1. What is the usable volume of a reservoir?

The usable volume is the difference between the maximum volume and the dead volume. It represents the portion of a reservoir’s water that can be effectively used to generate power.

2. What is a reservoir’s standard usable volume? And the optimal usable volume?

Every reservoir is unique. There is no standard or optimal volume that applies to all reservoirs.

3. What happens when the level of a reservoir reaches the dead volume?

The water level is below the intake level needed to drive the turbines, preventing power generation.

4. What can a reservoir do to avoid dead volume levels?

The NSO engages other power plants that have more water available or activates thermal generation to reduce hydro output and preserve the plant’s reservoir.

5. What is the NSO and what does it do?

The National Electrical System Operator (NSO) is responsible for coordinating and managing operation of electric energy generation and transmission plant operation within the National Grid (NG). It is tasked with streamlining operations and lowering costs, complying with technical standards and reliability criteria in the Grid Procedures approved by the National Electrical Energy Agency (Aneel), to ensure that every player in the electric industry has non-discriminatory access to the transmission network and can contribute towards expanding the Grid at lower costs and improve future operating conditions.

6. What are the factors that influence a decrease in a reservoir’s level?

A hydroelectric power plant's reservoir has several uses such as irrigation or supplying water and it can be used for fishing, leisure and tourism. The lack of rain and construction of unregulated dykes are the main causes of lower hydro plant reservoir levels.

7. Is it true that a hydroelectric power plant supplies the reservoirs of other plants downstream?

When a hydroelectric power plant, such as the Furnas Plant on the Rio Grande, in Minas Gerais, is located at the riverhead, the water driving the turbines also helps generate power at other plants downstream.

8. Does the power produced by a hydroelectric power plant supply nearby cities?

Most of a plant’s output in Brazil is sent to the Grid and distributed across the country. The NSO coordinates energy distribution in real-time based on consumer demand.

9. What is a spillway and what does it do?

The spillway is a structure that helps controls the reservoir’s water level. It is similar to the overflow system in a water tank. When a reservoir’s level is too high, the spillway opens to drain some of the stored water and safeguard the dam. The spillway water does not generate energy. It is returned to the river without passing through the turbines.

10. Do cities bordering a plant’s reservoir gain any compensation for flooded areas?

Yes. All cities bordering reservoirs receive Financial Compensation for Water Resource Utilization (CFURH). The is equivalent to 7% of all monthly hydro plant output, based on the Updated Reference Tariff (TAR) - which is set by the National Electrical Energy Agency (Aneel). The funds are shared among the states and cities located in areas of influence of hydro reservoirs and federal administrative departments. Aneel manages the collection and distribution of funds in line with current regulations. Financial Compensation funds for cities is based on two criteria: transfers for energy gain due to flow regularization and the area flooded by hydroelectric power plant reservoirs. (Source: Aneel)

11. How can a reservoir help control river flows to avoid flooding?

The plant’s dam controls the river's outflow from the reservoir. This mean the dam stores the water entering the reservoir and cam therefore control the outflow.

12. Is it possible to “close the tap” at a dam to conserve the water in a reservoir?

No, the water that leaves the reservoir is used to supply cities downstream. The National Water Agency (ANA) sets a minimum outflow needed to supply adjacent populations and maintain environmental and health conditions.