Avaliação do impacte da expansão de redes de drenagem de águas residuais numa ETAR
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2018-02-14
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O fenómeno do povoamento disperso surgiu durante o século XX quando a melhoria das condições de vida levou á procura das famílias por habitações unifamiliares em zonas mais aprazíveis, nomeadamente em zonas rurais. Este fenómeno foi também impulsionado por outros fatores, como a redução dos custos de transporte e o reduzido custo dos terrenos em zonas periurbanas.
A dispersão urbana causa uma variedade de problemas como a fragmentação de áreas florestais e agrícolas, aumento de consumo energético, a desagregação de laços sociais e comunitários e a segregação espacial de classes sociais. O âmbito deste trabalho foca-se nos impactes da dispersão urbana no provimento de infraestruturas de utilidade pública, mais especificamente drenagem de águas residuais domésticas. Este fenómeno dificulta a construção de esgotos em condições de sustentabilidade e eficiência e aumenta o custo do provimento e manutenção do serviço de esgotos. Logo, este padrão de ocupação espacial é prejudicial ao desenvolvimento e manutenção destas infraestruturas.
Os instrumentos de planeamento territorial ao nível municipal, nomeadamente os PDM (Planos Diretores Municipais) não estudam, na maioria dos casos, os impactes das áreas de expansão urbana em infraestruturas de utilidade pública como esgotos, abastecimento de água, de eletricidade ou gás natural, e como tal não previnem a dispersão urbana e muitos dos seus impactes negativos. Este estudo, toma em consideração isto, para saber se num concelho disperso como Fafe, que é o caso de estudo nesta dissertação, a ETAR de Serzedo (Guimarães) que serve a maioria do território do município, tem capacidade para lidar com o alargamento do serviço a todas as áreas urbanizadas assim como lidar com um aumento da urbanização e possível dispersão urbana.
Este trabalho usa metodologia baseada em SIG (Sistemas de Informação Geográfica) cruza informação geográfica sobre a demografia, altimetria, planeamento e ocupação do território assim como dados acerca dos caudais da ETAR. Esta metodologia tem como objetivo, também, saber as áreas ocupadas e urbanizáveis, a população servida e não servida por esgotos e a população que potencialmente ocupará os territórios.
Nos cenários estudados, em que o primeiro é o atual, dois com expansão da rede para áreas servidas por sistemas autónomos e não servidas por nenhuma rede, respetivamente e uma última com serviço à urbanização de todas as áreas disponíveis no PDM. Os três primeiros cabem na capacidade da ETAR, pois são de 7291 m³, 8209 m³ e 12867 m³. Já o último cenário estudado ultrapassa a capacidade da ETAR pois prevê um caudal de 39148 m³.
Com estes dados podemos concluir que a ETAR é suficiente para a ocupação atual do território, tendo, no entanto de se controlar as entradas indevidas no sistema e aumentar a rede de coletores a toda a bacia de drenagem de modo a aumentar a cobertura deste serviço. No entanto, em caso de aumento da urbanização para fins residenciais e outros para todas as áreas disponíveis no PDM, a ETAR não tem capacidade para responder ao aumento de fluxo.
The phenomenon of urban sprawl emerged during the XX century when the improvement of living conditions lead families to search for single family houses in more pleasant areas, namely in rural areas. This phenomenon was also boosted by other factors like the reduction of transportation costs and the low cost of properties in peri urban areas. Urban sprawl causes a variety of problems like the fragmentation of agricultural and forest areas, increase in energy consumption, the desegregation of social and community bonds and the spatial segregation of social classes. The scope of this work focuses on the impacts of urban sprawl in the provision of public utilities, mores specifically the sewer infrastructure. This pattern of spatial occupation makes more difficult the construction of sewers in conditions of sustainability and efficiency and increases the cost of provision and maintenance of the sewer services. So, this pattern of spatial occupation is harmful to the development and maintenance of these infrastructures. Territorial planning instruments in Portugal at the municipal level, namely the PDM (Municipal Director Plan) doesn’t study, in most cases, the impacts of urban expansion areas in public utility infrastructure like sewers, water supply electricity or natural gas, and so they don’t prevent urban dispersion and many of its negative impacts. This study, starts from these assumptions, to study if in a disperse municipality like Fafe, which is the case study, the ETAR of Serzedo (Guimarães) which serves most of the municipality, has the capacity to deal with the enlargement of the service to all urbanized areas in service and also deal with the spread of urbanization and possible urban areas. This work uses a methodology based on GIS (Geographic Information Systems) crosses geographic information about demography, altimetry, planning and occupation of territory as well as the data about the caudal in the ETAR. This methodology has the goal, as well, to know the occupied and available areas, the served and non-served population by