Chantha Oeurng

Sabine Sauvage
email: sauvage@cict.fr

José-Miguel Sánchez-Pérez

Dynamics of suspended sediment transport and yield in a large agricultural catchment, southwest France

Keywords: agricultural catchment, temporal variability, sediment transport, hysteretic loops, fl ood events

The dynamics of suspended sediment transport were monitored continuously in a large agricultural catchment in southwest France from January 2007 to March 2009. The objective of this paper is to analyse the temporal variability in suspended sediment transport and yield in that catchment. Analyses were also undertaken to assess the relationships between precipitation, discharge and suspended sediment transport, and to interpret sediment delivery processes using suspended sediment-discharge hysteresis patterns. During the study period, we analysed 17 fl ood events, with high resolution suspended sediment data derived from continuous turbidity and automatic sampling. The results revealed strong seasonal, annual and inter-annual variability in suspended sediment transport. Sediment was strongly transported during spring, when frequent fl ood events of high magnitude and intensity occurred. Annual sediment transport in 2007 yielded 16 614 tonnes, representing 15 t km -2 (85% of annual load transport during fl oods for 16% of annual duration), while the 2008 sediment yield was 77 960 tonnes, representing 70 t km -2 (95% of annual load transport during fl oods for 20% of annual duration). Analysis of the relationships between precipitation, discharge and suspended sediment transport showed that there were signifi cant correlations between total precipitation, peak discharge, total water yield, fl ood intensity and sediment variables during the fl ood events, but no relationship with antecedent conditions. Flood events were classifi ed in relation to suspended sediment concentration (SSC)-discharge hysteretic loops, complemented with temporal dynamics of SSC-discharge ranges during rising and falling fl ow. The hysteretic shapes obtained for all fl ood events refl ected the distribution of probable sediment sources throughout the catchment. Regarding the sediment transport during all fl ood events, clockwise hysteretic loops represented 68% from river deposited sediments and nearby source areas, anticlockwise 29% from distant source areas, and simultaneity of SSC and discharge 3%.

Introduction

Suspended sediment transport has been identifi ed as the main global mechanism of fl uvial sediment transport. [START_REF] Walling | Solutes in river systems[END_REF] estimated that the global amount of suspended sediment transport is about 3•5 times higher than that of solutes, while the bedload represents only a small component of fl uvial transport. Suspended sediment transport from agricultural catchments to stream networks is responsible for aquatic habitat degradation, reservoir sedimentation and the transport of sediment-bound pollutants (pesticides, particulate nutrients, heavy metals and other toxic substances). Quantifying and understanding the dynamics of suspended sediment transfer from agricultural land to watercourses is essential in controlling soil erosion and in implementing appropriate mitigation practices to reduce stream suspended sediment and associated pollutant loads, and hence improve surface water quality downstream [START_REF] Heathwaite | A tiered risk-based approach for predicting diffuse and point source phosphorus losses in agricultural areas[END_REF]. Appropriate assessment of suspended sediment yield is of particular importance for the purpose of catchment management and therefore interest in the dynamics of suspended sediment transport has increased in recent decades (Alexandrov et al., 2003a).

So far, many studies on suspended sediment transport dynamics have been conducted in small-scale agricultural catchments of less than 100 km 2 [START_REF] Gao | Suspendedsediment transport in an intensively cultivated watershed in southeastern California[END_REF][START_REF] Lefrançois | Suspended sediment and discharge relationship to identify bank degradation as a main sediment source on small agricultural catchments[END_REF][START_REF] Estrany | Suspended sediment transport in a small Mediterranean agricultural catchment[END_REF][START_REF] Deasy | Pathways of runoff and sediment transfer in small agricultural catchments[END_REF]. However, little attention has been paid to sediment dynamics in large agricultural catchments, where there are many diffi culties such as spatiotemporal variability in climatic conditions, land use and soil texture. Moreover, fi eld measurements and collection of data on suspended sediment are generally diffi cult tasks, rarely achieved over long timescales in large catchments. Understanding of the catchment-scale dynamics of suspended sediment transport is limited by this lack of data and by the high spatial and temporal variability of sediment output, which in turn is associated with various factors such as precipitation characteristics, the connectivity of sediment sources varying with physical settings and human activities, changes in contributing areas and hydraulic boundary conditions [START_REF] Schmidt | Sediment output and effective discharge in two small high mountain catchments in the Bavarian Alps, Germany[END_REF].

Analysis of the relationships between sediment transport, precipitation and discharge characteristics can help in understanding the factors and processes determining sediment responses [START_REF] Zabaleta | Factors controlling suspended sediment yield during runoff events in small headwater catchments of the Basque Country[END_REF][START_REF] Nadal-Romero | Temporal distribution of suspended sediment transport in a humid Mediterranean badland area: The Araguás catchment, Central Pyrenees[END_REF]. The study of hysteretic loops in a single fl ood event also helps to better interpret the spatial distribution of catchment sediment sources within a drainage system [START_REF] Peart | Recent Developments in the Explanation and Prediction of Erosion and Sediment Yield[END_REF][START_REF] Dickinson | A Program of Monitoring Sediment Transport in North Central Luzon, the Philippines, Erosion and Sediment Transport Monitoring Programs in River Basins[END_REF][START_REF] Kostrenzewski | Transport of suspended load in the Parseta River during the fl ash fl ood of June 1988, Poland[END_REF][START_REF] Lefrançois | Suspended sediment and discharge relationship to identify bank degradation as a main sediment source on small agricultural catchments[END_REF].

The Gascogne area, southwest France, located in highly contrasting zones with various climatic infl uences (the mountain region, the Atlantic and the Mediterranean), has been dominated by anthropogenic activities, particularly intensive agriculture, causing severe erosion in recent decades. This poses a major threat to surface water quality, since sediment transport within the catchment is the main factor in transporting contaminant sediments. Therefore, the 1110 km 2 Save catchment located in the Gascogne area was selected for this study.

The objective of this study was to analyse the temporal variability in suspended sediment transport and yield in a large agricultural catchment. Analyses were also undertaken to assess the relationships between precipitation, discharge and suspended sediment transport, and to interpret sediment delivery processes using suspended sediment-discharge hysteresis patterns.

Materials and Methods

Study area

The Save catchment, located in the area of Coteaux Gascogne, is an agricultural catchment of 1110 km 2 and has its source in the piedmont zone of the Pyrenees Mountains (southwest France) at an altitude of 600 m, joining the Garonne River after a 140 km course with a linear shape and an average slope of 3•6‰ (Figure 1).

This catchment lies on detrital sediments from the Pyrenees Mountains. It is bound on the east by the Garonne River, on the south by the Pyrenees and on the west by the Atlantic Ocean [START_REF] Echanchu | Géochimie des eaux du basin de la Garonne. Transfers de matières dissoutes et particulaires vers l'océan atlantique[END_REF]. Throughout the Obligocene and Miocene, this catchment served as an emergent zone of subsidence that received sandy, clay and calcareous sediments derived from the erosion of the Pyrenees Mountains, which were in an organic phase at that time. The heterogeneous materials were of low energetic value and produced a thick detrital formation of molasse type in the Miocene. From the Pleistocene onwards, the river became channelized, cutting broad valleys in the molasse deposits and leaving terraces of coarse alluvium [START_REF] Revel | Erosion due to cultivation of calcareous clay soils on the hillsides of south west France. I. Effect of former farming practices[END_REF]. The substratum of the catchment consists of impervious Miocene molassic deposits.

In this area, which has been cultivated since the Middle Ages, mechanical erosion by ploughing has had a greater impact on downward soil displacement than water erosion, with a major impact on surface relief, mainly on levelling and soil distribution [START_REF] Guiresse | Erosion due to cultivation of calcareous clay soils on hillsides in south-west France. II. Effect of ploughing down the steepest slope[END_REF]. Very weak erosion has led to the development of calcic luvisols (UN FAO soil units) on the tertiary substratum and local rendosols on the hard calcareous sandstone beds. On hillsides with very gentle slope, the calcic cambisols have been subjected to moderate erosion. Non-calcic silty soils, locally named boulbènes, represent less than 10% of the soil in this area. Calcic soils are dominated by a clay content ranging from 40% to 50%, while non-calcic soils are silty (50-60%). The upstream part of the catchment is a hilly agricultural area mainly covered with pastures and small amount of forest, while the lower part is fl at and devoted to intensive agriculture, mostly pasture and a rotation of corn, sunfl ower and winter wheat (90% of the area used for agricultural purposes) (Figure 1).

