Submitted By Pacific Northwest National Laboratory, Richland, Washington
Changes in water pressure and dissolved gas concentrations can affect the survival of fish passing downstream through turbines or tailwater environments at hydroelectric dams. To address this issue, the U.S. Department of Energy has asked the Pacific Northwest National Laboratory (PNNL) to evaluate the pressure changes that occur during turbine passage and the resultant injury and mortality to fish exposed to different dissolved gas concentrations in the laboratory environment.
Turbine Passage System
The turbine passage simulation system or hyperbaric chamber (Figure 1) will be used to replicate the pressure history that fish would experience in passing through a hydroelectric turbine. The test system is comprised of two 11-inch (27.5cm) diameter acrylic chambers, 22 inches (55 cm) long, a system of hydraulic and pneumatic cylinders, their control systems, and a water supply system.
The chambers are connected to the hydraulic cylinders, which in turn are connected to pneumatic cylinders. A computer-controlled air pressurization system attached to the pneumatic cylinders controls the positions of hydraulic cylinders to either pressurize or depressurize the chambers. The maximum pressure of the chamber is 100 feet of head. The system can drop the pressure from 100 feet of head to close to the vapor pressure of water in about 0.1 second.
The air cylinders used in the pressurization/depressurization sequence are controlled by a computer program, the Labtech Control Program (Labtech Control Version 10.12 for Microsoft® Windows&trade, Laboratory Technologies Corporation). For our testing requirements, only one chamber will undergo the turbine pressure condition. The second chamber will be the control chamber.
The water supply subsystem delivers atmospheric-equilibrated water or gas-supersaturated water to the chambers, depending upon the test scenario. Gas supersaturated water is produced by a gas supersaturation column (Figure 2). The 9-ft tall column has two inflow hoses, one each of gas and water. Inflow water is maintained at a constant pressure with the use of a centrifugal pump. Water enters at the top of the column where a gate valve controls flow rate as measured by a flow meter. Compressed air is injected either at the top or into the bottom of the column, and an air bleed vent is located at the top of the column. The injection air supply and air vent have individual control valves and flow meters for regulating flows. A pressure gage is located on the control panel for monitoring column internal pressure. Outflow occurs from the bottom of the column through a gate valve. A sight glass, located on the side of the column, has a proximity switch that can be moved up or down to control the injection air supply. The pressure in the column can be maintained at constant levels by manipulating the combination of water inflow and outflow, along with the column water level. A main valve controls water flow to the entire system. Water flowing from the column is discharged to a trough, flowing over the sensor of a Sweeney saturometer, which measures total dissolved gas. Water from the trough is pumped to the turbine chambers. Adjusting a main valve in the water supply line controls pressure. The supply line then splits to provide equal flow and pressure to each chamber. The turnover rate for each chamber is approximately 15/hr at programmed flows of 2.26 gpm under the high pressure (30 ft depth) scenario. Turnover rate for the surface pressure scenario is 30.2/hr at programmed flows of 4.53 gpm. These rates are sufficient to maintain adequate dissolved oxygen concentrations in the test chamber during fish holding periods. The outflow is collected via exit tubes and water quality measurements are made separately for the control and treatment systems. Fish are loaded into the chambers via a movable PVC fish inlet pipe. A metal fish isolation plate can be rotated to an open position, allowing fish to pass in or out of the chamber, or it can be rotated to cover the inlet and trap fish inside the chamber. Fish are removed using the same pipe after it has been rotated to a downward position.
The basic experimental design will consist of exposing fish to:
- Three gas saturation treatment levels: 100% of saturation, 120% of saturation and 135% of saturation
- Two pre-turbine acclimation water depths: near surface (101kPa) and approximately 30 ft (191 kPa).
The actual test sequence will be randomized among the six test conditions. The fish will be held in the test chambers overnight (16-20 hrs) to acclimate to the total gas pressure and pre-turbine water depth treatment levels. After acclimation, the turbine passage pressure scenario will be applied to the treatment fish. The control fish will be exposed to the same total dissolved gas and (pressure) depth exposure as the test group. However, they will not be subjected to the turbine pressure scenario. Based on previous tests (Montgomery and Watson 1995), the exposure time simulating pressure changes for turbine-passage will be ~50 sec (Figure 3). Fish will be held for up to 48 hours after the test to observe post-test mortalities. Gills will be microscopically examined for a random subsample of fish to quantify any damage to gill filaments.
Tests are planned with rainbow trout (Oncorhynchus mykiss), American shad (Alosa sapidissima), and bluegill sunfish (Lepomismacrochirus). Sufficient test groups of fish will be available to provide the same size/age for each test condition.
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