A jury found Dr. Melvin Morse, who has written about near-death experiences and appeared on "Oprah" and "Good Morning America," guilty of child endangerment charges dating back to July 2012.
Prosecutors in Sussex County Superior Court accused Morse of preventing the girl from bathing, suffocating her with water and denying her access to a bathroom.
"Never did I know I would cause this amount of pain to the people that I love," said Morse, 60, who spoke at his sentencing in the packed courtroom.
During a two-week trial that ended in February, the girl told the jury that Morse had physically abused her, including waterboarding and dragging her across a gravel driveway.
Morse's lawyers argued that the girl and her mother, who testified for the prosecution, were lying.
Morse was convicted on six of eight counts, including third-degree assault, endangering the welfare of a child and first-degree reckless endangerment, a felony.
At the sentencing, defense attorney Joe Hurley said Morse had recently been diagnosed with prostate cancer and requested that his sentence be postponed so he could get treatment.
Judge Richard Stokes denied the motion, saying Morse could get medical treatment in prison.
"We got whipped," said Hurley, adding that he plans to appeal to the Supreme Court on Monday.
In his testimony, Morse denied waterboarding the girl, the daughter of his now-estranged wife, Pauline Morse, and said he had only been trying to wash her hair.
The girl was put into foster care along with her younger sister in July 2012. Her mother pleaded guilty to misdemeanor charges in May. She did not appear at the sentencing on Friday.
Typically associated with the interrogation of terrorism suspects, waterboarding in general involves holding a cloth over a person's face and flooding it with water to simulate drowning.
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