The climatic conditions are oceanic, with annual precipitation of 700 to 900 mm and annual evaporation of 500 to 600 mm. The dry period runs from June to August (the month with maximum defi cit) and the wet period from October to May [START_REF] Ribeyeix-Claret | Agriculture et Environnement en Gascogne Gersoise. Erosion du sol et pollution diffuse par phosphore[END_REF]. The hydrology regime of the catchment is mainly pluvial, i.e. regulated by rainfall [START_REF] Echanchu | Géochimie des eaux du basin de la Garonne. Transfers de matières dissoutes et particulaires vers l'océan atlantique[END_REF], with maximum discharge in May and low fl ows during summer (July to September).

The catchment substratum is relatively impermeable due to its high clay content. Consequently, the river discharge is mainly supplied by surface and subsurface runoff, and groundwater is limited to alluvial and colluvial phreatic aquifers. The maximum discharge for the long-term period is 210 m 3 s -1 (14 June 2000), while summer discharge sustained by a nested canal at the catchment head is 0•004 m 3 s -1 at a point 100 km downstream since water is used for irrigation along its course. The mean monthly 31-year discharge is 6•29 m 3 s -1 .

Instrumentation and sampling method

A Sonde YSI 6920 (YSI Incorporated, Ohio, USA) measuring probe and Automatic Water Sampler (ecoTech Umwelt-Meßsysteme GmbH, Bonn, Germany) with 24 bottles of one litre were installed at the Save catchment outlet (Larra bridge) in January 2007. The Sonde was positioned near the bank of the river under the bridge, where homogeneity of water movement was properly considered for all hydrological conditions. The pump inlet was placed next to the Sonde pipe. The dissolved oxygen content, electrical conductivity, nitrate, pH, turbidity and water level were recorded at 10-minute intervals.

The values of the different parameters in water were detected by sensors on the Sonde YSI and the data then transferred to the ecoTech memory. We programmed the Sonde to pump water when there were water level variations, Δx (in centimetres), ranging from 10 cm to 30 cm, based on seasonal hydrological conditions for both the rising and falling stage. This sampling method provided high sampling frequency during storm events. Manual sampling was also carried out using a two litre bottle lowered from the Larra bridge, near the Sonde position, at weekly intervals when water levels were not remarkably varied. During the study period, several technical problems such as sensor derivation and crushing led to occasional diffi culties in measuring continuous water turbidity. We missed continuous measurements for some fl ood periods (15% of the total study period), but we carried out intensive manual sampling, particularly during the fl ood events, in order to get reliable estimates of suspended sediment load during the missing time.

Data source, treatment and analysis

Hydro-climatological data Rainfall data from fi ve meteorological stations in the catchment (Figure 1) were obtained from Meteo France. The mean total rainfall depth and intensity in the whole catchment were derived using the Thiessen Polygon method. Total annual rainfall during the study period in 2007 and 2008 amounted to 603 and 787 mm, respectively. Data on hourly discharge were obtained from CACG (Compagnie d'Aménagement des Coteaux de Gascogne), which is responsible for hydrological monitoring in the Gascogne region.

The discharge was plotted by the rating-curve in which water level was measured hourly by pressure at Larra gauging station in the form of a rectangular weir (length 12 m), then transferred by teletransmission. The mean total water yield of the two study years, 2007 and 2008, was 98 mm and 120 mm, respectively. These values are below the long-term mean value of 136 mm for the period 1985-2008. A year was considered dry if the annual water yield was below the long-term value. Within this context, both years can be classifi ed as dry but the fi rst year 2007 is very dry, since no major fl oods occurred in autumn. During the whole study period, between January 2007 and March 2009, there were 20 fl ood events and we had a reliable total of 17 recorded fl ood events with continuous measurement of turbidity (Figure 2). Mean discharge during the fi rst year was 3•45 m 3 s -1 and 4•23 m 3 s -1 Suspended sediment concentration (SSC) and turbidity data processing During the study period, we obtained 246 water samples through our manual and automatic sampling methods. These water samples were analysed in the laboratory to determine suspended sediment concentration (SSC) using a nitrocellulose fi lter (GF 0•45 μm) and drying at 40 °C for 48 hours. Volumes of water ranging from 150 to 1000 ml were fi ltered according particle load. SSC data determined from samples collected manually and by automatic sampling over a range of hydrological conditions and turbidity levels throughout the study period were used to generate a calibration equation between turbidity and SSC data.

The relationship between SSC and turbidity is generally a power function SSC = a(Turbidity) n [START_REF] Gippel | Potential of turbidity monitoring for measuring the transport of suspended solids in streams[END_REF][START_REF] Lewis | Turbidity-controlled sampling for suspended sediment load estimation[END_REF]. However, in this case, the SSC-turbidity relationship was polynomial because of the light weight of the particles. Figure 3 illustrates the SSC-turbidity relationship for the Save catchment (best fi tted with a second-order positive polynomial equation SSC = 0•0033(Turbidity) 2 -0•0582(Turbidity) + 67•601, where SSC is measured in mg l -1 and turbidity in NTU (nephelometric turbidity units). Continuous SSC data were derived from this equation for the turbidity range between 0 and 800 NTU, beyond which turbidity saturation occurred. For values of turbidity higher than 800 NTU (5% of fl ood periods) and during missing continuous measurements of turbidity, a linear interpolation method was applied between two close sampling points to construct the continuous SSC series.

Calculation of fl uxes

High frequency SSC records were derived from the relationship between SSC and turbidity. The sediment loads were calculated as the product of the hourly discharge and the corresponding SSC:

F Q NTU i i i i = ⋅ × × = ( ) < < ( ) = 0 0864 0 800 SSC SSC f NTU SSC Interpolation SSC C SSC i i - + [ ] ⎧ ⎨ ⎩ 1 1 ;
where F is daily suspended sediment fl ux (in tonnes per day); Q i is the hourly water discharge (in m 3 s -1 ), SSC i is the corresponding suspended sediment concentration (in mg l -1 ) and 0•0864 is the conversion factor. Accumulated suspended sediment fl uxes (monthly to annual load) were calculated as the sum of fl uxes during the period considered.

Statistical analyses

To assess the relationships between precipitation, discharge and sediment transport, statistical analyses were performed. A database was generated for each fl ood event and contained four groups of variables: antecedent conditions to the fl ood conditions, precipitation, discharge and suspended sediment during the fl ood. Variables used in the characterization of fl oods are summarized in Table I. Antecedent conditions are described by accumulated precipitation one day before the fl ood (P1d), fi ve days before (P5d), and ten days before (P10d), by beginning basefl ow (Qb) before the fl ood and by the antecedent fl ood corresponding to the fl ood (Qa). Precipitation that caused the fl ood was characterized by mean total precipitation (Pt) and hourly maximum intensity of the precipitation (Imax). Total water yield (Wt) during the fl ood was expressed by the total water depth of the event, total duration of the event (Td), and mean (Qm) and maximum discharge (Qmax) corresponding to the time of rise to reach the peak discharge (Tr). The discharge speed to reach the peak fl ow during a fl ood event is defi ned by fl ood intensity, If [If = (Qmax -Qb)/Tr]. Sediment load was expressed as the mean SSC (SSCm) derived from the SSC-turbidity relationship, the maximum SSC of the event (SSCmax) and the total suspended sediment yield transported during the fl ood event (SST). The relationships between all these variables were investigated using statistical techniques (Pearson correlation matrix) in the STATISTICA package.

Analysis of SSC-discharge dynamics

Relationships between SSC and discharge during fl ood events were studied using continuous measurements. We use the term 'fl ood' to mean a complete hydrological event with rising and recession limbs. The typology of the SSC-discharge relationship during fl oods generally depends on the simultaneity or interval between the SSC peak and the discharge maximum. Typology interpretation is not unique, but varies according to the study context. We used a typology with three classes, inspired by [START_REF] Williams | Sediment concentration versus water discharge during single hydrologic events in rivers[END_REF].

