Methods to calculate sedimentation rates of floodplain soils in the middle region of the Elbe River

Acta hydrochim. hydrobiol. 2006, 34, 175 – 187 F. Kr�ger et al. 175

Research Paper

Methods to calculate sedimentation rates of floodplain soils inthe middle region of the Elbe River

Frank Kr�gera, Ren� Schwartzb, Maritta Kunertc, Kurt Friesed

a ELANA – Boden, Wasser, Monitoring, Falkenberg, Germanyb Department of Environmental Science and Technology, Technical University of Hamburg-Harburg, Germanyc Department of Bioorganic Chemistry, Max-Planck-Institute for Chemical Ecology, Jena, Germanyd UFZ Centre for Environmental Research Leipzig-Halle, Department Lake Research (SEEFO), Magdeburg,

Germany

This study presents different methods to quantify the historic and recent sedimentation of flood-plain soils along the Elbe River. These methods include the comparison of surface elevations,the quantification of sedimentation with the aid of anthropogenic and geogenic tracers, sedi-ment trap studies, and the calculation of load balances. Selected results from sites at the lowersection of the middle Elbe River are presented and verified. The results show that severalmethods are suitable. In future work it should be possible, depending on the available soil andsediment data, to calculate sedimentation in Elbe River floodplain and the loss of retentionvolume for larger areas.

Keywords: Suspended load / sediment / flooding / Cs dating / b-HCH / Pb isotope / trace element / retention area /heavy metal /

Received: December 18, 2004; accepted: February 14, 2006

DOI 10.1002/aheh.200400628

1 Introduction

River and floodplain form an eco-systematic unit, theyare interrelated, requiring and influencing one another.The riparian areas along the middle section of the riverElbe are composed of Holocene sediments. More recentsedimentation processes are closely related to human set-tlements in the river’s catchment area. This regionunderwent two major waves of logging activity: in theearly medieval period (500–900 AD), when the popula-tion grew rapidly, and in the middle of the 18th century,with the advance of industrialization. In particular, theclear-felled areas of low mountain ranges suffered wide-spread erosion after heavy rainfalls. This was accompa-nied by the formation of an extensive alluvial loam layerin the downstream river valleys, in which some placeswere several meters thick.

In natural river systems, fluviatile sediments are sub-ject of frequent displacements (through erosion, trans-port, and sedimentation) because of changing dischargesand the meandering and shifting of the river channels.By this, the floodplains with their typical geomorphologi-cal forms, such as embankments, backwaters, flood chan-nels, depressions, and elevated plains are formed. Thesestructures, in turn, affect subsequent flowing, flooding,and sedimentation processes. Erosion and sedimentationare thus permanent and normal processes in a natural orat least semi-natural river system. They lead to continu-ous spatial and temporal changes in the riverside areas.This gives the active river system a relatively “young”character, at least as far as the soils are concerned. Sev-eral particularly young types of soils are usually confinedto the vicinity of the banks, which are the most dynamicareas of the riparian region [1].

The dikes, which were built along the river Elbe fromthe 12th century [2], protect about 75% of the alluvialareas against flooding [3]. On the other hand the dikescaused a confinement of the run-off cross-section, whichis vitally important in the event of great discharge

Correspondence: ELANA – Boden, Wasser, Monitoring, Dorfstr. 55,39615 Falkenberg, GermanyE-mail: [email protected]: +49 39386 97116

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176 F. Kr�ger et al. Acta hydrochim. hydrobiol. 2006, 34, 175 –187

volumes. The dikes on both sides of the river result in ahigher flow velocity in the channel and therefore to anincreased erosion. As far as the middle section of the riverElbe is concerned, the erosion processes currently takeplace mainly in groyne fields and bank areas, where nopermanent erosion-preventing vegetation can establishitself. An additional impact of extensive dikes is that itlimits flood-related sedimentation processes to the nar-row hydro-dynamically active space between the dikes(about 25% at the river Elbe). Consequently, over timetwo different types of alluvial floodplain areas haveformed. One is known as recent floodplain, because itcan still be flooded periodically, while the other, behindthe dikes, is described as relict floodplain, becausealthough it is composed of typical alluvial sediments itcan no longer be flooded directly [4]. Accordingly, thedepositing of present sediments is also limited to therecent floodplain.

Following the extreme flooding of the river Elbe inAugust 2002, the question arose of whether or not nat-ural sedimentation processes in the recent floodplainhave caused the retention space to diminish measurably,which would be crucial for the extent of hazards in theevent of flooding [5].

Figure 1 shows a river section and adjacent riparianareas near Wussegel, (river km 518…521 German kilome-tration) as a sample region for the investigation of long-term sedimentation processes in the floodplains of theriver Elbe. Whereas in 1889 the composition of the totalarea of recent floodplain between river km 518 and 521was 47% water and 53% land, this proportion hadchanged by 1990, when the area of water was 37% andland 63%. Along with the diminution of the water surfacearea, the ecologically important banks were straightenedand shortened. Moreover, the number of small watersdecreased substantially. It can be shown that the groynefield areas along the river Elbe and adjacent riparianareas clearly act as a major sink for suspended material

over a long period. The actual extent of this processrequires further investigation.

In the context of research projects funded by the Fed-eral Ministry of Education and Research, namely “Hoch-wassergebundener Schadstoffeintrag in kulturwirt-schaftlich genutzte B�den an Oka und Elbe” [6] and“M�glichkeiten und Grenzen der Auenregeneration undAuwaldentwicklung” [4], and the ad-hoc project, “Schad-stoffbelastung nach dem Elbe-Hochwasser 2002” [5],numerous analyses have been conducted on alluvial soilsand riverine sediments in the middle section of the riverElbe. With the help of these analyses conclusions can bedrawn about the sedimentation rates of suspended par-ticulate matter, and thus the corresponding materialretention processes, for individual river sections andlocations in the riparian region. Additionally, the FederalWaterways Engineering and Research Institute arrangedrecently a study to verify the possibilities to calculate theloss of retention volume by sedimentation. This studyaims to verify the individual results obtained by differentquantification methods, in order to obtain more preciseinformation about historic and recent sedimentation inthe alluvial floodplains. The examined area includes sec-tions in the lower middle Elbe River, stretching fromSch�nberg-Deich (river km 435) to Hitzacker (river km523). Figure 2 provides an overview of the study area.

