Upper San Marcos River Ws Scs Site 4 Reservoir Report

Last Updated: December 26, 2025

Upper San Marcos River WS SCS Site 4 is a vital flood risk reduction structure located in Hays, Texas, along the Purgatory Creek.


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Summary

Built in 1985 by the USDA NRCS, this earth dam stands at a height of 100 feet and spans 977 feet in length, providing a storage capacity of 8,421 acre-feet to mitigate potential flooding in the area. The dam is regulated by the Texas Commission on Environmental Quality (TCEQ) and undergoes regular inspections to ensure its structural integrity and operational effectiveness.

With a drainage area of 20.1 square miles and a maximum discharge capacity of 60,214 cubic feet per second, Upper San Marcos River WS SCS Site 4 plays a crucial role in managing water flow during periods of heavy rainfall and potential flooding events. The dam's spillway, with a width of 369 feet, helps to safely release excess water downstream. Despite its moderate risk assessment rating, the dam is reported to be in satisfactory condition as of the last assessment in 2018, highlighting its importance in protecting the surrounding community and environment from the impacts of flooding.

Managed by local government authorities in San Marcos, this flood risk reduction structure not only serves as a key component of water resource management but also contributes to climate resilience efforts in the region. Its strategic location and efficient design make Upper San Marcos River WS SCS Site 4 a crucial asset for safeguarding the area against potential flood hazards, showcasing the importance of infrastructure in addressing the challenges posed by changing weather patterns and extreme climate events.

Year Completed

1985

Dam Length

977

Dam Height

100

River Or Stream

PURGATORY CREEK

Primary Dam Type

Earth

Surface Area

21

Hydraulic Height

100

Drainage Area

20.1

Nid Storage

8421

Structural Height

100

Outlet Gates

Slide (sluice gate) - 1, Uncontrolled - 2

Hazard Potential

Not Available

Foundations

Unlisted/Unknown

Nid Height

100
       
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.