Mortenson Dam Reservoir Report
Nearby: A.W. Spiry Ted Molstad Dam
Last Updated: December 13, 2025
Mortenson Dam, located in Walworth, South Dakota, is a privately owned structure designed by the USDA NRCS and completed in 1984.
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Summary
This earth dam stands at a height of 27 feet and has a storage capacity of 56 acre-feet. The dam serves the primary purpose of regulating the flow of the TR-GRAND RIVER, with a maximum discharge capacity of 880 cubic feet per second.
Despite being classified as low hazard potential, Mortenson Dam is subject to state regulation, inspection, and enforcement by the DENR in South Dakota. With a moderate risk assessment rating of 3, the dam has not been rated for its condition assessment, emergency action plan preparedness, or inundation mapping. The spillway of Mortenson Dam is uncontrolled, with a width of 65 feet, and it falls under the jurisdiction of the St. Paul District of the US Army Corps of Engineers.
Water resource and climate enthusiasts will find Mortenson Dam to be an interesting structure in the South Dakota landscape. Its design, construction, and regulatory oversight provide insight into the management of water resources in the region. With its moderate risk assessment and low hazard potential, Mortenson Dam represents a balance between water storage and safety considerations in the face of changing climatic conditions.
Year Completed |
1984 |
Dam Length |
370 |
Dam Height |
27 |
River Or Stream |
TR-GRAND RIVER |
Primary Dam Type |
Earth |
Hydraulic Height |
27 |
Drainage Area |
1 |
Nid Storage |
56 |
Hazard Potential |
Low |
Foundations |
Soil |
Nid Height |
27 |
Seasonal Comparison
Weather Forecast
Nearby Streamflow Levels
Oak Cr Near Wakpala Sd
|
10cfs |
Grand R At Little Eagle Sd
|
47cfs |
Moreau R Near Whitehorse Sd
|
35cfs |
Beaver Creek Bl Linton
|
39cfs |
Dam Data Reference
Condition Assessment
SatisfactoryNo 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. Note: Rare or extreme event is defined by the regulatory agency based on their minimum
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. Investigations and studies are necessary.
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.
Not Available
Dams for which the condition assessment is restricted to approved government users.
Hazard Potential Classification
HighDams 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, environment 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.
Not Available
Dams for which the downstream hazard potential is restricted to approved government users.
Mortenson Dam