Toponce Ditch Dam Lower Reservoir Report

Last Updated: December 19, 2025

Toponce Ditch Dam Lower, located in Caribou, Idaho, plays a crucial role in irrigation, serving as a vital water resource for the surrounding area.


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Summary

This earth dam, constructed with a stone core, stands at a height of 18.1 feet and has a storage capacity of 78 acre-feet. The dam is regulated by the Idaho Department of Water Resources, ensuring proper inspection, permitting, and enforcement measures are in place to maintain its integrity and functionality.

The dam, situated on the Portneuf River and Toponce Creek, has a spillway type of "Uncontrolled" with a slide (sluice gate) for outlet gates. Despite its low hazard potential and fair condition assessment, the risk assessment indicates a moderate risk level. The last inspection in July 2018 revealed no significant issues, with a scheduled inspection frequency of every five years. With its historical significance and ongoing role in sustaining agricultural activities in the region, Toponce Ditch Dam Lower remains a crucial piece of infrastructure for water resource management in Idaho.

As a private-owned structure, Toponce Ditch Dam Lower's primary purpose of irrigation underscores its importance in supporting local agriculture and maintaining water supply reliability. With its unique design and location, this dam serves as a key component in the water management system of the area, contributing to the economic and environmental sustainability of the region. Despite being classified as having a moderate risk level, the dam's overall condition is deemed fair, highlighting the ongoing need for regular monitoring and maintenance to ensure its continued functionality and safety for the community.

Dam Length

1600

Dam Height

18.1

River Or Stream

PORTNEUF RIVER TOPONCE CREEK

Surface Area

12.4

Hydraulic Height

13.1

Nid Storage

78

Outlet Gates

Slide (sluice gate)

Hazard Potential

Low

Foundations

Rock, Soil

Nid Height

18
       
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.