Mcswain

Mcswain is a rockfill dam located in Mariposa County, California, built in 1966. It carries a High hazard potential classification and has a fair condition assessment.

About Mcswain

The primary purpose of Mcswain is hydroelectric. The dam generates hydroelectric power by channeling water through turbines, converting the energy of flowing water into electricity. The dam is owned by Merced Irrigation District (public utility). It impounds the Merced River near Snelling.

The dam stands 97 feet tall and stretches 1,620 feet across, creates a reservoir covering 310 acres, has a maximum storage capacity of 9,730 acre-feet, and collects water from a drainage area of 1,054 square miles. Completed in 1966, the structure is well into its service life at over 50 years old.

This dam carries a high hazard potential classification, which means that a failure or uncontrolled release of water would likely cause loss of human life. This classification reflects the consequences of failure, not the likelihood — it indicates that people live or work in the area downstream. Its condition is rated fair — the dam has minor deficiencies that are being addressed or do not pose an immediate safety threat. An emergency action plan is in place for this dam. The most recent inspection on record was 08/08/2023.

At 97 feet, this dam is taller than 98% of all dams in the United States.

Living Downstream

If you live or work downstream of this dam, consider taking these steps: learn your local evacuation routes, check whether your county emergency management office has a dam failure inundation map, and sign up for local emergency alerts. The California dam safety program can provide more specific information about emergency planning for this structure.

Search for dams near your address to see all dams in your area with hazard classifications and safety data.

High HazardFair ConditionEmergency Action Plan: Yes

Location

StateCalifornia
CountyMariposa
Nearest CitySnelling
River/StreamMerced River
Coordinates37.52100, -120.31090

Physical Characteristics

Dam TypeRockfill
NID Height97 ft
Dam Height97 ft
Dam Length1,620 ft
Year Completed1966 (60 years old)

Storage & Hydraulics

NID Storage9,730 acre-ft
Max Storage9,730 acre-ft
Normal Storage8,255 acre-ft
Surface Area310 acres
Drainage Area1,054 sq mi
Max Discharge250,000 cfs
Spillway TypeUncontrolled

Ownership & Safety

PurposeHydroelectric
OwnerMerced Irrigation District
Owner TypePublic Utility
Hazard ClassificationHigh
Condition AssessmentFair
Last Inspection08/08/2023
Emergency Action PlanYes

Identifiers

NID IDCA00242
Federal IDCA00242
More InfoState Dam Safety Program

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