NCSA NEWS

Nearly half of newly hatched salmon die as they run to the ocean. Understanding how water flows around dams may improve their odds.

Spring is precarious for young salmon in the Pacific Northwest. From their nurseries in the mountain tributaries of the Columbia and Snake rivers, they are driven by instinct and warm spring temperatures to dash to the ocean. Many are no bigger than a baby's thumb, yet they cover 500 to 1,000 miles over two months. Nearly half die along the way from exhaustion, disease, pollution, and predation, aggravated by the aftereffects of passing through dams and plunging over spillways.

These fatalities are disheartening to Larry Weber, a hydraulic engineer from, of all places, central Iowa. Since 1988 he and a team of researchers and model builders at the Iowa Institute of Hydraulic Research (IIHR) at the University of Iowa, an Alliance partner, have been working with a cadre of biologists and engineers in the Pacific Northwest to reengineer hydroelectric dams to be more salmon friendly.

Survival rates for young salmon have climbed steadily -- the rate is higher than it has been in three decades. Data from the U.S. Commerce Department's National Marine Fisheries Service (NMFS), which is the lead organization for salmon management, show that in the early 1960s, 50 to 60 percent of salmon safely navigated the four dams crossed en route to the Pacific. The construction of more dams in the 1970s -- bringing to eight the number of dams migrating salmon crossed -- saw the overall salmon survival rate plummet to a dismal 25 to 30 percent. Today rates are back up to 50 to 60 percent because of dam reengineering efforts.

But juvenile survival rates that were adequate for maintaining a healthy adult salmon population in the 1960s are insufficient today. Consequently federal agencies are pushing for higher juvenile survival rates. NMFS would like per dam survival rates, which now average 85 to 95 percent, to reach 95 percent or better. In what amounts to a race to save the salmon, the last few yards are the hardest. "We've already found the obvious fixes," says John Ferguson, a biologist with NMFS. "Now we're looking for the tough ones. And that's going to require even more focus on the details."

This is where Weber comes in. He and an IIHR team are helping engineers eke out incremental improvements by using their software called River3D, which models river dynamics -- where the currents are fastest and how different columns of water mix as they plunge over the dam.

Last year Weber turned to NCSA for help in parallelizing his code to run simultaneously on several processors of the SGI Origin2000 supercomputer. With the code now ten times faster, his team is producing some of the most detailed models available. Those details may be a way of making dams safer for salmon.