In the fi rst class, peaks of SSC and discharge arrive simultaneously. The SSC-discharge plot is symmetrical between rising and falling limbs, with little or no hysteresis. In the second class, the SSC peak arrives before the discharge peak and the relationship between SSC and discharge describes a clockwise hysteretic loop. In the third class, the SSC peak arrives later than the discharge peak and the SSC-discharge relationship describes an anticlockwise hysteretic loop [START_REF] Williams | Sediment concentration versus water discharge during single hydrologic events in rivers[END_REF]. Typology interpretation can also depend on other fl ood characteristics. We complemented this typology with an analysis of the range of SSC versus discharge during the fl ood. The SSC maxima depended simultaneously on stream transport capacity and discharge, and also on the availability of particles to be mobilized by the discharge [START_REF] Lefrançois | Suspended sediment and discharge relationship to identify bank degradation as a main sediment source on small agricultural catchments[END_REF]. We focused on SSC maxima versus discharge to compare the variation in particle availability during the different fl ood events. During recession fl ow, a decrease in discharge leads to sediment deposition. We focused on SSC at the discharge maxima to compare the deposition capacity of the stream during the falling stage of different fl ood events.

Results

General description of fl ood events analysed

During the study period, 17 fl ood events were analysed (Figure 3): six events occurred in winter (January to March), fi ve in spring (March to June) and six in autumn (October to December). The longest event (event 16; 351 hours) occurred on 27 January 2009 with total rainfall depth 74•54 mm, reaching an hourly peak discharge of 116•6 m 3 s -1 . This event is noteworthy since there was a 10-year return period and it represented a major fl ood event in winter 2009. During this event, sediment transport reached 23 374 tonnes. However, the event that the maximum sediment transport (event 10) took place in early June 2008, when the fl ood intensity was the highest of all the events observed during the study period. A total of 41 750 tonnes of sediment were transported during this extreme episode. Table II summarizes the main characteristics of fl ood duration, time of rise, fl ood intensity, precipitation, discharge and SSC associated with the fl oods analysed, which are described in detail later.

• The duration of the fl ood events varied between 105 and 351 hours, with an average value of 191 hours (Table II). Seven events were longer than average duration, while 10 events were shorter. The event on 1 June 2008 took the shortest time (16 hours) to reach the peak, while the general rising time of fl oods in our observed events varied from 16 hours (minimum) to 84 hours (maximum), with an average value of 41 hours. Sediment transport in early June 2008 showed the most extreme value observed during the study period (41 750 tonnes). • The maximum discharge during fl ood events varied from 6•75 m 3 s -1 to 112•60 m 3 s -1 , with an average peak value of 33 m 3 s -1 (median = 27•57 m 3 s -1 ; standard deviation (SD) = 25•05 m 3 s -1 ). Rainfall amount varied from 7•46 mm to 74•54 mm (median = 20•25 mm; SD = 17•18 mm). Average rainfall intensity in the whole catchment ranged between 1•32 and 17•23 mm h -1 (median = 3•97 mm h -1 ; SD = 3•72 mm h -1 ). • Peak SSC during fl ood events varied from 158 mg l -1 , recorded on 13 February 2007, to 15•74 g l -1 on 1 June 2008 (median = 691 mg l -1 ; SD = 565 mg l -1 ). A signifi cant quantity of suspended sediment was transported during fl oods, mainly in spring season when fl ood magnitude was signifi cant. The sediment load ranged from 177 to 41 750 tonnes (median = 1642 tonnes; SD = 5820 tonnes), indicating that 65% of each event transported more than 1000 tonnes. • In terms of the typology described in the previous section, 68% of total sediment transport during all fl ood events demonstrated clockwise hysteresis, 29% anticlockwise and 3% simultaneity of SSC and discharge.

Temporal variability in suspended sediment transport

Within-event sediment variability So far, due to differences between the catchments, there is only partial understanding of the internal dynamics of suspended sediment variability, even though many studies have been conducted on SSC-discharge relationships for individual events [START_REF] Mossa | Sediment dynamics of the lowermost Mississippi River[END_REF][START_REF] Williams | Sediment concentration versus water discharge during single hydrologic events in rivers[END_REF][START_REF] Sichingabula | Factors controlling variations in suspended sediment concentration for single-valued sediment rating curves, Fraser River, British Columbia, Canada[END_REF][START_REF] Rovira | Temporal distribution of suspended sediment transport in a Mediterranean basin: The Lower Tordera (NE Spain)[END_REF]. The scatter in SSC reported is attributed to the exhaustion of sediment available in the channel or to differences in sediment availability at the beginning and end of the fl ood [START_REF] Walling | Recent Development in the Explanation and Prediction of Erosion and Sediment Yield[END_REF][START_REF] Steegen | Sediment export by water from an agricultural catchment in the Loam Belt in central Belgium[END_REF][START_REF] Steegen | Correction factors for estimating suspended sediment export from loess catchments[END_REF][START_REF] Hudson | Event sequence and sediment exhaustion in the lower Panuco Basin, Mexico[END_REF]. As a result, SSC and discharge during a fl ood often present hysteretic behaviour, related to a time lag between peak discharge and sediment transport. For clockwise hysteresis, SSC on the rising limb of a storm hydrograph is higher than that measured at equivalent fl ows on the falling limb [START_REF] Rovira | Temporal distribution of suspended sediment transport in a Mediterranean basin: The Lower Tordera (NE Spain)[END_REF]. For instance, in event 16 (27 January 2009), the 50 m 3 s -1 discharge of the rising limb contained 1817 mg l -1 , while the 50•28 m 3 s -1 discharge of the falling limb discharge contained only 881 mg l -1 . The beginning of the discharge wave is supplied by easily available sediment in the channel and nearby source areas. As SSC reaches its maximum value before peak discharge, it is obvious that reduction in the amount of available sediment occurred on the falling limb. Moreover, an increase of portion of basefl ow on the falling limb may cause dilution of SSC. In the case of anticlockwise hysteresis, the SSC for a given discharge on the falling limb is higher than for the same discharge on the rising limb [START_REF] Salant | Suspended sediment dynamics at high and low storm fl ows in two small watersheds[END_REF]. As can be seen from fl ood event 4 (25 March 2007), the same discharge of 9•59 m 3 s -1 contained 251 mg l -1 for the falling limb and 71 mg l -1 for the rising limb. The suspended sediment transport in the Save catchment was also infl uenced by sediment exhaustion, as can be observed from three successive events which appear to show a progressive exhaustion of sediment supply (events 13, 14 and 15) and a decrease in sediment availability in the channel. These successive events were recorded on 26 November 2008 (Qmax = 27•57 m 3 s -1 ; SSCmax = 1613 mg l -1 ), 6 December 2008 (Qmax = 19•77 m 3 s -1 ; SSCmax = 569 mg l -1 ), and 14 December 2008 (Qmax = 26•74 m 3 s -1 ; SSCmax = 501 mg l -1 ).

Seasonal, annual and inter-annual variability

In terms of the temporal dynamics in suspended sediment transport, the Save catchment showed strong seasonal, annual and inter-annual variability during the study period (Figure 4). These seasonal variations can be analysed by considering seasonal climatic variations and weather forcing. Sediment yield in both years increased sharply in spring and slightly during summer and autumn. As can be seen in Figure 4, sediment transport from June to December 2007 nearly remained constant due to the absence of major fl ood events. The slope breaks of the sediment and discharge curve in early June 2008 showed drastically different conditions, since the sediment delivery during these extreme fl ood events reached 50 000 tonnes (63% of the annual sediment budget). Suspended sediment transport in autumn 2007 (October to December) was only 2% of annual sediment load, whereas in autumn 2008 it was 13% of annual load. This was because there was only a minor fl ood event (Qmax = 6•75 m 3 s -1 ) in autumn 2007, while many fl ood events reaching peak discharge of 27•57 m 3 s -1 occurred during autumn 2008. The sediment was strongly transported during spring (March to June), a period when there were many fl ood events with strong fl ood intensity and high amplitude occurring together with tillage operations in this agricultural catchment. In spring 2007, 79% of annual sediment load was transported, while spring 2008 accounted for 70% of annual sediment load. During summer, there were no major rainfall events that could cause fl oods and therefore sediment transport in summer 2007 and 2008 represented only 2% and 9% of the annual budget, respectively. During the study period there was signifi cant seasonal variability, with sediment transport during autumn

Relationships between precipitation, discharge and sediment variables

In order to assess the relationships between precipitation, discharge and suspended sediment transport, which might explain the hydrological and sedimentological responses during the fl ood events in the Save catchment, a Pearson correlation matrix and factorial analysis that included all the above-mentioned variables (Table III) were generated for the 16 fl ood events. Event 10 (1 June 2008) was excluded from the matrix because it was an extraordinary event.

