Detection of Seasonal Erosion Processes at the Scale of Anmarl Elementary Gully Black from Time Serieshi-Resolution of Dems J

Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | , 3 , J.-P. Malet 2 3,a , N. Mathys @unil.ch) 1 ff ff 1556 1555 , and J. Travelletti 1 (michel.jaboyedo , M. Jaboyedo 1 ff , B. Rudaz 2 , A. Loye 1 , J. Duc 1,† , C. Le Bouteiller 2 This discussion paper is/has been underPlease review refer for the to journal the Earth corresponding Surface final Dynamics paper (ESurfD). in ESurf if available. University of Lausanne, Risk-group – ISTE – Institute ofIRSTEA Earth Grenoble, Sciences, Unité de recherche Erosion Torrentielle, Neige et Avalanches,Institut BP de 76, Physique du Globe de Strasbourg, CNRS UMRnow 7516, at: Ecole BEG et – Observatoire Bureau des d’Etudes Géologiques SA, Rue de la Printse 4, deceased, 28 March 2015 Received: 1 December 2015 – Accepted: 3Correspondence December to: 2015 M. – Jaboyedo Published: 18 December 2015 Published by Copernicus Publications on behalf of the European Geosciences Union. Detection of seasonal erosion processes at the scale of anmarl elementary gully black from time seriesHi-Resolution of DEMs J. Bechet S. Klotz 1 Lausanne, Switzerland 2 38402 Saint Martin3 d’Hères, France Sciences de laa Terre, Université de Strasbourg, 5 rue Descartes,1994 67084 Aproz, Strasbourg, Switzerland France † Earth Surf. Dynam. Discuss., 3, 1555–1586,www.earth-surf-dynam-discuss.net/3/1555/2015/ 2015 doi:10.5194/esurfd-3-1555-2015 © Author(s) 2015. CC Attribution 3.0 License. Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | ”) cover especially ff et al., 2012) where erence between the ff Terres Noires ff activity with a very high point cloud ff , loose regolith soil sources are eroded at ff 1558 1557 generation. Time series of TLS observations have been ff erosion and shallow landslides (Antoine et al., 1995; Maquaire ff erent periods of the year. These are forming transient deposits in the main reach Among the cross-disciplinary research activities conducted in the Draix-Bléone Quantitative analyses of the seasonal erosion activity and of the sediment fluxes Since 2007, a monitoring of surface changes has been performed by comparing Terrestrial Laser Scanner (TLS) is a powerful tool to monitor erosion processes at the ff high spatial resolution data onresolution surface mapping changes of is erosion needed ratescatchment at (Jacome, is 2009). fine (e.g. Such innovative seasonal) high and temporal represents scale considerable for an progress entire in the field of erosion several sizes and vegetation cover, thiscontrolling work the focuses on annual the patternMeunier analysis and of of Mathys, the erosion 1995; processes Mathys rates et in al., 2005). elementary gulliesgully (Richard, scale at 1997; a relatively low cost (Perroy et al., 2010; Jaboyedo catchments (SOERE RBV), composed of seven nested catchments characterized by rates of surface erosion processesDescroix in summer and and Mathys, winter 2003); (Descroix theactivity and pattern. erosion Gautier, 2002; processes have therefore an annually-cyclic et al., 2003). The weathered marls can be mobilized by Hortonian runo large areas inshales South-East catchments France. is the The resultfactors. badland of Freeze–thaw the landscape and conjunction observed of wetting–dryingmarls favorable in formation cycles lithological thus these and progressively favoring climatic clay- disintegrateposed the to annual the surface development black runo of a weathered marly layerduring ex- high-intensity rainfalls intrated flows summer. inducing This significant problems causes in(Oostwoud flash sedimentation reservoirs Wijdenes floods and and river and Ergenzinger, systems 1998; hyperconcen- the Descroix and weathered Olivry, marls 2002). Saturation layerssediment of can loads also to the locally basins. triggercontributes In shallow addition, to rain landslides the infiltration supplying triggering inbedding high the of and fractured larger marls the landslides bedrock whose discontinuities. geometry There is is controlled a by strong the seasonal di di of erosion processes forsediment black production marls and badland-type the slopesserved temporal and surface storage/entrainment illustrates changes in the caused similar by modecomplete slopes. erosion TLS of time-series, The (ablation/deposition) and are ob- sediment quantifiedComparisons budget for maps of the are the presented for TLS(limnigraph each sediment and season. budget sedigraph) maprainfall in events with are the the the stream triggering in factor are situ of discussed. sediment the major monitoring Intense erosive and events. long duration 1 Introduction Jurassic black marls of Callovo-Oxfordian age (e.g. also called “ when routed downstream, evolving fromthrough a the year. transport-limited The to monitoring a allows a supply-limited better regime understanding of the seasonal pattern contributing to the rechargethe of transport tributary capacity gullies generated and by runo rills are presented. According to density ensuring achanges resolution over of a time the span of DEM 4 at years are the analysed. centimetre scale. The topographic capacity vs. rainfall and runo of high-resolution digital elevation modelsScanner (HR-DEMs) (TLS). produced The objectives from are Terrestrial (1) Laser tion to and detect and the (2) evolution of to quantify the the gully sediment morphology produc- in terms ofacquired sediment periodically availability/transport based on the seasonal runo Abstract The Roubine catchment located(south in French the Alps) is experimental situated research inprone station Callovo-Oxfordian black to of marls, Draix-Bléone a weathering lithologybeen processes. particularly monitored Since for 