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This paper questions the difference between child and adult considered as one of the main questions of contemporary educational issues. The question is particularly acute when the adult is an artist, when the relationship with the child is built on the grounds of art and aesthetics. Therefore the artistic residences with children can be considered as places where a new relationship with the child is experienced. The qualitative methodology points out the ways of thinking of artists caught by individual and collective interviews. Analysis shows that in the field of art and shared creation, the difference disappears in favor of equality within difference, whose different modalities are presented and discussed at the end of the paper.

Keywords: Enfance, art, résidence d'artiste, relation éducative, esthétique, Childhood, art, artist-in-residence program, educational relationship, aesthetic, Infancia, arte, intervención de artista, relación educativa, estética

AbstractThis study examines the teaching of the natural sciences at the primary level from the teacher's perspective. The author first presents some aspects of the teaching situation that are problematic, followed by a description of those factors, both group and individual, that affect the teacher. As one hypothesis, the author proposes a model describing a hierarchy of these factors and the direct and indirect relationship that could affect science teaching.

Many studies point to the presence of ethnic discrimination of visible minorities in Canada. They have shown that minorities with high levels of qualification hold jobs that receive less recognition and lower incomes than other Canadians. However, few studies are interested in ethnic discrimination from the angle of the relationship between the job and the level of qualification. This article examines, using data from Statistics Canada's national survey of university graduates from the year 2000, this question among visible minorities who hold university degrees obtained in Canada, and compares the situations of respondents residing in Quebec to those from Ontario. According to the results, assuming equivalent levels of schooling, members from visible minorities are more likely than others to hold jobs for which they are over-qualified. However, this finding varies depending on the province of residence and the minority group in question. These results call on us to question, at least in part, the human capital theory and to consider other theories, in particular social capital theories and discrimination theories for their interpretation.

Keywords: insertion professionnelle, qualification, diplômés, université, immigrant, etchnicité, professional insertion, qualification, university graduates, university, immigrant, ethnicity

AbstractThis article examines a program which integrates music into the curriculum for French as a second language as well as the influence of this on learning music and French. Classroom teachers experimented a program of "music-language" whose objective was the learning of melody-rhythm patterns and musical form which provided similarities to oral and written comprehension and production in French. The sample included six classes of Grade 2 children in French immersion in New Brunswick : a control group (n=64) and an experimental group (n = 63). All subjects were administered pre and post tests. Application of ANOVA and ANCOVA statistical procedures revealed significant differences between the two groups on music tests and in oral and written French tests.

Our article aims to examine the relationship between social ties, collective initiatives and conflictual processes from two perspectives. First, we consider the relational dimension of collective initiatives, looking at three concepts that can help us better understand the processes leading to the formation, reproduction and transformation of social ties. We then consider the role that collective initiatives can play in the context of social conflicts, namely to complement the emphasis placed on cooperation in a number of works on these initiatives. We examine these two perspectives by analyzing the mobilizations against gentrification observed between 2019 and 2022 in the Montreal neighbourhood of Parc-Extension, using ethnographic research conducted during this period with the Parc-Extension Action Committee (CAPE). Our analysis leads us to argue that collective initiatives can contribute to social reproduction in a given environment, respond to collective needs and aspirations, and increase the capacity for popular intervention in the context of conflictual processes that aim, among other things, to destabilize economic and political elites and achieve concessions.

Keywords: liens sociaux, conflits, initiatives collectives, gentrification, ethnographie, Parc-Extension, social ties, conflicts, collective initiatives, gentrification, ethnography, Parc-Extension