Table III shows the relationships between precipitation, discharge and suspended sediment transport in the Save catchment. Total precipitation (Pt) showed signifi cant correlations with mean discharge (Qm) (R = 0•83), maximum discharge (Qmax) (R = 0•87), total water yield (Wt) (R = 0•85), maximum suspended sediment concentration (SSCmax) (R = 0•76) and suspended sediment transport (SST) (R = 0•89). The discharge variables, Qm and Qmax, were well correlated with total rainfall (Pt), but antecedent discharge (Qa) and basefl ow (Qb) had only slight correlations with total precipitation (Pt).

Maximum suspended sediment (SSCmax) and suspended sediment transport (SST) showed strong relationships with total precipitation (Pt). SSCmax was well correlated with fl ood intensity (If) (R = 0•72) and fl ood duration (Fd) (R = 0•72). SST was found to be signifi cantly correlated with total water yield (Wt) (R = 0•97) and discharge variables (Qm and Qmax). Weaker correlations were found between sediment variables and maximum rainfall intensity (Imax). Suspended sediment did not show any relationship with antecedent fl ow (Qa, Qb) or antecedent precipitation (P1d, P5d and P10d). Taking all these data into account, principal component analysis (PCA) was performed. This analysis (Figure 5) grouped in the fi rst factor Fd, Qm, Qmax, Pt, Wt and SST, explaining 46•70% of the variance. In the second factor, If, SSCm, SSCmax and Imax were grouped, explaining 16•83% of the variance. In a 1-2 factorial plane, total sediment yield during fl ood events (SST) showed a strong relationship with these two factors, although the correlation was better with factor one, and no relationship was found with antecedent conditions to the fl ood event. The results indicate a direct response of the catchment to rainfall events in terms of discharge and suspended sediment transport during fl ood events.

SSC-discharge hysteresis patterns

The behaviour of suspended sediment and changes in SSC during fl ood events are not only a function of energy conditions, i.e. sediment is stored at low fl ow and transported under high fl ow conditions, but are also related to variations in sediment supply and sediment depletion. These changes in sediment availability result in so-called hysteresis effects [START_REF] Asselman | Suspended sediment dynamics in a large basin: the River Rhine[END_REF].

The relationship between discharge and SSC was analysed for all the individual fl ood events observed in the Save catchment. In general, we found highly variable relationships between discharge and sediment response during different seasonal fl ood events (Figure 6). The different patterns of hysteresis express various probable sources of sediment spreading throughout the catchment. Seven of 17 fl ood events recorded during the study period showed clockwise hysteretic loops (class 2) (Figure 6b), while seven events displayed anticlockwise hysteretic loops (class 3) (Figure 6c). Two events presented class 1 behaviour (Figure 6a), indicating that SSC and discharge arrived simultaneously. However, one event (event 10, which occurred in early June 2008), showed complex mixing of clockwise and anticlockwise loops (Figure 6d) when there were multiple peaks of discharge together with multiple peaks of SSC during a fl ood event, coinciding with extreme rainfall intensity.

Discussion

Temporal variability of suspended sediment transport and yield

The analysis of the SSCs collected at different temporal scales (within events, seasonal and annual variability) in the Save catchment provides an insight into the characteristics of the suspended sediment load variability in a large agricultural catchment in southern Pyrenees region. Increasing SSC on the falling limb during fl oods may be related to sources of relatively more available sediment with lower soil aggregate stability. Such sediment sources are located at the far end of the area contributing to surface runoff, and thus sediment reaches the stream mainly during the falling limb. This may be due to soil particles, eroded within the catchment, not reaching the stream during previous rainfall-runoff events and settling on the slope, before being transported by surface runoff into the stream during the next event. The variability in event sediment transport during successive peaks of similar magnitude is infl uenced by sediment exhaustion effects. The Save catchment shows a pattern similar to that observed in other catchments in the Mediterranean region, e.g. in the Tordera catchment [START_REF] Rovira | Temporal distribution of suspended sediment transport in a Mediterranean basin: The Lower Tordera (NE Spain)[END_REF]). An example is the progressive reduction in suspended load at different temporal scales (within fl oods and within multiple-peak events, during a succession of events, and seasonally) related to the exhaustion of sediment availability. Alexandrov et al. (2003b) observed that due to a sediment exhaustion effect, SSC levels during secondary fl oods in the Nahal Eshtemoa basin (Israel) were lower than those observed during a primary fl ood. This can be attributed to the role of in-channel sediment storage, which controls suspended sediment transport during inter-fl ood periods of stable fl ow (Smith and Dragovich, 2008). Therefore, after a period of relatively high sediment transport (supply-rich fl oods), sediment becomes less and less available from the channel (exhaustion phenomenon) and sediment concentrations recorded during successive fl oods events are consequently lower [START_REF] Walling | Suspend sediment and solute response characteristics of River Exe, Devon, England[END_REF]. The total specifi c sediment yields in 2007 and 2008 amounted to 15 t km -2 and 70 t km -2 , respectively. This may be linked to the different characteristics of fl ood events, such as fl ood duration, rainfall intensity and fl ood amplitude, and other controlling factors related to soil conditions and agricultural practices in the Save catchment during both study years. The fi rst hydrological year of the study (2007) was very dry, since there were very few rainfall events during autumn and less sediment was transported during fl oods with low duration and fl ood magnitude. Flood intensity is also a main factor to determine sediment transport. The maximum fl ood intensity in 2007 was only 1•27 m 3 min -2 , while one event in spring 2008 exhibited the maximum fl ood intensity of 2•48 m 3 min -2 , yielding a suspended sediment load of 63% of annual sediment yield in 2008. Sediment was slightly transported by basefl ow during summer (2% of annual load in 2007, 9% in 2008). Although there were some rainfall events in summer during the study period, soil conditions were dry and little runoff was generated, as large amounts of rainfall infi ltrated into the soil.

The annual total specifi c sediment yields in the Save catchment (15-70 t km -2 ) are within the range of specifi c yields reported for the Garonne River, which vary from 11 to 74 t km -2 yr -1 [START_REF] Coynel | Erosion mécanique des sols et transferts géochimiques dans le bassin Adour-Garonne[END_REF], but lower than the values for Mediterranean basins of the Iberian Peninsula (100-200 t km -2 yr -1 ) reported by [START_REF] Walling | Erosion and Sediment Yield: A Global Overview[END_REF]. Located in the same Gascogne region as the Save catchment, with the same climatic conditions, geology (molasse) and agricultural land use, the 1330 km 2 Baïs catchment and the 970 km 2 Gers catchment have specifi c sediment yields (63 and 41 t km -2 yr -1 , respectively) that are of a similar order of magnitude to that of the Save catchment [START_REF] Maneux | Assessment of dam trapping effi ciency from water residence time: Application to fl uvial sediment transport in the Adour, Dordogne, and Garonne River basins (France)[END_REF]. In comparison with other French catchments of similar size in the Mediterranean area, the Save values are higher than those reported for the 1100 km 2 Dronne upstream catchment (8-13 t km -2 yr -1 ) but similar to those in the 1172 km 2 upstream catchment at Ariège (57-59 t km -2 y -1 ) [START_REF] Veyssy | Transfers des matières organiques des basins versants aux estuaries[END_REF]. The Save values are also comparable to those of the 900 km 2 Tordera catchment (50 t km -2 yr -1 ) in northeast Spain [START_REF] Rovira | Temporal distribution of suspended sediment transport in a Mediterranean basin: The Lower Tordera (NE Spain)[END_REF], but much lower than the 414 t km -2 yr -1 reported for the 445 km 2 Isábena catchment (southern central Pyrenees). However, the latter catchment is highly erodible and experiences frequent fl oods [START_REF] López-Tarazon | Suspended sediment in a highly erodible catchment: The River Isábena (southern Pyrenees)[END_REF].

