Meridian sits well back from the Boise River, and most of its water damage has nothing to do with it. A few miles north, it's a different story. The river runs through Boise, along Garden City, around Eagle Island and on past Star and Middleton, and in a big snowmelt year it can run high for weeks. Homes in the low areas near it are the ones that feel it.
How the River Rises
The Boise River's flow is shaped by snow in the mountains and by the reservoirs upstream that store and release it. In a heavy snow year, the reservoirs have to make room, and flows through the valley go up in spring and early summer. That's different from a flash flood: the river can stay high for a long stretch, keeping groundwater up and low ground wet the whole time.
Flood Stage, in Numbers
The common reference point is the gauge at Glenwood Bridge in Boise. Flood stage there is 7,000 cubic feet per second, a level the river reaches on average about once every five years. Above that, the impacts grow:
| Flow at Glenwood Bridge | What has been reported or forecast |
|---|---|
| Below 7,000 cfs | Localized flooding on parts of the Eagle Greenbelt can begin even before flood stage |
| About 7,000 cfs | Flood stage; Greenbelt sections close in Boise and Garden City |
| About 9,500 cfs | In 2017, low-lying areas of Garden City had problems and Eagle Island State Park closed |
| About 10,500 cfs | Flooding in low areas near the river in Boise, Garden City, Eagle, Star and further west |
| 16,000 cfs | Major flooding near the river; a flood that large hasn't happened since 1943 |
Live flows are on the U.S. Geological Survey's Glenwood Bridge gauge, and forecasts come from the National Weather Service in Boise.
Who Feels It
- Garden City sits right on the river, and its low areas have taken water in high years. The city and the U.S. Army Corps of Engineers are studying flood risk there; the city posts its flood information.
- Eagle has the Greenbelt and Eagle Island, where the river splits into channels. Greenbelt flooding there tends to start early.
- Star and Middleton are further west, with the river running between them. The state has closed river access sites there for flooding in high years.
- Boise keeps flood control information for properties near the river.
For most homes in these towns, a high river shows up as wetter ground and higher groundwater rather than water at the door. Crawlspaces and basements on low lots near the river are where it appears first.
What It Looks Like at a House
What you see: water rising in a crawlspace or basement during a long high-water stretch, a soggy yard on a low lot, or, in the worst cases, river water in a garage or across a floor.
What it usually means: river water or river-raised groundwater, not a pipe.
What happens next: wait until it's safe and officials say so. Then extraction, removal of what the water soaked, and drying to readings. River water is dirty water, so carpet, pad and soaked insulation usually come out rather than get dried.
Getting Ready in a High-Water Year
- know whether your property is in a mapped flood zone; FEMA's Flood Map Service Center shows the official maps, and Ada County posts flood preparation guidance
- follow city and county flood notices when the reservoirs start releasing more
- move valuables and papers out of basements and up off garage floors
- photograph the house and your belongings before the river rises
- check whether your policy covers flood at all; most homeowners policies don't
After the River Drops
Once the water goes down, the damage stays. Groundwater can stay high for a while after the river falls, so a crawlspace may keep taking water. Photograph everything, keep power off in wet areas until it's safe, and call. Drying a house after river water takes longer than after a clean leak, because more comes out and the ground around it is still wet.
Questions
Does Meridian flood from the Boise River?
Meridian itself is well back from the river. River flooding mainly affects low areas in Boise, Garden City, Eagle, Star and Middleton.
Is flood water covered by homeowners insurance?
Usually not. Flood coverage is generally a separate policy, often through the National Flood Insurance Program; FloodSmart explains it.
How long does the river stay high?
In a big snowmelt year, it can run high for weeks in spring and early summer, depending on the snowpack and reservoir releases.
Around the River
High water matters most in Garden City, Eagle and Star. Water under the floor afterward is covered on crawlspaces and basements.
Canal Seepage and Summer Groundwater: Why Crawlspaces Get Wet in July
Where the valley's groundwater comes from, and why it peaks in summer.
Window Wells and Egress Windows in Newer Basements
Why a basement window is the low point for snowmelt and sprinklers.