Further development of small hydropower facilities will significantly reduce sediment transport to the Pantanal wetland of Brazil

Small hydropower (SHP) facilities, which are defined by installed capacities 20% net retention of suspended sediments, two others retained between 10 and 20%, seven were within 10%, and six showed >10% net release. Bedload sediment transport was a small component of total sediment transport in rivers with high total sediment loads. Multiyear series of satellite images confirm sediment accumulation in several cases. Model predictions of the impacts of future hydropower facilities on suspended sediment concentrations and transport show retention of a large fraction (often much >20%) of sediment inputs. Summing riverine transport rates for inflows into the Pantanal indicates that currently envisioned future hydropower development would reduce the suspended sediment transport by ∼62% from the current rate. This study shows that if SHPs are built on sediment-rich rivers, this may prove problematic for the facilities as well as for downstream ecosystems. These results support recommendations that several river systems presently lacking dams in their lower reaches should be excluded from future hydropower development to maintain the sediment supply to the Pantanal

PRECISÃO DO MODELO DIGITAL DE ELEVAÇÃO (SRTM-Topodata) COM BASE EM DADOS DE PROJETOS DE APROVEITAMENTOS HIDRELÉTRICOS

A precisão altimétrica do Modelo Digital de Elevação – MDE tem sido tema de diversos estudos. Essa precisão exerce forte influência sobre as informações extraídas desses dados. Nesse contexto, o presente estudo compara dados observados em projetos de aproveitamentos hidrelétricos com dados extraídos do MDE. A comparação de dados altimétricos de informações extraídas pelo MDE com as contidas no Projeto Básico Ambiental – PBA desses empreendimentos, assumido como informação verdadeira, foi feita com o intuito de analisar o erro das informações extraídas do MDE em relação aos dados contidos no PBA e assim verificar a confiança nesse tipo de estimativa. Foram calculados o erro e o coeficiente de determinação de Pearson entre a altura da barragem (determinada com base no MDE) em relação à altura apresentada no PBA. Também foi comparada uma seção topobatimétrica do PBA com a mesma seção extraída pelo MDE. O erro relativo médio e o coeficiente de determinação entre as cinco alturas (estimadas e de projeto) foi de 11% e 0,874, respectivamente. O coeficiente de determinação, o erro médio quadrático e o erro médio entre as seções foram de 0,98, 1,56 e -0,02, respectivamente. A análise evidenciou que há erros em relação às informações extraídas do MDE. Entretanto, considerando a escala utilizada nesse estudo, os erros foram menores que os observados na literatura.Palavras-chave: MDE validação, Altura de barragem, Seção topobatimétrica. ALTIMETRY ACCURACY OF THE DIGITAL ELEVATION MODEL (SRTM-Topodata) BASED ON DESIGNS OF HYDROPOWER PLANTS DATA ABSTRACT: The altimetry accuracy measurements of the Digital Elevation Model - DEM have been the subject of several studies. This accuracy plays an important role on information extracted from these data. In this context, this study compares data observed in designs of hydroelectric power plants with data extracted from the DEM. The comparison between the altimetry of data extracted from the DEM with those contained in the Basic Environmental Project - BEP of these facilities, assumed as the true information, was done with the purpose of analyzing the error of the information extracted from the DEM in relation to the data contained in the BEP and thus verifying the confidence in this type of estimate. The error and the coefficient of determination between the dam height (determined based on the DEM) and the dam height presented in the BEP were calculated. Moreover, a river cross section published in the BEP was contrasted with the same cross section extracted from the DEM. The mean relative error and the coefficient of determination between the five heights (estimated and projected) was 11% and 0.874, respectively. The coefficient of determination, mean square error and mean error between sections were 0.98, 1.56 and -0,02, respectively. The analysis evidenced that there are errors in relation to the information extracted from the DEM. However, considering the scale used in this study, the errors were smaller than those observed in the literature.Keywords: DEM validation, dam height, cross section