Sediment delivery process using SSC-discharge hysteresis SSC-discharge hysteresis patterns are the outcome of the complex interaction of processes and controls that determine event discharge and catchment erosion and sediment transport. These patterns refl ect the combination of sediment supply from dominant sources with the capacity of fl ows to transport the supplied sediment to the catchment outlets. Sediment delivery processes can be interpreted using SSCdischarge hysteresis patterns. For class 1, only two events were recorded in late winter and mid-autumn (events 2 and 13). This class is classically interpreted as the mobilization and transport of particles with unrestricted availability during the fl ood for the range of discharge concerned [START_REF] Jansson | Determining sediment source areas in a tropical river basin, Costa Rica[END_REF]. So far, there is little literature describing the sediment sources from this class. However, according to [START_REF] Hudson | Event sequence and sediment exhaustion in the lower Panuco Basin, Mexico[END_REF], at low discharge sediment could come from fi ne deposited sediment, whereas at high discharge sediment could originate from coarser deposited sediment and/or from bank and channel hydrological erosion. When discharge is principally linked to surface runoff, sediment could originate from remote areas, particularly via surface soil erosion [START_REF] Lefrançois | Suspended sediment and discharge relationship to identify bank degradation as a main sediment source on small agricultural catchments[END_REF]. Topsoil sources are therefore likely to dominate drain fl ow sediment in agricultural catchments [START_REF] Foster | Changing suspended sediment and particulate phosphorus loads and pathways in underdrained lowland agricultural catchment; Herefordshire and Worcestershire, UK[END_REF].

Clockwise hysteretic loops (class 2), which were observed in seven events in the Save catchment, generally occurred in late winter and mid-autumn, particularly in November when early seasonal rainfall started. During the periods when sediment was stored in the channel and distributed within the catchment tributaries, these sediments were transported only after there were fl ood events with suffi cient transport capacity. Therefore, this class could be explained by the transport of nearby available sediment and deposited sediment within the riverbed during the previous season. This can be also classically interpreted as the mobilization of particles with restricted availability during the fl ood event for the range of discharge concerned. Particles are believed to come from the removal of sediment deposited in the channel, with decreasing availability during the event [START_REF] Lenzi | Suspended sediment load during fl oods in a small stream of the Dolomites (northeastern Italy)[END_REF][START_REF] Steegen | Sediment export by water from an agricultural catchment in the Loam Belt in central Belgium[END_REF][START_REF] Jansson | Determining sediment source areas in a tropical river basin, Costa Rica[END_REF][START_REF] Goodwin | The temporal and spatial variability of sediment transport and yields within the Bradford Beck catchment, West Yorkshire[END_REF]. Particle production by erosion cannot resupply the decrease in sediment stock deposits. The hypothesis of an important contribution by hillslope soils can be dismissed. Various patterns of hysteresis have been reported previously in the literature, with clockwise hysteretic loops being the most common [START_REF] Walling | Assessing the accuracy of suspended sediment rating curves for a small basin[END_REF][START_REF] Klein | Anti-clockwise hysteresis in suspended sediment concentration during individual storms[END_REF][START_REF] Williams | Sediment concentration versus water discharge during single hydrologic events in rivers[END_REF][START_REF] Jansson | Determining sediment source areas in a tropical river basin, Costa Rica[END_REF][START_REF] Hudson | Event sequence and sediment exhaustion in the lower Panuco Basin, Mexico[END_REF][START_REF] Rovira | Temporal distribution of suspended sediment transport in a Mediterranean basin: The Lower Tordera (NE Spain)[END_REF]. [START_REF] Klein | Anti-clockwise hysteresis in suspended sediment concentration during individual storms[END_REF] assumed that clockwise hysteresis occurred when the sediment source area is the channel itself or an adjacent area located close to the catchment outlet, with runoff triggering the movement of sediment accumulated in the channel during the previous seasons and with little or no contribution from the tributaries. [START_REF] López-Tarazon | Suspended sediment in a highly erodible catchment: The River Isábena (southern Pyrenees)[END_REF] also emphasized that the clockwise phenomenon was found preferentially when rainfall was mostly located near the catchment outlet. For instance, in the Save catchment, this was the case for clockwise fl ood events in early autumn (events 1 and 12) and late winter (events 7, 16 and 17). For event 6, which happened on 11 December 2007 (late autumn), clockwise fl ood events were also found, since there was only one fl ood event during this season and sediment was apparently transported from deposited sediment along the channel. The role of agricultural practices in downstream areas of the Save catchment, which are mainly dominated by a crop rotation of corn, sunfl ower and winter wheat, was also a key determinant of sediment sources. Tillage activities here are generally carried out in April and September. Soil was eroded and then transported to the stream networks near the catchment outlet, characterized by a clockwise pattern when there were fl ood events reaching the capacity to bring those sediments to the outlet. [START_REF] Heidel | The progressive lag of sediment concentration with fl ood waves[END_REF] and [START_REF] Williams | Sediment concentration versus water discharge during single hydrologic events in rivers[END_REF] reported that for small streams, the maximum SSC usually occurs prior to peak discharge. However, other authors have suggested that clockwise hysteresis refl ects a progressive decline in sediment availability during the fl ood event or an early-stage depletion of suspended sediment [START_REF] Van Sickle | Supply-based models of suspended sediment transport in streams[END_REF][START_REF] Klein | Anti-clockwise hysteresis in suspended sediment concentration during individual storms[END_REF][START_REF] Lenzi | Suspended sediment load during fl oods in a small stream of the Dolomites (northeastern Italy)[END_REF][START_REF] Sayer | Pipefl ow suspended sediment dynamics and their contribution to stream sediment budgets in small rainforest catchment, Sabah, Malaysia[END_REF]. These explanations are considered to be unlikely in the Save catchment, as they imply events related to high water volume associated with the hydrological response across the entire catchment [START_REF] Nadal-Romero | Temporal distribution of suspended sediment transport in a humid Mediterranean badland area: The Araguás catchment, Central Pyrenees[END_REF]. In contrast, the arrival of clean water from the forested headwater area in the Save catchment could partly dilute fl ow to reduce SSC but not total transport.

Regarding class 3, anticlockwise hysteretic loops take place when sediment sources are widely spread throughout the catchment and sediment is not rapidly exhausted. Due to the very long thin shape of the Save catchment, sediment transport from upstream and far tributaries may take a long time to reach the catchment outlet. This type of hysteretic loop was mainly found in the Save catchment in spring and late autumn, when there were high fl ood magnitudes with the suffi cient capacity to transport sediments from distant areas of the upstream catchment to the outlet. As the upstream part of the catchment is a hilly agricultural area mainly dominated by pastures and a small amount of forest cover (Figure 1), the source of sediment could be distant sediments, hillslope soil erosion and upstream areas [START_REF] Braisington | Suspended sediment dynamics in small catchments in the Nepal Middle Hills[END_REF][START_REF] Goodwin | The temporal and spatial variability of sediment transport and yields within the Bradford Beck catchment, West Yorkshire[END_REF][START_REF] Orwin | The evidence for paraglacial sedimentation and its temporal scale in the deglacierizing basin of Small River Glacier, Canada[END_REF]. Tillage in upland pasture areas of the Save catchment is generally performed in April, a period of strong rainfall causing the major fl oods in the spring season. Thus sediment yield could be strongly transported from far upstream in an anticlockwise pattern. Suspended sediment can also originate from processes with slow dynamics (slower than the discharge rise), e.g. banks may collapse when bank material is suffi ciently saturated. [START_REF] Williams | Sediment concentration versus water discharge during single hydrologic events in rivers[END_REF] suggested that anticlockwise hysteresis results from at least one of the following causes: (i) a difference between the fl ood wave velocity and the mean fl ow velocity that carries the suspended sediment, (ii) a high soil erodibility in combination with a prolonged erosion process during the fl ood, and (iii) a seasonal distribution of sediment production within the drainage basin. Although there was no serious investigations of bank collapse along the Save river, bank erosion was taken into account in supplying sediment sources, particularly during major fl oods with high fl ood intensity, e.g. the event in early spring 2008 (If = 2•48 m 3 min -2 ).

Conclusions

The dynamics of suspended sediment transport and sediment yield were analysed at different temporal scales with high resolution through two years of data collection. Analysis of the variability in SSC at different temporal scales (event, seasonal, annual and inter-annual) monitored at catchment outlet (Larra sampling station) provided insights into the characteristics of suspended sediment transport in the Save catchment in southwest France. The temporal dynamics of suspended sediment transport in the Save catchment showed strong withinevent, seasonal, annual and inter-annual variability. The sediment was strongly transported during spring, when many fl ood events with high magnitude and intensity occurred and tillage work was performed. Sediment transport in 2007 yielded 16 614 tonnes (85% of annual load transport during fl oods for 16% of annual duration), while the 2008 yield was 77 960 tonnes (95% of annual load transport during fl oods for 20% of annual duration).

