu ti t should beadde d that for centuries thewate r discharges andlevel s have been influenced byman ,e.g .b ylan dreclamation ,th econstructio n ofwatermills ,etc . The geology and soil conditions of the Geul valley also reflect agricultural practicesi nth eSout h Limburgloes slandscape . 2. GEOLOGY Fivedifferen t stagescoul db edistinguishe di nth ehistor yo fth evalle yfil li nth e Geulbasin .Th efirs t stagei so fpre-Holocen eage ,th eothe r four areHolocene . 2.1. STAGEi (FIG. 3a) Theshap ean dth esiz eo fth eGeu lvalle yindicat ea Pleistocen eorigin .Durin g theformatio n ofth edissecte dplatea u landscapeth evalle yo fth eGeul ,a major tributary of the Meuse, was deepened and widened. As a result of various geological processes thecros s section ofth evalle yha sbecom e asymmetricali n manyplaces ,wit hon estee psid ean don egentl eslope .Smal lterrace-lik eirregula rities areoccasionall yfoun d alongth evalle ywalls .A tth een do fth ePleistocen e the dissected plateau landscape hasbee ncovere d byaeolia nloess . The valley was largely incised inUpper-Cretaceou s limestones. Inth e flood plain ofth epresen t valleysom emetre so fPleistocen e gravelwer elai d downb y braidedriver soverlyin gth eCretaceou smaterial .Holocen esediment shav ebee n deposited onto p ofit .Thes elas t depositsgiv eth evalle yit spresen t character. 2.2. STAGEi i (FIG. 3b) The temperature rose atth ebeginnin g ofth e Holocene andinitiate d anew , more thermophilic type of vegetation (JANSSEN, 1960). This led to a forest vegetation inth e wholeSout h Limburg loessarea . Thenatura l situation ofth e 4 Meded. Landbouwhogeschool Wageningen 80-8(1980) cretaceous limestone a. Stage I. Pleistocene; deposits of a braided river, gravel. aeolian loess |»°e°»| gravel I« ». «I Peat «] clay T fluvial material , '-J fine-silty ffijgffl fluvial material, b. Stage II. Holocene; oldest deposits, tiöiä coarse-silty (loess-like) clay and peat. Ij-.-'.-çj colluvial material \:°'':i (loess-like) I' * *,| fluvial material, sandy c. Stage III. Holocene; increased activity, fine-s1lty deposits. i •i •I r r -r r 'T i •i •i -r d. Stage IV. Holocene; increased activity, e. Stage V. Holocene; coarser-silty deposits. recent deposits, sandy. FIG. 3.Stage si nth efilling o f thevalle yo fth eGeul . Geulvalle yi nwoode dSout hLimbur gwa swette rtha na tpresen ta sa resul to fit s lowelevatio nwit hrespec tt oth esurroundin ghill san dth eoccurrenc eo fspring s along the valley at points where water rises over heavy, impermeable Lower- Cretaceouscla ylayer so rflow si nCretaceou slimestones .Th evegetatio nbecam e a marsh forest (HAVINGAan d VANDE N BERG VAN SAPAROEA,1980) . At the beginning of the Holocene, in such a densely forested landscape, the river mainly carried groundwater base flow that reached the valley through springs and seepages. In a wooded landscape when precipitation exceeds the évapotranspirationth esurplu swate rdoe sno treac hth erive rvi ath esurface ,bu t Meded. Landbouwhogeschool Wageningen80-8 (1980) through the soilan d after deeppercolatio n viath egroundwater . At thisperio d thedifferenc e between base flow and peak dischargeo fth erive rwa sno t great. Asth elandscap ewa scovere db yvegetatio nth esuspende dloa d ofth erive rwa s small.Ther ewa slittl eo rn osedimentation .Onl ysom ecla ywa sdeposited ,o rels e peat was formed. 2.3. STAGEm (FIG. 3C) Aslon ga sth eentir eloes sare awa sunde rpermanen tvegetatio n thedischarg e and activity of the Geul remained more or lessunchanged . It wasonl y slightly affected byclimati cchange si n the Holocene.Th e situation was again changed whenth evegetatio nwa scleare db yma nan dbar esoi lbecam esubjec t toerosion . The first human settlers in South Limburg to clear some parts of the forest wereth e Dutch Bandkeramik people.The ylive do n the boundaries ofth eleve l loessplateaus .The ywer efarmer s andthei rarabl elan dwa so nth eplateaus .Th e coarse-siltyto player so fth eloes ssoil sha da lowe rcla yconten ttha nth efine-silt y subsoils and were weakly acidic. This soil condition was conducive to arable farming, as sparse woodland was growing on loamy and weakly acidic soil (PONS, 1973). For reclamation and farming such situations were attractive because: - it wasrelativel y easy to clear the sparsewoodlan d and reclaim the land, - the original vegetation waseasie r to control than onclaye yan d richsoils , - tillage ofcoarse-silt y soilswa seasy . Owing to the situation of the arable land on plateaus and the sparse forests around the fields on the boundaries of the plateaus and on the hills, the hy- drologicalregim ewa sonl ysubjec t tosligh tchange .Erosio nwa sno tseriou san d mosto fth esurplu swate rstil lreache d therive rvi ath egroundwater .I nthi spar t ofSout hLimbur gn osettlement so fBandkerami k agehav ebee nfoun d (BAKELS, 1978),s otha t little if any silt reached the river and the sedimentation rate was low.Th esedimentatio n pattern inth eGeu lvalle yonl ydiffere d slightlyfro m the situation described in stage II.Thi swa schange d when larger parts of theloes s area,bot ho nth eplateau san do ngentl eslopes ,wer ecleare db yman .Th enatura l vegetationdisappeare d anderosio nstarted .I ti sno tknow nwhethe rerosio nwil l have become serious as early as from the beginning of intensive agricultural practise or later on (at theend?) . Itwa sdurin gth eRoma n eratha tlarg epart so fSout h Limburgwer euse d for arable farming. The clearance of the natural vegetation and resulting erosion then had amarke d effect on theregime so fth eGeu l and other rivers.I t caused that the hydrological regime of theloes sare a wasdrasticall y changed and that thesuspende d load increasedconsiderably . Upt o thisperio d thesurplu swate r entered the soil and when the soil was saturated, the water percolated to the groundwatervi awhic hi teventuall yreache dth eriver. Bu towin gt oth eclearanc e ofth evegetatio n inhill yarea sles swate r penetrated the soil;i n stead it flowed laterally down the slopes.Thi s meant that the surplus water took less time to 6 Meded. Landbouwhogeschool Wageningen 80-8(1980) reach the river, and that thewate r levelsan d discharges became higher and more irregular with great differences between base flow and peak discharge. Owing to the greater discharges the current velocity, turbulence and sediment load of the river Geul increased substantially. Soil particles eroded from the arable land to the lower parts of the landscape (colluvium) or to the riverstha t deposited themateria l in thevalley s (alluvium). Loess material, especially the coarse-silty top layers of the loess soils, is very liable to erosion. During heavy rainfall or thaw greater quantities of water and much silto floes sorigi n(i.e .wit ha hig hconten t ofsil tparticles )entere dth e river. This was transported and deposited elsewhere. The river's sedimentation pattern changed compared with that of stage II. Instead of clay and peat the river deposits now consisted of silty loess-like material, with a differentiation of texture from thelevee s to the basins.