Breckland Council had initially refused planning permission for the housing scheme, on the north side of Norwich Road, because the land was a floodplain.
However, developer The Hill Group appealed to the Planning Inspectorate, and the decision was overturned.
The new report found the blocked Besthorpe Stream, which runs underneath the A11 near the housing development, caused water to back up about 300m (about 330yds) upstream.
A council officer said: “This restricted the natural flow of floodwater along this stretch of the watercourse and contributed to the flooding of the affected properties in this sub-catchment.”
Following the flooding, The Hill Group was ordered to remove the temporary road by East Harling Internal Drainage Board.
The report also found that other ditches and culverts had not been properly cleared and debris had contributed to the flooding.
The Hill Group had received the report and was reviewing the information, a spokesperson said.