Henshaw Reservoir
Henshaw
Henshaw Reservoir is located in San Diego County, California, and was constructed in 1923 by the San Diego Flume Company. The reservoir is fed by the Santa Rosa Creek and the San Luis Rey River, which are important sources of water for agricultural use in the region. Henshaw Reservoir also stores water for recreational purposes, including fishing and boating. The hydrology of the area is influenced by the seasonal precipitation, and the snowpack in the mountains, which melt and run into the reservoir. The surface flow is monitored by the San Diego County Water Authority and the California Department of Water Resources. The reservoir also serves as a habitat for several species of fish and bird.
Inside the reservoir
The real shoreline of this water body, with a depth model scaled so the basin holds exactly its recorded storage. Drag to orbit, scroll to zoom, and use the slider to drain and refill it. Click anywhere on the basin for the modelled depth there.
How this is built. The shoreline is the National Hydrography
Dataset polygon for this water body (“Lake Henshaw”),
matched to the dam by proximity and confirmed by comparing its area with the
National Inventory of Dams surface area.
Depth is modelled, not surveyed: the basin is shaped by distance from
shore — deep in open water, shallow in the bays — and scaled so its
volume equals the recorded storage. No national bathymetric survey exists for
US reservoirs. Treat the shoreline, area and volume as measured, and the depth
distribution as an informed approximation.
Above normal pool, water is shown rising within the normal-pool
shoreline. Where it would actually spread depends on the surrounding
terrain, which is not modelled here — a reservoir in a steep canyon barely
widens, one on flat ground can spread a long way. This is a depth and volume
figure, not an inundation map. Official inundation mapping for a dam
comes from its Emergency Action Plan.
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 Henshaw -- inflows here typically show up in storage 24-72 hours later.
| Streamgauge | Discharge | View |
|---|---|---|
| Santa Ysabel C Nr Ramona Ca | · | → |
| Guejito C Nr San Pasqual Ca | · | → |
| Santa Maria C Nr Ramona Ca | · | → |
| Temecula C Nr Aguanga Ca | · | → |
| Santa Margarita R Nr Temecula Ca | 4 cfs | → |
| Rainbow C Nr Fallbrook Ca | 0 cfs | → |
Make a day of it
Boat launches, lakeside camping, fishing access, and other reservoirs near Henshaw.
Boat launches
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Campgrounds
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Fishing spots
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River runs
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About Henshaw
Where does the data for Henshaw 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.
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