Quebec municipal wastewater treatment facilities, like those elsewhere in Canada and the United States, generally are low efficiency energy consumers (ELECTRIC POWER RESEARCH INSTITUTE (EPRI), 1993; OWEN, 1982; ONTARIO-HYDRO, 1993; METCALF and EDDY, INC., 1992, SASSEVILLE et al., 1995). The work of METCALF and EDDY, INC. (1992) and of EPRI (1993) concluded that it would be possible to substantially reduce electricity demand and to improve the utilization of electrical energy in the municipal wastewater treatment processes by introducing Electricity Saving Measures (ESMs) in the processes and their management.In the province of Quebec, given the potential savings linked to the reduction of electricity consumption in municipal wastewater treatment facilities, and the progressive expansion of the province's wastewater treatment facilities, the adoption of energetically efficient wastewater treatment technologies is particularly timely. SASSEVILLE et al. (1995) estimated that it would be possible to save 5 M $ at the present level of wastewater treatment, based on a cost of about 24 M $ for the 400 GWh of electricity annually consumed in the municipal wastewater treatment facilities. This saving would come solely from the implementation of appropriate energy-saving measures.In hypothesizing on one hand that adding energy-saving measures can improve the energy consumption of a wastewater treatment chain, and on the other hand that the introduction of segments of processes can contribute in improving overall performance, we have elaborated from existing wastewater treatment facilities six hypotheses of liquid treatment chains that respect operational and regulation requirements, on the basis of the experience developed in the operation of municipal wastewater treatment facilities. The six hypothetical treatment chains were elaborated from facilities of the following types: biofiltration (chain 1), physico-chemical (chain 2), sequencing biological (batch) reactors system A (chain 3), sequencing biological (batch) reactors system B (chain 4), activated sludge (chain 5) and aerated lagoons (chain 6). The energy-saving measures utilized in the elaboration of these hypothetical treatment chains were chosen on the basis of a conjunctive analysis (KIBI et al., 1997). However, the problem of choosing among these treatment chains the one corresponding to the most adequate process for a particular situation is still present. The present article analyzes this choice for wastewater treatment facilities of a capacity between 5 000 m3/d (≈ 5 000 persons) and 100 000 m3/d (≈ 100 000 persons).How then to choose the most efficient of these hypothetical municipal wastewater treatment chains?Generally, the choice of the treatment technologies is done on the basis of single-criterion mathematical models: for example, the reduction of construction costs, or of exploitation and maintenance costs (ECKENFELDER, 1982; PINEAU et al., 1985; WANG and WANG, 1979; TYTECA et al., 1977). There are other approaches based on dynamic simulation models or on technological and econometric analyses (HYDRO-QUÉBEC, 1993; MACRAE 1989; LESSARD, 1989; BROCKTON, 1987; HOLDREN, 1987; FOSBERG and MUKHOPADHYAY, 1981; REID, CROWTHER and PARTNERS, 1978; KLEMETSON and GRENNEY, 1976).These different approaches are often insufficient to distinguish the real value of the different technological options. Furthermore, they do not take into account many important factors (technological, economic, financial and environmental, ergonomic and socio-political) that affect their implementation and should be considered in identifying an acceptable and viable solution.The multicriteria approach of decision-making advocated in this article can mitigate this difficulty. It will take into account key factors in the