30 analysing years,gullies. hillslope this erosion small processes watershed at (0.13 the ha) scale has of elementary 5 5 25 20 15 10 25 20 15 10 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | ) to ◦ Pina Negra ) in southeast France, near the city of ) watershed of the Draix experimental site 2 1560 1559 ) and a low vegetation coverage (ca. 20 %). The ◦ Systèmes d’Observation et d’Expérimentation pour la Recherche in the watershed of the Durance river (Légier, 1977; Phan and An- 2 s of grass restricted to the flatter interfluves near the sediment trap and on the ff A sediment trap, a stream gauge and an automatic sampler are installed at the bot- This elementary watershed has a typical badland morphology characterized by V- In this study, time series of intra-annual TLS observations are used to quantify sur- marl and limestone sequences whosesequence ages which range outcrops from in Lias thefordian, to Draix-Bléone catchments Cretaceous. and is The its from marly the thicknessMaquaire Bathonian et can to al., Ox- exceed 2003). A 2000 m limestone ridge in overlies some the black places marls (Antoine (Ballais, 1999). et al., 1995; toine, 1994; Mathys et al., 1996). This sedimentary lithology is composed of alternating from the Roubine outlet. 2.2 Geology Large areas of Southeast Francethan are 10 covered 000 by km black marls which outcrop over more top of the crests. tom of La(Mathys Roubine et in al., 2003). order Rainfall to observations are monitor collected the by a sediment rain gauge yield located and 20 m the water discharge Roubine elementary catchment isEast constituted to by West. oneslope. This main On gully the gully south-facing that separates slope,North-east crosses a the to secondary it catchment South-west gully from and crosses into confluences diagonallyBoth with a in north the the north- main direction and gully anddecametric south-facing at widths. a the slopes A catchment few south-facing are un-weathered outlet. marlsections braided outcrops of with can both be slopes. many On observed small these in outcrops, the gullies the steepest dip and ofand rills the black tu of marl formation is 30 shaped gullies, steep slopes (35–45 (Mathys et al., 2003).the No setup human of the actions observatory have in been 1983. conducted within the gully since the East. The scarce vegetation cover is constituted of a few black pines ( Digne-les-Bains (Alpes-de-Haute-Provence). Draix-Bléone observatoryof seven is small mountain composed watersheds. Itter was understand created erosion by IRSTEA and in sedimentfloods, 1983 and transfer in to processes, order improve including to the bet- hyperconcentrated experimental design of site protections selected in for response thiswhich to work erosion is is processes. the the The Roubine smallest elementary monitored catchment (Fig. (1030 m 1), en Environnement Réseau de Bassins Versants and transient storages of sedimentwith within previous the work rills on and similar gullies. This black is marls put slopes. in perspective 2 Physio-geographic settings of the study2.1 area: the Roubine catchment Morphology The research has been conductedERE in RBV the network, Draix-Bléone experimental catchments (SO- face erosion. The mainevery objectives season, are: (ii) (i) to tovolume estimate calculation create the at ablation sediment the andtion budget catchment deposition and and scale maps (iii) by evaluate for to the comparing proposeof ablation it accuracy a and conceptual to of deposition. model The sediment the results explainingchanges trap allow the of observa- identifying observed and the seasonal quantifying catchment the pattern in topographic terms of regolith development, slope transfer processes, assessment (Lopez Saez etTLS al., to 2011). measure Preliminarymillimetric-scale studies and changes show map at a short surface great range erosion distances potential (50 (Puech of m; Abellán et et al., al., 2009). 2009) since it can detect 5 5 20 15 10 25 20 15 10 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | 3 3 − − C, ◦ TOF). In (Richard, × 1 c − = to 1800 kgm d 3 − × er more cycles than the north- ff (Olivier, 1999). Micro-debris flows during a few minutes (Yamakoshi for La Roubine catchment. In the 1 respectively during 1, 5, 15, 30 and (Olivry and Hoorelbeck, 1989), and 1 − erences in temperature and rainfall. 1 C with a standard deviation of 8.7 − ◦ 1 1 ff − − − yr 1 − 1562 1561 ), to the reflecting surfaces (2 or 13 mmyr c 1 − yr 1 − , while the regolith density can be as small as 1300 kgm 3 − at the same rate as the interfluves and the upper parts the slopes; ff ), at the light velocity ( d , which is approximately 100 t ha 1 − The slope surfaces evolve dynamically through the year. The un-weathered black but it varies greatly in space(Maquaire and et time al., according 2003; tothe the Travelletti et presence black of al., marl local 2012). discontinuities deposited The(Mathys in measurements et of the al., the sediment 1996).a densities trap In popcorn of vary structure the from and springand 1500 therefore kgm season, structural a the low thin regolith density.intense crusts In observed wetting the can in summer (Malet develop the season, et at8 mmyr sedimentary gullies al., the has 2003). surface The of mean the erosion regolith rate because of of the the black marls is of marls density is 2650 kgm (Rovera and Robert, 2005). Howeverfrozen the soils. north-facing The slopes pattern presentexposition higher of and depths aspect. erosion In of rates addition, it iswith has therefore been increasing demonstrated strongly slope that angle controlled erosion rates on by increase bare the marls slope (Lopez-Saez et al., 2001). 