Saint John Reservoir Report

Last Updated: December 6, 2025

Saint John, also known as St Johns, is a privately owned irrigation dam located in Oneida, Idaho.


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Summary

Completed in 1918, this earth dam stands at a height of 43.4 feet and has a hydraulic height of 39 feet, serving the primary purpose of irrigation for the surrounding area. With a storage capacity of 630 acre-feet and a drainage area of 10.6 square miles, Saint John utilizes a controlled spillway type with slide gates for water release.

Despite its age, Saint John poses a high hazard potential due to its unsatisfactory condition assessment and very high risk rating. The dam has a history of modifications and inspections are conducted every four years to ensure its safety. In the event of an emergency, the dam lacks an Emergency Action Plan (EAP) and its inundation maps are not prepared, raising concerns for the surrounding community's safety in case of a breach.

Located on Birch Creek and the Malad River, Saint John is regulated by the Idaho Department of Water Resources (IDWR) and is subject to state permitting, inspection, and enforcement. With its critical role in providing irrigation water, the dam's maintenance and risk management measures are essential to safeguard both the structure and the downstream population from potential hazards.

Year Completed

1918

Dam Length

680

Dam Height

43.4

River Or Stream

BIRCH CREEK MALAD RIVER

Surface Area

41

Hydraulic Height

39

Drainage Area

10.6

Nid Storage

630

Outlet Gates

Slide (sluice gate)

Hazard Potential

High

Foundations

Rock, Soil

Nid Height

43
       
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.