conception and operation of treatment technologies, especially energy and environmental factors, likely to give rise to efficient treatment facilities from both an energy and a treatment point of view. However the analysis of decisional factors to consider in this multicriteria analysis gives rise to a particular problem. They affect the decision that can be appreciated by deterministic relationships, offering a high level of certainty as to its evaluation, while others have a non-deterministic nature (uncertainty and imprecision). Research using the multicriteria analysis approach has been performed in similar situations over the last twenty years, in some cases applied to the environmental and energy sectors (e.g. KEENEY and NAIR 1977; ROY and VINCKE 1981; TEGHEM and KUNSCH 1985; SIMOS 1990; HANSON 1991; ROUSSEAU and MARTEL 1994). Here again, these approaches have limits since the cases were treated either in a situation of certainty or a situation of uncertainty and imprecision. The proposed model deals with the case of certainty and uncertainty at the same time, therefore improving the applicability of the multicriteria approach in the situation under study. The solution retained consists of applying this type of modelling in order to classify from the best to the worst, the six hypothetical treatment chains. This approach utilizes in the modelling process, fourteen evaluation criteria, various criteria weights, quantitative and qualitative evaluations, as well as the indifference, preference and veto thresholds. The main steps of the model are the construction of evaluated outclass relationships and the exploitation of these outclass relationships. The multicriteria aggregation procedure utilizes an elaborated mathematical model based upon the methods of ELECTRE III (Roy, 1978) and PROMETHEE II (BRANS et al., 1984), as well as the works of DÉROT et al. (1994). The ranking of these treatment chain hypotheses, elaborated on an empirical level in consultation with the operators and others involved in wastewater treatment and obtained on the basis of this procedure, can discriminate among their overall performance characteristics rather well. It also emphasizes their energy efficiency, since the energy criteria have on average in the analysis a weight that is 28% higher than the other evaluation criteria. The results obtained show that the hypothetical chain 3 is ranked first, chain 1 occupies the second rank, whereas chain 4 is in the third rank. The last three ranks are occupied respectively by chains 6, 5 and 2.In a decisional and strategic approach, the first three treatment chain hypotheses can be considered overall as being the highest achievers. This result signifies that in the scope of investments related to the expansion of treatment facilities and the construction of facilities with a flow rate contained within the considered range, these three treatment chains (when considering different modification hypotheses), should be preferred over the other chains when the emphasis is on their overall performance including energy efficiency. However, other analyses would be necessary in the case of the construction of a new wastewater treatment facility with a flow rate above the level considered in this study.Generally, the results of this analysis can assist in discriminating among the behaviors of the technologies considered, and in judging their relative performance in the investments of the construction of new wastewater treatment facilities, in addition to a technico-economic analysis. Overall, the multicriteria model described in this study identified a compromise solution between evaluations of a different and conflicting nature. This result demonstrates that this type of analysis is appropriate for tackling multidimensional problems.

