Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | cult ffi erent processes can ff ect of tide and river flow ff 1 2844 2843 erent time scales: during river floods and over the in the last decade, and it is quite unique in having ff ff , and A. Sottolichio 1 , S. Schmidt 1,* Invited contribution by I. Jalón-Rojas, recipient of the EGU Outstanding Student Poster This discussion paper is/has beenSciences under (HESS). review Please for refer the to journal the Hydrology corresponding and final Earth paper System in HESS if available. UMR5805 EPOC, CNRS-Université de Bordeaux, Pessac, France on turbidity in the fluvial estuaryhydrological is conditions detailed, (river focusing on floods, dynamicsbidity periods related shows to of changes hysteresis low-water, in loops inter-annual at changes). di Tur- Macrotidal estuaries are highlyboth tides variable and systems river as discharge.(SPM) In and result the particular of occurrence dynamics of the of a strong suspended turbidity maximum particulate influence zone matter (TMZ) of are complex and di a long-term and high-frequency monitoring of turbidity. The e transitional period between the installationpatterns, and expulsion that of the reveal TMZ. the Thesethe origin hysteresis watershed, may of be sediment, aturbidity locally tool data to resuspended bound evaluate or the thefluvial transported presence range stations. of from Hydrological of remained indicators river mud. ofare Statistics flow the persistence also on that and defined. promotes turbidity The level the long-termdischarge of TMZ decrease evolution the of on TMZ installation the these in intensification indicatorsto the of confirms evaluate the future the TMZ scenarios. influence in of tidal rivers, and provides a tool 1 Introduction to predict (Fettweis etinduce al., the 1998; formation of Mitchell the andMusiak, TMZ Uncles, (for 1994; details 2013). Talke see et Di Allen al., et al., 2009). 1980; This Dyer, 1988; highly Jay and concentrated zone plays an important Abstract Climate change and human activitiesto impact the estuaries. volume These and timing modificationstuarine of in suspended freshwater input fluvial sediment dynamics, discharges(TMZ). and are Located in expected in particular to thean the influence turbidity ideal southwest es- context maximum France, to zone thea address decrease Gironde this in issue. fluvial-estuarine mean It systems is annual has characterized runo by a very pronounced TMZ, Turbidity in the fluvial Gironde(S–W Estuary France) based on 10continuous year monitoring: sensitivity to hydrological conditions I. Jalón-Rojas Hydrol. Earth Syst. Sci. Discuss.,www.hydrol-earth-syst-sci-discuss.net/12/2843/2015/ 12, 2843–2883, 2015 doi:10.5194/hessd-12-2843-2015 © Author(s) 2015. CC Attribution 3.0 License. 1 * Award 2014 Received: 12 February 2015 – Accepted: 26Correspondence February to: 2015 I. – Jalón-Rojas Published: ([email protected]) 10 MarchPublished 2015 by Copernicus Publications on behalf of the European Geosciences Union. 5 10 15 20 25 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | ect the ff ect of cli- ff ect of floods ff , a shift to earlier snow melting ff erences in SPM concentrations of the ff 2846 2845 , the Gironde is a macrotidal fluvial-estuarine sys- was well described in many estuaries (Grabemann 2 ff ects of shifts in freshwater inflow on sediment regime are not yet ff interannual variability. tion/expulsion, concentration, persistence). The goal of this work is to analyse the response of fine sediments to hydrological The Gironde fluvio-estuarine system (SW France) is quite unique in having a long- Quite recently, considerable attention has been paid to evaluate the e 1. Document the trends of SPM at all representative2. timeAnalyse scales, the from role intratidal of to floods3. on theDiscuss sedimentary dynamic the of the influence tidal rivers. of hydrological conditions on TMZ features (installa- tem located on thea Atlantic regular coast funnel (South-West shape ofand of the France, Dordogne 75 Fig. rivers. km Tidal 1). between rivers The presentand the a narrow estuary single mouth sections sinuous shows and (about channel 300, with thespectively, weak 250 Fig. junction slopes and 1). of 200 m At the at therespectively Garonne Bordeaux, Portets Gironde 2.5 and mouth, Libourne and the re- 180 5 mean km m neap from (Bonneton and the et springzone estuary tidal al., are mouth. ranges (Fig. 2015). Thereby, are 1): The theand La Pessac uppermost tidal for Réole the limits wave for Dordogne for propagates River theagates (90 the Garonne up km upstream, from dynamic River tidal to the (95 tidal river currents kmand confluence). from weaker undergo As ebb the the an tide currents; river increasing prop- shorterfied confluence); ebb-flood and (Allen asymmetry stronger et flood (longer al.,from currents) 1980). the and mouth The the (Bonneton tidal wave et is wave al., ampli- reaches 2015), before its decaying maximum in the value fluvial at narrow about sections. 125 km 2 The study site With a total surface area of 635 km in mountainous areas and2013). more In severe addition, low-flow conditions accordingduplicated (Hendrickx to its and data surface Sauquet, of in the several agricultural regions census, of irrigated the areas watershed have between 1988 and 2000, promoting strong water storage andtuary abstractions. a This good context makes example the to Gironde evaluate es- how changes in freshwater regime may a fluctuations, based on aGironde estuary, 10 in years, order high-frequency to: database of turbidity in the fluvial over the basin induces a decrease in mean annual runo estuarine particle dynamic. term and high-frequencynounced monitoring TMZ so of far documented in water1973; the Allen quality. lower et and This central al., reaches 1980;the estuary (Allen Sottolichio largest and presents Castaing, and water Castaing, structural a 1999). deficit pro- The in Gironde France watershed (Mazzega has et al., 2014). Warming climate TMZ in the Weserhamper estuary a detailed between analysis. a TheTMZ dry transitional periods and and of of a installation its and wetare associated expulsion year, partly of mobile due although the mud to