3.1 Terrestrial Laser Scanner (TLS) measurements The study site hasThis been remote monitored scanning using device a islaser a Terrestrial beam Laser monochromatic pulses Scanning laser are pulse systemically oriented transmitter/receiver. (TLS). The or using mirrors both. or Thedistance by time ( moving of the flight laser (TOF) source mechan- is the time for the pulses to travel the double this system yields to relativelyMathys, constant 2003). slope gradient values over time (Descroix and 3 Methodology more specifically ofabsence 100 t ha of shalloweroded mass by movements, runo the lower parts of the slopes are, generally, 2.3 Climate Slope erosion rates aretain influenced by climate the with specific strongAt features Draix, seasonal of the a and Mediterranean mean yearly400 moun- annual mm di rainfall over is the 920 periodthunderstorms mm 1970–2000. with can The an occur, summer interannual- variability which is of relatively intensity nearly dry, sometimes but several exceeds heavy 60 mmh 1997) and can even reach more than 100 mmh et al., 2009), i.e. 210, 138, 90, 74 and 45 mmh facing ones, but in the gullies the south-facing slope are equivalent to north facing slope over the period 1970–2000. 2.4 Hillslope activity processes The alternating of freezing-thawingtrolling and the wetting-drying development cycles of is aet weathered the al., loose key 2002; regolith process Brochot on con- of black et marl Meunier, loose slopes 1994). regolith (Maquaire At canof the accumulate the end of gullies. in the The theering winter south-facing lower cycles season, slope parts than a is the of thickthe characterized north-facing layer the freezing by slope and slopes (Maquaire a thaw and et higher cycles al., the at number south-facing 2002). the of slope But weath- outlets su considering only 60 min (Mathys, 2006).by These suspended events sediment trigger discharge of hyper(MDFs) up concentrated to have 800 flows also gL characterized beenclearly observed associated (Oostwoud with Wijdenes high erosive andare events Ergenzinger, not (Yamakoshi et 1998), unusual. al., During and 2009,maxima. spring 2010). During Hailstorms and the autumn winter, seasons, verycycles the small of rainfall amounts freezing-thawing amounts of are are observed rainfallRovera at are and (Oostwoud measured, their Robert, Wijdenes but and 2005). over A Ergenzinger,winter. 100 1998; snow The cover daily can average air form temperature but is does 10.9 not usually last the whole 5 5 10 25 20 15 20 25 15 10 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | . 0.5 ) 1 erent − ff n 1 σ ( = 1.2 and 12 pts n σ = erent scenes, the n ff ( 2 − erence images of Fig. 2, including ff 8 mm, but the average is performed on = 1 σ 1564 1563 erence images: location of erosion-prone areas ff 2cm), with density ranging from 0.3 to 3 pts cm × erence images have been calculated from the 9 May 2007 to the erence image of the corresponding season. These comparisons allow the . ff 2 ff − ) we obtain an accuracy ranging from 6.7 to 2.3 mm, because , (2cm 2 2 and quantification of volume changes erent ablation and deposition areas is carried out for each season by taking into ac- For each TLS campaign, the measures were performed from up to five di The software Polyworks V.10 (InnovMetric, 2010) has been used to process the TLS Eleven di ff final point cloud densityusing is Surfer variable; thus, (GoldenSoftware each 8) TLSmogeneous inverse high point distance resolution cloud (0.02 method m) has (Shepard, High ResolutionA been 1968) Digital interpolated high Elevation into Model density a (HRDEM). point ho- due cloud to produces the an too over-defined manyconsider problem points the during present systematic in the error one interpolation (thatnumbers grid will (Kromer cell be et (Schürch discussed al., et separately 2015)is al., later), performed, indicates 2011). assuming the that If that law the we the of accuracy doexample, surface large considering will is not the locally increase lower planar, when accuracy at is average thea centimetre 4 scale. cm As an in 4 cm To quantify and mapwas the subtracted ablation from and the earlier depositionhave (DeRose through negative et pixel time, al., values 1998). the representing The ablation mostdeposition. resulting and recent elevation positive changes DEM pixel values representing 4 November 2010to (Fig. each 2). season, Because the thedi images occurrence are of sorted processes out is by strongly seasonal related periods. The mapping of the (Fig. 3), and the characterization1999). These of maps the represent annual a pattern synthesis of of erosion the (Betts di and DeRose, count the di detection and mapping of the most ablation-deposition-prone areas in the catchment In some cases, TLS datalaw can of allow large detecting number movements (Kromer below et 1 al., mm, 2015). because of3.3 the Calculation of vertical di the interpretation in terms of dominant ablation or deposition process. On these maps campaigns are aligned to180 mm a diameter styrene-spheres reference located campaign arounding the on (e.g. catchment the June since TLS 2008. 