Geddes Reservoir Report

Last Updated: December 12, 2025

Geddes is a state-regulated earthen dam located in South Dakota, specifically in Charles Mix County.


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Summary

Built in 1940 by the Works Progress Administration (WPA), Geddes stands at a height of 29 feet and spans a length of 1040 feet across Pease Creek. The dam has a storage capacity of 2100 acre-feet, with a normal storage level of 820 acre-feet and a drainage area of 40 square miles.

Despite its low hazard potential, Geddes has a moderate risk assessment of 3 out of 5 due to its age and condition rating of "Not Rated." The dam features an uncontrolled spillway with a width of 70 feet and vertical lift outlet gates. The last inspection of Geddes took place in October 2016, with a scheduled inspection frequency of every 3 years. While the Emergency Action Plan (EAP) status and risk management measures for Geddes are not specified, the dam is deemed to meet safety guidelines.

Overall, Geddes serves as a vital structure for water resource management in the area, playing a key role in flood control and water storage along Pease Creek. As a state-owned and regulated dam, Geddes' historical significance, design characteristics, and risk assessment highlight its importance in the region's water infrastructure and climate resilience efforts.

Year Completed

1940

Dam Length

1040

Dam Height

29

River Or Stream

PEASE CREEK

Primary Dam Type

Earth

Hydraulic Height

29

Drainage Area

40

Nid Storage

2100

Outlet Gates

Vertical Lift

Hazard Potential

Low

Foundations

Soil

Nid Height

29
       
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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. 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

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, 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.