Keywords: Épuration des eaux usées municipales, modélisation multicritère, aide à la décision, performance globale, Mesures d'Efficacité Énergétique Électrique (MEEE), Wastewater treatment, multicriteria approach, decision making, electricity saving measures, global performance

In arid and semiarid Tunisian regions, water and soil conservation is an important way to decrease erosion and to collect runoff in hill-slope catchments.However, few studies have focused on the impacts of runoff on water harvesting techniques. This paper deals with the hydrological effects of contour ridges in the El Gouazine catchment located in central Tunisia.Hydrological observations were used to calibrate a conceptual rainfall-runoff model. The H2U hydrological model was used for this purpose (CUDENNEC, 2000; DUCHESNE et al., 1997). This model is built around a production function that defines the net storm rainfall (portion of rainfall during a storm that reaches a stream channel as direct runoff) from the gross rainfall (observed rainfall in the catchment) and a transfer function based on the most complete possible definition of the surface drainage system (CUDENNEC, 2000).The runoff production function defined by NASRI et al. (2001) was used for the El Gouazine catchment. Observed rainfall during 5-min time steps was used in the model.The 18.1 km2 El Gouazine catchment is located 15 km south of the town Oueslatia. With an annual average rainfall of 411 mm and a potential evapotranspiration of 1680 mm, the climate can be regarded as semiarid. The main annual rainfall is usually received between September and January. All runoff from the catchment is collected in a small artificial lake, created in 1990. Its initial storage capacity was 233,370 m3. Water level observations in the lake were used to estimate total runoff from the catchment. The altitude of the drainage area varied from 575 m in the south to 375 m in the north at its outlet. The land surface of the catchment is partitioned into the following uses: 40% cereal production alternating with fallow land; 33% pasture, shrub-land (carob trees, lentisk), and Esparto grass steppe; 20% Aleppo pine forest (both dense and degraded forest); 6% arboriculture (olive trees, almonds); and 1% lake and dyke area.Between July 1996 and July 1997, soil contour ridges covering 43% of the total area were constructed in the El Gouazine hillside catchment. The length of each ridge is typically about 100 m with an average height of 1.5 m and an average perpendicular distance between ridges corresponding to about 25 m.Construction of the contour ridges significantly changed the hydrological conditions in the catchment. Before contour ridges, average global runoff coefficients were 20-30% for autumn rainfalls (september to october) and 4-10% for rainfalls in winter and spring (November to May). Rainfalls during autumn were usually characterized by high intensity and soils were usually compacted with an impermeable surface crust. From November to February, soils usually become more permeable due to agricultural activities (e.g., ploughing) and during March to May infiltration is increased due to increasing crop cover.During this period, before introducing contours ridges in the El Gouazine catchment, the conceptual rainfall-runoff model based on surface topography and the drainage network was calibrated to reproduce observed runoff satisfactorily. Geomorphologic data (topography and drainage system characteristics) for the catchment were extracted with the geographic information software ERDAS IMAGINE of ESRI (Environmental Systems Research Institute, Inc.). The procedure allows extracting the actual probability density function (p d f) of watercourse lengths in the network (L) for the catchment, the catchment Strahler order (n), and the average length of the watercourse in the network L. These parameters are used in a gamma law type transfer function called H2U (unit hydrograph). For this study, in order to be in the usual situation of flood designing practitioners, we used topographical maps with a scale of 1:50000, which are the commonly available maps in Tunisia, and digital grids with a 10 m resolution. Due to the semiarid landscape and relief, there is no ambiguity in identifying the drainage networks.Simulated runoffs using both the actual and theoretical pdfs were compared.The theoretical functions give better results, especially with respect to peak flow. This is probably due to smoothing of the drainage system represented by the theoretical density function. The empirical function calculated from maps probably includes errors and uncertainties, which are smoothed in the theoretical function. For both calibration and validation events, results showed an excellent agreement between observed and simulated runoff volumes as well as peak flows. For the Nash criteria, results varied from case to case (from 0.62 to 0.96).After introduction of the contour ridges, runoff coefficients changed to below 10%. Similarly, inflow to a reservoir at the outlet of the catchment decreased by 50-80%. Observed erosion virtually disappeared after introduction of the contour ridges. Similarly, peak discharge was reduced 60-90%. The changes made in the semiarid catchment will allow agriculture to more efficiently use existing water resources. In practical terms it means that pasture lands can be diverted into cultivated areas (e.g., cereals, olive trees, and almond trees).However, it also means that most surface water infiltrates and eventually replenishes the groundwater, thus leaving downstream areas with almost no surface runoff. Soil contour ridges covering 43% of the El Gouazine catchment area increased the total runoff storage capacity by approximately 258 000 m3. Consequently, contour ridges may be said to present an alternative to the construction of small hillside reservoirs. The introduction of contour ridges therefore has dramatic consequences for downstream runoff conditions. To improve runoff management for both upstream and downstream conditions, it may be necessary to a) simulate runoff effects using a conceptual rainfall-runoff model and b) allow a certain part of the catchment to deviate a part of the runoff to the downstream natural watercourse.A conceptual rainfall-runoff based on surface topography and the drainage network was seen to reproduce observed runoff accurately. By applying the model for runoff simulation with and without contour ridges a more detailed comparison of the changed runoff conditions could be made. The detailed hydraulic function of water harvesting techniques is still to a major extent unknown. A detailed study of the hydrological function of contour ridges in a cascade system is necessary to calibrate hydrological models such as H2U and their associated production function on hill-slope catchments with soil surface management.