the have thein also gaps absence of estuaries not in relevant (Garel been long-term data et detailed. datasets, al., which These 2009; are limitations Contreras not so and common Polo, 2012). or long-term hydrologicalOnly variability Grabemann on and Krause sediment (2001) dynamics showed di is scarcely documented. role on estuarine morphodynamics.mud, Sediment may depositions generate from gradual accretion the ofet TMZ, bed al., termed and 2006; fluid banks Uncles (Ponteeagainst et et al., ongoing al., 2004; siltation 2006). Schrottke events to Therefore, maintain many the estuaries depth require of regular navigationmate channels. dredging changes (Fettweis2013; et Winterwerp al., and 2012) Wang, 2013;ral and Yang distribution et human al., of 2013; interventions SPM De-Jongeabstractions in (Schuttelaars et estuaries. to al., et There an 2014) al., are on increasedNevertheless numerical natu- potential the evidences e for linking freshwater up-estuarytotally transport understood (Mitchell (Uncles and et Uncles,sult 2013). al., of The 2013). seasonal longitudinally TMZ variability migration of as runo re- et al., 1997; Uncles et al., 1998; Guézennec et al., 1999). However, the e 5 5 15 20 25 10 25 20 15 10 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | erent time scales. ff (Allen, 1971). Measure- 1 − 2848 2847 (Schmidt et al., 2014). One may refer to Etcheber 1 − according to Sottolichio and Castaing (1999). Estuarine suspended sedi- 1 − In addition, two tide gauges, managed by the port of Bordeaux (Grand Port Maritime The first implemented station was Pauillac the 15 June 2004. Acquisition at Portets The tidal asymmetry toward upstream and the subsequent tidal pumping coupled ments have a dominant terrestrialand origin silts and (Fontugne are and mainly Jounneau,12 composed 1987). and of 24 SPM months, clays residence depending (45–65 time %) moves on is river the discharge comprised TMZ (Saari between along etestuary al., the 2010). and estuary Freshwater vice inflow axis: versa duringTMZ (Castaing in high and the Allen, river middle 1981). flow estuarysion There the possibly maximum is zone” related TMZ (Allen also to moves et a a al., down- sediment 1980; high secondary Sottolichio deposition dynamic steady and zone, occurs Castaing, so 1999). on called Atform the slack the water, elongated river “ero- bed patches, and with banks. concentrations In up the to channel 300 fluid gL mud can ments over a maximumimages of (Doxaran 3 et days al., (Romaña 2009) 1983;ing showed the Castaing the summer-autumn et presence period. al., ofestuarine However, 2006) the region the TMZ and are suspended in satellite largely sediments the unknown. dynamics tidal rivers in dur- this 3 Materials and methods 3.1 The multiyear high-frequency monitoring system The Gironde estuary countsMAGEST on (MArel Gironde an ESTuary), automated toquality. continuous address MAGEST the monitoring network current network, and includes called future(52 km four estuarine from sites water the (Fig. mouth);and Libourne 1): Bordeaux in Pauillac and the in Portets Dordogne the tidal inrespectively). river the The central (115 Garonne automated km estuary tidal stations from river record the (100 mouth); dissolved and oxygen, 115 temperature, km turbidity from the mouth To better identify intertidal trends,sponding we tidal calculated range. tidal-averaged In turbidity order with its to corre- avoid biased averaged values, we only consider the Turbidity was analysed as function of river flow and water height at di and salinity every ten minutescontroller at measures 1 the m water below depth theThe in surface. the turbidity In stations sensor addition, of (Endress an Bordeaux, andand ultrasonic Portets Hauser, and 9999 level CUS31-W2A) NTU Libourne. measures with values asensor between corresponds precision 0 to of about 10 6 %. gL The saturation value (9999 NTU) of turbidity de Bordeaux), record tidestations height record at each Pauillac 1Saint and to Martin) Bordeaux and 24 of h every the discharges Garonne 5on min. River of the (La Hydrometric national the Réole; Tonneins) web (Fig. Dordogne site: 1).. River Datahttp://www.hydro.eaufrance.fr/ are (Pessac; available Lamonzie 3.2 Data treatment 1 March 2005. Portets stationmental was conditions, stopped electrical/mechanical the failures 11 andmissing January sensor or 2012. wrong malfunctions data. The could Therefore severe cause thein environ- database turbidity. needed By a cleaning example for 9999errors erroneous NTU values correspond in, to these saturation laterretain values, need only but turbidity also to values to be corresponding sensor bidity removed. to corresponds A saturation. routine The to validated underThis 1.223.486 database Matlab corresponds data of was to tur- points developed aPortets, recorded to rate Libourne between of and correct 2005 Pauillac stations operating and respectively. of mid-2014. 71, 70, 70 and 57 % for Bordeaux, et al. (2011) for a descriptionof of monitoring the MAGEST system survey and program, forLanoux for the et examples technical al. of features (2013) the for trends a in detailed measured analysis of parameters; oxygenand and records. to Libourne stations began the 16 November 2004 and at Bordeaux stations the to density residual circulation developranges a and turbidity the maximum great zone length2002). (TMZ). of In The the surface high waters estuary tidal of promote theand a middle 10 highly gL estuary, SPM turbid concentrations TMZ range (Uncles between et 0.1 al., 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 | 1 1 − − for s 1 3 − 1 gL s 3 > 0.993). Previous Dordogne) is de- = + 2 ) with a period of 12 h R 2 M and Kruskal–Wallis tests). In , (Fig. 1a) strongly regulated 2 U test and ANOVA) when datasets or its T erent” datasets when these tests on tidal- . Turbidity shows a large range of values be- ff 1 2850 2849 (Fig. 3a). For this period, the inter-annual vari- − 0.5. These tests were carried out using STATA s 1 − 3 s 3 p < in winter (21 December to 20 March) and 190 m 1 − s 3 and the wetter one was 2013 with a total mean discharge 1 − s 3 (percentile 75 of river flow during the study period). A time shift was . In contrast, during