For years, Matadero Creek in Palo Alto's Barron Park neighborhood flowed year round. But on June 27, the water level dropped by a foot, with sections of the creek suddenly turning bone dry. Even the birds seemed nervous about the change, nearby residents said.
Creekside Inn Manager Luis Carreno said the disappearing water has economic significance. Visitors who stay at the inn because of its location next to the usually burbling creek were asking what had happened, he said.
Carreno asked the City of Palo Alto and the U.S. Department of Fish and Game to look into the disappearing water, but no one seemed to know what happened.
Residents and experts are speculating about a number of possible causes. For one thing, three earthquake faults run through the area.
"Faults can act as a barrier to the movement of groundwater, and there can be significant differences in groundwater levels across faults," said Vanessa De La Piedra, senior water resources specialist for the Santa Clara Valley Water District.
The faults cause folds in subsurface layers that can channel underground water in different directions.
The cleanup of toxic groundwater could be another factor. Groundwater removal in the area since 1996 has included pumping, cleaning and discharging the clean water into Matadero Creek, according to the state Department of Toxic Substances Control.
Wells extracted 104,180 gallons of water per day beginning in 1996, according to the department. The pumping doubled the water in the creek during the driest months, according to U.S. Geological Survey statistics from 1953 to 2011. In fact, from 1953 to 1963, no water was found in the creek from May through September, the USGS reported.
Because of the discharges, though, the creek levels have risen from their historic levels, said Randi Jorgensen, Department of Toxic Substances Control spokesperson meaning that residents have grown accustomed to an unnatural level of water in the creek.
Could the summer's sudden drop in water have been caused by changes in the cleanup effort?
Brenda Ma, senior project engineer for Arcadis, a contractor working on the water remediation at 3400 Hillview Ave., said the pump there did shut down for a few days due to a malfunction around the end of June. But it was put back on line.
She said the creek's water drop is probably due to the dry winter rather than the pump malfunction.
"The dates don't correspond from the malfunction to when the creek went dry," she said.
Jorgensen said last week that fewer wells are running overall in the cleanup effort, which means less water discharged into the creek.
"As the contamination has reduced, we've needed fewer wells to operate," she said.
Another possibility is that the groundwater pumping removed too much water near and under Matadero Creek. That, said De La Piedra, could cause a drop in both the groundwater table and stream flow if the water is not replenished by rainfall, runoff or water from other tributaries.
Ma also did not think the wells were lowering the underground water table.
"There are so many factors. Our system is relatively small," she said.
Then there are seasonal variables, along with the natural contours of the creek.
A certain stretch of Matadero Creek where Barron Park historian Doug Graham lives "was observed to have a constant, year-around low flow even during drought periods." But starting at the Laguna Avenue bridge, "It was generally dry below that bridge from mid-summer until the winter rains started in earnest."
De La Piedra agreed that water levels in Matadero Creek are variable.
"There are reaches of Matadero Creek that dry out during the summer or drought conditions," she said.
Water still flowed in the neighborhood's Bol Park last week, and it continued to Josina Avenue. But where the creek runs under Matadero Avenue at the Matadero Avenue Bridge, the water stopped abruptly. The creek bed was bone dry.
The likely culprits for now are three extraction pumps that have been shut down for repairs since mid-to-late July, Jorgenson said. Those wells were expected to be running again by the end of the week. But after the pumping is completed, the creek some residents have come to know could look and act differently, she said.
"We don't know if those areas of the creek are dry because they were dry originally during this time of year or if it is because of drought," she said.