PNNL

Abstract

The Mekong River is one of the most biodiverse rivers on the planet. As a result, many communities located near the river and its tributaries rely on fisheries for sustenance as well as economic viability. Along the Mekong River mainstem, there are plans for 11 new hydropower projects with potentially several hundred smaller hydropower projects along the tributaries. Currently, there is little information to guide construction of fish-friendly hydropower systems. Preliminary guidelines for construction on the mainstem Mekong call for safe upstream and downstream fish passage for 95% of target species. To understand the hydraulic conditions at existing dams in the region, Sensor Fish, a small neutrally buoyant autonomous sensor package capable of measuring and collecting in situ motion and force data, were deployed at Nam Ngum Dam in Lao PDR. The Sensor Fish were released through two turbine units—Unit 1, which contains an older 17.5-MW Francis turbine, and Unit 4, which contains a slightly newer 40-MW Francis turbine. Comparisons were made between the results from the two turbine units at Nam Ngum Dam to results for four hydroelectric dams in the U.S. Pacific Northwest for which live fish survival studies had been conducted. Three of the U.S. dams have Francis-turbine units and the other has a fish-friendly Kaplan turbine. Based on the occurrence of severe acceleration events, the survival rate of juvenile salmonids at a dam like Nam Ngum Dam would be expected to between the 11.1% to 54.1% survival rates experienced at the U.S. with Francis turbines and the 97.0% survival rate at the U.S. dam equipped with fish-friendly Kaplan turbines. Between the newer and older turbine units tested at Nam Ngum Dam, the newer Unit 4 had a higher median nadir pressure of 126 kPaA compared to 99 kPaA for Unit 1. Based on a dose-response relationship for juvenile Chinook salmon, these nadir pressures predict probabilities of mortal injury of 5% for Unit 4 and 12% for Unit 1. With respect to both pressure and acceleration, the older 17.5-MW Francis turbine had more severe hydraulic conditions than the newer 40-MW Francis turbine. Francis turbines, like the ones involved in this study, are the most common type of hydropower turbines in the throughout the world. The results from this study can be used to guide the construction of new hydropower structures and make design and operational changes to existing hydropower structures that will improve fish passage conditions.