2 Methods for quantifying material retentionand sedimentation

2.1 GeneralAn extensive overview of methods which can be used todetermine sedimentation rates in alluvial areas andgroyne fields is provided by Rommel [7]. He differentiatesbetween summary and event related methods of sedi-mentation analysis. While summary methods integratethe aggradations of a number of flooding events, event-

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Figure 1. Cartographic documentation of long-term sedimentation processes in twogroyne field chains between river km 518 and 521.

Acta hydrochim. hydrobiol. 2006, 34, 175 – 187 Sedimentation rates of Elbe River floodplain soils 177

related methods allow to measure or to calculate thematerial input during individual flooding events imme-diately.

Summary methods include e.g. the comparison of sur-face elevations and the analysis of buried paths and roadsas well as buried edifices. In sedimentation rate analysis,the 137Cs dating method for soils and sediments is of parti-cular interest, as it can be employed for both integrativeanalyses and the identification of different sedimenta-tion rates in individual periods of time. Event-relatedmethods include e.g. sediment trap analyses and loadbalancing.

In the case of the river Elbe, results of just two radio-chemical dating analyses were found in the literature. Inthe first study by Barth et al. [8] an integral average sedi-mentation rate of about 3 cm/a since 1945 was measuredon an embankment erosion ridge near Aken (river km275). The second study on the middle section of the riverElbe was conducted by the Hamburg EnvironmentAuthority [9] in a flood channel location near Pevestorf(river km 485). An average sedimentation rate of0.58 cm/a since 1940 was calculated.

For this paper, both summary and event-related meth-ods are used, depending on their suitability to describesedimentation periods of different length.

2.2 Long-term processesIn this study, long-term processes are considered as thosewhich take place over one to several centuries. Theyrepresent the summation of all the effective short- andmedium-term processes.

The method of surface elevation comparison bases onthe assumption that in time of construction of the dike,the surfaces before and behind the dike were on the sameelevation. Figure 3 shows the classified surface elevationvalues of the recent and relict floodplain areas in the Len-zen valley region (river km 472…485) in relation to thereference mean water level of the river Elbe. It can beseen that recent and relict areas have an average heightdifference of 75 cm. Assuming that no significant erosionor sagging processes have taken place in the relict flood-plain since the dikes were completed in the middle of the13th century, the remaining recent floodplain experi-enced an average net sedimentation rate of 1 mm/a overlarge areas. Given an average soil density of 1.5 g/cm3,this represents an average sediment input of1.5 kg/(m2 a). In not drained depressions near the river,this figure may rise to as much as 4.0 kg/(m2 a) due tomore frequent and sustained flooding. In contrast, at ele-vated and thus rarely flooded spots, it can be as low as0.2 kg/(m2 a).

2.3 Medium-term processes2.3.1 Comparison of cross-section profilesMedium-term processes include sedimentation processeswhich have taken place during the last few decades untilone century. Rommel [7] compares historic and recentsurface-cross-section measurements provided by the Fed-eral Waterways Engineering and Research Institute. Fig-


Figure 2. Area under investigation, lower middle reaches of theriver Elbe.

Figure 3. Comparison of the relative surface elevation in therecent and relict alluvium between river km 472 and 485. MW:mean water level; SD: standard deviation.


ure 4 shows for example the surface elevation compari-son at Elbe river km 506 between 1902 and 1993. Along a20 km river stretch between river km 505 and 525 10 pro-files from 1902 were available, allowing the calculationof an average sedimentation of 16 cm during 91 years.This corresponds to an average annually sedimentationrate of 0.17 cm. Assuming a soil density for topsoils of1 g/cm3 an average sediment load of 1700 g/m2 results.

Unfortunately, these old cross-section profiles are notavailable along the whole Elbe River, and very often theydo not extend along the whole cross section of the flood-plains. One of the biggest problems for this method is tofind the reference point allowing a comparison with ahigh accuracy.

2.3.2 Anthropogenic accumulation of trace metalsDeducing sedimentation rates in alluvial soils from thespecific anthropogenic accumulation of trace metalsmust be limited to a period of less than 100 years, due tothe beginning of accelerated industrialization in the Elberegion. It is a useful method to calculate the proportion ofincorporated fine grained polluted sediments in soils. Thesedimentation of sandy, unpolluted material can not beestimated. Another problem might occur on the analyti-cal side, when heavy metal concentrations are very lowand the anthropogenic proportion cannot be identifiedcorrectly. Detailed knowledge of both, correct input per-iod and load development of the trace metal forms anessential condition for the application of this method.

The development of heavy metal pollution in the Elbecatchment area was worked out by Prange et al. [10]. Thefindings of the 137Cs dating studies of an underwater sedi-ment core taken from the ,Bucher Brack’ backwater (riverkm 380) show that, of the many anthropogenic elements,nickel proves to be the most suitable reference elementfor the beginning of the accumulation of pollutants. Thisis because its concentration in the layers depositedbefore 1940 equals that of the catchment area specific

geogenic background content of 23…54 mg/kg [11]. Allother anthropogenic enriched heavy metals seem to havea longer pollution history. Consequently, the anthropo-genic nickel accumulation in the alluvial soils of the Mid-dle Elbe is confined to the last 60 years. The average fine-grain sediment content during this period wasCNi = 105 mg/kg [10], which represents an anthropogenicproportion of 61%.

According to Kr�ger [12], the anthropogenic nickelaccumulation in alluvial soils can be calculated by sub-tracting the grain-size-specific geogenic content,

CNi-geo = 0.51 N P20 lm-(%) + 2.32; (R2 = 0.82)

from the measured total content (CNi-geo: grain-size-spe-cific geogenic content; P20 lm-(%): proportion of 20 lm frac-tion of the topsoil).

Taking into account the soil density, which is between0.7 g/cm3 and 1.5 g/cm3 in the examined alluvial soils,the individual nickel balance can be calculated for differ-ent locations. Table 1 shows essential ancillary condi-tions used in the sample calculation of a plateau locationnear river km 438, and Table 2 shows the resulting find-ings for several locations which are differently exposedin the riparian area. No calculations were made for thebayou location, i.e. the first flood channel behind theembankment. It is a coarse-grained soil profile with ahuge number of event-related layers. It is only possible toidentify the anthropogenic influenced layers below adepth of 55 cm.

