Little Grassy Dam Reservoir Report

Last Updated: December 5, 2025

Little Grassy Dam is a Federal-owned structure located in Carbondale, Illinois, along the picturesque Little Grassy Creek.


°F

°F

mph

Wind

%

Humidity

Summary

Built in 1942, this Earth dam stands at a height of 88 feet and serves multiple purposes, including fish and wildlife pond management, flood risk reduction, and recreation. With a normal storage capacity of 24,000 acre-feet and a drainage area of 15.6 square miles, the dam plays a crucial role in managing water resources in the area.

Managed by the US Fish & Wildlife Service, Little Grassy Dam has undergone several modifications over the years to enhance its hydraulic, seismic, and structural capabilities. The dam has a spillway width of 598 feet and a maximum discharge capacity of 35,943 cubic feet per second. Despite its high hazard potential, the dam is currently assessed to be in fair condition, with inspections conducted every three years to ensure its safety and functionality.

Water resource and climate enthusiasts will appreciate the significance of Little Grassy Dam in maintaining ecosystem health and mitigating flood risks in the region. Its strategic location, multiple purposes, and ongoing maintenance efforts by the Fish and Wildlife Service highlight the importance of this structure in sustaining water resources and preserving the natural environment for future generations.

Years Modified

1992 - Hydraulic, 1992 - Seismic, 1992 - Structural, 2003 - Foundation, 2013 - Structural, 2016 - Other

Year Completed

1942

Dam Length

3650

Dam Height

88

River Or Stream

Little Grassy Creek

Primary Dam Type

Earth

Surface Area

960

Hydraulic Height

87

Drainage Area

15.6

Nid Storage

30900

Structural Height

88

Outlet Gates

Other Controlled, Valve

Hazard Potential

High

Foundations

Rock, Soil

Nid Height

88
       
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.