the studied period (January 2005–July 2014), the 1 1 − − . River discharge varies also seasonally reaching the highest values in s s 1 3 3 − s 3 Tides are semidiurnal (the main harmonic component is the We performed statistical analysis on tidal-averaged data. We compared turbidity val- in summer (21 June to 20 September) for the Garonne River (38025 and min. 105 Between m January 2005of and tidal July ranges 2014, were the respectively minimal, aboutand mean 4.1, 6.6 and 1.9 m and maximal at 6.1 values m Bordeauxwere at (see defined Pauillac and as the about the whole 4.9,75 tidal 2.5 time cycles and series which below in tidal the Fig.Pauillac, range percentile and 3b). is 25. about Spring respectively 4.3 These and above (p25) values the neap and were percentile 5.4 tides about (p75) at 3.54.2 Bordeaux. (p25) and 4.7 Short-term variability (p75) in at turbidity Figure 4 presentsunder examples two of contrasted conditions high ofturbidity fluvial frequency patterns discharge. (10 Continuous related min) measurements to reveal data tidal cycles, recorded and to at changes4.2.1 Bordeaux in fluvial discharges. Tidal cycles The first selected datasetGaronne discharge (Fig. was 4, below 120 columntween m 740 I) and corresponds 9999 to NTU, a testifying low-water the period: presence the of the TMZ in the tidal river. It is mean annual discharge was 680 m creasing, flood events are increasingly scarcedurable. and In drought the periods period are between becomingwas the more 1000 m 1960’s and the 1980’s, the mean annual discharge the Dordogne River). of 961 m ability in freshwater inflow wasdischarge also remarkable: of the 433 driest m year was 2011 with aJanuary mean to February and themean discharges smallest were in 720 August m to September. For the studied period, tidal averages corresponding toperiod at of least time. 70 % Sinceand of management daily measured directives values averages are for wereshows often the compared. a based considered Figure on very 2 daily good compares values, agreement tidally both between turbidity the averages two and calculations ( works have defined the TMZ in the Gironde estuary by a SPM concentration ues according to stations (Portets,and Bordeaux, tidal Libourne range), and and their Pauillac),ysis period interactions of (e.g. (months, variance. station We within period), used by parametric performing test anal- ( (Allen et al., 1977; Castaing and1000 NTU. Allen, River 1981), floods which are defined corresponds by tothan a a 480 daily turbidity m increase of of about theadded Garonne discharge to higher discharge timelocated series tens for of kilometres the upstream study ofon the of the MAGEST floods, ones. velocity It since of has the hydrometric been peak stations estimated floods based are between two hydrometric stations. 4 Results 4.1 Hydrological trends The Gironde estuary drains a watershed of 81 000 km transforms (like log or cubicerwise root) met we the used normality non-parametric and homoscedasticity tests criteria. (Mann–Whitney Oth- averaged data were significantsoftware at (v. 12.1, StataCorp, 2011). by dams and reservoirs.tively The to Garonne 65 and andin the 35 hydrological Dordogne % Rivers conditions: of contributes the the respec- annual freshwater mean input. discharge Historical (Garonne data reveal drastic changes the following, we refer to “significantly di 5 5 15 20 25 10 10 20 25 15 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | er- ff 0.0001) 0.0000001) p < , during sev- 1 − p < 6 gL > 0.0018) and wet ( . As shown in the middle and 1 − p < s 3 2852 2851 1000 NTU). Only such a continuous record can capture turbidity signatures of < 0.001) higher than in February: mean values in August are 8, 27 and 54 times Figure 5 summarizes the main characteristics (mean, percentiles) of turbidity to com- Table 1 collects maximum discharge value and its associated maximum turbidity p < pare the four stationsences during between contrasted periods hydrological of periods hightions (Bordeaux, and and Portets, low tidal Libourne). river In ranges. discharges( these Di stations, are turbidity obvious in in August the ishigher significantly fluvial than sta- in Februaryat Pauillac at station, Bordeaux, in Portetsthe the year et (see central Fig. Libourne, estuary, 3). respectively. However,than turbidity turbidity By in in remains February, August contrast, when relatively is TMZ significantly moves highferent upstream. lower throughout between Turbidity ( values the are also three significantly fluvialmonths. dif- stations Summer in turbidity both values at dryand Bordeaux ( Pauillac, and reaching Libourne are valuesmost higher above than upstream 7500 at stations, NTU. Portets with In mean February, tidally-averaged turbidity turbidity is values lower of in 1322, the 401, 93 bidity spring after the flood period. Inmoderate the and middle show estuary an (Fig. inverse 3c)in trend. seasonal this This changes estuarine is are zone, more due which to isCastaing, the possibly 1999). existence related of to a a permanent mud-trapping zone TMZ (Sottolichio and a flood that often occurs for a few hours. 4.3 Long-term variability in turbidity 4.3.1 From fortnightly to seasonal variability The 10 year timerelated series to neap-spring of tide cycles tidal andturbidity averaged seasonal values trends turbidity are induced recorded by (Fig. hydrology. during Maximum the 3) spring resuspension reveals of tides, sediments since short (Allen higherlow oscillations et current al., waters velocities 1980). favour (usually The highest betweenand turbidities July f) occur during and due to November) in the upstream the displacement up of estuary the waters TMZ. (Fig. Turbidity 3e is usually minimal in noticeable that turbidity is higher than the saturation value, i.e. The second selected datasetto (Fig. 4, a column spring II) flood represents with the a turbidity signal discharge related peak at 1730 m eral hours per tidal cycle.due These to raw data deposition-resuspension illustratethroughout processes the the induced short-term tidal changes by in cycles. changes(Allen turbidity This et in pattern al., current was 1980; velocities level of already Castaing the reported