The calculation results found for the individual mor-phologic expositions, as shown in Tables 1 and 2, sub-stantiate Schwartz's [4] findings, which were based onthe zinc balance at the L�tkenwisch location (river km472…475), examined for an estimated input period of100 years. According to Schwartz [4], assuming an aver-age topsoil density of 1.0 g/cm3, sedimentation ratesrange from 0.02 to 0.4 cm/a, depending on the elevationof the sample point above mean water level.


Figure 4. Comparison of cross section profiles from 1902 and 1993 at Elbe river km 506.


2.3.3 Anthropogenic and geogenic tracers2.3.3.1 b-HCH (hexachlorocyclohexane, benzene

hexachloride, HCH)This method bases on geochemical stratification. Sedi-mentation rates can be calculated from the first occur-rence of selected anthropogenic or geogenic tracer sub-stances in the environment under investigation, and thedepth profiles of these tracers in the alluvial soils. In thecalculation method used, considerable overestimation ofthe mean sedimentation rates must be assumed whenthe occurrence of a tracer is limited to the top soil layer

like at the locations ,low depression’ and ,plateau’. This isthe case if the pollutant is not distributed homoge-neously in the investigated soil layer, which was rathercoarsely sampled in 10-cm steps. The sampling techniquemay thus have caused a significant dilution of the pollu-tant by mixing heavily contaminated and less contami-nated fine layers.

b-HCH is an isomer of the substance hexachlorocyclo-hexane, or benzene hexachloride, which was used as themain ingredient of the insecticide ,Lindan’. According tothe

,

Hexachlorocyclohexane’ substance report issued bythe Landesanstalt f�r Umweltschutz Baden-W�rttemberg[13], it can be assumed that Lindan was widely used inagriculture from 1950. In Saxony-Anhalt, a federal stateof Germany that represents a large part of the Elbe catch-ment area, there were two major Lindan productionplants: Lindan production commenced in 1953 in thetown of Bitterfeld and at the site of the Fahlberg-List com-pany near Magdeburg.

Regarding b-HCH deposits, Witter et al. [14, 15] showedthat the b-HCH isomer was the dominant hexachlorocy-clohexane compound in alluvial soils of the Middle Elbe.The samples of six depth profiles between river km 435and 440 [14] were taken in 1997. Consequently a maxi-mum calculation period of 47 years can be assumed. Fig-ure 5 shows two depth profiles of HCH compounds. It canbe clearly seen that HCH occurred until a soil depth of10…20 cm at the location at the bottom of the dike, anddown to a depth of 50…60 cm at the flood channel loca-tion behind the embankment near the river.

Although some authors [16–19] characterize b-HCH asa mobile metabolite, the concentrations of 3…38 lg/kgfound in the relevant layers suggest an on-site metabo-lism of the original product (b-HCH) rather than geotro-pic displacement processes in the profile. Table 3 indi-cates the deepest layers in which b-HCH was foundtogether with the corresponding concentrations and thederived minimum and maximum possible sedimenta-


Table 1. Ancillary conditions used in the calculation of sedimentinput of a plateau location near Elbe river km 438.

Depths ofcontamina-ted layer

cm

Soil density

g/cm3

Nickel –total con-centrationof soil

mg/kg

Proportionof20 lmfraction

%

Nickel –anthropo-genic con-centrationof soilmg/kg

20 1.18 31 44 6.3

Amount ofsoil materialof the con-taminatedlayer

kg/m2

Totalamountof nickel

g/m2

Anthropo-genicamountof nickel

g/m2

Averagenickel con-centrationof sedi-ments

mg/kg

Averageanthropo-genic nickelconcentra-tion of sedi-mentsmg/kg

236 7.32 1.50 105 64

Amount ofcontamina-ted sedi-ment tocause thesoil con-taminationkg

Time ofnickel con-taminationin middlereachesof riverElbea

Calculatedannualsedimentload

g/(m2 a)

Calculatedannual sedi-mentationrate

cm/a

Sedimenta-tion rateduring60 yearsperiod

cm

23.4 60 390 0.04 1.8

Table 2. Sediment input and sedimentation rates of different locations between Elbe river km 435 and 440 determined using themethod of analyzing anthropogenic accumulation of trace metals.

Morphological exposition Distance tothe river

Elevation tomean water

Sedimentation

m m

Annual load

g/(m2 a)

Annual rate

cm/a

During 60 yearsperiodcm

Flood Channel behind embankment 50 0.3 10 950 0.92 55High depression 105 1.6 940 0.11 6.6Main flood channel 170 0.4 2773 0.24 14.4Bottom of dike 290 0.8 1030 0.15 9Plateau 360 1.5 390 0.03 1.8Low depression 990 –0.3 430 0.05 3


tion rates. The samples for the chemical analyses weretaken from the depth profiles in steps of 5 cm or 10 cm.The sediment loads were calculated on the basis of thesedimentation rate and the soil density of the particularsample points.

2.3.3.2 206Pb/207Pb isotope ratios and uranium contentsDetermining the 206Pb/207Pb isotope ratios aims to finddifferent input paths of the element lead. Krause [20]found, for example, a geogenic background 206Pb/207Pbisotope ratio of 1.18…1.22 in soils taken from an unpol-luted reference sampling point on the North Sea islandof Helgoland. The input of lead into the river systemcaused by an increasing consumption of leaded fuel withisotope ratios of 1.095 to 1.105 must consequently resultin lower isotope ratios in the river system.

In 1998 an underwater sediment core taken from abackwater location in the area under investigation (riverkm 435…440) was dated using the 137Cs method [21]. The206Pb/207Pb isotope ratios were also determined in thissediment core. Figure 6 shows the results of the 137Cs dat-ing and the changes in the 206Pb/207Pb isotope ratio at vari-ous depths. The distribution of the 137Cs activity concen-tration over depth shows several clearly identifiablepeaks, which allow timescale matching. The concentra-tion of 137Cs activity has increased since the early 1950s.

