Colwil Lake Dam Reservoir Report

Last Updated: December 19, 2025

Colwil Lake Dam, also known as Colwill Dam, is a privately owned structure located in Shannon, Missouri, near the city of Van Buren.


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Summary

Completed in 1959, this earth dam stands at a height of 47 feet and spans 180 feet in length, with a storage capacity of 360 acre-feet. The dam is primarily used for recreational purposes and is situated on Matthews Branch, within the jurisdiction of the DAM AND RESERVOIR SAFETY PROG.

Despite its low hazard potential and satisfactory condition assessment, Colwil Lake Dam is subject to state regulation, permitting, inspection, and enforcement. The dam's spillway is of the uncontrolled type, with a maximum discharge of 3200 cubic feet per second. With a moderate risk assessment rating of 3, the dam has undergone regular inspections, with the last one conducted in November 2014. Overall, Colwil Lake Dam serves as a vital water resource and recreational area within the region, showcasing the importance of proper management and maintenance for sustainable water infrastructure.

Year Completed

1959

Dam Length

180

Dam Height

47

River Or Stream

MATTHEWS BRANCH

Primary Dam Type

Earth

Surface Area

15

Drainage Area

2400

Nid Storage

360

Structural Height

47

Hazard Potential

Low

Foundations

Rock, Soil

Nid Height

47
       
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.