Peterson, E. B. 2023. Retrospective analysis of the relevance of Trinity River flows to Trinity Lake (reservoir) levels, water years 1965-2021. Report. Trinity River Restoration Program, Weaverville, California. Available: https://www.trrp.net/library/document?id=2617.
Water from Trinity Lake (a reservoir) flows in two directions: releases to the Trinity River and diversions to the Central Valley Project (CVP). Releases to the river are scheduled ahead of time, are publicized, and are highly visible to the public through direct observation of the river. Diversion to the CVP is done largely out of public view through tunnels to Whiskeytown Lake, where flow is not readily perceived, and diversion rates can only be found from data issued afterward. The result is a common, intuitive assumption is that the level of Trinity Lake is primarily affected by restoration releases to the river, both in terms of timing of peak volumes and in the water surface elevations experienced during recreational use. That assumption does not consider the volume of water diverted, the timing of diversions, or other factors.
This paper analyzes the timing of peaks in Trinity Lake water volume, and the fullness experienced on the 4th of July, to determine the relative importance of carryover (storage) volume, inflow, diversion, and allocated release for restoration and maintenance of the Trinity River.
Results demonstrate that while the allocated release to the river is relevant to the timing of lake volume peaks and lake fullness on the 4th of July, the relevance is small compared to other factors. For timing of the peak volume, inflow was of greatest relevance, followed by diversions to CVP; allocated volume for river release had weak statistical significance and carryover volume had no discernable relevance. For lake fullness on the 4th of July, inflow was of greatest relevance again, followed by carryover, then diversions and finally allocated volume for the river. Diversion explained more than two times more variation than did allocation to the river.