Rock Rapids Milldam dam
Rock Rapids Milldam
Rock Rapids Milldam in Iowa, built in 1931, serves as a crucial water supply structure for the region. It is a gravity dam standing at 7 feet high and 220 feet long, with a storage capacity of 75 acre-feet and a normal storage of 49 acre-feet. Located on the Rock River in Lyon County, this dam is state-regulated by the Iowa Department of Natural Resources, ensuring proper permitting, inspection, and enforcement measures are in place.
The dam's primary purpose is water supply, supporting the surrounding community with its storage capacity and surface area of 10 acres. Though categorized as low hazard potential with a moderate risk assessment, its condition has not been rated since its last inspection in 1989. Despite its age, the Rock Rapids Milldam continues to play a vital role in water resource management and climate resilience efforts in the area, with the state ensuring regulatory oversight to safeguard its operations and structural integrity for years to come.
With a state-regulated status and low hazard potential, the Rock Rapids Milldam stands as a testament to effective water management practices in Iowa. Its historical significance and role in water supply underscore the importance of maintaining and monitoring such structures to ensure their continued functionality and safety. As climate change impacts water resources, the presence of well-regulated dams like Rock Rapids Milldam becomes increasingly crucial for sustainable water supply and management in the region, making it a notable site for water resource and climate enthusiasts to study and appreciate.
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.
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 Rock Rapids Milldam -- inflows here typically show up in storage 24-72 hours later.
| Streamgauge | Discharge | View |
|---|---|---|
| Rock River Below Tom Creek At Rock Rapids | 106 cfs | → |
| Rock River Near Rock Valley | 505 cfs | → |
| Split Rock Cr At Corson Sd | 14 cfs | → |
| Big Sioux R At North Cliff Ave At Sioux Falls Sd | 566 cfs | → |
| Big Sioux R At Sioux Falls Sd | 64 cfs | → |
| Skunk Cr At Sioux Falls Sd | 7 cfs | → |
Make a day of it
Boat launches, lakeside camping, fishing access, and other reservoirs near Rock Rapids Milldam.
Boat launches
- 310th Street Sioux County
- Copperwood Court Lincoln County
- Split Rock Park Road Garretson
- Park Avenue Worthington
Track Rock Rapids Milldam in the Snoflo app
Save this dam as a favorite and get the local NOAA / yr.no forecast plus regional flow context wherever you are.
About Rock Rapids Milldam
Where does the data for Rock Rapids Milldam 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 Low 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 above 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.
Other water bodies near here
Snoflo-tracked reservoirs and dams within driving distance of Rock Rapids Milldam.