above and raw in Allen, data,at showing the 1981). mid-flood more central clearly and Figure the mid-ebb, estuary 4Ic intratidal dueIn patterns: relates to contrast turbidity the turbidity peaks minimum resuspension turbidity and by valuesto the water are deposition maximum always processes. current recorded velocities. at high tide and low4.2.2 tide due Flood events (when recorded) of eachwere flood identified event in at Bordeauxbidity the and peaks time Portets were series stations. calculatedvial of Flood as signature) events river the in discharge maximum ordershown of in in to the Fig. Table consider turbidity 1, 3a. onlypared values turbidity The to the at maxima TMZ associated during low sediments maximum flood tide tur- transported values events (flu- (50 by are % river of 5 flow. the to As recorded 30 floods times present lower a com- maximum tur- lower panels, throughout river floodscurrents turbidity is are the against lowest river duringstream, flow; rising turbidity tide from values when high begin tidal tide,mid-ebbing to river increase and sediments and low are thepresent tide. transported SPM a down- peak Peculiar turbidity usually floods, peak occurs alsoresuspension specially between at processes the mid-rising and tide. first their Theseexistence after of occurrences peaks remained low-water are are mud associated periods, likely trapped with in to local the give tidal an rivers. indication of the 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 | er- ff 0.22) and Libourne = p 0.017 at Libourne) higher p < 2854 2853 0.000025 at Pauillac, p < ) were calculated per year as the number of days tidal- TMZ erences in the concentration and in the duration of the TMZ for ff 0.000001) at high tide than at low tide during this month. p < The first floods thatestuary occur show at clockwise the end (C)in Fig. of hysteresis 7). the loops This low (e.g. indicatesbed water and the f3, banks. and advection During f8, expel of the the occurrence resuspended f11, of sediments TMZ f24, the from down TMZ Table the in 1; the close fluvial f24 section, there is an 0.37). Only Pauillac and Bordeaux stations present turbidity values significantly – = p 5 Discussion The presence of TMZand (duration, better turbidity documented level, inthe hibernal Bordeaux tidal occurrence) waters. Garonne. is The more following discussion marked is5.1 dedicated to Mobile mud expulsion rhythm basedRiver on floods sediment expel dynamics the during floods TMZtuary (and as its showed associated in mobilestrong Fig. flood mud) events, from 3. along fluvial According withtoward to spring to the middle tides, Castaing sea. es- favours Floods the and also expulsiontribute Allen of transport to (1981), a the eroded part the TMZ. sediments of Identifying from repetitionon the both the the of TMZ processes watershed sedimentary is that budget important of con- analysis to tidal discuss rivers. to The the search literature role proposes ofKlein, specific the floods hysteresis-based 1984; patterns López-Tarazón of etwithin sediment al., the transport catchment 2009). in is Thewise analysed rivers relative through or (Williams, the counterclockwise). position 1989; flow In of sedimentsediments short, sediment from hysteresis anti-clockwise shapes upstream sources loops (clock- distant correspond sources,iment to while source a clockwise is transport loops the occur of database, channel when flow itself the or sediment sed- adjacent hysteresisfloods areas. recorded shapes Based at were on Bordeaux systematically the (13used analysed at MAGEST to Portets; turbidity for trace Table the the 1).of loops Only 26 local the in resuspension values order by at tidal toteresis low currents preserve shapes on tide the over the were several fluvial levels years of signal(Table follows turbidity. 1, The and a illustrated succession seasonal to for of pattern the avoid hys- in year the 2013 the impact in Garonne Fig. tidal 7). river In the case of Bordeaux: ences in turbidity at the most upstream stations of Portets ( averaged turbidity overtakes 1000for NTU the (Fig. more 6). upstream Inbetween 93 reaches. general, and Annual the 259 days; durations TMZtween years decrease is 91 2013 and and from less 171 2011, present Bordeaux days; respectively),between years (varying to 2006 33 Portets and (varying and 2008, be- 143also respectively), days; and during years to dry 2007 Libourne winters6 (varying and days (striped at 2011, bars Libourne). in respectively). Fig. The 6) TMZ like appeared in 2012 (39 days at Bordeaux and ( higher ( 4.3.2 Interannual variability The observation of theinterannual entire variability dataset in of tidally-averagedpreciate SPM turbidity marked in evidences di the a strong fluvial Gironde estuary. Figure 3 allows to ap- and 52 NTU at Pauillac, Bordeaux,tidal Portets range and is Libourne, significantly respectively. (e.g. Turbiditythan at high at low tideand Libourne, at mean all turbidity stationpared at to in high low tide August: was tide. respectively 2.7, However, for in 2.3, February Pauillac, 1.7 tidal Bordeaux, and range 1.6 Portets times does higher not com- induce significant di turbidity was always belowtively. Portets 6700 station and is 4400 lesstween documented: NTU 4730 tidal-averaged and at turbidity 6880 Bordeaux NTU maximaTMZ (years and ranged occurrence 2009 be- Libourne (Duration and respec- 2006, respectively). The durations of the the monitored years atues Bordeaux, exceeded Portets 7200 NTU andyears in Libourne. 2010 the The and years maximum 2012 2010, turbidity at 2011 val- and Libourne. 