Cogswell Reservoir reservoir
Cogswell Reservoir
Cogswell Reservoir is a man-made reservoir located in the San Gabriel Mountains of Los Angeles County, California. The reservoir was built in 1954 by the Los Angeles County Department of Public Works as part of the San Gabriel River Watershed. It is a significant source of drinking water for the region and can store up to 8,000 acre-feet of water.
Cogswell Reservoir is fed by both surface flow and snowpack from the San Gabriel Mountains. The San Gabriel River, which originates from the mountains, is the primary surface flow provider to the reservoir. Snowmelt from the surrounding mountains also contributes to the reservoir's water supply.
The water from Cogswell Reservoir is used for both agricultural and recreational purposes. The water is mainly used for irrigation in the San Gabriel Valley, while recreational activities such as fishing, boating, and hiking are also popular in the area. The reservoir is managed by the Los Angeles County Department of Public Works and is an important source of water for the region.
Daily levels at Cogswell Reservoir
Storage volume, pool elevation, and total release plotted from the operating agency's daily observations.
Storage
acre-ft · code 2
Plan around the weather
Same NOAA / yr.no feed Snoflo's iOS app uses. Watch the precipitation column on the meteogram -- rain on the basin upstream typically lifts inflow 24-72 hours later.
Next 5 days, hour by hour
Temperature line with weather symbols on top, snow + rain accumulation as columns, humidity as a dotted line.
5-day forecast table
Every 3 hours, broken out across temperature, snow, rain, humidity, and wind. Each cell is colour-coded relative to the column min/max.
| Time | Condition | Temp (°F) | Snow (in) | Rain (in) | Humidity (%) | Wind (mps) | Wind dir |
|---|---|---|---|---|---|---|---|
| Loading detailed forecast… | |||||||
15-day temperature & precipitation
Daily temperatures, snow, and rain projected over the next two weeks.
Nearby streamflow gauges
USGS streamgauges around Cogswell Reservoir -- inflows here typically show up in storage 24-72 hours later.
| Streamgauge | Discharge | View |
|---|---|---|
| San Gabriel R Bl Santa Fe Dam Nr Baldwin Pk Ca | · | → |
| Arroyo Seco Nr Pasadena Ca | 2 cfs | → |
| Big Rock C Nr Valyermo Ca | 21 cfs | → |
| Rio Hondo Ab Whittier Narrows Dam Ca | 1 cfs | → |
| San Gabriel R Ab Whittier Narrows Dam Ca | 10 cfs | → |
| Rio Hondo Bl Whittier Narrows Dam Ca | · | → |
Make a day of it
Boat launches, lakeside camping, fishing access, and other reservoirs near Cogswell Reservoir.
Boat launches
See all →
Campgrounds
See all →
Fishing spots
See all →
River runs
See all →
About Cogswell Reservoir
Where does the data for Cogswell Reservoir come from?
Daily storage, pool elevation, and release rates are sourced from USGS, USBR, and USACE monitoring stations. Weather forecast comes from NOAA / yr.no -- the same feed Snoflo's iOS app uses.
How often is the report updated?
Storage observations are updated daily by the operating agency. The 15-day weather forecast refreshes throughout the day. Snoflo caches and renders the most recent observation -- check the "as of" timestamp on the storage card.
What does the Hazard hazard rating mean?
The Corps of Engineers' hazard potential classification grades probable consequences if the dam fails: High = probable loss of human life; Significant = no probable loss of human life but possible economic loss / environmental damage; Low = no probable loss of human life, only minor economic / environmental losses. See the Dam Data Reference card below for the full definitions.
What's "% of normal"?
The current storage value compared to the historical average storage on this calendar day. 100% = right on average; values above 100% mean above-normal storage (wet year); values below mean below-normal (dry year or drought).
Can I get alerts when storage crosses a threshold?
Yes -- alerts are managed in the Snoflo iOS app. Favorite this reservoir, set a threshold, and you'll get a push the moment conditions cross.