DEVELOPMENT OF A RIVER SEDIMENT TRANSPORT MONITORING SYSTEM FOR LARGE RESERVOIRS

Abstract

Determining the amount of sediment being transported by rivers is fundamental to determine the environmental impact on reservoirs, as well as to estimate their life span. This monitoring is particularly important for large hydroelectric dams such as the Itaipu hydroelectric facility on the Parana River, which provides over 24% of the electricity needs for Brazil. A system was developed to continuously monitor sediment transport in the main rivers of the watershed acting on this reservoir using specifically developed turbidity sensors, commercial water level meters, manual sediment sampling, and laboratory analyses. The turbidity sensor was designed using a single optical sensor chip and light source LED that works with a single 9V battery, which can last over 4 months of continuous hourly monitoring. An economical commercial data logger was used to trigger readings and store the sensor response. This data, together with laboratory analyses of sediment samples were used to constantly calibrate sensor readings and determine sediment concentrations in the rivers. Total suspended loads were calculated using river water flow rates as determined by the water level meters and velocity profile measurements. Furthermore, two types of structures were developed to house the sensors in the rivers: 1) buoys and 2) structures fixed to the pillars of bridges. Although both structures protected the sensors well during extreme flow conditions, the buoys required less maintenance because of their constant movement, which limited fouling of optical sensors. Comparisons of laboratory analyses showed good correlation between turbidity sensor readings and manual sediment sampling. This system enabled an economical and continuous monitoring of suspended sediment load for a variety of river conditions. The monitoring results were used to determine total sediment contribution to reservoirs.