2012 By at contrast, Bordeaux during and the in year the 2008 tidal-averaged 5 5 10 15 20 25 20 25 10 15 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | , 1 er- − ff s 3 at Bordeaux and Portets 1 − s 3 2856 2855 ), turbidity increases up to about 2450 NTU with increasing 1 − s 3 because of the saturation of the turbidity sensor. For the highest 1 − s 3 1500 m > accretion of sediments thatby remain river after flood. the TMZ expulsion. ThisWinter mud is and eroded some earlyclockwise loops spring with a floods counterclockwise loop presentSome around mixed the events flood (M) show peak a (f25 hysteresisf4, in predominance curves, Fig. f17, of 7). i.e., Table 1), the or clockwiseble of 1). loop This the (M(C), pattern counterclockwise e.g. suggests loopTMZ-originated the floods (M(CC), mud, presence f1, e.g. and of also floods local the f15, sediments,predominant transport probably f18 of loop remained Ta- sediment could from remotesource. be places. The interpreted in term ofSpring proportion floods follow of counterclockwise (CC) eachf10, hysteresis sediment f28, patterns Table (e.g. 1; floodstransported f2, f26, f7, from f27, upstream f28 areas; in theexpelled. Fig. TMZ-derived 7). mud is This expected means to that be sediments totally are mainly – – Determining a precise discharge threshold of the TMZ installation per station is tricky, This first detailed study of 10 year continuous turbidity records suggests that deposi- Therefore, hysteresis curves are indicators of the presence of mobile mud in tidal due to the large variability in turbidity, more than one order of magnitude at 200 m on turbidity measurements overthe the TMZ last at 10 Portets,mainly years, on 15 reveals km the a upstream freshwater seasonalSeine, Bordeaux. inflow occurrence Scheldt, in The of Humber, major presence seebetween macrotidal of Mitchell, turbidity European the and 2013). estuaries TMZ river To (e.g.and flow depends better Weser, daily in understand (b) the the averaged Garonne(central turbidity relationships tidal estuary) as river, the a Fig. dependence function 9 onwhen of river shows the flow river the TMZ is flow tidally elongates the (3 to (a) daysediments weakest: seaward. the turbidity average). In is upper In the slightly reaches, tidal Pauillac lower Garonne butflow River, also turbidity for when increases with floods discharges decreasing push river lower suspended than about 1000 and 600 m river flow. tion of mobile mudestuary also (Allen, occurs 1971; in Sottolichio and the Castaing,to tidal 1999). mid-2014 Gironde, Two-third of as contributed the already floods to fromturbidity reported the 2005 values in progressive associated the expulsion to central of floodsdemonstrates fluid are that significantly mud floods lower from play than a Bordeaux.than those more in As in important increasing the the role TMZ, TMZ in this concentration. flushing sediment downstream 5.2 Occurrence of the TMZ inThe the prediction tidal river ofparticular TMZ interest location to improve is regional sediment a management. The challenge present work, in based the fluvial Gironde estuary and of discharges ( partly explained byspring the tides, tidal current velocities range and and thus bed the shear stress locally-available are sediment stronger, promoting stock. sedi- During respectively. At Bordeaux, the maximumrange turbidity 50–200 values m remain rather constant in the rivers, as schematized in Fig. 8, and permit to discuss its rhythm of expulsion for di in relation with itsmixed upstream and counterclockwise position: loops the already appearflood flow in f1 sediment winter (31 (Table curves 1). January For of 2006)indicating example, presented the the dominant a first mixed, local floods buttraced sediments, predominantly are a C, whereas loop distant the at originand Bordeaux simultaneous of more CC quickly sediments. expelled loop The in the TMZ-originated at uppermost mud Portets section. is less present locally ent hydrological conditions and positions along2008 the and tidal river 2009 axis. the Duringwinter the mud with wet disappeared years the from first Portetsyears floods. and 2007 In and Bordeaux contrast, 2012. inyear In mud the in the was beginning the case only of absence of expelled of the CC in year pattern May 2010, and during we marked the assume floods (Table it dry 1). was present all the A similar seasonal evolution of hysteresis also exists at Portets, but it is subtler probably 5 5 25 15 10 20 20 25 15 10 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | . 1 − 1000 NTU, > erence in sampling ff cult to judge the evo- ffi promote the TMZ expul- 1 − s 3 (spring tide) (Castaing et al., ect of tidal range is null during just before high tide for spring 1000 NTU, Fig. 12b). The dis- ff 1 1 − − < ensure the complete expulsion. 1 , daily-averaged turbidity at Bordeaux was 8 − 1 2857 2858 s − s 3 3 present the highest probabilities to promote the TMZ 1 ) during the transitional periods of installation and ex- − 1 (mean tide) and 2.5 gL s . Although these values seem lower than current turbid- − 3 1 s 1 − − 3 erent discharges. The dependence is strong when the TMZ is installed ff erences on turbidity between the periods of decreasing and increasing river flow ff A distinction in turbidity values corresponding to the periods of TMZ installation or Di Fig. 12a) or TMZcharges between expulsion 200–300 m (tidal averaged turbidity pulsion of the TMZto at Bordeaux a station. probability It of allows TMZ to installation associate (as a river defined discharge by range tidal averageinstallation. turbidity The expulsion threshold is lessof bounded first since floods the are intensity and variable. Discharges the amount greater than 350 m expulsion is then necessary toin precise tidal the rivers. Figure discharge 12 thresholdriver summarizes of flow the the (intervals distribution TMZ of of installation turbidity 30 m values as a function of local sediment inventory. We explainsediments these during hysteresis the patterns presence byThis of an agrees accumulation the with of TMZ theafter that the existence need passage a large of deposition the river TMZ. flux flow of to be mud expelled. remained at upper reaches to 50 times higher duringwere the also falling discharge recorded curve inKrause, in the the 1998), year Weser suggesting 2009. estuary an Such association (Grabemann hysteresis with et delays al., in 1997; TMZ Grabemann movements and or with the floods, when turbidity isdetail associated the to relationship sediments between these transportedof variables, from Fig. tidal the 10 range presents watershed. for turbiditypresence To as raising-falling and a expulsion neap-spring function of cyclesing the during the TMZ TMZ the at installation Bordeaux periods (a)lower in and of during 2009 when neap-spring installation, the (see tide