2009) distance Depend- of using acquisition eight and white the overlapping of the di point clouds. First, theder vegetated to areas keep are forare the deleted then analysis from aligned using only the the1992; the raw Iterative Besl bare point Closest and Point soil clouds McKay, (ICP) 1992) surface. in procedure to The (Chen obtain or- scans and a point Medioni, of cloud each of campaign the entire catchment. The TLS practice the laser as athe footprint target. that The increases in operationgrid diameter is with of repeated increasing XYZ millions distances points to ofTLS1 (Shan times and is Toth, giving an 2008). access Ilris TwoGermany) types to 3-D scanner. of a The (Optech, TLS TLS1 very Canada) were laser dense from scanner, used is and infrared the for (1535 this TLS2 manufacturer nm) study: is indicates anda the a that performance spot TotalStation it coming II diameter produces (Leica, of dataspectrum 22 (give with mm wavelength) an with at a accuracy 100 6 m. of mm The 8 accuracy mm and TLS23.2 with a laser 6 mm is spot in Data size acquisition at the and 50 green m. processing electromagnetic Twelve TLS campaigns were performed from(Table 1). the 9 The May data 2007protocol to of were the being the 4 developed. years In November 2009 2010 larly 2007 and through and 2010, the TLS 2008 year data in isseasonal were order acquired rainfall. sparser to more take as regu- into the account more methodology precisely and the influencesscan of positions the in orderremain to minimize because shadow of areas. theof However, some presence vegetation. shadow of All areas scan foreground still range. in spatial The point resolutions the cloud are line densityto of of is 3 very less pts sight cm high than of for 10 all the mm the scanner at time series or a and 50 m range among distance 0.3 5 5 10 15 20 25 25 10 20 15 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | er- ff erences rang- ff erences are summed ff ). To obtain the sediment 2 erent (Table 2). ff ) of the black marls deposits mea- 3 − ected by deformation due atmospheric ff erences ff 1566 1565 erences above 10.0 cm in absolute value. The ff ected by instrumental errors as described by Abellán ff erence images had some misalignment characterized by ff erences ranging from 1.8 to 4.0 cm, moderate height di ff erences in three classes is proposed both for the ablation and deposition; ff transport erence images outline the slope surface changes at a centimetre scale (Fig. 2). All A possible procedure to estimate the overall errors is to define the quality of the To quantify the volume of soil surface changes, the elevation di ff the images are presented inlimit a of plan the view catchment on a lacks hillshade in of data the because watershed. of The eastern a dense vegetation cover. The di ences under 1.8 cm areprocedure, not and displayed. assuming This limit thatimum has it error been contains chosen of in on alignmentheight most a di of cases trial 6 and above mm, error threesmall except times height for di the the max- ing scans from of 4.0 2007. to 10.0 A cm, clustering high height of di the alignments for each campaign (1) andsures between of them the (2). dispersion This of correspondsby the to identifying points the mea- between the two areas mergedetc.) scans that match. (1). have This The is not averagedeviation performed changed distance is (fixed between performed surfaces two usingbe like scans the applied the to and point sphere; successive the to campaigns.reducing wall, associated Note surface the that standard method. noise the and (2) interpolation minimizing Similar of other measurement the procedure errors. HRDEM can allows 4 Results 4.1 Analysis of soil surface height di ablation pattern is displayed inin warm cold colours. colours while the deposition pattern is displayed Di slight tiling due to scan deformationof and/or error scan is alignment for inaccuracies; such instancesion a clearly of source visible the on two Fig. successivereferencing” 4f. vary alignment In from procedures, a fact, i.e. measurement the campaign thescan quality to scan deformation precision another and merging and as the and the preci- spatial TLS the instrument, resolution “geo- the were di sured in the sedimentvolumes, trap because (Mathys of et the al.,the vegetated 1996) area scans. is The and used density the to ofto occlusions correct the the which the seasons eroded are estimated as material not shown TLS changes imaged in throughout by Table 2. the year3.4 according Comparisons of the TLS sediment budget to the observedThe bedload results have beentrap, compared which to is the measured bedloadaverage manually transport of after monitored 20 % each in of significant theflows the rainfall. sediment total the Because eroded budget annually sediment an sedimentnoted exits that the trap during catchment sediment major in storm have water-suspended in hyperconcentrated events, been up flows increased (Mathys, to 2006). 40 by % of 20 %. sediments can It3.5 exit must the be catchment Sources of errors The use of TLSFirst, observations TLS resulted measurements in are several sourceset a of al. errors (2009). that Second, are some quantified. scans are also a budget, the totalThis volume calculation of provides deposition theminimize is final scan results subtracted of alignment to topographic inaccuracygraphic the changes changes on outside in total the the cubic active volume erosion–prone quantification meters.ignored. areas of To previously Finally, of mapped erosion. an the have been average volumes, density the (1500 kg topo- m conditions. Third, some di and multiplied by the DEM squared cell resolution (0.004 m (Fig. 3), the ablation areas are(see displayed also in the orange video and in the deposition the areas Supplement). are in blue 5 5 15 20 10 25 10 20 15 25 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | erence image erence image are not able to erence images erence images erence images which probably ff ff ff ff ff 2 1 − occurs on a saturated and the weathered re- 1 − cient. To give an order of ff ffi 1568 1567 ected by Hortonian runo ected by the late spring erosion pattern are contin- , the discharge will be of 0.5 L min ff ff ff erence images between the 9 May 2007 to the 24 June 2007 and ff Winter seasons erosion pattern is illustrated by the elevation di between the 3 November 2009 and the 23Spring March seasons 2010 erosion (Fig. pattern 2g). isbetween represented the by the 14 