English (United Kingdom)

https://curated-unify.zendy.io/wp-json/zendy-region/v1/featured_content/oa?rat=en

https://curated-unify.zendy.io/wp-json/zendy-region/v1/highlighted_journal/

Global: Zendy Plus annual

Presents the access of premium content as premium feature

Premium Content

Presents the keyphrase highlighting as premium feature

Keyphrase Highlighting

Presents the summarisation as premium feature

Summarisation

Insights

Presents the pdf analysis as premium feature

PDF Analysis

Presents the zaia usage as premium feature

ZAIA

Global: Zendy Plus monthly

Global: Zendy Tools annual

Global: Zendy Tools monthly

Global: Zendy Free Plan

Le programme d'assainissement des eaux de Québec (PAEQ), mis en place à la fin desannées 1970, s'est d'abord attaqué au problème de la pollution ponctuelle d'origine urbaine.Plusieurs stations de traitement des eaux usées municipales ont été construites dans lecadre de ce programme réduisant de façon importante les charges de polluants d'origineurbaine. La question demeure toutefois de savoir dans quelle mesure les charges urbainesrejetées avant et l'après l'instauration de ce programme peuvent entraîner des dépassementsde différents critères de l'eau. La présente étude a pour objectif d'examiner cetteproblématique pour le bassin versant de la rivière Chaudière en utilisant le système demodélisation intégrée GIBSI (Gestion Intégrée par Bassin versant à l'aide d'un SystèmeInformatisé). Deux scénarios d'assainissement urbain ont été examinés, l'un représentatif dela période avant la mise en place du programme, le début des années 1980, et un autrereprésentatif de la période plus récente. Deux chroniques météorologiques ont été utilisées(années 1983 et 1994). L'estimation des probabilités de dépassement de différents critèresde l'eau montre une nette réduction de ces probabilités après mise en place du programme.Pour la DBO5 et l'azote total, les charges urbaines rejetées actuellementn'entraînent pas de dépassement des critères de qualité de l'eau pour les deux annéesretenues. Toutefois, les résultats montrent que les charges en phosphore total d'origineurbaine peuvent à elles seules entraîner des probabilités de dépassement importantes lorsd'étiage.In 1978, the Québec Government put in place a provincial municipal clean waterprogram, referred to as the Programme d'assainissement des eaux du Québec (PAEQ), to restorethe province's rivers to their natural state. The program focussed primarily on the problemof municipal waste loads and, hence, a large number of wastewater treatment plants (WWTP)were constructed during the 1980's and the 1990's. At the beginning of the 1980's, only afew percent of the population had their waste water treated, but this figure had increasedto over 95% by 1997 (Figure 1). In the Chaudière river watershed, this program resulted inthe construction of more than 35 WWTP over an 18-year period. Although an impressive effortwas devoted to reduce municipal waste loads, a question remains: how does this reductiontranslate into terms of overall improvement of water quality at the watershedlevel?The Chaudière river watershed was considered for this application. This watershedcovers an area of 6682 km2 and is located south of Quebec City. Land use is dominated byforest (62%) followed by agricultural land (33%), urban area (3.6 %), and water (1.7 %). Thetotal population in 1996 was 173129 and was mainly located in the northern part (i.e., thedownstream region) of the watershed. A total of 44 municipal point loads were identified(see Figure 2 and Table 1), most of them corresponding to WWTP. Characteristic data onmunicipal WWTP for year 1995 were obtained from the Quebec Department of the Environment(MINISTERE DE L'ENVIRONNEMENT ET DE LA FAUNE DU QUEBEC, 1997) and used to estimate averageconcentrations of total phosphorus and the biological oxygen demand (BOD). Data includedaffluent and effluent concentrations at various WWTP. Since no data were available fornitrogen, a concentration of 40 mg-N/l was used (TCHOBANOGLOUS et SCHOEDER, 1985; NOVOTNY etCHESTERS, 1981). Nitrogen removal efficiency for different types of treatment was estimatedfrom available data compiled by the Environment Quebec (Table 2). An average, per capita,daily wastewater volume of 0.73 m3 was derived. This large valueindicates a large infiltration capacity in the sewer network and, on average, a poorstructural state.Results were analysed at four locations distributed along the river. These pointscorresponded to the locations of the four major water quality monitoring stations (Figure3). Total annual loads within the sub-watersheds defined by these points were estimated(Table 3). Affluent characteristics were considered for the simulation of the pre-PAEQperiod. Figure 4 represents the evolution of total phosphorus loads at station 2340012(water intake for the town of Charny, the most downstream point). It shows that an importantreduction occurred in 1986. For the same sub-watershed, the overall reduction for the1982-1999 period was 38% for total phosphorus, 37% for total nitrogen and 83% forBOD.Assessment of the impact of the PAEQ was done using the integrated modelling systemGIBSI ("Gestion Intégrée par Bassin versant à l'aide d'un Système Informatisé") (ROUSSEAU etal., 2000; MAILHOT et al., 1997 ; VILLENEUVE et al., 1998). Only pollutant loads originatingfrom sewer networks were considered; pollutant loads from industrial plants not connected toa municipal sewer network were not considered in this study. Similarly, diffuse sources ofpollution from urban area or agricultural land were not taken into account. Two scenarioswere considered: a first scenario associated with the 1983 year corresponding to thepre-PAEQ period; and a second scenario associated with the 1994 year describing thepost-PAEQ period (following load reductions). Two hydrological reference years were alsoselected, namely, years 1983 and 1994. The former corresponded to a significantly drier yearthan the latter. At station 2340012 (Charny water intake), this difference was even morepronounced when considering that the cumulative summer flow was 6.9 times larger in 1994than in 1983. Four simulations corresponding to different combinations of representativemunicipal waste loads and meteorological conditions were performed (Table 5).Simulation results at the four control points were compared with water qualitystandards (WQS) for total phosphorus (0.03 mg-P/l, aesthetic WQS for prevention ofeutrophication in rivers) and BOD (3 mg-BOD5 /l, sanitary WQS for domesticuse of water requiring disinfection treatment only). The probabilities of exceeding theseWQS were defined (equation 1) as the number of days (daily computational time step) wheresimulated values exceeded a given value (complementary cumulative distribution function).Table 8 introduces annual probabilities of exceeding WQS at the four control points and forthe different simulations whereas Table 9 introduces those for the summer period. At station2340012 (Charny water intake), for hydrological year 1994, a comparison of pre- andpost-PAEQ conditions for total phosphorus shows that post-PAEQ condition lowered the numberof days exceeding WQS by 49. Similar reductions were reached at the other control points.For the 1994 summer period, the reduction was not as pronounced since the probability ofexceeding WQS was 0.24 for pre-PAEQ situation and it decreased to 0.21 for the post-PAEQcondition. These probabilities worsened under the 1983 summer conditions as concentrationsexceeded the WQS 98% of the time at station 2340014

revue des sciences de l'eau

Évaluation de l'impact de l'assainissement urbain sur la qualité des eaux du bassin versant de la rivière Chaudière à l'aide du système de modélisation intégrée GIBSI