An activity concentration peak can be identified at adepth of 55…60 cm, which can be matched to the maxi-mum level of over ground nuclear weapons testing until1963. The maximum activity concentration was found ata depth of 15…20 cm. This peak can be traced back to theChernobyl reactor accident in 1986. These findings allow


Table 3. Sedimentation rates derived from b-HCH occurrence in depth profiles of the lower middle reaches of river Elbe; n/a: notapplicable.

Morphological exposition Depth

cm

w(b-HCH)

lg/kg

Minimumsedimentationratecm/a

Minimumload

g/(m2 a)

Maximumsedimentationratecm/a

Maximumload

g/(m2 a)

Flood channel behind embankment 50…60 18 1.06 13 780 1.28 16 640High depression 10…20 24 0.21 1743 0.42 3570Main flood channel 15…25 24 0.32 3400 0.53 4550Bottom of dike 10…20 36 0.21 1407 0.42 2814Plateau 0…10 3 n/a n/a 0.21 2100Low depression 0…10 38 n/a n/a 0.21 1800

Figure 5. Depth profiles of HCH com-pounds taken from locations betweenriver km 435 and 440.

Figure 6. Findings of the 137Cs dating and changes in the206Pb/207Pb isotope ratio and lead and uranium concentrations ina sediment core taken from a backwater location near riverkm 438.


individual sedimentation rates to be calculated. The aver-age sedimentation between 1950 and 1997 was 1.7 cm/a.Integration over the entire submerged sediment yieldsthe result that the layer at a depth of 165…170 cm wasdeposited around 1900.

An analysis of the 206Pb/207Pb isotope ratios shown inFigure 6 indicate a ratio of approximately 1.19 in the sub-merged sediment in the period about 1900, which sug-gests the lead input to be of merely geogenic and miningorigin. The corresponding lead concentration curve overdepth is also shown in Figure 6.

From the beginning of the last century to the early1950s a continuously decreasing isotope ratio can beobserved. These results can be traced back to the increas-ing use of lead as an additive in engine fuels. However,this continuous development is interrupted in the periodbetween 1954 and 1965. The rising 206Pb/207Pb isotoperatio at a depth of 55…75 cm in the submerged sedimentwas caused by additional geogenic lead input. In thesame period, the river Mulde was flooded in 1954, and anaccident in an industrial sedimentation plant in Ober-rothenbach in 1963 caused tailings from uraniummining to be swept into the river Mulde [8], which is a tri-butary of the river Elbe. This explains the above-men-tioned lead isotope anomaly. The submerged sedimentunder investigation exhibited an increased uranium con-centration for that time (see Fig. 6), which is confirmed instudies conducted by Prange et al. [10] and Barth et al. [8].

As shown in Figure 6, the lead and uranium peaksdemonstrate that geochemical disturbances in a tribu-tary, such as the river Mulde, are reflected over a long dis-tance and time in the river Elbe when there is insignifi-cant erosion and/or bioturbation, in particular when itcomes to major one-off events involving a large pollutantload (see above). Such disturbances form good time mar-kers for sedimentation history.

Sedimentation rates for soils can be verified indirectlyby applying the findings from the submerged sedimentsto the alluvial soil depth profiles. In this context, Kunertet al. [22] published 206Pb/207Pb isotope ratios of two soilprofiles between river km 435 and 440. In their study,they determined 206Pb/207Pb isotope ratios as well as leadand uranium concentrations. It was found that two chan-nel locations, which were separated by just 120 meters,differed greatly, both in their lead and uranium levelsand in their sedimentation development.

The flood channel soil profile taken behind theembankment, shown in Figure 7, indicates a develop-ment of the 206Pb/207Pb isotope ratios which is comparablewith the submerged sediment in Figure 6. Time scalematching of individual layers was based on both theabsolute 206Pb/207Pb isotope ratios and their development,

which again corresponds to the uranium concentrationsthat can be traced back to the flooding of the river Muldecatchment area and the accidents at the uranium miningwaste water treatment installations, as described above.

Taking the individual findings as integral, the ,firstflood channel’ location exhibits average sedimentationrates of 1.5 cm/a in the two periods, 1932–1997 and1954–1997. This corresponds to an average annual sedi-ment load of 21 000 g/(m2 a).

The ,main flood channel’ location reveals a develop-ment in 206Pb/207Pb isotope ratio and uranium contentwhich differs from that found in the submerged sedi-ment (Fig. 8). Time marker identification seems to bemore difficult here. However, the increase in the 206Pb/207Pb isotope ratio in the 1950s and 1960s, originatingfrom the river Mulde tributary, can at least be assumedto be found within the top 15 cm. The submerged sedi-ment only revealed isotope ratios of less than 1:1.18 after1932. Applying this information to the flood channel pro-file results in a total sedimentation of 35 cm over 65 yearsand thus an average sedimentation rate of 0.54 cm/a. Theaverage annual sediment load at this sample point wascalculated to be 6 520 g/(m2 a).

2.4 Short-term processes

2.4.1 Sediment trap analyses (STA)Short-term processes are sedimentation processes whichoccur in the context of individual flooding events. Onemethod of determining event-related material input is toquantify suspended sediment input with the help of sedi-ment traps. This method was also used by Asselmann and


Figure 7. Development of the 206Pb/207Pb isotope ratio and ura-nium concentration in a flood channel near the river.


Middelkoop [23] to determine sediment load in the Rhineareas. And also Kronvang et al. [24] used synthetic turftraps to measure sedimentation at the Gjern River. Thesedimentation rate calculation is based on the alluvialsoils bulk density.