Statistical analyses revealed a signifi cant correlation between total precipitation, peak discharge, total water yield and sediment variables during the fl ood events, but no relationship with antecedent conditions. These results indicate a direct response of the catchment to rainfall events, discharge and fl ood intensity, as well as suspended sediment transport during the fl ood events. The variability over different temporal scales of discharge and SSC resulted in different hysteretic patterns. Two classes (classes 2 and 3) were the most common types observed in the Save catchment. Clockwise hysteresis (class 2) mainly occurred in late winter and mid-autumn, particularly in November, while anticlockwise hysteresis (class 3) was mostly found in spring and late autumn. The hysteretic shapes obtained for all fl ood events refl ected the distribution of probable sediment sources throughout the catchment. Of sediment transport during all fl ood events, clockwise hysteretic loops represented 68% from river deposited sediments and nearby sources areas, anticlockwise 29% from distant source areas, and simultaneity of SSC and discharge 3%.

With only two years of recordings, it is diffi cult to characterize inter-annual variability in a large agricultural catchment like the Save due to strong seasonal and annual hydrological variations. Therefore, modelling work should be conducted to characterize long-term variability in fl ux and to study past soil erosion following the identifi cation of critical sediment source areas in the catchment.

Figure 1 .

 1 Figure 1. Location, land use and topographical maps of the Save catchment. This fi gure is available in colour online at wileyonlinelibrary.com/journal/espl

Figure 2 .

 2 Figure 2. Hourly discharge (in m 3 s -1 ) within 17 recorded fl ood events between January 2007 and March 2009.

  during the second year. These values are below the mean annual discharge of the long-term discharge (1985-2008), which was 4•79 m 3 s -1 . Maximum instantaneous discharge during fl oods ranged from 6•75 m 3 s -1 (observed on 11 December 2007) to 112•60 m 3 s -1 (27 January 2009).

Figure 3 .

 3 Figure 3. Relationship between recorded turbidity (in NTU) and suspended sediment concentration, SSC (in mg l -1 ) at Larra sampling station.

  in bold typeface and minimum values shown in bold/italic typeface.

  2007 being signifi cantly different from that in the corresponding season in 2008. Similar variations were observed in winter 2007, 2008 and 2009. Sediment transport during fl ood events in winter 2009 was strongly signifi cant due to the high magnitude of two fl ood events (event 16 and 17), which yielded 30 241 tonnes, equivalent to 182% and 39% of mean total annual load in 2007 and 2008, respectively. The sediment transport in 2007 accounted for 16 614 tonnes (85% of annual load transport during fl oods for 16% of annual duration) while transport in 2008 amounted to 77 960 tonnes (95% of annual load transport during fl oods for 20% of annual duration). Although there was only a non-signifi cant difference of 18% between total water yield in 2007 (98 mm) and 2008 (120 mm), the sediment yield in 2008 was 4•7 times higher than in 2007. In one extremely eroding event in early June 2008 (event 10), sediment transport contributed 63% of the total annual sediment budget.

Figure 4 .

 4 Figure 4. Cumulative water yield (in millimetres) and sediment transport (Mt) during (a) 2007 and (b) 2008.

Fd

  is signifi cant at p < 0•01 level for bold numbers and p < 0•05 for italics.

Figure 5 .

 5 Figure 5. Location of variables included in the correlation matrixes in the factorial plane of principal component analysis. The fi gure is available in colour online at wileyonlinelibrary.com/journal/espl

Figure 6 .

 6 Figure 6. Examples of different types of hysteresis observed in the Save catchment during the study period (2007-2009).

Table I .

 I Names, abbreviations and units for the variables used to characterize fl ood events and to perform Pearson correlation matrix and factorial analysis

		Abbreviation	Unit
	Antecedent conditions
	Accumulated precipitation 1 day before the fl ood	P1d	mm
	Accumulated precipitation 5 days before the fl ood	P5d	mm
	Accumulated precipitation 10 days before the fl ood	P10d	mm
	Basefl ow before the fl ood	Qb	m 3 s -1
	Antecedent maximum discharge	Qa	m 3 s -1
	Flood event conditions
	Flood duration	Fd	hours
	Time of rise (time to reach maximum discharge)	Tr	hours
	Total precipitation during the fl ood	Pt	mm
	Maximum rainfall intensity of the fl ood	Imax	mm h -1
	Flood intensity	If	m 3 min -2
	Total water yield	Wt	mm
	Mean discharge	Qm	m 3 s -1
	Maximum discharge	Qmax	m 3 s -1
	Mean suspended sediment concentration	SSCm	mg l -1
	Maximum suspended sediment concentration	SSCmax	mg l -1
	Total suspended sediment yield in tonnes	SST	tonnes

Table II .

 II General characteristics of all fl ood events observed in the Save catchment during the study period (January 2007 to March 2009) a

	Rainfall	intensity	(mm h -1
	Total	rainfall	(mm)
	Flood	intensity	(m 3 min -2 )
	Time of	rise	(hours)
	Flood	duration	(hours)
			Season
		Flood event	date
			Event

Table III .

 III Pearson correlation matrix among all variables (n = 16)

	Fd	Tr	If	Pt	Imax	P1d	P5d	P10d	Qa	Qb	Qm Qmax	Wt	SSCm SSCmax	SST

Acknowledgements-This research was fi nancially supported by a doctoral research scholarship from the French government in cooperation with Cambodia. This study was performed within the framework of the GIS-ECOBAG, Programme P2 "Garonne Moyenne" and "IMAQUES", and supported by funds from CPER and FEDER (grants n°OPI2003-768) of the Midi-Pyrenees Region and Zone Atelier Adour Garonne (ZAAG) of PEVS/CNRS347 INSUE. We sincerely thank the CACG for discharge data and Meteo France for meteorological data. The authors would like to thank Gael Durbe and ECOLAB staff for access to the site and assistance with monitoring instruments. The authors would also like to acknowledge helpful comments from Alexandra Coynel and Eric Maneux and particularly from two anonymous referees whose comments greatly improved the manuscript.


Rafika Thabet
email: rafika.thabet@inp-toulouse.fr

Elyes Lamine
email: elyes.lamine@univ-jfc.fr

Hervé Pingaud
email: herve.pingaud@univ-jfc.fr

Development of a Risk-aware Business Process Modeling Tool for Healthcare processes

Keywords: Risk-aware Business Process Management, Healthcare Risk Management, BPRIM, Modeling Method, Healthcare process

Healthcare organizations are environments of high management complexity and are subject to risk. Indeed, risk management is one of the most relevant aspects put forward in the literature which highlights the necessity to perform comprehensive analyses intended to uncover the root causes of risks. However, the healthcare sector still suffers from a lack of attention in this context, especially with regard to the establishment of risk management and process-oriented management, which is the motivation for the study described in this paper. In light of these observations, it would be essential for healthcare organizations to explore new risk management approaches. Contributing to this field, the present paper applies a risk-aware business process management method to work out a systemic methodology to study risks impacting healthcare processes. This framework aims to improve healthcare organizations' maturity towards risk management. A case study related to the management of potential risks in a given healthcare process shall illustrate the usage of the developed framework.

I. INTRODUCTION

Risk management is an important aspect of healthcare practices due to the complex interaction of multiple potential hazards, and the possibility of serious adverse events if these are not prevented or controlled [START_REF] Institute | Guide to the Project Management Body of Knowledge[END_REF].

In the healthcare field, risk management can be defined as a set of activities and methods that is used to identify circumstances which put patients at risk of being harmed and to act to prevent or control those risk for improving quality in healthcare [START_REF] Senna | A systematic literature review on supply chain risk management: is healthcare management a forsaken research field?[END_REF]- [START_REF] Liu | Improved FMEA methods for proactive healthcare risk analysis[END_REF]. The aim is to both improve safety and quality of care for patients and to reduce the costs of such risk for healthcare providers [START_REF] Senna | A systematic literature review on supply chain risk management: is healthcare management a forsaken research field?[END_REF], [START_REF] Ferdosi | Risk management in executive levels of healthcare organizations: insights from a scoping review (2018)[END_REF].

