Spatial and temporal variation of the sedimentation rate in Salto Grande Reservoir (Americana-SP) and its influence on the limnological caractheristics of the system.

Author(s)

Mauricio Augusto Leite

• Document type: Master's Dissertation
• Press: São Carlos.
• Institution: Universidade de São Paulo (USP). Escola de Engenharia de São Carlos (EESC/SBD)
• Defense date: 1998-08-31

Examining board members

Evaldo Luiz Gaeta Espindola; Maria do Carmo Calijuri; Iva de Haro Moreno

• Advisor: Evaldo Luiz Gaeta Espindola

Abstract

The present work shows the study developed in Salto Grande Reservoir (Americana-SP), from August 1996 to July 1997, to determine the sedimentation rate of allocthonous material, inputted in the reservoir by its main tributary (Atibaia river) and by the watershed, relationed with the physical, chemical and biological characteristics of the system and its relationship with the landuse, climatology and operational mechanisms of the dam. Five samplig stations were selected considering the reservoir morfometry, where sedimentation traps (aspect ratio 3:1) were incubeded monthly, at 30 e 70% of the local depht, during 24 hours. At the moment of incubation, water temperature, pH, conductivity, dissolved oxigen, light penetration, suspended matter and nutrients (total phosphorus and nitrogen) were measured. In the settled material, dissolved and total nutrients, suspended matter (total, inorganic and organic), chlorophyll a and phaeopigments were determined. The data shows a deposition gradient of the suspended matter from Atibaia river (sampling station 1) toward to the dam (sampling station 5), with higher values in rainy season (90,0 mg.cm -2 .day -1 and 2,23 mg.cm -2 .day -1 at station 1 and 5 respectively) compared with dry season (6,0 mg.cm -2 .day -1 and 1,0 mg.cm -2 .day -1 at station 1 and 5, respectively). The major contribution of the suspended matter is given by the inorganic component (60 to 90%) at all stations in the rainy season, however, in dry season the organic component became more expressive at stations 3, 4 and 5 (about 50%). The settling flux of total nitrogen and total phosphorus shows the same pattern of the suspended matter, with maximun values in the traps incubeded at 70%. The sedimentation rate for total nitrogen varied from 0,1 mg.cm -2 .day -1 to 1,0 mg.cm -2 .day -1 (sampling station 1, in July and December 1996, respectively) and for total phosphorus from 4 µg.cm -2 .day -1 to 50,0 µg.cm -2 .day -1 (sampling station 1, in July and December 1996, respectively). The main factors that influence the sedimentation process are precipitation, inflow, residence time of water and the different land use around the reservoir, mainly the sugar cane culture. Regarding to allochtonous material sources inputted in the reservoir, was observed that the principal contribution is from Atibaia river, settling about 90% of the suspended matter between station 1 and 2, where there is the formation of a delta. Sedimentation rate data for suspended matter and nutrients (total phosphorus and nitrogen), are considered very high when comparing with other systems, showing a increase on eutrofication process, lost of multiple uses and the siltation of the reservoir’s entry. (AU)