Pieces of synthetic turf measuring 30 cm x 40 cm wereused as sediment traps [25]. These artificial mats aim tosimulate natural soil coverage (pasture or mown grass-land). Five traps were used at each sample point. Themats were fixed to the ground using 30-cm long metalpins. The sediment traps were set up at typical morpholo-gical units immediately before the sample points wereflooded and were then collected when the water levelwent down again. The collected sediment temporarilyremained on the traps and was air-dried, before it wasbeaten off using a plastic rod. A high-pressure cleanerwas used to remove the residual particles from the plasticbristles. The residual sediment rinsed out was collectedin plastic containers. After 24 hours, the supernatant wasremoved and the sediment was dried so that the total

amount of dry matter could be determined. Then thesediment load was calculated on the basis of the meas-ured dry matter input. The mean sedimentation rate canbe estimated if the average density of the topsoil isknown. Table 4 contains the characteristic data for sedi-ment trap analyses conducted at representative locationsalong the lower section of the middle Elbe, near river km438. It shows the development of sediment loads since1997. The selected sample points cover a typical spec-trum of morphological units in riparian areas (edge of agroyne field, bayou or flood channel, not drained depres-sion, and plateau). As was anticipated, it can be observedthat the individual sample points experienced widelyvarying sediment loads over time. The greatest loadswere always found in the immediate vicinity of the river,specifically at the edge of the groyne field. During theextreme flooding of the river Elbe in August 2002, the ele-vated plateau location also showed sediment input forthe first time. This event is further characterized byroughly doubled sediment inputs at the depression andflood channel locations, compared with the flood eventsin the years 1997 and 1998/1999, when this method wasinitially employed. The sediment appeared to be a film ofjust a few tenths of a millimeter in each of the above-mentioned cases.

The year 2003 was characterized by a long draught pe-riod with low water levels and thus by relatively littlesediment input into the Middle Elbe floodplains. In addi-tion to the generally low discharge, this may also beexplained by the extreme floods in August 2002 and inwinter 2002/2003, during which large portions of themobilizable sediments were swept away from slack waterzones. These slack water zones, like groyne fields, aredominant secondary sources of sediments and pollution,and may account for this difference, as described byF�rstner et al. [26].

The sedimentation rate calculation below is based onthe assumption that the alluvial soils have a uniformdensity of 1 g/cm3. Table 5 shows the sedimentation ratesof isolated flooding events at the selected locations dur-ing the 1997–2003 study period.


Figure 8. Development of the 206Pb/207Pb isotope ratio and ura-nium concentration in the main flood channel location near riverkm 438.

Table 4. Characteristics of the sediment input into the alluvial areas in 1997, 1998/1999, 2002, 2002/2003, and 2003 at locationsnear Sch�nberg-Deich (river km 435…440); MW: mean water level; n/a: not applicable.

1997 1998/1999 2002 2002/03 2003Season Spring Autum/winter Summer Summer/winter Spring

Maximum discharge, m3/s 1800 2360 3800 3260 1300Edge of groyne field; 0.4 m MW, g/m2 3810 8321 1485 n/a 127Main Flood channel; 0.4 m MW, g/m2 204 242 n/a 405 70Depression; 0.7 m MW, g/m2 298 397 n/a 502 78Plateau; 1.5 m MW, g/m2 n/a n/a 220 n/a n/a


2.4.2 Solid matter load balancing (SMLB)Suspended sediment retention in the recent floodplainareas of the researched river section can be assessed usingthe data provided by the Federal Institute of Hydrology[27]. A precise estimation of discharge and calculation ofsuspended particulate matter load is very difficult. Thereis a spatial and temporal inhomogeneous distribution ofsuspended material along the river cross section, whichis a critical point of this method. The used data can bequalified as tested estimations. These data contain dailyaverages of the suspended matter concentration and dis-charge volume, e.g. at the permanent monitoring sta-tions in Wittenberge (river km 455) and Hitzacker (riverkm 523) over a period of three years (November 1, 1996 toOctober 31, 1999). The mean flow time between thesetwo measuring stations at the river Elbe is about 19hours, depending on the actual discharge. During theflooding phases, the daily average at the upstream meas-uring station (Wittenberge) was compared with thevalues at the downstream measuring station (Hitzacker)the day after, in order to assess the suspended sedimentload. The selected river section has the advantage that itonly receives minor tributaries (Stepenitz, Aland, Seege,

Elde, L�cknitz, and Jeetzel) with low discharge volumesand suspended sediment loads [28]. Consequently, thedifferences in the suspended sediment load detected inthis river section are almost exclusively caused by inter-nal processes (sedimentation, erosion, displacement, pro-duction, reception, and decomposition).

Furthermore, to be able to determine the suspendedsediment load input into the floodplain, it is necessary toknow the surface area between the dikes involved in thesedimentation processes. This area is estimated to be12500 ha, based on data from the International Commis-sion for the Protection of the Elbe (IKSE) for the selectedriver section [29]. It is assumed that in the event of flood-ing there will be no significant sedimentation in the riverchannel itself and in the groyne fields, as is shown bySchwartz and Kozerski [30].

The beginning of a flood situation is defined as thetime at which the location Sch�nberg-Deich (river km435…440) in the study area is first flooded. Floodingoccurs if the specific discharge at the Wittenberge gaugeexceeds 1000 m3/s. The end of a flood situation is markedby the time the specific discharge falls below this value.Table 6 provides an overview of the flooding phases in


Table 5. Sedimentation rates at selected locations in the floodplain near Sch�nberg-Deich (river km 435…440) in the years 1997,1998/1999, 2002, 2002/2003, and 2003; n/a: not applicable.

1997 1998/1999 2002 2002/03 2003Season Spring Autum/winter Summer Summer/winter Spring

Edge of groyne field; cm/event 0.4 0.8 0.15 n/a 0.015Main flood channel; cm/event 0.02 0.025 n/a 0.04 0.007Depression; cm/event 0.03 0.04 n/a 0.05 0.008Plateau; cm/event n/a n/a 0.02 n/a n/a

Table 6. Flooding phases (A1000 m3/s at the Wittenberge level) in the lower middle reaches of the river Elbe from 1997 to 1999,cumulative suspended sediment loads and concluded sediment input into the flooded area.

Year Period of flooding Cumulated suspended loadt

Difference = Sedi-ment retention

t

Sediment load

g/m2

Wittenberge Hitzacker

1997 09.01.—24.01. 11 220 9 030 2180 1718.02.—15.03. 153 940 94 690 59 250 47422.03.—29.03. 23 700 14 790 8910 7103.04.—07.04. 11 320 5 170 6150 4909.04.—14.04. 12 180 11 830 350 324.07.—02.08. 53 150 30 960 22 180 177Total 99 030 792

1998 22.03.—26.03. 19 780 15 915 3870 3102.11.—27.11. 107 600 82 095 25 500 20420.12.—27.12. 14 790 16 075 –1280 –10Total 28 090 225

1999 08.02.—06.04. 199 750 129 170 70 580 565


the years 1997–1999 and indicates the summary sus-pended sediment loads at the two measuring stations.The differences indicate the retention of material duringflood events in the flooded parts of the recent floodplain.