TMZ transition periods than isteresis in during completely pattern, the Fig. installed spring-neap- already 3). (b), tide observed turbidity Dur- one.of was This in hys- other deposited estuaries, material isare during explained lower by neap (Grabemann the tides, et consolidation al., when2001). During 1997; currents the Guézennec installation velocities et of al., andafter the 1999; TMZ resuspension the the Grabemann maximum maximum and turbidity tidal Krause, crease occurs in 4–5 range sediment tidal (Fig. cycles availability at 10,the the curve upstream riverbed shift as a). river of This dischargethe the is decreases, TMZ. hysteresis promoting explained During curve the by isresuspended TMZ a and reversed expulsion gradual expelled period, (Fig. in- down following 10, estuarywere river also curve flood, and found the c), in stock Portets the decreases. station. sediments These are behaviours progressively are also notable in the fluvialintensity, estuary the (Fig. smallest 9b). turbidity In the values(decreasing tidal are Garonne, discharge) always for and same associated discharge the withdischarge). highest the This TMZ values indicates installation during thatteresis the the over TMZ the discharge expulsion transitional turbidity (increasing periodsFor curve example, of for follows installation a a and river clockwise expulsion flow of hys- of the 500 m TMZ (Fig. 11). sion and discharges above over 610 m 5.3 Has the TMZ intensified inIn the the tidal absence Garonne? of historical turbidity data in tidal rivers, it is di in the fluvial estuary at low water. On the opposite, the e ment resuspension and hence higherin turbidity. Fig. This 9a process for di is visible and quantifiable lution of the TMZ. Therepaigns. By are example only in few September limiteddeaux 1960, available SPM range dataset, concentrations between issued of 1 from surface gL2006). waters field At at cam- Portets, Bor- SPM concentration reached 2.5 gL tide, while at mean and neap tides, SPM concentrations was always bellow 1 gL Romaña (1983) presented alsomented quasi-instantaneously by helicopter turbidity along measurements the imple- in estuary the for years 3 days 1981–1982. of At contrasteda low-water hydrological TMZ maximum conditions appeared value 10 km of upstream 1.7 gL Portets reaching ity trends, the extremely limited measurement periods and the di points prevent to draw conclusions about a possible TMZ intensification in the tidal 5 5 10 10 15 25 20 15 20 25 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | LW 0.78, = 0.75) as 2 1965 and R = at Portets; ( 3 2 1 − R ( s HW Hm , as an indicator 3 3 LW 10 max × , especially since the 90’, and Volume LW max . However, the sum of Volume max ) of the TMZ were compared to three 0.90). This is because the water volume TMZ = 2 R 2859 2860 in 1969 and 1977 and 30 3 at Bordeaux (Fig. 12) and 160 m at Bordeaux since 1960 to 2013 (Fig. 15). There is 1 and increasing Duration Hm ect can favour this intensification. As the TMZ is con- − ff s 3 ect of changes in topography and in river flow on the HW 3 ff HW 10 × cient in flushing the TMZ in the central estuary, even to the ffi is not correlated to Turbidity LW in both stations is well correlated to the Duration : the duration of low water, calculated as the number of days per year reached 25 and the Volume improves the correlation ( LW TMZ LW HW HW : the river water volume passed during the presence of the TMZ at the : the river water volume passed during the previous high water period, i.e., ect of river discharge is assumed to be a major factor in the longitudinal shift HW TMZ ff river flow is below 250 m these values were evaluated as theis mean installed critical in river two flows stations. above which the TMZ between the last expulsion and the reinstallation of the TMZ; considered station. In summary, the duration of the low water period mainly determines the TMZ du- The e There is also a good correlation between Turbidity The 10 year dataset of the MAGEST stations of Bordeaux and Portets was used to 1. Duration 2. Vol 3. Vol a trend in decreasingwhich Volume has changedtributed the to TMZ climate characteristics. changein The and the human decrease years activities 1963 in (Mazzega andand river 1976 et Volume the al., discharge low 2014). water is For period at- example, lasted respectively only 20 and 9 day, suggested by Sottolichio etumented al. yet. (2011). The The combinedTMZ importance e evolution of needs be these analysed changes by is numerical modelling. not doc- 6 Conclusions The high-frequency and long-termon turbidity suspended monitoring sediment provides dynamics detailedtime in informations the scales fluvial and Gironde hydrological estuary conditions. over Tide, a river wide range flow of and sediment stock (mobile ration, and the freshwaterHigh volume river during flows high are water e periods the TMZ concentration. of the TMZ. However morphologicaltribute changes to (natural the or TMZ anthropogenic) intensification mayby (Winterwerp also and con- amplifying Wang, 2013; tidal De-Jonge asymmetry et al., and 2014), hence enhancing trapping of fine sediments, as of turbidity level) andhydrological the characteristics: duration (Duration during very wet summers is enough to expel partly the TMZ. coastal waters, and expelder higher to quantity discuss of the mobilethe mud, potential Duration as evolution seen of in the Sect. TMZ 5.2. in In the or- last decades, we calculated 1976. Considering the relationship betweenassume TMZ that and the hydrology TMZ (Figs.Furthermore, is 13 an and at accumulation 14), present e we morecentrated persistent and and persistent, turbid thethe than required next 40–50 TMZ years water to ago. volume be to more pronounced. expel it increases, promoting and Volume shown in Fig. 13.a more Years with persistent TMZ aof than long low years river low like flow. 2013 water or period 2010 like characterized 2011, by shorterFig. 