In this way, performing risk management in the healthcare field is particularly difficult due to the highly dynamic, complex, and multi-disciplinary nature of healthcare processes. In this context, several healthcare risk management methods exist [START_REF] Senna | A systematic literature review on supply chain risk management: is healthcare management a forsaken research field?[END_REF]- [START_REF] Malicki | Patient safety in external beam radiotherapy, results of the accirad project: Current status of proactive risk assessment, reactive analysis of events, and reporting and learning systems in europe[END_REF] and are used in healthcare organizations. However, none of the currently available methods consider the complexity of risk, its strong connection to the healthcare process activities, and the influence of organizational and human factors. Following these findings, healthcare organizations must investigate new risk management techniques that take into account all relevant concepts to risk, as well as the dependencies that exist within the healthcare process activities.

To fill the shortcoming of existing approaches, in this work, we suggest studying the potential of a Risk-aware Business Process Management (R-BPM) approach [START_REF] Thabet | Ingénierie dirigée par les modèles d'un pilotage robuste de la prise en charge médicamenteuse[END_REF]- [START_REF] Suriadi | Current Research in Risk-Aware Business Process Management -Overview, Comparison and Gap Analysis[END_REF] to manage risk related to the complex healthcare processes.

This paper is structured as follows. First, Section II provides an overview of the risk management methods in the healthcare field and a short overview of the related works on R-BPM. In Section III, we present the adopted framework. The Section III-C is dedicated to illustrate the use of this framework for studying several potential risks which might arise from a given sterilization process. Finally, the paper is closed with a conclusion and some directions for future work.

II. BACKGROUND A. Risk management in the healthcare field

The risk management (RM) in hospitals includes processes, methods, tools and activities used in handling risks in patient care to increase the safety of patients and those involved in their care [START_REF] Senna | A systematic literature review on supply chain risk management: is healthcare management a forsaken research field?[END_REF], [START_REF] Ferdosi | Risk management in executive levels of healthcare organizations: insights from a scoping review (2018)[END_REF], [START_REF] Amantea | A simulation-driven approach in risk-aware business process management: A case study in healthcare[END_REF]. A RM process has to describe the procedure for handling risk and consists of: risk identification, risk analysis, risk assessment and risk treatment [START_REF] Amantea | A simulation-driven approach in risk-aware business process management: A case study in healthcare[END_REF].

In the literature, various risk management methods have been proposed to assist healthcare professionals in ensuring patient safety [START_REF] Senna | A systematic literature review on supply chain risk management: is healthcare management a forsaken research field?[END_REF]- [START_REF] Malicki | Patient safety in external beam radiotherapy, results of the accirad project: Current status of proactive risk assessment, reactive analysis of events, and reporting and learning systems in europe[END_REF]. However, studies and literature reviews we have conducted on some of them reveal their limitations.

A comparative study of the most relevant risk assessment methods currently used in the healthcare domain can be found in Table I. This comparison is carried out in accordance with the following criteria: (1) Process based: whether the method describes in which system process or activity the risk occurred;

(2) Reactive/Proactive: whether the method is reactive or proactive. Proactive methods are based on a systematic data collection. Reactive methods apply a systematic investigative technique to analyze adverse events that aims to achieve a comprehensive identification of both systemic aspects as well as individual causes; (3) Qualitative/Quantitative: whether the method follows qualitative and/or quantitative analysis; (4) Causes ranking: whether the method classifies different risk causes; (5) Causes chronology: whether the method provides a chronological reconstruction of risk causes; [START_REF] Thabet | Ingénierie dirigée par les modèles d'un pilotage robuste de la prise en charge médicamenteuse[END_REF] As shown on Table I, only three out of seven methods attempted to incorporate system processes or activities where the causes occurred in the analysis process. However, among these approaches, none of these methods provides a graphical representation to represent system activities and relationships between multiple risk causes. In fact, working with graphs enables a wide range of analysis to be covered. In addition, none of them qualifies the dynamics of risk, as well as to the detailed explanation of the relationships that generate risk.

In summary, as shown on Table I, none of these methods is able to satisfy all the following aspects:

• Identify and classify potential risks;

• Deal with the complex healthcare processes at the correct level by describing all related and collaborative activities composing the process; • Provide a complete description of risk causes;

• Understand the strong relationships between risks and activities of healthcare processes; • Consider the organizational and human factors which intervene the risk occurrence; • Produce a dynamic map ranking all risks;

• Produce a graphical representation of process activities and relationships between multiple risk causes; • Provide a modeling tool that ensures the easy use to manage risks related to healthcare processes.

As a result, in order to improve patient safety, healthcare organizations must implement an effective detection policy, as well as prevention and management of hazards associated with complicated healthcare processes. To address this problem, we recommend looking into new research domains, particularly the integrated management of risk and business processes.

B. Risk-aware Business Process Management Methodology

For several years, there has been a strong interest in combining the two traditionally separated fields of risk management and business process management into a single concept known as Risk-aware Business Process Management (R-BPM) [START_REF] Thabet | Ingénierie dirigée par les modèles d'un pilotage robuste de la prise en charge médicamenteuse[END_REF]- [START_REF] Suriadi | Current Research in Risk-Aware Business Process Management -Overview, Comparison and Gap Analysis[END_REF]. This integration improves the efficiency of risk detection, assessment, and mitigation in relation to business processes. The relevance of this integration has been acknowledged by the scientific community [START_REF] Neiger | Integrating risks in business process models with value focused process engineering[END_REF], industry guidelines [START_REF] Neiger | Integrating risks in business process models with value focused process engineering[END_REF], and a number of studies [START_REF] Thabet | Ingénierie dirigée par les modèles d'un pilotage robuste de la prise en charge médicamenteuse[END_REF]- [START_REF] Suriadi | Current Research in Risk-Aware Business Process Management -Overview, Comparison and Gap Analysis[END_REF].

Business Process-risk management -Integrated Method (BPRIM) [START_REF] Lamine | Bprim: An integrated framework for business process management and risk management[END_REF] is one of the important approaches in the R-BPM context. The method suggests an integrative approach with three components: (1) A conceptual unification between the business process conceptual-model proposed by the ISO/DIS 19440 and a risk conceptual-model, (2) a modeling language extending the ISO/DIS 19440 constructs with risk modeling constructs, and (3) A synchronized lifecycle that forms a procedure for integrated business process and risk management.

III. PROPOSED FRAMEWORK

In this work, we adopt a framework based on the BPRIM method, called e-BPRIM. The latter consists on the digitalization of BPRIM. The e-BPRIM framework, with ADOBPRIM, a modeling environment based on the ADOXX meta-modeling platform [START_REF] Adoxx | Official homepage of the ADOxx meta-modeling platform[END_REF], promotes and supports risk-aware process management methodology. The adopted framework suggests three main components: a modeling language, a modeling procedure, and mechanisms & algorithms. These latter form, according to [START_REF] Karagiannis | Metamodelling Platforms[END_REF], the main components of a modeling method.

In the next section, we present our proposed framework with an explanation of all its features and components.

A. e-BPRIM core components e-BPRIM Modeling Procedure: As mentioned before, the BPRIM [START_REF] Lamine | Bprim: An integrated framework for business process management and risk management[END_REF] proposes an integration of the two lifecycles of risk Fig. 1: e-BPRIM modeling procedure, some meta-models viewpoints and some operations management and business process management. The BPRIM lifecycle identifies four main phases (1-Contextualize, 2-Asses, 3-Treat and 4-Monitor), each of which is divided into steps. Considering information exchanged between the three first steps, a set of eleven viewpoints was identified. The e-BPRIM modeling procedure introduces then the sequence to be applied while creating and working with these multiple viewpoints. The complete modeling procedure is illustrated in the middle of Fig. 1. e-BPRIM Modeling Language: The latter is composed of abstract and concrete syntax. The abstract syntax is described by a meta-model based on the BPRIM conceptual model, called e-BPRIM meta-model. The concrete syntax is based on the BPRIM modeling notation and describes the graphical representation of each e-BPRIM meta-model concept, called e-BPRIM notation. It needs to be noted, that the e-BPRIM metamodel can be divided into eleven meta-models corresponding to the eleven viewpoints of e-BPRIM. Fig. 1 shows an example of some e-BPRIM viewpoints meta-models annotated with corresponding notations. For example, a blue rectangle is used to represent the "Resource" concept. e-BPRIM mechanisms & algorithms: These latter support the e-BPRIM modeling procedure and also provide functionalities to use and evaluate viewpoints.