elevation April di (respectively to Fig. the 2d and 1 h); June 2009 andThe the erosion 23 pattern March ofthe to elevation late the di spring 28 - Maythe 2010 early 28 summer May rainy toamount the season 23 is at June illustrated this 2010 by seasonbelow (respectively was Fig. average for 2a 30 % the and belowlast i). whole average In year, days up 2009, only of the to thanks thecorresponds rainfall to 20 for calendar some December, that year, late period and in most precipitations 19 % 2009; in probably the snow.Summer season Thus erosion no pattern is di representedbetween by the the elevation 1 di Juneber to 2010 the (respectively Fig. 11 2e August and 2009 j); andAutumn season the erosion 23 pattern June isbetween represented to the by the the 11 elevation 22 August di Septem- November to 2010 the (respectively 3 Fig. November 2f 2009 and k). and the 22 September to the 4 – – – – – During the autumn seasons (Fig. 3d), the rainfall pattern is characterized by long During the summer seasons (Fig. 3c), characterized by a relatively dryness except During the spring seasons, (Fig. 3a), the sediment accumulated during winter in the During late spring–early summer rainy seasons, (Fig. 3b), the rainfall can be rela- During winter seasons, (Fig. 3e) the alternating freezing-thawing cycles favour the and low intensity events with some very short intense precipitation prone to a slow soil ued to be eroded intheir their lower steepest parts. parts Most of whileThe the deposits less loose and weathered frequent small regolith but levees has are moreerosion already formed pattern, intense been in now storms washed sediment-limited. away. observed in this season do not impact the the occurrence of asmall few gullies thunderstorms, and rills there than is those very a little erosion activity. The same golith developed during winterprone can to be such washed type out. ofwinters. The erosion Very pattern south-facing often, as slopes small more are depositionthe weathered more levees sediment gullies. are is observed produced at during the lower (flatter) parts of magnitude, if an intense event of a few minutes at 0.5 mmmin mobilize material if the daily rainfall or the intensity isground, and not assuming su 100 % runo main gullies is transportedlimited at to the the two outlet maingullies of with gullies. the the Ablation catchment. larger is contributing This transport-limitedby surface transport and the are consequently limited is drained. only This amount generally the mulation, is of probably the intense mainly gullies rainfall caused that during have that a contributive period. area Looking smaller at than the 100 m flow accu- on the south-facing slopes of theresult in watershed. a Higher higher number amount of of freezing-thawinget regolith cycles al., that can 2005) be and mobilized therefore (Maquaire more et al., production 2002; of Raclot sediment along the slopes. steepest slopes can be strongly a tively intense (Mathys et al., 2005). Consequently, the secondary rills, gullies and the permits to erode the rills. 4.2 Cartography and temporal pattern ofFive erosion erosion processes patterns arespring–early distinguished summer, for summer La and Roubine autumn: catchment; winter, spring, late regolith development. Gelifluction (and solifluction duringthe thawing) gullies in and the on upper parts thematerial of steep in slopes the surrounding lower the parts gullies of lead the to gullies. an The accumulation soil of surface changes are mostly located 5 5 25 20 10 15 10 15 20 25 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | 3 measured 3 and rain totalling (during four min- 1 1 − − . This limitation also erent types. The first ff ff . The maximum intensity of the 1 − erence is in an acceptable range ff are transported but most of the volume 3 ) were very close. 3 during 10 min. The measurements by TLS 1 1570 1569 out of the catchment. For the period Novem- − 3 from TLS for the period 28 May–23 June 2010. The 3 erences smaller than the TLS threshold we used, i.e. ) after antecedent precipitations since 1 May of 70 mm. ff 1 − after 42 mm of antecedent precipitation (from the 14). It ap- was transferred out of the catchment during that period. The 1 3 − in the sediment trap, with an intensity reaching 0.8 mmmin ects the TLS sediment budget as erosion-prone areas can be hidden from the 3 ff ) and within the sediment trap (1.7 m 3 Also, topographic height di The maximum eroded volume is produced for the period March–June 2010 (Table 2) 1.8 cm, are notimportant integrated sediment in volume the becauseduring of sediment the their budget summer possible while storms widespreadinfluences that they occurrence, the trigger could mainly important sediment contribute Hortonian budgetbecause to runo by of an underestimating the theinterpretation coherence total of of volume the catchment of the erosional ablation. results, system. But we consider that it can be a base for an laser pulse. When these erosion-pronebe areas are estimated hidden, as the deposited morepositive, sediments important can as than for the exampleareas ablation for are volumes. the usually The period located balance June–Septemberto in is 2010 the the therefore (Table crests upper 2). of parts The theTherefore, of shadow catchment; it the these is slopes, areas often hypothesized arethe very that periods. highly steep In the productive and addition, source sediment although close of the budgetet swelling sediments al., is or 2015) inflation can underestimated of have an for theit influence regolith most on at surface the of (Bechet the georeferencing, level it of was not La possible Roubine to catchment. quantify 5 Interpretation and discussion The two values of eroded volumes (TLSthe and suspend sediment trap sediments) increased by aremeasurements, 20 % underestimations the to of include balance the valuelarger true is than erosion the negative deposited rate. when sediment With volumes.scans the The a the presence ablation of TLS sediment shadow areas volume in is the TLS (1.6 m in the trap andlast estimated important at 6 event m occurred onevent. 