The results shown in Table 6 can only be understood asindications of the actual sediment loads and sedimenta-tion rates, as they integrate the entire alluvial region of12500 ha, thus neglecting the very heterogeneous sedi-mentation pattern in individual areas (see above). Assum-ing a uniform density of 1 g/cm3, the information takenfrom the above-mentioned register suggests a totalannual sedimentation rate between 1996 and 1999 of0.02…0.08 cm/a.

3 Discussion

The above-mentioned methods of determining flood-related sediment input into the recent floodplain exhibitdifferences related to method. They apply to differenttimescales and they are used to describe regions of differ-ent surface area. For example, the elevation comparisonsare based on a number of individual elevation measure-ments along a 13-km-long section of the river Elbe. In con-trast, the determination of medium-term sedimentationprocesses was only undertaken at between two and sixsample points along a meander loop between river km435 and 440. The same applies to the sediment trap stud-ies. The results of the solid matter assessment calcula-tions describe a 68-km-long section of the river Elbe. Therange (spatial and temporal) of sediment loads and sedi-

mentation rates determined using the individual meth-ods are compiled in Table 7.

Assessing the individual methods, it can be said thatthe surface elevation method is a very robust technique.The surface elevation comparison itself can be achievedby leveling. However, this method is very laborious if it isapplied to a large section of the river. It can be stated inthis context that the averaged results of the surface eleva-tion comparison are in line with the recent sedimentinput determined in a small section of the study areausing the sediment trap method, and with solid matterbalance calculations conducted for the entire section ofthe river. Summarizing these three results it can be saidthat actual sedimentation rates are within the averagerange of the long-term processes. However, it remainsunclear whether or not more heavy layers were depositedper unit of time in the past and sedimentation rates havedecreased more recently.

When calculating the medium-term sediment input,the individual methods differ more significantly fromeach other. Dating the anthropogenic trace metal occur-rence, for instance, is inappropriate for calculating sedi-ment input if the analyzed soil is of pure sandy texture(see above). All calculations are based on the assumptionthat fine-grained sediments are deposited during flood-ing, and consequently the concentration of the tracersubstances in the sediment was always analyzed in thegrain size fraction of a20 lm. This assumption results ina slight underestimation of the calculated sedimentinput, because although fine-grained sediment wasindeed deposited together with the corresponding pollu-


Table 7. Overview of sediment loads and sedimentation rates in the river Elbe floodplain obtained by different calculation and meas-urement methods.

Method Period Minimum sedimentloadkg/(m2 a)

Maximum sedimentloadkg/(m2 a)

Minimum sedimen-tation ratecm/a

Maximum sedimen-tation ratecm/a

Long-term processesSEC* Since 13th century 0.2 4 0.01 0.3

Medium-term processesCSP 1902–1993 average load: 1.7 average rate: 0.17AATM* Since 1940 0.4 10.9 0.03 0.9HCH* Since 1950 1.4 16.6 0.21 1.3PbI*a Since 1932 6.5 21 0.54 1.5

Short-term processesSTA** 1997–2003 0.07 8.3 0.007 0.83SMLB*** 1997–1999 0.2 0.8 0.02 0.08

* spatial differences** spatial and temporal differences*** just temporal differencesa based on a calculation of two soil profiles


tant load, the real material input was greater due to thecoarser texture of the actual sediment. However, theadvantage of this method is that it allows the estimationof individual sediment load at any location with fine-tex-tured sediments which is subject to the same historicload development. Tracer methods like HCH or isotopemethods are not precisely enough when the pollutantand tracer analysis is restricted to the top layer as a resultof the dilution effect by unpolluted soil.

A further disadvantage of this method is that resultsare dependent on the width of the analyzed horizons, ifthe individual horizons do not exhibit a uniform distri-bution of the tracer. It was thus necessary to calculatesedimentation rates for each depth profile twice. Thefirst calculation was conducted with the depth from theupper face and the second with material from the lowerface of the deepest horizon which showed a positiveoccurrence of the tracer substance. The results of the cal-culations which were based on the depth of the lowerface of the horizon in question lead to an overestimationof the sedimentation rates. The results based on thedepth of the upper face lead to an underestimation. Gen-erally, the tracer method appears to be the most arduousone as regards the work of analysis. The soil profileshould be divided into the thinnest possible horizons forthe analysis. However, taking into account the discusseddisadvantages, these methods also allow the determina-tion of reliable sedimentation rates.

Generally, the methods used to describe the short-termand event-related sedimentation processes, i. e. the aver-age sediment loads and sedimentation rates, in recentfloodplain areas exhibit a surprisingly high degree of cor-respondence (see Tables 4–6). However, a wide range ofresults can only be found using direct on-site measuringmethods, such as sediment traps. The sediment trapmethod is a robust technique and provides high-qualityspot data. It has been shown that several measuringpoints at typical morphological locations must beincluded in the analysis in order to quantify the sedimen-tation rates in a meander loop representatively. Whenstudying several locations along large sections of theriver, the amount of work required thus increases consid-erably. In order to transfer the results to large areas (e.g.in the context of GIS-based extrapolation), it is necessaryto identify what proportion of the potential alluvial areais actually flooded. Alternatively the sediment inputmust be simulated using flux and solid matter transportmodels [31, 32].

The solid matter load balancing method integrates alarge section of the river and all the various morphologi-cal units in the adjacent floodplain. Consequently, it isan inappropriate technique for determining the sedi-

ment load at individual locations. Again, precise infor-mation of the actually flooded surface area is required tobe able to validate the results. However, it is a simple cal-culation method which describes well the overall sus-pended sediment inventory that is available for deposi-tion in the floodplains. Nevertheless, this method canonly reasonably be applied if temporally and spatiallyhighly resolved suspended sediment and discharge dataare available for the river section under consideration.Data collection, i.e. daily quantification of the suspendedsediment load, is significantly more laborious than thesubsequent load balance calculation itself. Such high-resolution data are probably not available for most loca-tions along the river Elbe.