B. Current functionalities of ADOBPRIM modeling tool

The ADOBPRIM tool supports the steps of the e-BPRIM modeling procedure and also provides functionalities (i.e. operations) to use and evaluate viewpoints. In Fig. 1, we present some of these functionalities. In the following, we present a short description of some functionalities :

• Editing of eleven e-BPRIM viewpoints corresponding to the viewpoints depicted in Fig. 1 • Verification of created models. This functionality ensures the validity/accuracy of created models by checking their structure according to several defined syntactic and semantic rules. • Risk Assessment of identified risks. The risk analysis model is analyzed and evaluated using a risk assessment matrix. The latter is a classical method to conduct qualitative risk assessment. The objective of this mechanism is to automatically produce a risk matrix which visualizes the different risk levels.

• Navigation & Synchronisation between all e-BPRIM

viewpoints and between all objects in different models. • Process decomposition (Op 1 ), indicated as red dotted arrows in Fig. 1, which deals with breaking down a system into progressively smaller subsystems that are responsible for some part of the problem domain. • Reuse (Op 2 ), indicated as blue dotted arrows in Fig. 1, which allows the reusing of one or several concepts from one or more existing viewpoints. • Synthesis (Op 3 ), indicated as green dotted arrows in Fig. 1, which allows the gathering the information of several viewpoints and then generating a synthesis viewpoint.

A comprehensive introduction to the ADOBPRIM modeling tool has been developed as a project within the Open Models Laboratory. A free download and further information on ADOBPRIM are available through the corresponding project page 1 .

C. Application on healthcare processes

To evaluate usage, feasibility, relevance, and capabilities of the proposed framework and tool, we applied the e-BPRIM framework with the ADOBPRIM modeling tool on three realworld healthcare processes, in France, to manage related risks:

• The first application deals with the management of Adverse Drug Event (ADE) risk related to the Medication Use Process (MUP) of elderly patients. The application was carried out in collaboration with several actors of the Intercommunal Hospital Center of Castres-Mazamet (CHIC) in the Geriatric Department. The result of this application can be found in great details in [START_REF] Thabet | Ingénierie dirigée par les modèles d'un pilotage robuste de la prise en charge médicamenteuse[END_REF]- [START_REF] Lamine | Bprim: An integrated framework for business process management and risk management[END_REF], [START_REF] Thabet | Adobprim: Towards a new healthcare risk-aware business process management tool[END_REF] • The second application deals with the crisis management process of the COVID-19 pandemic in France. The result of this application can be found in great details in [START_REF] Lamine | The integration of risk aspects into business process management : The e-BPRIM modeling method[END_REF] • The third application deals with the management of risks of Medical Devices (MD) contamination related to the Sterilization process. The application was based on the works of Di Mascolo et al. [START_REF] Mascolo | Decision support methods for efficient flow management in medical device sterilization departments[END_REF], [START_REF] Di Mascolo | Simulation in degraded mode of sterilization services[END_REF]. In these works, a real-world case study was conducted in the sterilization service of the University Hospital of Grenoble. The result of this application will be presented in great details now. In the following, we present the application of the ADOBPRIM modeling tool on a given hospital sterilization service to analyze its robustness [START_REF] Mascolo | Decision support methods for efficient flow management in medical device sterilization departments[END_REF], [START_REF] Di Mascolo | Simulation in degraded mode of sterilization services[END_REF]. In order to understand the sterilization process and analyzing related risks, the following presentation focuses to demonstrate how an ADOBPRIM user should address the environment tool to create models. For greater clarity, we exclusively work on selected e-BPRIM viewpoints namely the "Process Landscape", "Business Process", "Risk Taxonomy", "Risk-extended Business Process", "Risk Analysis", and "Risk Mapping" viewpoints.

To this end, an ADOBPRIM user should follow the phases of the e-BPRIM modeling procedure:

1) Contextualization phase: In this phase, the user should create: a) A "Process Landscape -(PL)" model which describes an overview of the value-added processes of the system under study. In our case study, this model describes eight sub-processes of the hospital sterilization process (see the top left of Fig. 2). b) A "Business Process -(BP)" model which provides a deeper understanding of the functioning of each identified sub-process in the PL model. In our case study, each identified hospital sterilization sub-process can be described by a BP model. For example, in the top right side of Fig. 2, the "Wash Fig. 2: ADOBPRIM modeling tool screenshots medical devices" process is described in greater detail.

2) Assessment phase: In this phase, the user should create: a) A "Risk Taxonomy -(RT)" model which provides an inventory of potential risks. In our case study, we differentiate between five risk classes (see the middle left of Fig. 2).

b) A "Risk-extended Business Process -(R-BP)" model which aims to assign individual activities of the BM model to potential risks from identified risks in the RT model. In our case study, as shown in the right middle side of Fig. 2, we can assign the "Contaminated MD" risk to the "Washing MD" activity. c) A "Risk Analysis -(RA)" model which aims to analyze each identified risk in the RT model by the calculation of the likelihood and the severity levels of each identified risk. In our case study, we focus the analysis on the "Contaminated MD" risk (identified in the RT model). The analysis result is given in the bottom left side of Fig. 2. d) A "Risk Mapping -(RM)" model which aims to produce a two-dimensional risk matrix showing the risk level of each analyzed risk. The risk position in the matrix will be according to likelihood and severity levels as calculated in its RA model. In our case study, the bottom right side of Fig. 2 illustrates the mapping of different analyzed risks. For example, according to the analysis result, we can see the risk "R2" (corresponding to the "Contaminated MD" risk) placed in the position [START_REF] Malicki | Patient safety in external beam radiotherapy, results of the accirad project: Current status of proactive risk assessment, reactive analysis of events, and reporting and learning systems in europe[END_REF][START_REF] Ferdosi | Risk management in executive levels of healthcare organizations: insights from a scoping review (2018)[END_REF]. Thanks to the ADOBPRIM tool use, all developed models using the ADOBPRIM tool allowed to: (i) improve the understanding of a hospital's risk profile, and (ii) clarify thinking about the nature and impact of risks, taking into account both the organization as a whole and the context of the risk situation and its relationship to healthcare process activities. In this way, vulnerabilities can be more effectively mitigated or managed.

The application result of the ADOBPRIM tool on the three real-world healthcare processes has proved the feasibility and the relevance of the e-BPRIM framework with the ADOBPRIM modeling tool. Indeed, according to ADOBPRIM users feedback, the tool has been valued as: (1) an easy tool giving a comprehensive vision of risks, and (2) a useful brainstorming and analyzing tool for improving the quality of management as well as the patient care processes.

CONCLUSION

To assist healthcare professionals in ensuring patient safety, various risk management methods have been proposed in the literature. However, our research and literature reviews on a few of them have shown their shortcomings. To move forward a more efficient approach, we introduce, in this paper, a new R-BPM framework called e-BPRIM, which is a recent result of our research in this field. To evaluate the usefulness and relevance of this framework, we used ADOBPRIM, the dedicated tool for e-BPRIM, to analyze the vulnerability of three real-world healthcare processes: the medication-use process, the management process of the COVID-19 pandemic, and the sterilization process. Users ADOBPRIM feedback have shown that R-BPM approaches can overcome some of the limitations of conventional risk management methods. Obviously, the e-BPRIM framework is not restricted to analyze risk related to healthcare processes, it may be used to other industries as well. At this stage, we are working on a new version of ADOBPRIM, which will add new features such as simulation capabilities to study risk propagation and to assess the effectiveness of the risk mitigation activities.

  Input: the

	Method	Process based	Reactive	Proactive	Qualitative	Quantitative	Causes	ranking	Causes	chronology	Input	Output
	Association of Litigation And Risk Man-										Questioning	Form/ Report
	agement (ALARM)
	Causal Tree Analysis (CTA)										Questioning	Tree
	Failure, mode, effects, and criticality anal-										Identified	Table
	ysis (FMECA)										causes
	Fault Tree Analysis (FTA)										Identified	Graph
											causes
	Ishikawa										Questioning	Graph
	ORION										Questioning	Table/ Report
	Preliminary Risk Analysis (PRA)										Identified	Table
											causes

TABLE I

 I Output: which description type is used to represent results.

	: Comparing current healthcare risk assessment methods
	reasons for which the method has to start being applied; and
	(7)

e-BPRIM project space within OMiLAB [online]: https://austria.omilab. org/psm/content/BPRIM, last visited: 01.08.2021