BPA, in coordination with the United States Army Corps of Engineers and the U.S. Bureau of Reclamation, has created a modified streamflow database based on its hydroregulation studies of the Columbia River basin. Modified streamflows are historical streamflows that would have been observed if current irrigation depletions (as of year 2018) existed in the past and if the effects of river regulation were removed (except at the upper Snake, Deschutes, and Yakima basins, where current upstream reservoir regulation practices are included). Since irrigation practices have changed since the historical streamflows were observed, the historical streamflows have been adjusted to account for current levels of irrigation depletions.This database accounts for environmental impacts, changes to operation criteria from Biological Opinions, power revenue forecasts, flood control studies, operations planning, downstream benefit calculations and effects of new projects or plant data.

The 2020 data includes 90 years of streamflows (1929-2018) adjusted to 2018 irrigation depletions.