The Five-Mile Basin is a flood-control system that the U.S. Army Corps of Engineers built in the 1960s. It diverts peak flows from Big Chico Creek around central Chico toward Lindo Channel. Sediment builds up in the basin during high water, and that deposit affects how the system carries water over time.
Key takeaways
- The Five-Mile Basin was built by the U.S. Army Corps of Engineers in the 1960s.
- It diverts peak flows from Big Chico Creek around central Chico toward Lindo Channel.
- Sediment settles in the basin during high-water events, and the deposit changes the room the system has.
- A 2021 state notice limited the County's periodic removal of deposits from the basin.
- The basin's flows and the post-fire estimates describe the system, not individual lots or houses.
- A homeowner's concern is what water does on their own property, and that is read on site.
What is the Five-Mile Basin, and who built it?
The Five-Mile Basin is a flood-control system at Chico. The U.S. Army Corps of Engineers built it in the 1960s to take peak flows off Big Chico Creek.
A flood-control basin is a system that receives water during high flows and routes part of it away from the area that needs protection. The Five-Mile Basin does that for central Chico. When the creek runs high, the system diverts the peak flow around the city instead of letting it pass through the middle of town.
The Corps built the system in the 1960s, and it has been part of Chico's drainage ever since. Its design is one reason the creek is managed the way it is, and any change to it affects the city's flood planning.
How does the basin send water toward Lindo Channel?
The basin routes the peak creek flow away from central Chico toward Lindo Channel. The water leaves the creek corridor through the system and reaches the channel, which carries it on.
A diversion takes water from one path and sends it along another. At the Five-Mile Basin the peak flows leave the creek before they reach central Chico and are carried toward Lindo Channel. The city is spared the full force of the flow in the middle of town.
Diversion is not the same as removal. The water still has to go somewhere, and the capacity of the diversion and the channel below it decide how much can be carried without overtopping. The County's estimates address that question for the Five-Mile diversion.
The basin also shows how a single system can serve a whole city. A decision about maintenance, sediment or capacity affects many properties at once, and that is why the County and the City publish technical work. A homeowner benefits from knowing that the work exists, even when its detail is technical.
The practical point for a reader is that the diversion and the channel below it work as a pair. A channel that cannot carry what the diversion sends it would cause problems downstream, which is one reason the system is discussed as a whole rather than as separate parts.
Why does sediment matter to the basin?
Sediment settles in the basin during high-water events. The deposit takes up room the system needs for water, and it changes how the basin behaves in the next high flow.
Water slows down in a basin, and when it slows it drops what it carries. Over many events the fine material forms a deposit. The deposit reduces the space water has to move through, and it changes how high the water rises for a given flow.
That is why sediment is a concern for the system as well as for individual homes. A basin that holds more material has less capacity, and the County's maintenance of the deposit is part of how the system keeps its room.
What did the 2021 state notice do?
A 2021 state notice limited the County's periodic removal of deposits from the basin. Limited removal means deposits can remain in the system longer between events.
Removal is how a basin keeps its capacity. A notice that limits removal changes the schedule the County can follow, and it means deposits can build up between events. The practical consequence depends on the flows and the maintenance that follows.
The notice is a state document, and the County's technical work is the place to read its detail. This guide does not interpret the legal reasons behind it, but it does explain why the basin's deposit matters to the city.
How do the Park Fire and the County's estimates connect to the basin?
The Park Fire began in Bidwell Park on July 24, 2024. The County's November 25, 2024 technical memo estimated the diversion overtops at about 1,950 cubic feet per second under pre-fire conditions, and higher post-fire flows for storms of different return periods.
After a fire, storm water runs off faster and carries more sediment. The basin receives that flow, so the post-fire estimates describe the load it may have to carry. The memo's figures are the planning numbers for that load.
The estimates are system figures. They show the scale of the challenge at the diversion and do not describe any particular street, lot or house. A homeowner should not read them as a forecast for their own property.
What does this mean for a homeowner in Chico?
The basin is designed to lower the risk to central Chico from peak creek flows, but it does not remove every risk to every property. A homeowner's exposure depends on their lot, its grade and its openings, and on how the water reaches the house.
A house can take water from the creek side, from the yard, from a storm drain that backs up or from a failed line inside the house. The basin is designed for the creek side at the system scale. The other routes are the homeowner's concern and the crew's work.
A homeowner who wants to understand their risk can walk the lot in a storm, note where water runs and keep a record. The crew that dries a house after water reads the path the water took, and that path is the most useful local evidence.
Where should a reader go for the detailed planning documents?
The City of Chico's General Plan update covers the Chico drainage system in its draft environmental impact report, under section 4.9 on hydrology and water quality. The County's technical memo and the state notice are the sources of the figures quoted here.
The City's draft environmental impact report contains a hydrology and water quality section that covers the same drainage system. It is the planning document to read for the wider picture, and it is published on the City's own website.
The County's technical work and the state notice are the places to read the flow estimates and the removal limits in full. A reader should take the figures in those documents as they are written, rather than as a summary of this guide.
What should I do if water reaches my house from the creek side?
Keep people and pets out of standing water, turn off power to wet areas if you can do so safely, photograph the water line and call for extraction. Keep the damaged materials until your insurer has seen them.
Calls for water extraction are answered 24/7 at (833) 490-5225, and a crew is sent as fast as one is available. No arrival time is promised. The crew reads the silt and the water line to show how the water arrived.
Keep a written record of the water, the time you first saw it and each step you took. That record and the crew's readings are the best evidence of what reached your house.
How should a reader use the basin's figures?
Use the basin's figures to understand the system, and use the house's own readings to understand the property. The two answer different questions, and mixing them up leads to the wrong conclusion about a specific address.
The Corps design, the diversion capacity and the County's post-fire estimates describe the system as a whole. They help explain why central Chico is protected in the way it is, and why the burn raised questions for the city. They do not tell a reader which street will take water.
For a specific house, the evidence is the grade, the openings, the drains and the water marks from past storms. A crew that dries a house reads those points and records the path the water took. That record is the most useful local evidence a homeowner can have, and it complements the system figures rather than replacing them.
If you are unsure whether your property is affected, ask a restoration crew to read the grade and the openings the next time water is near the house. The reading is practical, and it answers the question for your lot in a way that no system-scale figure can.
Frequently asked questions
Who built the Five-Mile Basin?
The U.S. Army Corps of Engineers built it in the 1960s as a flood-control system that diverts peak flows from Big Chico Creek around central Chico.
Where does the diverted water go?
The diverted peak flow is carried toward Lindo Channel, which takes the water on from the basin.
Does the basin stop all flooding in Chico?
No. It addresses peak creek flows at the system scale. Water can still reach a property through its own lot, its drains or a failed line, and the crew reads those routes on site.
Why does the County remove sediment from the basin?
Removing deposits keeps the basin's capacity for water. A 2021 state notice limited how often and how much the County could remove, which is part of why sediment matters.
Is my house in the basin's path?
The basin is a system at the city scale and the County's estimates do not map individual houses. Walk your lot in a storm and note where water goes, since that tells you more about your property than the system figures do.
Can I ask the County for the flow figures for my street?
The memo gives system-scale estimates, and it does not map individual streets. For a property-specific question, a site walk and a record of past storms will tell you more than the system figures.
Who maintains the basin day to day?
The County and the State handle the basin's maintenance and the removal of deposits, subject to the state notice. Questions about current maintenance should go to those agencies, since a restoration crew does not run the system.
Sources
This guide is general information for Butte County homeowners, not a substitute for an on-site inspection. Prices are estimates. See our disclaimer.