The different methods used to determine the materialretention and thus to describe soil-forming sedimenta-tion in the recent floodplain exhibit a high degree of cor-respondence as regards the location-specific sedimentinput, which ranges from 0.07 to 21 kg/(m2 a). However,both the analysis of medium-term sedimentation beha-vior at typical alluvial locations and the sediment trapanalyses along the river Elbe clearly show that there is nouniform sedimentation rate in the floodplain areas. Thiscorresponds to the findings of G�tz and Lauer [9] (riverkm 485) and Barth et al. [8] (river km 278). Barth et al.found highest sedimentation rates of 3 cm/a in a soil sam-ple taken from an erosion edge at the river Elbe alluviumnear Aken, which were not found in the middle reachesof the river Elbe studied. This can also be seen as an indi-cation of the spatial variability of the sedimentation pro-cess along the river channel. Moreover, Barth et al. [8]described different sedimentation rates when they con-sidered medium-term processes. In the context of themethods employed in this study, this can only be verifiedby comparing medium-term and short-term sedimentloads.

Summarizing the findings of this study, it can be saidthat high average sedimentation rates of more than0.2…1.5 cm/a are mainly restricted to channel locationsmore or less in the near of the river. These low-lying areaswith a surface elevation of no more than 0.5 m above themean water level account for up to 30% of the researchedfloodplain areas [4] (see also Fig. 3). It remains to futureprojects to validate these results and to verify them forlarger areas and other sections of the river. Several meth-ods are suitable and can be used, depending on the soiland sediment data, which are available.

Furthermore, the surface area proportions of the indi-vidual morphological units for which sediment load datawere established must be quantified, so that the loss ofretention volume by sedimentation can be determinedaccurately. Erosion and sedimentation in river bank



areas and groyne fields have not received much consid-eration so far; although Schwartz [33] has shown thatthese processes are very variable (see Fig. 2). Moreover,the loss of sub-aquatic retention space in backwatersneeds to be studied in more detail to achieve a full consid-eration of this subject.

References

[1] Gr�ngr�ft, A., Schwartz, R., Nebelsiek, A., Miehlich, G.:Eigenschaften und systematische Stellung von Flussufer-b�den an der Mittelelbe. Mitteilungen der DeutschenBodenkundlichen Gesellschaft 102-I, 2003, pp. 15–16.

[2] Eckoldt, M. (Ed.): Fl�sse und Kan�le – Die Geschichte derdeutschen Wasserstraßen. DSV-Verlag, Hamburg, 1998.

[3] Simon, M.: Hochwasserschutz im Einzugsgebiet der Elbe.Wasserwirtschaft Wassertechnik 7/94, 25–31 (1994).

[4] Schwartz, R.: Die B�den der Elbaue bei Lenzen und ihrem�glichen Ver�nderungen nach R�ckdeichung. Disserta-tion. Hamburger Bodenkundliche Arbeiten 48, 2001.

[5] Geller, W., Ockenfeld, K., B�hme, M., Kn�chel, A. (Eds.): Schad-stoffbelastung nach dem Elbe-Hochwasser 2002. FinalReport. Ad-hoc Project “Schadstoffuntersuchungen nachdem Hochwasser vom August 2002 – Ermittlung derGef�hrdungspotentiale an Elbe und Mulde”. Magdeburg,2004.

[6] Rupp, H., B�ttner, O., Kr�ger, F., Kunert, M., Meissner, R.,Muhs, K., Witter, B., Friese, K.: Wirkung von Hochwasserer-eignissen auf die Schadstoffbelastung von Auen und kul-turwirtschaftlich genutzte B�den im �berschwem-mungsbereich von Oka und Elbe. Unver�ffentlichterAbschlußbericht zum BMBF-Forschungsvorhaben (FKZ:02WT9617/0), Falkenberg, 2000.

[7] Rommel, J.: Quantifizierung der Gel�ndeh�hen-Ver�nde-rungen im Vorland der freifließenden deutschen Elbe.Bundesanstalt f�r Wasserbau, Karlsruhe, 2005.

[8] Barth, A., Jurk, M., Weiß, D.: Concentration and distribu-tion patterns of naturally occurring radionuclides insediments and flood plain soils of the catchment area ofthe river Elbe. Water Sci. Technol. 37 (6–7), 257–262(1998).

[9] G�tz, R., Lauer, R.: Ursachen der Dioxinkontamination inder Elbe, im Hamburger Hafen und in den Hamburgerinnerst�dtischen Gew�ssern. Hamburger Umweltbe-richte 57/99, 1999.

[10] Prange, A.: Geogene Hintergrundwerte und zeitlicheBelastungsentwicklung, Final Report, FKZ 02 WT 9355/4.GKSS-Forschungszentrum Geesthacht GmbH, Band 3/3,1997.

[11] Kr�ger, F., Prange, A., Jantzen, E.: Ermittlung geogener Hin-tergrundwerte an der Mittelelbe und deren Anwendungin der Beurteilung von Unterwassersedimenten. Ham-burger Bodenkundliche Arbeiten 44, 39–51 (1999).

[12] Kr�ger, F., Friese, K., Gr�ngr�ft, A., Rupp, H., Schwartz, R.,Miehlich, G.: Geochemische Charakterisierung von boden-bildenden Substraten in Auen der unteren Mittelelbe.DBG-Mitteilungen 91 (2), 1053–1056 1999.

[13] Fiedler, H., Hub, M., Hutzinger, O.: Stoffbericht Hexachlor-cyclohexan (HCH). Texte und Berichte zur Altlastenbear-beitung der Landesanstalt f�r Umweltschutz Baden-W�rttemberg 9/93, 1993.

[14] Witter, B., Winkler, M., Friese, K.: Depth distribution ofchlorinated and polycyclic aromatic hydrocarbons infloodplain soils of the river Elbe. Acta Hydrochim. Hydro-biol. 31, 411–422 (2003).

