Johnston City Lake Dam Dam
Johnston City Lake Dam
Johnston City Lake Dam, also known as Johnston City Reservoir, is a significant water supply structure located in Williamson County, Illinois. Completed in 1921, this earth dam stands at a height of 14 feet and spans 855 feet in length, with a storage capacity of 601 acre-feet. The dam serves the primary purpose of providing water supply to the local community, with a normal storage capacity of 466 acre-feet.
Managed by the local government and regulated by the Illinois Department of Natural Resources, Johnston City Lake Dam poses a significant hazard potential and is classified as having a moderate risk level. The spillway, with a width of 80 feet, is uncontrolled, and the dam has uncontrolled outlet gates. The dam's condition assessment is currently not available, and the last inspection was conducted in December 2020 with a frequency of every three years.
Enthusiasts of water resources and climate will find Johnston City Lake Dam an interesting structure to study, given its historical significance and the crucial role it plays in providing water supply to the area. With its unique design features, regulatory oversight, and risk assessment, this dam serves as a valuable example of how infrastructure can impact water management and community resilience in the face of climate challenges.
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 Johnston City Lake Dam -- inflows here typically show up in storage 24-72 hours later.
| Streamgauge | Discharge | View |
|---|---|---|
| Crab Orchard Creek Near Marion | 3 cfs | → |
| Big Muddy River At Plumfield | 131 cfs | → |
| South Fork Saline River Nr Carrier Mills | 71 cfs | → |
| Big Muddy River At Rte 127 At Murphysboro | 1,520 cfs | → |
| Lusk Creek Near Eddyville | 5 cfs | → |
| Cache River At Forman | 826 cfs | → |
Make a day of it
Boat launches, lakeside camping, fishing access, and other reservoirs near Johnston City Lake Dam.
Boat launches
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Campgrounds
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Fishing spots
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River runs
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About Johnston City Lake Dam
Where does the data for Johnston City Lake Dam come from?
Structural and regulatory data come from the U.S. Army Corps of Engineers' National Inventory of Dams (NID). Weather forecast comes from NOAA / yr.no -- the same feed Snoflo's iOS app uses.
How often is the report updated?
NID structural data refreshes annually as the Corps publishes updated assessments. The weather forecast refreshes throughout the day.
What does the Significant 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 dam, set a threshold, and you'll get a push the moment conditions cross.
Dam data reference
Condition Assessment
- Satisfactory
- No existing or potential dam safety deficiencies are recognized. Acceptable performance is expected under all loading conditions (static, hydrologic, seismic) in accordance with the minimum applicable state or federal regulatory criteria or tolerable risk guidelines.
- Fair
- No existing dam safety deficiencies are recognized for normal operating conditions. Rare or extreme hydrologic and/or seismic events may result in a dam safety deficiency. Risk may be in the range to take further action.
- Poor
- A dam safety deficiency is recognized for normal operating conditions which may realistically occur. Remedial action is necessary. POOR may also be used when uncertainties exist as to critical analysis parameters which identify a potential dam safety deficiency.
- Unsatisfactory
- A dam safety deficiency is recognized that requires immediate or emergency remedial action for problem resolution.
- Not Rated
- The dam has not been inspected, is not under state or federal jurisdiction, or has been inspected but, for whatever reason, has not been rated.
Hazard Potential Classification
- High
- Dams assigned the high hazard potential classification are those where failure or mis-operation will probably cause loss of human life.
- Significant
- Dams assigned the significant hazard potential classification are those dams where failure or mis-operation results in no probable loss of human life but can cause economic loss, environmental damage, disruption of lifeline facilities, or impact other concerns. Significant hazard potential classification dams are often located in predominantly rural or agricultural areas but could be in areas with population and significant infrastructure.
- Low
- Dams assigned the low hazard potential classification are those where failure or mis-operation results in no probable loss of human life and low economic and/or environmental losses. Losses are principally limited to the owner's property.
- Undetermined
- Dams for which a downstream hazard potential has not been designated or is not provided.