4 The October intensity 2010, reached with a 1 mmmin small but intense 12 mm rain transported out of therainfall events. catchment It based must be onof noted 1.7 TLS m that observations, the event with of some the 21 significant October 2009 led to a deposit with a sediment transfer of ca. 8.7 m wetting and consecutive increase in soilis moisture. created, Progressively, a and new in layer most of of regolith the rills and4.3 gullies, sediment transport Quantification is of reactivated. seasonal sediment budgetFor changes the quantification ofyears the 2007 seasonal sediment and budget 2008largest changes, possible have area the of been TLS the catchment ignored, dataTLS as because other of (Table did. 2) the TLS The are eroded data volumes intransfer estimated were agreement with at with not the the covering outlet integrated(5.5 the % measurement trap for of (Table the coarse 3; periodvolumes). sediment Fig. from 4), 14 the April 2009 di to 4 November 2010 on theber total 2009–March cumulated 2010 (Table 2) moreis than 4 redistributed m within thetransport catchment the because sediments the out rainfallare of were the characterized not catchment. by intense The enough moderate autumns to sediment 2009 and transfers 2010 with (Table 2) respectively 0.9 and 1.7 m occurred during the 14 firstprecipitation days of event May occurred for a on total 10 of precipitation May of which 155 mm. reached The main 1 mmmin 36 mm during the day. The three main events of 2010 are of di utes more than 0.5 mmminA volume of nearly 3 m 5.5 mm including an intensity maximum15 of was 0.8 mmmin of 0.6pears mmmin that this event was able to transport out of the catchment around 3 m second occurred on the 15 June 2010 with a daily rainfall of 69 mm, with the day before 5 5 25 20 15 10 10 15 20 25 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | use ff . The 1 − erent depending on ff 1571 1572 , if it is coupled with significant precipitation, which in a larger similar catchment (Laval) after more than ff ff may be generated. This process could not be measured ff ), which is the limit to trigger MDF’s (Yamakoshi et al., 2009) 1 − , 2008). The winter period, because of frost/thaw cycles and low rainfall 60 mmh ff = ( 1 erence between rills and inter-rills erosion depends on rainfall intensity, and − ff The di It is also clear that sediment transfer depends on the material available (Bardou During the spring and summer seasons, the sediment transfer consists of the ab- The main events summarized above all occurred after more than 9 mm rainfall, which intensity, permits to create and accumulatefall weathered intensities material. of The these relatively winter lowwithin periods rain- the permit slope to and mobilize gullies. partially material that remains antecedent rainfall amounts. The accumulatedmoderate material rainfall in intensities for the fine rills material,and/or can while a be inter-rills well-developed mobilized need upper intense by part precipitations moves of by the solifluction regolith. In of winter,In the the spring, upper material probably the regolith only on materialand short accumulated rills distance, in with i.e. small the contributing cm rillside areas to the is can catchment. a washed be Autumn few permits away, eroded and meters. in to and clean later the the the material the material main transported inter-rills accumulatedprecipitation rills. out- during summer occurs This and scheme onlyconcentrate may the intense change full rainfall depending erosion in event on one remains. the or The a future few system climate, events. A could if warmer then climate less may also reduce and Jaboyedo grain size distribution. Mathyscentimetres (2006) of indicated the regolith that contain inand 45 the % silts. clay area This and of shows siltsantecedent Draix period that and in 4–8 the the cm terms four contains size ofthe first 35 rainfall of % and beginning clays climate. material of In transported the addition,concentrating it year will the has the change material been sediment shown in with moves that the time,the in but gullies. stay This i.e. quantity non-linearity partially and is within type supportedthe the of by rainfall. catchment, the material Partitioning fact mobilized that oflow depends discharge the on the total the suspended load duration materialclose to exported and part 40 % from ranges intensity for between higher of the dischargeprecipitations 0 catchment (Mathys, can and 2006). mobilize shows This 40 %, indicates the that that whereas wholein only at it upper high smaller intensity part is particles, of the whereaspart regolith small of and/or intensities the split regolith depend marl at on plates the the time grain of the size event. of this upper permits to induce ansediment erosion yield pulse is with controlled by lower the intensities availability such of as the 0.6 upper mmmin part of regolith and by the rainfall eve occurs. Most ofof the the sediment exiting winter the weathering.