2006 periods 14a). or Years 2007 with have a numerous less and turbid large TMZ. floods Thisseen (like can in be 2008, Sect. 5.2) the 2009 and result1981). and of of The 2013) the the Volume further present total flushing expulsion of of the mobile previous sediment TMZ (as (Castaing and Allen, evaluate the impact of hydrologicalin conditions the on tidal TMZ Garonne. (turbidity The level annual and maximum persistence) turbidity value (Turbidity river. However, the remarkable dependence of turbidity(Fig. to 9) river suggests flow in that the themay fluvial lead decreasing section to trend an in upstream river intensification flow of in the the TMZ. last decades (Sect. 4.1) The Duration 5 5 25 10 20 15 25 20 10 15 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | ort” ff ects of ff , actually retained 1 ciently the TMZ and − s ffi 2 ect of morphological changes. erent hydrological and climate ff ff erent scales, which reveal the local or ff 2862 2861 respectively, showing the need to a higher “water e 1 − s 3 I. Jalón-Rojas thanks the Agence de l’Eau Adour-Garonne (AEAG) and Finally this work will be useful to improve the calibration of numerical models cou- The extrapolation of hydrological conditions suggests an intensification of the TMZ Gironde, C. Roy. Acad. Sc. Paris, 273, 2429–2431, 1971. onto the adjacent continental shelf, Mar. Geol., 14, 47–53,in 1973. the GirondeAcademic Estuary, Press, France, New York, in: 63–81, 1977. Estuarine Processes, 2nd edn., edited by: Wiley, M., tides on mixing and suspended26, sediment 69–90, transport 1980. in macrotidal estuaries, Sediment. Geol., Allen, G. P., Sauzay, G., and Castaing, P.: Transport and deposition of suspended sediment Acknowledgements. the Aquitane Region for thecially financial supported support by of her theDEST PhD following grant. (Syndicat organisms: The MIxte AEAG MAGEST pour (Agence network(Syndicat le de is Mixte Développement finan- l’Eau Durable d’Etudes Adour-Garonne); de et SMID- Interdépartemental l’ESTuaire d’Aménagement de de de la la la Gironde); Dordogne);(Communauté SMEAG Garonne); EDF; EPIDOR Urbaine GPMB (Etablissement de Public (Grandde Bordeaux); Port Gironde); Conseil Maritime Ifremer; Régional de CNRS;the Aquitaine; Bordeaux); Université OASU CUB CG-33 de (Observatoire Bordeaux. (Conseil Aquitaind’Observation The des Général du authors Sciences Littoral thank AQUItain) de program. alsotion l’Univers) MAGEST program the through is DYNALIT. a support the contribution SOLAQUI of to (Service the CNRS observa- References Allen, G. P.: Déplacements saisonniers de la lentilleAllen, de G. “crème P. and de Castaing, vase” P.: Suspended dans sediment transport l’estuaire from de the la Gironde estuary (France) Allen, G. P., Salomon, J. C., Bassoullet, P., Du Penhoat, Y., and De Grandpré, C.: E scenarios (naturals and anthropogenic), including the e pling hydrodynamics and suspendedallow evaluate sediment the transport. turbidity Numerical in the simulations upper will estuary for di by the SMEAG is far tooproblems low (dissolved to oxygen prevent consumption, the pollutant installation accumulation of . the . . TMZ, ). and the subsequent to expel the TMZ. Twothe hydrological duration indicators of of low the water TMZvolume periods intensity passing as have indicator before been of and defined: theturbidity during persistence level. of the Higher the presence water TMZ, volumeto of and contributes expel water the higher to TMZ quantity move as moreThe of indicator existence e remained of of mobile mobile mud, the mudturbidity-discharge resulting TMZ during hysteresis in and patterns less after concentrated the over TMZ. TMZ di presence is confirmed through uate future scenarios. Thisder can be to very address useful theThe to global estimate water change management of strategies impactsgreat in discharge as or- interest thresholds Garonne to 2050 ofnetwork,). (www.garonne2015.fr TMZ local the installation public SMEAG,Garonne and is authorities. to expulsion in By ensure isplan-de-gestion-detiage-garonne-ariege.html charge example, a). also to water a Their of maintain quality criteria partnerfrom upstream favourable a to dams of to release are minimum the the ecosystems waterfrom discharge levels of (http://www.smeag.fr/ this stocks MAGEST dissolved level work oxygen in of that Bordeaux the the waters. It discharge appears threshold, below 100–110 m occurrence in the fluvial Gironde during the last decades and could be used to eval- mud patches) induce large variabilityics on related turbidity levels. to Suspendedcesses tidal sediment in dynam- cycles the (semidiurnal tidal1977). section, and The as fortnightly) TMZ previously follows occurrence describedlogical the in in conditions. the River the same discharge tidal lower cyclicconcentration is estuary rivers of pro- a (Allen is the key et very TMZ variable al., promoting sensitive for and the to the its installation installation, changes associated and expulsion in expulsion mobile250 and of hydro- mud. and the River at TMZ discharge at least thresholds Bordeaux 350 m have been delimited, remote location of theover river sediment floods source. can Moremobile serve particularly, mud. as these an hysteresis indicator patterns of the rhythm of downstream expulsion of 5 5 10 15 20 25 10 25 20 15 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | 2864 2863 erent time scales of suspended matter dynamics in the ff and to storms, in: Physics of Estuaries and Coastal Seas, edited ers, M., Balkema, Rotterdam, the Netherlands, 83–92, 1998. ff ff ocean by a macrotidalmatter estuary: from evidence the from Gironde measurements system, of Estuar. carbon Coast. isotopes Shelf in S.,The 24, organic autonomous 377–387, Simpatico 1987. system fority real-time monitoring: continuous water-quality examples and of331–341, current, doi:10.1007/s00367-009-0147-5 veloc- application 2009. in three Portuguese estuaries, Geo-Mar.pulses Lett., in freshwater 29, runo by: Dronkers, J. and Sche Weser Estuary, Estuaries, 24, 688–698, 2001. in the Tamar (U.K.),doi:10.1006/ecss.1996.0178 1997. and Weser (F.R.G.) 