Comparison of potential increases in juvenile salmonid rearing habitat capacity among alternative restoration scenarios, Trinity River, California

River restoration plans often propose multiple rehabilitation actions to address key habitat impairments, but they rarely attempt to quantify the potential benefits of alternative sets of actions for targeted biota. We use geomorphic and biological analyses to estimate restoration potential under three alternative scenarios for a 64-km section of the Trinity River, California, between the North Fork Trinity River and Lewiston Dam, which is the focus of habitat rehabilitation efforts under the Trinity River Restoration Program. The three scenarios are (1) increasing habitat quality by wood additions and alcove construction, (2) increasing habitat quantity by increasing sinuosity and side-channel length, and (3) increasing both habitat quality and quantity. For each scenario, we used existing stream habitat and juvenile salmonid data from previous studies to estimate potential improvements in fry or pre-smolt production. The potential increase in Oncorhynchus tshawytscha (Chinook salmon) and O. mykiss (steelhead) fry rearing capacity was 62 and 67%, respectively, for Scenario 1 (increasing habitat quality), and 36 and 44% for Scenario 2 (increasing habitat quantity). Only the most optimistic Scenario 3 (increasing both habitat quality and quantity) more than doubles potential juvenile salmonid production (112% increase in Chinook fry capacity and 107% increase in steelhead fry capacity). These quantitative predictions are useful in developing realistic restoration targets and evaluating whether proposed restoration actions can achieve the aims of a restoration program.