(at Roubine The the catchment are beginning erosion a of progressively product spring) evolves to from a a supply-limited transport-limited (in summer) pattern. However, di permits to initiate earlier the runo lation of the weatheredtransient storages loose of regolith accumulated layer sediments on in the the rills slopes and and gullies, a if mobilization no of exceptional the or with immediate antecedent rainfall that has saturated the soil. This last situation 5.1 Synthesis All the resultspattern can of be ablation synthesized and(Fig. in deposition 5). and This a quantifying seasonalability conceptual of pattern the model sediment volumes is during describing of each controlledthe period. the year sediment by The but the seasonal transfer results the may sequence rainfall thusevents will distribution will be not change. di and change, only the the avail- time lapses between major erosive is also the limit for5 initiating runo antecedent drydry days period (Mathys et goes1 al., below mm min 2000), 5 that days. These threshold events going possess down either with intensity if that the reaches ablation may happen during intenseparticles summer and storms Hortonian as runo heavy dropswith may detach the small TLS techniquea as new layer a of higherhas loose occurred accuracy regolith before is is in necessary. progressively summersediment In as created, is it limited. the and is if autumn usually an seasons, the intense case, rainfall then event the quantity of available 5 5 20 25 15 10 10 25 20 15 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | - ffi erent processes. This first results are show- ff 1573 1574 , M.: Debris Flows as a Factor of Hillslope Evolution controlled by ff ective to map and quantify topographic changes, but some di , M., Oppikofer, T., and Vilaplana, J. M.: Detection of millimetric defor- ff ff To the IRSTEA who let us work on his field and who gave us precious data. erent Time and Space Scales, edited by: Gallagher, K., Jones, S. J., and ff Such procedures are not possible in the Roubine catchment, which must not be per- Here we have shown the limits of the methods. Further investigations with HRDEM The TLS permits mainly to locate the di a Continuous or atonics Pulse over Process? Di in: LandscapeWainwright, J., Evolution: J. Denudation, Geol. Climate Soc. London, and 296, Tec- 63–78, 2008. mation using a terrestrialHazards laser Earth scanner: Syst. experiment Sci., and 9,. http://www.nat-hazards-earth-syst-sci.net/9/365/2009/ application 365–372, to 2009, a rockfall event, Nat. erties of the “Terres Noires” ininstability, Eng. southeastern Geol., France: 40, weathering, erosion, 223–234, solid 1995. transport and l’exemple de Draix,de CAGÉP Provence, - 1999. URA 903 du CNRS, Institut de Géographie de l’Université Thanks to the GISfirst Draix author and Jacques particularly Bechet, who topaper died S. is in Klotz a an snow (IRSTEA). expression avalancheco-worker We of 28 Julien dedicate March his Duc. this 2015. We great The paper will ingenuity, content ever to curiosity remember of the and his this enthusiasm. research spirit he shared withReferences his Abellan, A., Jaboyedo Antoine, P., Giraud, A., Meunier, M., and van Asch T. W. J.: Geological and geotechnicalBallais, prop- J.-L.: Apparition et évolution du modeléBardou, de E. roubines and Jaboyedo dans les Préalpes du Sud: turbed by human activity.mented A on new the site small of Draix, catchmentitself. which Another (Roubinette) will next permit has step to thus install will instruments be been inside to instru- the acquire watershed TLS data during a stormThe event. Supplement related to thisdoi:10.5194/-15-1555-2015-supplement. article is available online at Acknowledgement. throughout the year (seasonvolume correction. by season) would be a great help to improve the TLS must be carefully set upsurface in order monitoring to must avoid the be errorsimultaneously coming coupled such from with data as acquisition. more soil These tribution, variables moisture, the monitored the density, during etc. swelling, the rain Furthermore event drop density size, map the of grainsize the dis- regolith of the catchment ing that the rainfall pattern, i.e.delivery time-series, intensity sequence, and but duration, the controls process the ofeither sediment weathering suspended is load fundamental or to bed provideseasonal load. material pattern. The for interplay of rainfall and weathering creates the culties have still to solve to fully quantify the sediment transfer. the number of frost-thawgenerated cycles every year. and But in thus anywill also case remain the reduce seasonality in the that the depth leadsmobilized. to cold of weathered period, the material regolith which layer is the main producer of6 sediments that can Conclusion be By their strong and rapidare responses favourable to to climate forcing, the theprevious analysis black works. marls of The of erosive Draix-Bléone strong processes.(Jacome, dependence This 2009) to article or the confirmed the(Mathys, seasons results 2006). sediment and The of trap prediction the measurementsmatic of cycle and the events of responses is the processes of improved. densityerosion small TLS while of mountain has being the watersheds proved easily to regolith to reproducibleing cli- and be at accurate an the all appropriate at centimeterDEMs tool once. proved scale It to very also with e monitor allowed success. gully work- The method used to create and compare 5 5 25 10 20 25 15 20 15 10 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | , M.: A 4D filtering and erosion in the ff ff 1576 1575 érentes échelles de mécanismes d’érosion et de ff el, M., Rovéra G., Astrade, L., and Berger, F.: Mapping of ff , M., Loye, A., and Mathys, N.: Erosion processes in black marl ff -erosion model, Catena, 50, 527–548, 2003. ff , M., Oppikofer, T., Abellán, A., Derron, M.-H., Loye, A., Metzger, R., and Pe- ff Black Marls of the63, French 261–281, Alps: 2005. observations and measurements at the plot scale, Catena, transport de matériaux(Draix, solides. 