Keywords: Tunisie, dorsale semi-aride, aménagements anti-érosifs, banquettes, modélisation hydrologique, petits barrages collinaires, Surface management, geomorphic hydrological model, anti-erosive measures, runoff reduction, hill reservoir, hill-slope catchment, arid region, Tunisia

The aim of this study was to investigate the potential of a helophytic plant, Phragmites australis (Cav.) Steudel, to remove chromium from concentrated tannery effluent in comparison to unplanted soil, under arid climate conditions. The experiment was conducted from August 2002 to August 2003. Six plots (capacity: 120 L, diameter: 50 cm) were filled to depths of 15 cm and 60 cm with gravel and soil respectively (texture: 3.5% clay, 8.5% silt, and 88% sand). Three plots were planted with Phragmites australis (Cav.) Steudel. Young shoots of plants (36 stems/m2) were taken from local and natural reed stands. Three unplanted plots were used as controls. The soil for the study was from the Tensift River (Marrakech). The experimental plots were supplied exclusively with diluted tannery wastewater, 3 times a week (approximately 10 L each time). The water flowed vertically through the substratum.To investigate the capacity of the systems to increase pH, to decrease conductivity chemical oxygen demand (COD), and to remove total chromium, concentrations in the inflow and outflow of each plot were determined during the experiment. System hydrology indicated that for planted systems, the mean flow varied from 18 mL/min (in winter) to 49 mL/min (in summer), with an average value of 35 mL/min. For the unplanted system, the mean flow varied from 5 mL/min (in winter) to 15 mL/min (in summer) with an average value of 12 mL/min. Water recovery at the outflow of the planted system (PP) and unplanted system (NPP) was 40% and 60% respectively. This may be related to the phenomenon of evapotranspiration from the PP system, which was more significant than simple evaporation from the NPP system. No sign of clogging was observed in the planted systems due to the plant rhizomes that ensure a better aeration of the soil. The study of the hydrological operation showed that mean flow in the planted system was three times higher than that in the unplanted soil, which makes it possible to treat a larger volume of wastewater and to reduce the required per capita surface for treatment. The presence of Phragmites australis ensured a sufficient porosity for the percolation of water for treatment.The pH of the effluent at the outlets of the planted and unplanted systems increased by two to three units in comparison with the raw wastewater at the inlet. The average inflow pH was 5.5; at the outflow of the two systems, the pH was 7.30 and 8.20 respectively for the planted and unplanted soil. The electrical conductivity (EC) of the treated wastewater increased for the two systems. The average inflow conductivity was 54±5.5ms/cm. At the outflow of the two systems, the EC was about 75±14 ms/cm and 68±11 ms/cm respectively for the planted and unplanted systems. The EC removal for all systems varied significantly from season to another (p< 0.05).The planted system was more efficient in removing total COD (74%) than the unplanted one (61%). There were significant differences (ANOVA) between the PP and NPP systems (p<0.05). Total chromium concentrations at the inflow varied from 534 mg/L to 1000 mg/L with an average content of 780±196 mg/L. At the outflow, total chromium concentrations varied from 2.2 mg/L to 3 mg/L with an average content of 2±0.5 mg/L for the PP system and from 2.5 mg/L to 4 mg/L with an average value of 2.4±1.3 mg/L for the NPP system. Total chromium removal of 99% occurred for the two pilots, which provides limpid purified water. Despite the shorter retention time for the planted system, which was three times less than in the unplanted one, total chromium was almost completely removed.The aquatic macrophyte plant seemed to play a physical role by enhancing the hydrological conductivity of the substratum and consequently the operation and management of these systems. Phragmites australis (Cav.) Steudel has the ability to transfer oxygen from the rhizome towards the roots through an internal lacunar system, which offers the creation of an aerobic zone around the roots. This aerobic zone allows the proliferation of micro-organisms, which are the principal decomposers of the organic matter in the root zone.The treatment of tannery effluent by reed beds is a clean approach from an ecological point of view and constitutes a viable economic alternative in comparison to purely chemical approaches and is thus better adapted to the complexity of the systems used in the leather industry.

