Modelagem do aporte de sedimentos aplicada à bacia hidrográfica do rio Una (SP): Uma proposta para o diagnóstico de assoreamento
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Data
2021-11-24
Autores
Silva, Rita de Cassia Ferreira da [UNESP]
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Universidade Estadual Paulista (Unesp)
Resumo
O transporte e deposição de sedimentos em bacias hidrográficas causado pela erosão hídrica, pode causar prejuízos irreversíveis, sobretudo quando são deflagrados em períodos de ocorrência de eventos extremos de precipitação pluviométrica. Os modelos hidrológicos são ferramentas com alto potencial de contribuição para estudar esses impactos e a simulação de cenários nesses modelos, é essencial para predizer impactos ambientais e dar suporte tecnológico para mitigar esses impactos. Esta pesquisa se propôs a investigar os processos que resultam na erosão em uma bacia hidrográfica, e a partir da sua dinâmica espacial elaborar um Indicador de Exposição e Risco Ambiental (IERA), capaz de mensurar os impactos do assoreamento nos rios da área de estudo. Para isto, foi aplicado o modelo de perda do solo em razão dos efeitos da intensidade da chuva sobre o solo (SWAT). A pesquisa foi realizada na Bacia Hidrográfica do Rio Una (BHRU), localizada na região sudeste do Estado de São Paulo, a qual apresenta um histórico de uso intensivo do solo para a olericultura, além de ser responsável por abastecer uma demanda considerável de hortaliças para vários municípios da grande São Paulo, justificando a preocupação com o uso da terra e o manejo de suas atividades agrícolas. O modelo obteve bons resultados em cinco das seis Sub-bacias da BHRU durante a calibração, apresentando o coeficiente NSE Bom e Muito bom (> 0,6) para 4 das 6 sub-bacias, enquanto o desempenho alcançado no PBIAS foi Muito bom e Bom para três sub bacias (< 25%) e Satisfatório para duas sub-bacias. Após validar o desempenho do modelo SWAT foram realizadas simulações considerando quatro cenários após a calibração: Cenário A, referente ao ano de 2007, Cenário B, referente ao ano de 2018 Cenário C, que seria um cenário hipotético conservacionista e Cenário D, referente uma previsão para o ano de 2028. Deste modo, foi elaborado o IERA que considerou 4 variáveis como fatores de impacto no assoreamento do rio Una (PPA, DP, ESCO, SED) e essas variáveis foram normalizadas e combinadas a partir da análise multicritério (AHP). Os resultados do índice demonstraram que em todos os cenários mais de 50% do território da BHRU está comprometido, das sub-bacias analisadas, as sub-bacias 1, 2, 4 apresentaram os piores resultados nos quatro cenários e sofrem maior risco de assoreamento, demandando priorização para ações de mitigação do assoreamento na BHRU. Espera-se que o método proposto possa contribuir com o desenvolvimento de um sistema de gestão e sirva de instrumento de apoio à decisão para o planejamento ambiental para priorizar áreas que necessitam de ações para mitigar os impactos dos processos erosivos em rios.
The transport and deposition of sediments in hydrographic basins caused by water erosion can cause irreversible damages, especially when they are triggered in periods of extreme rainfall events. Hydrological models are tools with a high potential to contribute to studying these impacts and the simulation of scenarios in these models is essential to predict environmental impacts and provide technological support to mitigate these impacts. This research aimed to investigate the processes that result in erosion in a watershed, and from its spatial dynamics to develop an Exposure and Environmental Risk Indicator (IERA), capable of measuring the impacts of silting in the rivers of the study area. For this, the soil loss model due to the effects of rainfall intensity on the soil (SWAT) was applied. The research was carried out in the Una River Basin (BHRU), located in the southeastern region of the State of São Paulo, which has a history of intensive use of soil for horticulture, in addition to being responsible for supplying a considerable demand for vegetables for several municipalities in greater São Paulo, justifying the concern with land use and the management of their agricultural activities. The model obtained good results in five of the six BHRU Sub-basins during the calibration, presenting the NSE coefficient Good and Very Good (> 0.6) for 4 of the 6 sub-basins, while the performance achieved in the PBIAS was Very Good and Good for three sub-basins (< 25%) and Satisfactory for two sub-basins. After validating the performance of the SWAT model, simulations were carried out considering four scenarios after calibration: Scenario A, referring to the year 2007, Scenario B, referring to the year 2018 Scenario C, which would be a hypothetical conservation scenario and Scenario D, referring to a forecast for the year 2028. In this way, the IERA was prepared, which considered 4 variables as impact factors in the silting of the Una River (PPA, DP, ESCO, SED) and these variables were normalized and combined from the multicriteria analysis (AHP) . The results of the index showed that in all scenarios more than 50% of the BHRU territory is compromised, of the sub-basins analyzed, sub-basins 1, 2, 4 presented the worst results in the four scenarios and are at greater risk of silting, demanding prioritization of actions to mitigate silting at BHRU. It is expected that the proposed method can contribute to the development of a management system and serve as a decision support tool for environmental planning to prioritize areas that need actions to mitigate the impacts of erosion processes in rivers.
The transport and deposition of sediments in hydrographic basins caused by water erosion can cause irreversible damages, especially when they are triggered in periods of extreme rainfall events. Hydrological models are tools with a high potential to contribute to studying these impacts and the simulation of scenarios in these models is essential to predict environmental impacts and provide technological support to mitigate these impacts. This research aimed to investigate the processes that result in erosion in a watershed, and from its spatial dynamics to develop an Exposure and Environmental Risk Indicator (IERA), capable of measuring the impacts of silting in the rivers of the study area. For this, the soil loss model due to the effects of rainfall intensity on the soil (SWAT) was applied. The research was carried out in the Una River Basin (BHRU), located in the southeastern region of the State of São Paulo, which has a history of intensive use of soil for horticulture, in addition to being responsible for supplying a considerable demand for vegetables for several municipalities in greater São Paulo, justifying the concern with land use and the management of their agricultural activities. The model obtained good results in five of the six BHRU Sub-basins during the calibration, presenting the NSE coefficient Good and Very Good (> 0.6) for 4 of the 6 sub-basins, while the performance achieved in the PBIAS was Very Good and Good for three sub-basins (< 25%) and Satisfactory for two sub-basins. After validating the performance of the SWAT model, simulations were carried out considering four scenarios after calibration: Scenario A, referring to the year 2007, Scenario B, referring to the year 2018 Scenario C, which would be a hypothetical conservation scenario and Scenario D, referring to a forecast for the year 2028. In this way, the IERA was prepared, which considered 4 variables as impact factors in the silting of the Una River (PPA, DP, ESCO, SED) and these variables were normalized and combined from the multicriteria analysis (AHP) . The results of the index showed that in all scenarios more than 50% of the BHRU territory is compromised, of the sub-basins analyzed, sub-basins 1, 2, 4 presented the worst results in the four scenarios and are at greater risk of silting, demanding prioritization of actions to mitigate silting at BHRU. It is expected that the proposed method can contribute to the development of a management system and serve as a decision support tool for environmental planning to prioritize areas that need actions to mitigate the impacts of erosion processes in rivers.
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Palavras-chave
Geotecnologias, Modelos hidrológicos, MUSLE, BHRU, SWAT