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J.: EstuarinePontee, sediments N., in macrotidal Whitehead, estuaries: P., future and re- Hayes, C.: The e 5 5 15 30 10 20 25 10 15 20 25 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | plus f (NTU) Hysteresis (NTU) Hysteresis max max T T 2011 2012 2013 2010 2009 2006 2007 2008 2868 2867 (NTU) Hysteresis (NTU) Hysteresis max max BordeauxT Portets BordeauxT Portets ) ) 1 1 − − s s 3 3 max max Q (m Q (m 31.03.2013 2510 – – – – 08.11.201207.01.2012 1890 1390 – – – – – – – – Date 30.04.2009 2870 – – – – 11.12.2007 127022.04.2008 – 3130 – – – – – – – Date 10.12.200503.01.2006 865 938 – – – – – – – – f24f25 07.12.2012f26 21.01.2013 834 09.03.2013 3460 1150f27 914f28 01.06.2013 1075 20.06.2013 4020 175 1980 768 C M 1304 CC CC CC – – – – – – – – – – f15f16 16.01.2010f17 07.02.2010 1880 02.04.2010 1410f18 1070 06.05.2010 747 1770 358f19 471 24.12.2010f20 971 M(CC) 1480f21 24.02.2011 No 18.03.2011 1090 M(C) 2150 425 – M(CC) 1598 – – 152f22 474 Mf23 01.05.2012 M – 23.05.2012 1760 3110 No – CC 335 – – 963 (C) M 723 CC 164 – CC – – – – f11f12 03.11.2008f13 06.12.2008 1450f14 25.01.2009 1830 13.04.2009 4750 2200 1950 476 1578 – C CC CC 993 – – – M(CC) 203 – – CC f3f4 13.02.2007f5 27.02.2007 2140f6 18.04.2007 1600f7 03.05.2007 1210 1460 28.05.2007 953 414 1730 – C 349f8 1794f9 M(C) 08.01.2008 19.01.2008 1120f10 – 2180 C CC 975 28.05.2008 292 1008 2640 835 495 – 400 M C M – No CC CC – 313 – 795 – M CC – f1f2 31.01.2006 12.03.2006 1820 4160 989 1446 M(C) CC 908 1326 CC CC Continued. Discharge and turbidity characteristics of flood events for the period 2005–mid 2014 in Table 1. Table 1. the tidal Garonne River (Bordeaux and Portets stations). Flood events were numbered by a number according toterclockwise; Fig. [M] 3. mixed; Hysteresis [No]clockwise loops no [M(CC)] were trend. predominance classified were Mixed specified. as: loopsto Floods [C] facilitate with without the clockwise; turbidity a interpretation record [CC] clear of were coun- clockwise the included hysteresis [M(C)] succession. or counter- Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | the estuary with its main tributaries. Red location map (SW France), the grey area (b) (a) ). 2 2870 2869 R cient ( ffi Comparison of tidally-averaged turbidity and daily-averaged turbidity for Bordeaux The Gironde fluvial-estuarine system: station showing the correlation coe Figure 2. Figure 1. shows the watershed of Garonne and Dordogne; circles locate the MAGEST stations; blue squares indicate the hydrometric stations. Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Relationships between (c) turbidity and water level (dotted (b) Libourne stations. Red dotted lines represent the 2872 2871 river flow, and (e) (a) tidal range recorded at Bordeaux tide gauge; and tidally-averaged Bordeaux and (b) (d) Pauillac, Daily mean flow of the Garonne River and the Dordogne River showing the river (c) Examples of 48H raw data of low-pass filtered data performed with running averages in order to highlight the turbidity trends. flood events of Table 1; turbidity at Figure 4. lines) at Bordeaux for twois contrasted hour, hydrological while conditions. turbidity Theturbidity and mean and water time water level step level were of records recorded river of flow the each middle 10 min. panels. Figure 3. (a) Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | 2874 2873 Mean (red cross), median (red bars), percentiles 25–75 (blue bars) and minimum– Duration of the TMZ presence per year at the three tidal rivers stations. Striped bars Figure 6. designate the duration of thein TMZ the when years it 2005, appears in 2008, winter: 2011 17, and 18, 2012 9 at and Bordeaux; 39 6 days days respectively in the year 2012 at Libourne. Figure 5. maximum (black bars) valuesof of February tidally-averaged and August) turbidity andranges depending correspond the on to tidal values the range above (TR) seasonof the in the percentile (months each entire 75 TR MAGEST and dataset station. below the of High percentile each and 25, station. low respectively, tidal Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | 2876 2875 Relationship between discharge and turbidity and corresponding hysteresis patterns Schematic representation of suspended sediment dynamics in tidal rivers associated erent types of hysteresis (clockwise, anticlockwise, mixed) during river floods. ff for the successive floodsthe occurring TMZ, since in the August departure, 2013. in December 2012, and the return of to the di Figure 8. Figure 7. Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | presence and (b) as a function of 3 days : values corresponding (b) (b) installation, (a) 2878 2877 and daily-averaged turbidity (a) : values were classified in function of tidal range (TR). Turbidity as a function of tidal rage (2 days running averages) for three neap-spring- (a) Tidally-averaged turbidity expulsion of the TMZ. erentiated. ff Figure 10. neap cycles (see the cycles in Fig. 3) during a period of (c) averaged river flow for thesentation). MAGEST stations of Pauillac,to Bordeaux the and Porters periods (log-log ofdi repre- installation (blue diamonds) and expulsion (green square) of the TMZ were Figure 9. Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | intervals of river flow during 1 − s 3 2880 2879 Examples of clockwise Discharge/Turbidity hysteresis curves during the transition Mean (red cross), median (red bars), percentiles 25–75 (blue bars) and percentiles Figure 12. 9–91 (black bars) values of tidally-averaged turbidity per 30 m the installation and expulsion of the TMZ. Figure 11. periods of installation and expulsion of the TMZ (see these periods in Fig. 3). Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | during (a) due to the number of at Portets station. 1 max − the presence of the TMZ. s 3 + 2882 2881 at Bordeaux station and 160 m 1 during the previous wet period − s 3 (b) Turbidity maxima of the TMZ as a function of the water volume passed: Duration of the TMZ presence as a function of the number of days per year where Portets is not considered as it was not possible to estimate Turbidity the previous wet period; and missing data. Figure 14. Figure 13. the river flow was below 250 m Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | 2883 Evolution of the duration of low water period and the water volume during high water Figure 15. periods between 1960 and 2013);eaufrance.fr/ (calculated from red discharge lines data represent available the on 5http://www.hydro. days running averages in order to highlight the trends.