Keywords: Phragmites australis (Cav.) Steudel, climat aride, tannerie, rejet industriel, chrome, lits à roseaux, Phragmites australis (Cav.) Steudel, arid climate, chromium, tannery, industrial wastewater, reed beds

This study was carried out in order to evaluate the variations in the physicochemical characteristics of the water in an experimental distribution system.The primary objectives of the study were :- to compare the disinfectant efficiency of chlorine and monochloramine- to establish quantitative correlations among bacterial density, concentration of residual disinfectant, and concentration of biodegradable organic matter.The finished waters were obtained from a water treatment pilot plant characterized by : prechlorination (average treatment rate : 1.4 mgCl2 l-1 and residual alter sand filtration : 0.08 mgCl2 l-1), coagulation-flocculation-sedimentation (FeCl3 treatment rate : 30 to 60 mg l-1 adjusted to the raw water turbidity below 0.3 NTU), sand filtration (filtration rate : 6 h-1) and post-disinfection with chloramine (average treatment rate : 1.8 mgCl2 l-1) or chloramine (average treatment rate : 1.66 mgCl2 l-1). The concentrations of post-disinfectant used were chosen in order to maintain chlorine at 0.2 to 0.5 mgCl2 l-1 and monochloramine at 1 mgC2 l-1 after the first 24 hours residence time in the experimental distribution system.The experimental distribution system is composed of three parallel loops connected in series (31 m length, 100 mm diameter, cement lined cast iron, water velocity : 1m s-1). The configuration and operation of the system permitted a residence time of 24 hours in each loop (that is 72 hours for the whole system). Appropriate sample tap locations facilitated removal of bulk water samples. Special sampling parts also permitted sampling of cement coupons for determination of attached biofilm.The measured parameters were : residual oxidant (DPD method), DOC, BDOC (28 days of incubation at 28 °C with a bacterial inoculum), cell density in the bulk water phase (CFU ml-1) and in the biofilm (CFU cm-2) after 15 days of incubation at 20-22 °C. Total cells were enumerated using the epifluorescence direct count technique.For each experiment, all the sampling sequences were carried out on each of three days, after quasi steady-state was achieved in the system (4 to 6 weeks after starting each experiment). The data were analysed in order to characterize the treated and distributed waters; the results discussed here are based on the averages of the measured parameters tram the water samples and biofilm samples taken after the system achieved quasi steady-state.Characteristics of the treated watersThe treated waters were characterized by important variations at the DOC, BDOC and cell density. For example, the concentrations of DOC showed a seasonal variation ranging from 0.8 to 1.3 mg Cl-1 in winter to 1.6 to 2.6 mg Cl-1 in summer.The treated waters contained approximately the same concentrations of residual disinfectant, averaging 1.6 mgCl2 l-1 for chlorine and 1.5 mgCl2 l-1 for monochloramine.However, a significant difference cell density was found between the two post-disinfectants. Cell densities by the epifluorescence direct count technic were 1.6 x 103 ml-1 (0.3 % of CFU ml-1) with chlorine and 6.3 x 104 ml-1 (0.03 % of CFU ml-1) with monochloramine. The difference on cell density between the post-chlorination and the post-chloramination treatments has been observed systematically, and may be explained either as cellular lysis with chlorine or an interference when using epifluorescence counting for chlorinated waters.Characteristics of the distributed watersWhatever the season, depletion of oxidant (chlorine or monochloramine), and elimination of dissolved organic matter (DOC, BDOC) occured during the first hours of circulation of water