Williams Reservoir Report

Last Updated: December 15, 2025

Williams is a privately owned dam located in Twin Falls, Idaho, along the North Cottonwood Creek and Cottonwood Creek.


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Summary

Built in 1952 for irrigation purposes, this earth dam stands at a height of 52.5 feet and has a maximum storage capacity of 1025 acre-feet. With a significant hazard potential and fair condition assessment, Williams poses a moderate risk that is being managed through regular inspections and emergency preparedness plans.

The dam features an uncontrolled spillway and slide gates for outlet control, with a drainage area of 3.3 square miles and a maximum discharge capacity of 3400 cubic feet per second. Despite its age, Williams continues to serve its purpose efficiently, storing water for agricultural irrigation in the region. Its inspection frequency of 4 times a year ensures that any maintenance or repairs needed are promptly addressed, maintaining its operational integrity for the benefit of the surrounding community.

With the Sacramento District overseeing its regulation and operation, Williams remains a vital water resource infrastructure in Idaho. Its strategic location and design contribute to the sustainable management of water resources in the area, showcasing the importance of maintaining and monitoring such critical infrastructure for the resilience of water supply systems in the face of changing climate conditions.

Year Completed

1952

Dam Length

415

Dam Height

52.5

River Or Stream

NORTH COTTONWOOD CREEK COTTONWOOD CREEK

Surface Area

60

Hydraulic Height

42.7

Drainage Area

3.3

Nid Storage

1025

Outlet Gates

Slide (sluice gate)

Hazard Potential

Significant

Foundations

Rock, Soil

Nid Height

53
       
Seasonal Comparison

Weather Forecast

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.