New Underwood Reservoir Report
Last Updated: December 5, 2025
New Underwood, located in Pennington, South Dakota, is a state-regulated dam on Box Elder Creek Trib, with a low hazard potential and a moderate risk assessment.
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Summary
Built in 1946 by GF&P, this earth dam stands at 22 feet high and spans 1000 feet in length, providing a storage capacity of 164 acre-feet for the surrounding area. The dam, managed by the South Dakota Department of Agriculture and Natural Resources, is regularly inspected and maintained to ensure public safety and water resource protection.
With a spillway width of 10 feet and a maximum discharge of 380 cubic feet per second, New Underwood serves a crucial role in flood control and water management in the region. The dam does not have outlet gates and is classified as uncontrolled in terms of spillway type. Despite its age, the dam has not been rated for its current condition, highlighting the need for ongoing monitoring and risk management measures to be put in place to safeguard against potential hazards.
Dusty Johnson (R) represents New Underwood in the United States House of Representatives, ensuring that the community's water resource needs and environmental concerns are heard at the federal level. As a vital piece of infrastructure in the area, New Underwood plays a key role in regulating water flow, providing irrigation, and protecting against flooding, making it an essential component of the region's water resource and climate management strategies.
Year Completed |
1946 |
Dam Length |
1000 |
Dam Height |
22 |
River Or Stream |
BOX ELDER CREEK TRIB |
Primary Dam Type |
Earth |
Hydraulic Height |
22 |
Drainage Area |
3 |
Nid Storage |
164 |
Outlet Gates |
None |
Hazard Potential |
Low |
Foundations |
Soil |
Nid Height |
22 |
Seasonal Comparison
Weather Forecast
Nearby Streamflow Levels
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.
New Underwood