In 1907, the Southern Pacific Company began to acquire water rights for the Oak Grove fork.[2] These rights were transferred in 1911 to the Portland Railway, Light and Power Company,[2] which later became PGE.
In 1923, the concrete diversion dam at Lake Harriet was completed.[2] This lake holds 300 acre-feet (370,000 m3)[3] with a surface area of 150 acres (0.61 km2).[4] A 9-foot (2.7 m) pipeline goes downstream from Lake Harriet to the powerhouse.[3] Power generation from the Oak Grove fork began in August 1924.[5]
In 1953, Frog Lake was completed, adding 430 acre-feet (530,000 m3) of storage with 13 acres (53,000 m2) of surface, which was later reduced to 266 acre-feet (328,000 m3) on 6 acres (24,000 m2) in 1997.[2][3] Finally, in 1956,[2] the compacted-earth dam for Timothy Lake was completed, creating the largest lake in the system at 1,430 acres (5.8 km2) and 69,000 acre-feet (85,000,000 m3).[3] The Oak Grove Powerhouse contains two Francis turbines.[3]
