Big Lake Dam Reservoir Report

Last Updated: December 5, 2025

Big Lake Dam, located in Hillister, Texas, was completed in 1949 and serves primarily for irrigation purposes.


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Summary

This private-owned earth dam has a height of 21 feet and a length of 630 feet, with a hydraulic height of 15 feet. It holds a maximum storage capacity of 357 acre-feet, with a normal storage level of 161 acre-feet. The dam is situated on the TR-Magnus Branch river and covers a surface area of 22 acres, with a drainage area of 3.24 square miles.

Despite being unregulated by the state, Big Lake Dam underwent a major reconstruction by its owner after a breach in 1996. The spillway type is uncontrolled with a width of 60 feet, and it has two uncontrolled outlet gates. The dam has been inspected periodically, with the last inspection taking place in September 2009. The overall risk assessment for the dam is moderate, indicating a potential for hazards, although the condition assessment is currently not rated. With its rich history and importance in the local water supply and irrigation system, Big Lake Dam remains a significant structure in the region for water resource and climate enthusiasts to explore and study.

Years Modified

1997 - Other

Year Completed

1949

Dam Length

630

Dam Height

21

River Or Stream

TR-MAGNUS BRANCH

Primary Dam Type

Earth

Surface Area

22

Hydraulic Height

15

Drainage Area

3.24

Nid Storage

357

Structural Height

15

Outlet Gates

Uncontrolled - 2

Hazard Potential

Not Available

Foundations

Unlisted/Unknown

Nid Height

21
       
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.