[15] Witter, B., Francke, W., Franke, S., Knauth, H.-D., Miehlich, G.:Distribution and mobility of organic micropollutants inRiver Elbe floodplains. Chemosphere 37 (1), 63–78(1998).

[16] Kalbitz, K.: Untersuchung zur Freisetzung der gel�stenorganischen Substanz des Bodens (DOM) und zum Ein-fluss der DOM auf die Mobilisierung ausgew�hlter Schad-stoffe in Abh�ngigkeit von Boden- und Standortei-genschaften. Dissertation. UFZ-Bericht 23/1996, 1996.

[17] Klimanek, E.-M., Lehmann, J., Schulz, E.: Untersuchungenzur in situ-Sanierung von ß-HCH belasteten B�den derMuldeaue. In: Friese, K., Witter, B., Miehlich, G., Rode, M.(Eds.): Stoffhaushalt von Auen�kosystemen. Springer,Berlin, 2000, pp. 289–300.

[18] Heinrich, K., Lehmann, J., Schulz, E., Klimanek, E.-M.: Unter-suchungen zum Transport von beta-HCH aus Muldeauen-b�den in Kultur- und Wildpflanzen. In: Friese, K., Witter,B., Miehlich, G., Rode, M. (Eds.): Stoffhaushalt von Auen�ko-systemen. Springer, Berlin, 2000, pp. 301 –308.

[19] Schwatz, R., Gerth, J., Neumann-Hensel, H., Walkow, F., F�r-stner, U.: Geochemisch-�kotoxikologische Charakterisie-rung und Bewertung der Schadstoffbelastung in der Spit-telwasserniederung bei Jeßnitz (Sachsen-Anhalt) alsGrundlage zur Beurteilung nat�rlicher R�ckhaltungs-prozesse in Auenb�den. Unver�ffentlichter Beitrag zumKORA-Statusseminar in Leipzig, 2004.

[20] Krause, P.: Entwicklung von Anwendungsm�glichkeitender ICP-MS und der Laser-ICP-MS in der Umweltanalytik.Dissertation, Universit�t Hamburg, 1993.

[21] Vogt, M., Zachmann, D., Treutler, C., Kr�ger, F., Friese, K.:Zeitliche Belastungsentwicklung von Sedimenten ausElbaue-Stillgew�ssern. In: Friese, K., Witter, B., Miehlich, G.,Rode, M. (Eds.): Stoffhaushalt von Auen�kosystemen.Springer, Berlin, 2000, pp. 209–217.

[22] Kunert, M., Kr�ger, F., Friese, K.: 206Pb/207Pb-Isotopenverh�lt-nisbestimmungen in ausgew�hlten Bodenprofilen derElbaue bei Wittenberge. In: Friese, K., Kirschner, K., Witter,B. (Hrsg.): Stoffhaushalt von Auen�kosystemen der Elbeund ihrer Nebenfl�sse. UFZ-Bericht 1/1999. 1999, pp.89–93.

[23] Asselmann, N. E. M., Middelkoop, H.: Floodplain sedimenta-tion: quantities, patterns and processes. Earth Surf. Pro-cess. Landforms 17, 687–697 (1995).



[24] Kronvang, B., Falkum, O., Svendsen, L. M., Laubel, A.: Deposi-tion of sediment and phosphorus during overbank flood-ing. Verh. Int. Verein. Limnol. 18, 1289–1293 (2002).

[25] Schwartz, R., Duwe, J., Gr�ngr�ft, A.: Einsatz von Kunstra-senmatten als Sedimentfallen zur Bestimmung des parti-kul�ren Stoffeintrages in Auen und Marschen. Mitteilun-gen der Deutschen Bodenkundlichen Gesellschaft 85-I,1997 pp. 353 –357.

[26] F�rstner, U., Heise, S., Schwartz, R., Westrich, B., Ahlf, W.: His-torical contaminated sediments and soils at the riverbasin scale – examples from the Elbe River catchmentarea. J. Soils Sed. 4 (4), 247 –260 (2004).

[27] BfG: Schwebstoffdaten der Elbe in den Jahren 1996–2000. Unver�ffentlichte Rohdaten, Bundesanstalt f�rGew�sserkunde, Koblenz, 2002.

[28] BfG: Bedeutung der Nebenfl�sse f�r den Feststoffhaus-halt der Elbe. Abschlussbericht BMBF-Forschungsvorha-ben 0339600/1. Bundesanstalt f�r Gew�sserkunde,Koblenz, 2003.

[29] IKSE: Bestandsaufnahme des vorhandenen Hochwas-serschutzniveaus im Einzugsgebiet der Elbe. Internatio-nale Kommission zum Schutz der Elbe, Magdeburg,2001.

[30] Schwartz, R., Kozerski, H.-P.: Entry and deposits of sus-pended particulate matter in groyne fields in the MiddleElbe and its ecological relevance. Acta Hydrochim.Hydrobiol. 31, 391–399 (2003).

[31] B�ttner, O., Hagemann, H., Suhr, U.: Modellierung von�berflutungsfl�chen in einem Auengebiet der mittlerenElbe. 5. Deutsche Anwenderkonferenz, ESRI, 1997, pp.225–227.

[32] B�ttner, O., Otte-Witte, K., Kr�ger, F., Meon, G., Rode, M.:Numerical modelling of floodplain hydraulics and sus-pended sediment transport and deposition at the eventscale in the middle river Elbe, Germany. Acta Hydro-chim. Hydrobiol. 34, 265 –278 (2006).

[33] Schwartz, R., Kozerski, H. P.: Bestimmung des Gefahrenpo-tenzials feink�rniger Buhnenfeldsedimente f�r die Was-ser- und Schwebstoffqualit�t der Elbe sowie den Stoffein-trag in Auen. In: Geller, W., Ockenfeld, K., B�hme, M., Kn�-chel, A. (Eds.): Schadstoffbelastung nach dem Elbe-Hoch-wasser 2002. Final Report Ad-hoc Project “Schadstoffun-tersuchungen nach dem Hochwasser vom August 2002– Ermittlung der Gef�hrdungspotentiale an Elbe undMulde”. 2004, pp. 258 –274.


Methods to calculate sedimentation rates of floodplain soils in the middle region of the Elbe River

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