In situ characterization of turbine hydraulic environment to support development of fish-friendly hydropower guidelines in the lower Mekong River region

•The first physical & biological evaluation of hydro turbines in Lower Mekong River.•Testing was conducted on an older 17.5-MW turbine and a newer 40-MW turbine.•The newer turbine had fewer occurrences of severe acceleration events.•The newer turbine had better pressure environment for fish during runner passage.•This study can be used to guide the design of new hydropower in the region. The Mekong River is one of the most biodiverse rivers on Earth. Many communities located near the river rely on fisheries for sustenance and economics. Along the Mekong River mainstem there are plans for 11 new hydropower projects, with potentially several hundred smaller projects along tributaries. To understand the hydraulic conditions at existing dams in the region, Sensor Fish were deployed at Nam Ngum Dam in Laos. The data collected by Sensor Fish can be used to predict fish injury/mortality if there is a dose-response relationship for the species of interest. The Sensor Fish were released through two units—Unit 1, an older 17.5-MW Francis turbine, and Unit 4, a newer 40-MW Francis turbine. Comparisons were made between the Sensor Fish measurements at Nam Ngum to those from four hydroelectric dams in the U.S. Between the newer and older turbine units tested at Nam Ngum, the newer Unit 4 had a higher median nadir pressure of 126 kPaA compared to 99 kPaA. With respect to both pressure and acceleration, the older Unit 1 had more severe hydraulic conditions. By understanding the physical conditions within existing hydropower projects, and the potential ecological impact those conditions could have on the local fauna, better informed decisions can be made regarding project operations. The results from this study can also be used to guide the engineering design of new hydropower turbines that will improve ecological conditions.