A “flood pulse” is one of the most important — and least understood — natural processes that shape healthy rivers. After heavy rain or snowmelt, water spreads across a river’s floodplain, soaking into soils, replenishing groundwater, and reconnecting seasonal wetlands. These temporary expansions of the river are essential drivers of life.

For fish such as salmon, flood pulses create nutrient-rich shallow areas that teem with insects and plant material — perfect rearing habitat for young fish before they migrate downstream. When these pulses are reduced or blocked, rivers lose much of their natural productivity, and species that evolved alongside these seasonal rhythms struggle to survive.

Flood pulses also recharge groundwater aquifers, support riparian forests, and help carry sediment that shapes channels and gravel beds. Understanding and restoring these pulses is one of the keys to resilient rivers throughout the Central Valley.

Common-sense dam management at Friant and other Central Valley Project facilities plays a valuable role in helping facilitate these beneficial pulses. By coordinating releases during wet periods, managers can mimic some of the river’s natural rhythms while still meeting human water needs. After fish benefit from these essential flows, a portion of this water is recaptured in the Delta and pumped south through the State Water Project and the Federal Central Valley Project pumps at Tracy — two of California’s most valuable water delivery assets. This coordinated system allows the state to support both thriving ecosystems and reliable water supplies for farms, cities, and communities across the Valley and in Southern California.

At the Fresno Aquarium, we’re committed to helping our community understand how water truly works — from the mountains to the river to the Delta.