The April 1, 1946 tsunami (not tidal wave) wreaked havoc on the Big Island. "The 1946 tsunami was generated by a magnitude-8.6 earthquake in the Aleutian Islands. It took five hours for the waves to reach the Hawaiian Islands. Unfortunately, there was no warning system at that time. There was devastation to homes, schools and businesses in Hilo and elsewhere, to the piers at the Port of Hilo, and to the railroad track and train cars." (Source: Barbara Muffler, Hawaii Tribune Herald, 4/1/2017). 126 Big Island residents died.

Fortunately no lives were lost on the Hakalau Plantation. However, damage was extensive and the impact on the process and profitability of sugar production was felt for years.  Key impacts of the tsunami included:
  • Sugar production was drastically reduced in 1946, 10,595 tons instead of the projected 26,000 tons. 
  • ​The mill was destroyed and needed to be replaced.The mill reconstruction was not finished until March 1947 and full efficiency not reached until May 1947.
  • Major flumes were destroyed.
  • The railroad system was destroyed, to be replaced by heavy trucks.
  • The Port of Hilo, the point from which sugar was shipped to the Mainland for processing, was severely damaged. Cane could not be shipped until late June 1946.
According to the Scripps Institute of Oceanography in its publication The Tsunami of 1946:
  • At Hakalau Gulch, it [the water] reached 37 feet above sea level on the south side of the valley mouth and 23 to 29 feet on the north side.
  • Fourteen noticeable large waves at intervals of about 10 minutes were counted at Hakalau Mill, the seventh or eighth being the largest.
  • At Kolekole Stream, the water reached 37 feet above sea level.
Excerpt from C. Brewer's 1946 Annual Report, ​courtesy of John Cross, Custodian of the Records, the Olson Trust Sugar Plantation Archives.
Excerpt from the Hakalau Plantation's 1946 Annual Report, ​courtesy of John Cross, Custodian of the Records, the Olson Trust Sugar Plantation Archives.
Photo taken by head bookkeeper Ralph Murray shows people watching the devastation at the top of the cliff near the warehouse. The trolley tracks are clearly visible, along with the chute from the top down to the mill and the flume along the cliff on the left side of the picture. 
Picture
Photo courtesy of Darrellyn Bates, granddaughter of Ralph Murray and grand niece of Guy Murray.
A slide show of the devastation is below.
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Hawaii Tribune Herald, May 5, 1947, accessed via Newspapers.com.
The financial and operational impacts of the tsunami on the Hakalau Plantation were felt for years to come:
Excerpt from Hakalau Plantation's 1951 Annual Report, ​courtesy of John Cross, Custodian of the Records, the Olson Trust Sugar Plantation Archives.
The new Hakalau Mill complex finished in 1947. C. Brewer Annual Report 1947, courtesy of John Cross, Custodian of the Records, the Olson Trust Sugar Plantation Archives. 
Hakalau Plantation's 1947 Annual Report recounts difficulties recovering from the tsunami:
Excerpt's from Hakalau Plantation's 1947 Annual Report, ​courtesy of John Cross, Custodian of the Records, the Olson Trust Sugar Plantation Archives.
The aftermath at the Mill Site: photos courtesy of Akiko Masuda, photographer unknown. Contact us if you know who took these pictures so we may acknowledge him or her.
 Other sources of information on the Tsunami of April 1, 1946: