Grassy Creek Watershed Dam G- 61a Reservoir Report

Last Updated: December 6, 2025

Grassy Creek Watershed Dam G-61a, located in Lewis County, Missouri, was completed in 2005 with a primary purpose of flood risk reduction.


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Summary

The dam, constructed by the Natural Resources Conservation Service, is an earth-type structure with a hydraulic height of 27 feet and a structural height of 36 feet. It has a normal storage capacity of 29.5 acre-feet and a maximum storage of 97 acre-feet.

The dam, situated on Grassy Creek, has a spillway type of 'Uncontrolled' with a spillway width of 30 feet. The dam length is 440 feet with a drainage area of 243.2 square miles. It has a hazard potential of 'Low' and a moderate risk assessment rating. The dam is in good condition and was last inspected in 2005. The emergency action plan for the dam has not been updated recently.

In the event of an emergency, the dam has uncontrolled outlet gates and an uncontrolled spillway type. Despite being rated as having a low hazard potential, the dam is subject to moderate risk according to the risk assessment. While the dam is well-maintained and in good condition, regular inspections and updates to the emergency action plan are essential to ensure its continued safety and effectiveness in flood risk reduction for the surrounding area.

Year Completed

2005

Dam Length

440

Dam Height

27

River Or Stream

GRASSY CREEK

Primary Dam Type

Earth

Surface Area

7

Hydraulic Height

27

Drainage Area

243.2

Nid Storage

97

Structural Height

36

Outlet Gates

Uncontrolled

Hazard Potential

Low

Foundations

Soil

Nid Height

36
       
Seasonal Comparison

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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.