in the distribution system. The net result was an increase in bacterial cell density.During the first hours of circulation of the waters in the distribution system, depletion of the disinfectant occured. Depletion was more rapid for chlorine (-0.05 mgCl2 l-1 h-1) titan for monochloramine (-0.02 mgCl2 l-1 h-1), winch is considered more stable titan chlorine.Even in the presence of a residual disinfectant in the distribution system, microorganisms are present in the water phase (104 to 106 cells ml-1 by epifluorescence direct count; 1 % CFU ml-1 after 15 days of incubation at 20-22 °C) and in the biofilm (105 to 106 cells cm-2 by epifluorescence direct count; 1 % CFU ml-1 after 15 days of incubation at 20-22 °C). The bacterial density increased white the disinfectant residual decreased. The apparent growth rate of the attached biomass (µfix) in loop 2 of the chlorinated distribution system (equivalent to 48 hours detention), was close to the µfix calculated for loop 2 of the chloraminated distribution system : the values were 0.0043 h-1 and 0.005 h-1 respectively.In addition, the change in the organic matter (expressed as DOC) occured in two steps :- a slight increase in DOC during the 24 first hours of residence time (loop 1), when increased residual disinfectant were present.- a bacterial consumption of DOC after 24 hours of residence time (loops 2 and 3), even in the presence of small concentrations of disinfectants.In loop 2 (48 hours residence time of the water in the system; chlorine : 0.01 mgCl2 l-1, chloramine : 0.3 mgCl2 l-1 h-1), the rates of DOC elimination averaged 13 mgCl2 l-1 h-1 and 0.42, mgCl2 l-1 h-1, respectively in the chlorinated and chloraminated distribution systems. This decrease in DOC concentrations was related to the increase in bacterial density.Relationships between cell density, oxidant and organic matterLinear relationships between the concentration of residual oxidant (chlorine or monochloramine) and the cell density in the water phase or in the biofilm show that :- whichever oxidant was used, the pipe loop sections without residual disinfectants were characterized by about 5 x 106 attached cells per cm2 (4 to 10% were able to grow on agar medium in 15 days at 20-22 °C) and by 4 x 105 planktonic cells per ml (1 % CFU ml-1);- consistently, in the sections of the system with a residual disinfectant, the bacteria (CFU and epilluorescence counting) in the water phase were more sensitive to the residual disinfectant (chlorine or monochloramine) than the bacteria attached to the pipe walls (biofilm).However, there was a difference in effectiveness between the two disinfectants; chlorine was more efficient in controlling planktonic bacteria and biofilm bacteria than was monochloramine.For example, to achieve complete inactivation of the planktonic bacteria (CFU ml-1) a constant chlorine residual of 0.5 mgCl2 l-1 was required throughout the whole distribution system, compared to 2.5 times more chloramine to achieve the same efficiency.Finally, with equivalent concentrations of residual disinfectant, the microbiological quality of the chlorinated distribution waters was better than that of the chloraminated distribution waters.From loop to loop, linear relationships between ∆DOC and cell density pointed out that the presence of biodegradable organic matter can explain the bacterial proliferation in the distribution system. For example, a concentration of BDOC as low as 0.1 mgC l-1 resulted in an increase in the cell density : an additional accumulation of 7.5 x 105 attached cells cm-2 and 4 x 104 planktonic cells ml-1 was observed in the experimental distribution system at quasi steady-state.Consequently, the control of the biodegradable organic carbon remains one of the prime objectives in order to achieve biologically stable distribution waters.

