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Seven Oaks Dam

Seven Oaks Dam is one of the largest earth and rock filled dams in the world. It is as high as a fifty story building and ten football fields in length from side to side. Situated between the north and south branches of the San Andreas fault, the dam has been designed to withstand an earthquake of eight plus on the Richter scale. Seven Oaks Dam is a zoned earth and rock fill dam with a maximum height of 550 feet above the existing streambed at the dam axis and 650 feet above the lowest foundation bedrock contact. The dam crest is 40 feet wide, 2,760 feet long and has a minimum crest elevation of 2610 feet NGVD.

The dam crest incorporates a 3-foot maximum camber to anticipate future crest settlement. The alignment of the embankment arches upstream to provide suitable abutment contacts to bedrock while optimizing the embankment geometry at the dam site. The dam section includes a moderately inclined upstream sloping core, single upstream filter, inclined and horizontal drains, wide transition zones and rockfill shells. The inclined drain discharges into the rock toe at the downstream toe of the embankment though an 8-foot blanket drain.


The spillway which is 500 feet wide and 1400 feet long is excavated into rock in a natural saddle on the east side of the dam. The trapezoidal spillway is unlined except for a 10-foot wide by 10-foot deep unreinforced concrete control sill transverse to the flow located 900 feet from the downstream end along the centerline. The sill is recessed across the spillway invert and extends up each side slope to el. 2610. The sill provides defense against degradation of the spillway invert in the event of spillway flow. The top of control sill across the invert is at elevation 2580 feet NGVD with an upstream approach channel slope of 0.025 and a downstream channel slope of 0.02. The peak water surface elevation during a Probable Maximum Flood (PMF) event is estimated at elevation 2604.7 feet NGVD.

Outlet Works

Reservoir water will be regulated and released from Seven Oaks Dam downstream to the Santa Ana River through the outlet works in the left abutment. The outlet works features provide flexibility for reservoir releases and redundancy for safe operations. The features include: intake structure wet wells and trash structures, tunnel maintenance bulkhead gate, wet well sluice gate, stoplogs, access bridge, upstream outlet tunnel, mid-tunnel gate control chamber with slide (control) gates, gate chamber air shaft and air supply structure, downstream outlet tunnel and accessway, tunnel access structure/control room, valve structure, exit channel, plunge pool, minimum discharge line pipeline (MDL), MDL ball valve, MDL cone valves, MDL bulkhead gate, and MDL extension pipeline (MDLE), MDLE ball valve and vault, MDLE orifices and manholes, MDLE energy dissipater and outlet channel.


The Seven Oaks Dam watershed drains approximately 177 square miles, excluding the closed area of 32 square miles tributary to Baldwin Lake. The headwaters lie within the rugged San Bernardino Mountains. Elevations vary from 10,664 feet NGVD at Anderson Peak and 11,502 feet NGVD at San Gorgonio Peak to 2,060 feet NGVD at the dam site, which is approximately 1 mile upstream from the canyon mouth.

Seven Oaks Location

Dam is located in the foothills of the San Bernardino Mountains, 2 miles north of Redlands, 4 miles North-Northeast of Mentone and 1 mile upstream of the confluence of Mill Creek and Santa Ana River. The dam is accessible from Greenspot Road, 6 miles east on State Highway 30.

Purpose of Dam

The authorized purpose of Seven Oaks Dam is for flood control and debris storage only. Seven Oaks Dam provides flood protection to portions of San Bernardino, Riverside and Orange Counties. Seven Oaks Dam has a capacity of 145,600 acre-feet at spillway crest elevation of 2580 feet NGVD, of which 32,000 acre-feet is allocated to 100 - year estimated sediment accumulation. Approximately 38,373,000 cubic yards of soil and rock were used for the construction of the embankment and adjoining overbuild sections.

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