Mason1 Dam Reservoir Report

Last Updated: December 12, 2025

Mason1 Dam, located in Norwalk, Iowa, is a private-owned structure regulated by the Iowa Department of Natural Resources.


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Summary

Built in 2004, this earth dam stands at a height of 24 feet and has a storage capacity of 289 acre-feet. The dam serves the primary purpose of water retention for the Tr- North Branch river/stream, with a normal storage capacity of 163 acre-feet and a surface area of 23.5 acres.

With a low hazard potential and a moderate risk assessment rating, Mason1 Dam has not been fully assessed for its condition but is noted to be in a satisfactory state. The spillway type at the dam is uncontrolled, with a width of 20 feet. Despite being a private-owned structure, the dam meets state regulations for permitting, inspection, and enforcement. The dam is situated within the Kansas City District and falls under the jurisdiction of the Iowa DNR, ensuring its compliance with safety and environmental standards.

Water resource and climate enthusiasts will appreciate Mason1 Dam for its role in water management and flood control in the region. The collaboration between the NRCS and the private landowner in designing and maintaining the dam showcases a successful partnership in sustainable water resource management. Its location in Madison County, Iowa, adds to the significance of Mason1 Dam in supporting the local ecosystem and contributing to the overall water infrastructure in the area.

Year Completed

2004

Dam Height

24

River Or Stream

Tr- North Branch

Primary Dam Type

Earth

Surface Area

23.5

Drainage Area

0.75

Nid Storage

289

Hazard Potential

Low

Foundations

Rock, Soil

Nid Height

24
       
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.