Abstract
Construction of dams for hydroelectric power requires significant quantities of soil and rock, which are often extracted in borrow pits from adjacent regions. Although the effects of dams on stream processes has received significant attention, the effects of borrow pits has not. The main objective of this study was to analyze the geomorphological and sedimentological aspects of two second-order streams, one of which was directly affected by the borrow pit located upstream of its source (Pedra Branca stream). Flow rates were measured and cross-sections of 600m stretches in both streams were monitored over a hydrological year. At the same time, sediments from the bed of the channels and soils on their banks had their physical and chemical characteristics evaluated. Streams sediments differed in their chemical and organic matter composition. The mean particle size of the sediment particles was different between the reference and degraded streams. The water flow was very similar to both streams, only varying along the seasonal seasons. However, the fluvial channels presented great geomorphological differentiation, mainly downstream, due to the location of the Pedra Branca stream and its proximity to the borrow pit. Despite the great importance for the production of clean electric energy, the construction of hydroelectric plants promotes persistent impacts that affect structural and functional aspects of the adjacent aquatic habitats. Borrow pits used for the construction of projects become large sources of sediment for aquatic environments, affecting the drainage network of the hydrographic basin and the balance of river erosion, transport and deposition processes. The results show the need to review the intervention protocols in borrow pits and the environmental legislation that regulates their rehabilitation.
Highlights
The 20th century was marked by the construction of large hydroelectric plants in response to the demand for cheaper and cleaner energy [1] and hundreds of reservoirs were built around the world
Differences in chemical composition of the fluvial sediments from degraded stream (DS) and reference stream (RS) were marked by the concentrations of K+ (135.56 mg/dm3 in RS and 44.55 in DS) and P (5.63 mg/dm3 in RS and 0.90 mg/dm3 in DS)
Sediments from RS tends to be richer in phosphorous (5.63 mg/dm3average) in relation to DS (0.90 mg/dm3), while organic matter contents of the sediments were similar in RS (0.50 dag/Kg) and in DS (0.74 dag/Kg)
Summary
The 20th century was marked by the construction of large hydroelectric plants in response to the demand for cheaper and cleaner energy [1] and hundreds of reservoirs were built around the world. The construction of large hydroelectric plants is among the most. Brazil is the country that most uses renewable sources in the production of electric energy, and almost 83% of its energy matrix coming from renewable sources [3]. Out of the total electric energy produced in the country, more than 63% is hydroelectric energy, with 1375 plants spread across the national territory [3,4]. Despite being a source of renewable electricity and the most cost-effective electricity, especially for large urban centers, they are responsible for a wide range of environmental impacts [5,6,7]
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