What does record runoff mean for Mono Basin stream restoration?

Exceptional runoff offers exceptional restoration opportunities

by Robert Di Paolo

The seasonal runoff (April through September) in the Mono Basin this year is forecasted to be 243% of the long-term (1971–2020) mean runoff, which will make it the single wettest seasonal runoff period in more than a century. While this impressive percentage provides us with a general sense of what kind of runoff will occur this year, the stream restoration benefits associated with an exceptionally wet runoff year are best understood in terms of three factors: magnitude, timing, and frequency.

Larger flows restore more

Runoff magnitude is perhaps the most exciting consideration in a wet year like this. When I look at a hydrograph (streamflow over time), say during one of the Los Angeles Department of Water & Power’s (DWP) planning meetings, my eyes can’t help but jump to the highest point of the graph to examine how big the peak flow will be. While DWP’s presentations often discuss the logistical challenges of operating their outdated water conveyance infrastructure, I’ve found my attention swept away by daydreams of 1,000 cubic feet per second (cfs) of water spreading across Rush Creek’s floodplains and through braided channels, with stream banks armored by willows, black cottonwoods, and Jeffrey pines. What large trees might fall into the creek? What kind of log jams will form, creating fish habitat and stream complexity? What new channels, pools, and delta habitat will establish after such a large flow recedes? Bottom line, large-magnitude flows are destined for Mono Lake, which will bring tremendous stream restoration potential.

Timing is everything

Runoff magnitudes indicate what restoration processes will occur, but runoff timing affects how those magnitudes will be enhanced or diminished, and their duration. DWP’s current runoff forecast predicts a peak flow of more than 930 cfs occurring in the Rush Creek bottomlands near the end of June, but temperatures will ultimately determine when and how quickly the snow will melt, which in turn will dictate runoff magnitudes. In this way, runoff timing plays a critical role in what kinds of flow magnitudes will occur—before, during, and after the peak runoff period. As Greg Reis explains on page 12, “there is a chance that the minimum required peak flow of 750 cfs could be reached, however, an early peak could be captured by [Grant Lake] reservoir and a cool summer could result in a lower peak but extend high flows well into August.” Critically, ecological processes such as willow seed dispersal or trout spawning rely on a “natural” timing of runoff. It’s for this reason that DWP is required to mimic the natural runoff

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