In an open letter, Andrea Albutt said not enough prison officers were being recruited, training for recruits was "poor" and "unsuitable people" were being selected.
In July, a former prisoner, Mark Cavendish spoke out about conditions in The Mount on his social media account.
"Staff shortages at HMP The Mount (Herts) are so severe that this is 3rd weekend of total lockdown. Meals given at cell door. Trouble brewing," he said on Saturday, July 29.
Sure enough at around 2pm on Monday, July 31, a riot broke out.
A message from the PGA President to members (Bulletin 724) re the crisis in prisons: https://t.co/lAdh9d8qoG— PGA (@PGA_Prisons) August 1, 2017
Later specialist riot police officers, known as Tornado Teams, were sent in to restore order.
"Specialist prison staff resolved an incident involving a number of prisoners at HMP The Mount on Monday evening. There were no injuries to staff or prisoners," said a prison service spokesman.
"The offenders responsible will be referred to the police and could spend longer behind bars," he added.
Another disturbance broke out, almost simultaneously as Erlestoke prison in Wiltshire, where around thirty prisoners became violent.
The Prison Officers' Association (POA) blamed the uprising on budget cuts and lack of staff which had led to worsening of conditions for inmates.
"This highlights the dangers prison officers face every single time they go on duty," said Mark Fairhurst, of the POA, which is the union which represents prison guards.
Ms. Albutt said the disturbances were causing "grave concern" to governors, who faced "unacceptable stress and anxiety."
The Ministry of Justice recently published data, which showed a 20 percent rise in violent assaults in prisons in England and Wales, up to 26,643 in the year to March 2017.
Many of these were attacks on staff — 7,159, which amounts to around 20 assaults every day.
The Ministry of Justice had said action has already been taken to increase the number of prison officers.
But a former inmate at The Mount said many new recruits change their minds when they see conditions at the prison.
"You'll get five trainees come round the prison maybe the week before they're due to start on the Monday — they'll see the conditions and only one will turn up for work," he said.
Shadow Justice Secretary Richard Burgon said overcrowding had risen and staff shortages meant fewer prisoners were able to go on courses which might equip them for life back on the street.
"Prisoners are not being rehabilitated and this is putting the public at risk," he said.
As of last week, there were 86,230 people in prison in England and Wales, 3,961 of whom were women.
That is only fractionally below the record of 86,654 which was reached in August 2011, after hundreds of people were arrested during that summer's riots.