PRECISÃO DO MODELO DIGITAL DE ELEVAÇÃO (SRTM-Topodata) COM BASE EM DADOS DE PROJETOS DE APROVEITAMENTOS HIDRELÉTRICOS

A precisão altimétrica do Modelo Digital de Elevação – MDE tem sido tema de diversos estudos. Essa precisão exerce forte influência sobre as informações extraídas desses dados. Nesse contexto, o presente estudo compara dados observados em projetos de aproveitamentos hidrelétricos com dados extraídos do MDE. A comparação de dados altimétricos de informações extraídas pelo MDE com as contidas no Projeto Básico Ambiental – PBA desses empreendimentos, assumido como informação verdadeira, foi feita com o intuito de analisar o erro das informações extraídas do MDE em relação aos dados contidos no PBA e assim verificar a confiança nesse tipo de estimativa. Foram calculados o erro e o coeficiente de determinação de Pearson entre a altura da barragem (determinada com base no MDE) em relação à altura apresentada no PBA. Também foi comparada uma seção topobatimétrica do PBA com a mesma seção extraída pelo MDE. O erro relativo médio e o coeficiente de determinação entre as cinco alturas (estimadas e de projeto) foi de 11% e 0,874, respectivamente. O coeficiente de determinação, o erro médio quadrático e o erro médio entre as seções foram de 0,98, 1,56 e -0,02, respectivamente. A análise evidenciou que há erros em relação às informações extraídas do MDE. Entretanto, considerando a escala utilizada nesse estudo, os erros foram menores que os observados na literatura.Palavras-chave: MDE validação, Altura de barragem, Seção topobatimétrica. ALTIMETRY ACCURACY OF THE DIGITAL ELEVATION MODEL (SRTM-Topodata) BASED ON DESIGNS OF HYDROPOWER PLANTS DATA ABSTRACT: The altimetry accuracy measurements of the Digital Elevation Model - DEM have been the subject of several studies. This accuracy plays an important role on information extracted from these data. In this context, this study compares data observed in designs of hydroelectric power plants with data extracted from the DEM. The comparison between the altimetry of data extracted from the DEM with those contained in the Basic Environmental Project - BEP of these facilities, assumed as the true information, was done with the purpose of analyzing the error of the information extracted from the DEM in relation to the data contained in the BEP and thus verifying the confidence in this type of estimate. The error and the coefficient of determination between the dam height (determined based on the DEM) and the dam height presented in the BEP were calculated. Moreover, a river cross section published in the BEP was contrasted with the same cross section extracted from the DEM. The mean relative error and the coefficient of determination between the five heights (estimated and projected) was 11% and 0.874, respectively. The coefficient of determination, mean square error and mean error between sections were 0.98, 1.56 and -0,02, respectively. The analysis evidenced that there are errors in relation to the information extracted from the DEM. However, considering the scale used in this study, the errors were smaller than those observed in the literature.Keywords: DEM validation, dam height, cross section

Further development of small hydropower facilities will significantly reduce sediment transport to the Pantanal wetland of Brazil

Small hydropower (SHP) facilities, which are defined by installed capacities 20% net retention of suspended sediments, two others retained between 10 and 20%, seven were within 10%, and six showed >10% net release. Bedload sediment transport was a small component of total sediment transport in rivers with high total sediment loads. Multiyear series of satellite images confirm sediment accumulation in several cases. Model predictions of the impacts of future hydropower facilities on suspended sediment concentrations and transport show retention of a large fraction (often much >20%) of sediment inputs. Summing riverine transport rates for inflows into the Pantanal indicates that currently envisioned future hydropower development would reduce the suspended sediment transport by ∼62% from the current rate. This study shows that if SHPs are built on sediment-rich rivers, this may prove problematic for the facilities as well as for downstream ecosystems. These results support recommendations that several river systems presently lacking dams in their lower reaches should be excluded from future hydropower development to maintain the sediment supply to the Pantanal