Big Chico Creek: Bidwell Park’s Thread of Life
By Jon Aull
Lately, it seems like it has been raining every day, and many of us have had enough of it. But a few soggy, gray days are a small price to pay for our precious water. Soon enough it will be 100 degrees and the wind will feel like a hair dryer. The rain that’s falling now (and the snow that falls higher up in the watershed) will supply the drinking water for Chico, irrigation for agriculture, and water for wildlife for another year. Where it can, that precipitation filters into the ground, saturating the pores between soil particles and rocks. This saturated area is what we call an aquifer. Much of the Big Chico Creek watershed is covered with a hardpan of ancient volcanic mudflows (the Tuscan Formation that you can see in Upper Bidwell Park), and the water can only permeate that layer where it is cracked. The water that finds its way to the lower aquifer keeps flowing downhill, just as the creek does but more slowly. This groundwater takes years to reach the valley floor. The water that comes out of our faucets now is the rain and snow of past years, filtered through the aquifer. The water that can’t filter into the ground runs off the surface, downhill to Big Chico Creek.
Below: ”Dragon’s Teeth“
Big Chico Creek starts off at about 6000 feet of elevation on Colby Mountain above Butte Meadows and flows 45 miles to the Sacramento River, nearly 11 miles of that through Bidwell Park.
At Five Mile recreation area in Bidwell Park, the creek meets a dam, which is always kept open, allowing about 1500 cubic feet of water to go through every second (cfs). The water that can’t go through the dam takes a right turn towards another dam at the beginning of the Lindo Channel (Sandy Gulch), which allows another 6000 cfs into the channel. The rest (up to 8500 cfs) goes down the Sycamore Channel, over cement “dragon’s teeth,” which break up the force of the water to reduce erosion, to Mud Creek, eventually rejoining Big Chico Creek before it joins the Sacramento River. This flood control project was built in 1965 and includes 23 miles of levees along Sycamore Channel/Mud Creek.
Below: The Chico Creek Diversion Structure. Click here for larger image.
While in Chico we get an average of about 26 inches of precipitation a year, at the headwaters in the mountains, the average is about 80 inches.
Much of the precipitation in the mountains falls as snow. That snow is like a reservoir, holding extra water for delivery to the valley into the spring. With climate change and rising temperatures however, we are seeing earlier snowmelts, so this snow reservoir will have less and less water available for later in the season.
Reduced creekflows and higher creek temperatures affect all kinds of wildlife, from the fish, frogs and insects that live in the creek, to the beavers, raccoons, kingfishers, and others who depend on the narrow riparian corridor of Big Chico Creek for their survival.
Spring run salmon are one example. Adult Chinook (King) salmon enter Big Chico Creek some time between March and June and spend the summer in deep, cool pools like Salmon Hole in Upper Bidwell Park. Amazingly enough, these salmon, which depend on cold water for survival, survive the blazing summer heat without eating, just waiting for their chance to spawn during September and October when the water cools. Higher water temperatures provide less oxygen for the fish and make them more susceptible to disease. In low water years, salmon are not able to make it past Salmon Hole, where a damaged fish ladder obstructs passage to spawning sites further upstream. Big Chico Creek is a valuable habitat, as few streams support these fish, listed as threatened on the Federal Endangered Species List.
There has been talk of farmers selling their surface water allocations downstream and possibly increasing groundwater pumping to replace that water.
There is a lot that is unknown about the aquifer: how the water flows through it, where the water enters it, the rate of flow, and what the impact of increased groundwater pumping will have. What we do know is that water connects all of us in this watershed, mountains and valley, people and wildlife, and changes anywhere can affect all of us.