Keywords: Matière organique biodégradable, COD, CODB, prolifération bactérienne, réseau de distribution, biofilm, désinfection, chlore, chloramine, Biodegradable organic matter, DOC, BDOC, bacterial proliferation, distribution systems, biofilm, disinfectant efficiency, chlorine, chloramine

The concept of partial membership of a hydrometric station in a hydrologic region is modeled using fuzzy sets theory. Hydrometric stations are represented in spaces of hydrologic (coefficient of variation: CV, coefficient of skewness: CS, and their counterparts based on L- moments: L-CV and L-CS) and/or physiographic attributes (surface of watershed: S, specific flow: Qs=Qmoyen/S, and a shape index: Ic). Two fuzzy clustering methods are considered.First a clustering method by coherence (Iphigénie) is considered. It is based on the principle of transitivity: if two pairs of stations (A,B) and (B,C) are known to be "close" to one another, then it is incoherent to state that A is "far" from C. Using a Euclidean distance, all pairs of stations are sorted from the closest pairs to the farthest. Then, the pairs of stations starting and ending this list are removed and classified respectively as "close" and "far". The process is then continued until an incoherence is detected. Clusters of stations are then determined from the graph of "close" stations. A disadvantage of Iphigénie is that crisp (non fuzzy) membership functions are obtained.A second method of clustering is considered (ISODATA), which consists of minimizing fuzziness of clusters as measured by an objective function, and which can assign any degree of membership between 0 to 1 to a station to reflect its partial membership in a hydrologic region. It is a generalization of the classical method of mobile centers, in which crisp clusters minimizing entropy are obtained. When using Iphigénie, the number of clusters is determined automatically by the method, but for ISODATA it must be determined beforehand.An application of both methods of clustering to the Tunisian hydrometric network (which consists of 39 stations, see Figure 1) is considered, with the objective of obtaining regional estimates of the flood frequency curves. Four planes are considered: P1: (Qs,CV), P2: (CS,CV), P3: (L-CS,L-CV), and P4: (S,Ic), based on a correlation study of the available variables (Table 1).Figures 2, 3a, 4 and 5 show the clusters obtained using Iphigénie for planes P1 through P4. Estimates of skewness (CS) being quite biased and variable for small sample sizes, it was decided to determine the influence of sample size in the clusters obtained for P2. Figure 3b shows the clusters obtained when the network is restricted to the 20 stations of the network for which at least 20 observations of maximum annual flood are available. Fewer clusters are obtained than in Figure 3, but it can be observed that the structure is the same: additional clusters appearing in Figure 3 may be obtained by breaking up certain large clusters of Figure 3b. In Figure 3c, the sample size of each of the 39 stations of the network is plotted in the plane (CS,CV), to see if extreme estimated values of CS and CV were caused by small samples. This does not seem to be the case, since many of the most extreme points correspond to long series.ISODATA was also applied to the network. Based on entropy criteria (Table 2, Figures 6a and 6b), the number of clusters for ISODATA was set to 4. It turns out that the groups obtained using ISODATA are not very fuzzy. The fuzzy groups determined by ISODATA are generally conditioned by only one variable, as shown by Figures 7a-7d, which respectively show the fuzzy clusters obtained for planes P1-P4. Only lines of iso-membership of level 0.9 were plotted to facilitate the analysis. For hydrologic spaces (P2 and P3), it is skewness (CS and L-CS) and for physiographic spaces (P1 and P4) it is surface (Qs and S). Regionalization of the 100-year return period flood is performed based on the homogeneous groups obtained (using an index-flood method), and compared to the well-known region of influence (ROI) approach, both under the hypothesis of a 2-parameter Gamma distribution and a 3-parameter Pareto distribution. For the ROI approach, the threshold corresponding to the size of the ROI of a station is taken to be the distance at which an incoherence first appeared when applying Iphigénie. Correlation of the regional estimate with a local estimation for space P1 is 0.91 for Iphigénie and 0.85 both for ISODATA and the ROI approach. Relative bias of regional estimates of the 100-year flood based on P1 is plotted on Figures 9 (Gamma distribution) and Figure 10 (Pareto distribution). The three methods considered give similar results for a Gamma distribution, but Iphigénie estimates are less biased when a Pareto distribution is used. Thus Iphigénie appears superior, in this case, to ISODATA and ROI. Values of bias and standard error for all four planes are given for Iphigénie in Table 3.Application of an index-flood regionalization approach at ungauged sites requires the estimation of mean flow (also called the flood index) from physiographic attributes. A regression study shows that the best explanatory variables are watershed surface S, the shape index Ic and the average slope of the river. In Figure 8, the observed flood index is plotted against the flood index obtained by regression. The correlation coefficient is 0.93.Iphigénie and ISODATA could also be used in conjunction with other regionalization methods. For example, when using the ROI approach, it is necessary to, quite arbitrarily, determine the ROI threshold. It has been shown that this is a byproduct of the use of Iphigénie. ISODATA is most useful for pattern identification when the data is very fuzzy, unlike the example considered in this paper. But even in the case of the Tunisian network, its application gives indications as to which variables (skewness and surface) are most useful for clustering.

Keywords: Hydrologie, régionalisation, crues, flou, gamma, pareto, iphigénie, ISODATA, Hydrology, regionalization, 100-year flood, fuzzy sets, gamma, pareto, Iphigénie, ISODATA