Hull's drainage system was overwhelmed when severe flooding affected the area in June, a report has said.
About 16,000 homes were flooded in Hull at the end of June
The Independent Review Body's task was to establish the causes but also to see if lessons could be learned to prevent any future floods.
The report also raised concerns about the city's storm drain pumps and a lack of co-operation between agencies.
Hull was among several parts of the UK to suffer when two bouts of severe flooding struck in June and July.
The city was hit in the June floods with an estimated 7,000 homes affected and many of those evacuated.
The interim report, written by senior staff at the University of Hull, looks at the geological reasons for the floods.
It also has an analysis of the co-operation between the Environment Agency, the city council, and other bodies in the aftermath.
The team of experts said the magnitude of the storm was greater than one in every 150 years.
Hull's low lying position increased its vulnerability and the report said there should be additional levels of protection above and beyond a 1-in-30 year storm.
Blocked gullies did not appear to have been a major factor, although there were no contingency plans for the failure of the Bransholme pumping station or appropriate protection from flood waters, it found.
The authors said no one organisation was to blame for the problems, but it was critical of the lack of co-operation between the different agencies during the aftermath of the floods.
More research will be undertaken by the group to come up with recommendations on how flood prevention and response can be improved.
Hull City Council, which commissioned and set up the review body, welcomed the interim report and made a call for the recommendations to be implemented quickly.
Council leader, Councillor Carl Minns said: "The report analyses the problem clearly and makes practical, affordable recommendations.
"I am now calling on all those concerned, especially the Government, Yorkshire Water and the Environment Agency, to work with the council to ensure these recommendations are carried out as quickly as possible."
A final more comprehensive analysis is expected in November.
Hull City Council said at the time of the flooding the city was the victim of a "humanitarian disaster".
It earmarked some £18m for repairs to the affected homes.