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A.: ComparisonPhan, of T. gully S. erosion H. and Antoine, A.: Mineralogical and geotechnical characterization of the “Black Poesen, J., Nachtergaele, J., Verstraeten, G., and Valentin, C.: Gully erosion andPuech, environmental C., Thommeret, N., Kaiser, B., Bailly, J.-S., Jacome, A., Rey, F., andRaclot, Mathys, D., N.: Puech, C., MNT Mathys, N., Roux, B., Jacome, A., Asseline, J., and Bailly, J.-S.: Photogra- Richard, D.: les Les bassins versants experimentaux expérimentaux de Draix (04): éetudeRovera, de G. and Robert, Y.: Conditions climatiques hivernales et processus d’érosion Meunier, M. and Mathys, N.: Panorama synthétiques des mesures d’érosion e 5 5 10 15 20 10 20 25 15 30 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | ] 3 . [m] ff ] di 2 − ] Cum.Vol. [m 3 . Pts. density SD mean ff Inter-period 0.000270.000060.00017 72.4310.00011 3.4037E-05 4.9750.00013 2.621 1.0768E-05 4.3454E-06 –0.000080.00022 –0.00035 8.693 3.2734E-06 9.991 – 1.5214E-06 – – – − − − − − − − − 0.2950.0060.9411.195 0.8 2.722 0.8 6.034 1.7 0.366 2.9 1.618 5.6 11.7 12.0 13.7 − − − − − − − − –––– erence between two scans (either ] Balance [m 3 ff SD inter Mean di 0.01500 0.01328 0.00694 0.00547 0.00556 0.005200.003850.00517 0.00546 0.000280.00544 0.000380.00455 0.00929 – – – – – – period [m] Inter period [m] [pts cm . [m] ff erence. ff ] Deposit [m 1580 1579 3 ] di 2 − 0.5600.3821.992 0.265 4.537 0.376 2.743 1.051 6.290 3.342 0.419 0.021 1.778 0.256 0.053 0.160 − Volume added for the 14 Apr 2009 0.48 − − − − − − − . Pts. Density SD mean ff 0.000002 0.179 1.5709E-06 − LiDAR Leica TotalStation II. = Alignment scans of each period have been added to the first period to the cumulative volume. 3 Measured volume of ablation and deposition. In order to perform comparison with Characteristics of the TLS alignment with, for each time period, with the information on LiDAR Optech Ilris 3-D L = O Date start14 Apr 2009 Date end 31 May 2009 Erosion [m 31 May 200911 Aug 2009 11 Aug 2009 3 Nov 2009 3 Nov 2009 23 Mar 2010 2328 Mar May 2010 2010 28 May23 2010 Jun 23 2010 Jun 2010 22 Sep 2010 22 Sep 2010 4 Nov 2010 of time scans -Surf. [m] align. [m] [pts cm May 2007 (O)Jun 2007 3 (O)Jun 2008 (O) 1Apr 2009 (O) 3Jun 2009 (O) 6Aug 0.0060 2009 (O) 4Nov 2009 (L) 7 0.000010Mar 2010 0.0070 (L) 4May 2010 0.0120 – (O) 3 0.000020Jun 2010 0.0046 6 (O) 0.000034 1.257Sep 0.0052 2010 (L) 6 0.000070 2.0895E-06 Nov 2010 0.0042 (L) 0.000008 3 1.374 0.0034 3 0.000020 – 0.0046 2.2674E-06 1.487 0.000043 1.315 3.0478E-06 0.0048 0.000009 1.585 1.2685E-06 0.0026 0.000007 1.3217E-06 0.610 0.776 0.0027 1.8677E-06 0.348 0.000030 3.094 2.0170E-06 7.6515E-07 3.255 7.8926E-07 – 0.409 1.5128E-06 Period Num. SD Pts. Mean di Table 3, 0.48 m Table 2. used for to align onthe period standard or deviation of for the inter average period mean comparison), di the used average point density and Table 1. the number of scans usedto to create the a surface scene. matched The (point table indicates to standard surface deviation ICP), of the the point mean di Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | ] 3 aerial (b) ] volumes [m 3 Location of la Roubine catchment; (a) ] volumes [m 3 1582 1581 ] volumes [m 3 Photograph of the Roubine catchment (1 June 2011) with the con- (c) volumes [m Location and picture of la Roubine. Measured volume in the sediment trap. Date26 Jan 20099 Feb 200917 Apr Measured 20095 May 20092 Cumulative Jul 200910 Date Aug 2009 –20 0.48 Aug 2009 0.6727 Sep 200928 0.02 Sep 200922 Oct 2009 0.20 0.094 Nov Measured 2009 0.02 0.56 Dec – 2009 1.2 0.03 5 Cumulative May 2010 13 7 Feb 0.24 1.2 May 2010 2010 11 1.72 May 2010 1.4 1.5 0.61 17 1.5 16 May Jun 2010 2010 0.12 1.5 24 Aug 2010 0.01 1.42 13 1.7 Sep 0.01 2010 22 2.87 3.5 Sep 2010 27 Sep 4.1 0.01 2010 3.31 4.2 5 Oct 0.49 2010 5.6 5.6 25 Oct 0.08 2010 5.6 8.5 0.02 0.32 11.8 8.5 12.3 1.74 12.4 0.01 12.4 12.7 14.5 14.5 tours indicated in redland line. morphology, Foreground: many la small Roubinecatchment scale catchment outlet rills characterized is and located by gullies, at aBackground: steep the surrounding typical western slopes badlands bad- extremity and and with limestone scarce the ridge. vegetation. sediment The trap and the limnigraph. Figure 1. image of La Roubine. Table 3. Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | 1584 1583 erences for the period 2007–2010 highlighting the soil surface ff Observed height di Typical pattern of slope activity (e.g. ablation in orange, deposition in blue) for each changes of La Roubine catchment. The red outline indicates the boundary of the catchment. Figure 3. predefined seasons. The redvideo in outline the indicates Supplement). the boundary of the catchment (see also the Figure 2.

] y a d / m m [ y a d / m m 0 2 r e v o n o i t a t i p i c e r P

0 0 0 0 0 0 0 0

8 7 6 5 4 3 2 1 0

] m m [ n o i t a t i p i c e r p d e t a l u m u C 0 0 0 0 0 0 0 0 0 0 0 0 1 6 4 2 0 0 0 0 0 1 1 1 1 1 8 6 4 2 0 2 n a J 0 1 0 2 l u J ] m m [ ] 0 h 1 n ] / 0 s 3 o i 2 m e t t n m a [ a m a t [ ] i 1586 1585 ] J . e D 3 p i n n ] g i 3 c m o n i [ e t m a m / r [ r a p t P i a m e e r p t e i m m m [ t v c 9 i u u t n 0 e l l y r t 0 a e o o i l p 2 l s V V u m u i y n l J m i d S S e t u a e L L n T S C T D I 9 0 0 2

5 0 0 5 0 n

2 1 1 a

m [ e m u l o v d e d o r E ] J 3 0 2 8 4 . . .

1 0 0

Conceptual model describing the seasonal pattern of ablation and deposition and ] . n i m / m m [ n o i t a t i p i c e r p f o y t i s n e t n I Cumulated TLS measured volumes (in bold black line) against cumulated sediment Figure 5. quantiﬁcation of the volumes of sediment transfer at La Roubine catchment. Figure 4. trap measured volumes (thin black line)precipitation for are the years shown 2009 as and wellevent. 2010. as In the addition, the main cumulative daily precipitations events and the largest intensity