Longmont Wtp Forebay Embankment Reservoir Report

Last Updated: December 5, 2025

The Longmont Wtp Forebay Embankment, also known as the Nelson Flanders Forebay, is a crucial water resource infrastructure located in Boulder County, Colorado.


°F

°F

mph

Wind

%

Humidity

Summary

Owned by the local government, this embankment serves the primary purpose of water supply and was completed in 2005 by Lyman Henn Inc. The structure is designed as an earth dam with a height of 20 feet and a hydraulic height of 19 feet, providing a storage capacity of 129 acre-feet with a maximum discharge of 369 cubic feet per second.

Situated along the St. Vrain Creek, the Longmont Wtp Forebay Embankment is state-regulated and inspected regularly by the Colorado Department of Water Resources to ensure its safety and functionality. With a moderate risk assessment rating and a high hazard potential, it is crucial for water resource and climate enthusiasts to monitor and maintain this critical infrastructure. The embankment has a satisfactory condition assessment as of June 2020, but emergency preparedness measures, such as an Emergency Action Plan, may need updating to meet current guidelines.

In the event of a breach or failure, the embankment has an uncontrolled spillway with a width of 28 feet to manage excess water flow. With its strategic location and vital role in water supply for the city of Hygiene, the Longmont Wtp Forebay Embankment serves as a significant asset in the management and distribution of water resources in the region.

Year Completed

2005

Dam Length

2855

Dam Height

20

River Or Stream

ST. VRAIN CREEK-OS

Primary Dam Type

Earth

Surface Area

10

Hydraulic Height

19

Nid Storage

129

Structural Height

20

Hazard Potential

High

Foundations

Soil

Nid Height

20
       
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.