Sonoma Ecology Center

Why did the creeks start flowing again?

After the August 24 earthquake, centered in Napa, people all over the Valley began to report a strange phenomenon: Creeks that had been dry suddenly filled with water and flowed robustly, in the middle of dry season.

Reports of this kind came in for Carriger Creek, Felder Creek, Nathanson Creek, Arroyo Seco Creek, Calabazas Creek, Stuart Creek (where construction had to be halted for the fish-passage project when water arrived a few days after the quake), Hooker Creek, Yulupa Creek, and Sonoma Creek at Sugarloaf. As SEC Executive Director Richard Dale commented, “Calabazas Creek was roaring! It looked like spring.”

Sonoma Ecology Center has been monitoring area streams and tributaries at 18 sites each month in Sonoma Valley. Sonoma County Water Agency is funding this study, which will continue for at least two years, to understand the relationship between stream flows and ground water levels, and the effects of rainfall on both. The monthly monitoring at the 18 sites are focused on portions of Sonoma Creek and tributaries that historically go dry seasonally. Twice a year, we monitor approximately 70 locations throughout the watershed. We measure instantaneous stream flow in cubic feet per second, specific conductivity, water temperature, and air temperature.

With this detailed data set, collected since March 2014, Sonoma Ecology Center has been able to support research on this natural post-earthquake occurrence. UC Berkeley Professor Chi-Yuen Wang, who has studied earthquake effects on stream flow for many years, contacted the Center, and we were able to provide him with a great deal of information. On September 9, Professor Wang joined our researchers Alex Young and Bryan Sessor for their stream monitoring visits.

“Results of this monitoring cycle revealed that four streams that had gone dry in previous months were indeed flowing with water again,” remarked Sessor, citing Carriger Creek, Felder Creek, Nathanson Creek and Arroyo Seco Creek.  While on the monitoring visits, Professor Wang collected water samples for laboratory analysis. He has agreed to share his results with Sonoma Ecology Center as they both pursue answers to this natural riddle.

Thanks to Rebecca Lawton for her partnership on this project.