sewers and potential population that will occupy the available areas for urbanization. This study, reaches several conclusions at the end related to the capacity of the Serzedo ETAR, which is studied in this dissertation. Of the period in analysis of almost a year, there are 34 days in which the percentage of pluvial waters in total influx surpasses the 20% foreseen in PEASAAR II, there being inclusively 3 days in which the influx surpassed the capacity of the ETAR which is 13772 m³. Only 22049 residents in 44831 inhabitants are served, of the drainage area in study in the municipality of Fafe. To these residents we have to add the residents of the freguesias served by the ETAR in the municipalities of Felgueiras and Guimarães. Regarding economic activities areas, only 17,8 hectares of the 38 hectares occupied are served by sewers. Of the urban expansion areas, only 22840 of 63800 potential residents and 96,8 hectares of 159,4 potential hectares of economic activities areas would be served with the current network, configuring better potential service in non-residential areas. With this data, one can conclude that the ETAR is sufficient for the current occupation of the territory, having nevertheless the need to control the illegal influxes into the system and increase the coverage of this service. In contrast, in case of urban expansion for residential and non-residential purposes to all areas available in the PDM, the ETAR doesn’t have the capacity to treat the increased influx.
The phenomenon of urban sprawl emerged during the XX century when the improvement of living conditions lead families to search for single family houses in more pleasant areas, namely in rural areas. This phenomenon was also boosted by other factors like the reduction of transportation costs and the low cost of properties in peri urban areas. Urban sprawl causes a variety of problems like the fragmentation of agricultural and forest areas, increase in energy consumption, the desegregation of social and community bonds and the spatial segregation of social classes. The scope of this work focuses on the impacts of urban sprawl in the provision of public utilities, mores specifically the sewer infrastructure. This pattern of spatial occupation makes more difficult the construction of sewers in conditions of sustainability and efficiency and increases the cost of provision and maintenance of the sewer services. So, this pattern of spatial occupation is harmful to the development and maintenance of these infrastructures. Territorial planning instruments in Portugal at the municipal level, namely the PDM (Municipal Director Plan) doesn’t study, in most cases, the impacts of urban expansion areas in public utility infrastructure like sewers, water supply electricity or natural gas, and so they don’t prevent urban dispersion and many of its negative impacts. This study, starts from these assumptions, to study if in a disperse municipality like Fafe, which is the case study, the ETAR of Serzedo (Guimarães) which serves most of the municipality, has the capacity to deal with the enlargement of the service to all urbanized areas in service and also deal with the spread of urbanization and possible urban areas. This work uses a methodology based on GIS (Geographic Information Systems) crosses geographic information about demography, altimetry, planning and occupation of territory as well as the data about the caudal in the ETAR. This methodology has the goal, as well, to know the occupied and available areas, the served and non-served population by sewers and potential population that will occupy the available areas for urbanization. This study, reaches several conclusions at the end related to the capacity of the Serzedo ETAR, which is studied in this dissertation. Of the period in analysis of almost a year, there are 34 days in which the percentage of pluvial waters in total influx surpasses the 20% foreseen in PEASAAR II, there being inclusively 3 days in which the influx surpassed the capacity of the ETAR which is 13772 m³. Only 22049 residents in 44831 inhabitants are served, of the drainage area in study in the municipality of Fafe. To these residents we have to add the residents of the freguesias served by the ETAR in the municipalities of Felgueiras and Guimarães. Regarding economic activities areas, only 17,8 hectares of the 38 hectares occupied are served by sewers. Of the urban expansion areas, only 22840 of 63800 potential residents and 96,8 hectares of 159,4 potential hectares of economic activities areas would be served with the current network, configuring better potential service in non-residential areas. With this data, one can conclude that the ETAR is sufficient for the current occupation of the territory, having nevertheless the need to control the illegal influxes into the system and increase the coverage of this service. In contrast, in case of urban expansion for residential and non-residential purposes to all areas available in the PDM, the ETAR doesn’t have the capacity to treat the increased influx.
Descrição
Dissertação de Mestrado em Sistemas de Informação Geográfica
Palavras-chave
Rede de drenagem , Fafe (Distrito de Braga, Portugal) , Águas residuais domésticas , Sistema de informação geográfica , Análise espacial , Estação de tratamento de águas residuais