I’m going by what happens in the USA but I’m licensed as a land surveyor in Illinois. I’m not allowed to do drainage calculations under my license but some states do allow it. In Illinois a professional engineer would do the drainage calculations. Maybe in Canada surveyors are allowed to do drainage calculations?
They can’t use your data, they have no idea what your education or qualifications are. They will probably use existing topo data such as LIDAR and work off of that. They will probably visit the site to determine runoff coefficients and what the stream bed looks like.
The question is what if the area is really close to the flood zone? Say within a foot of elevation. I’d turn around and tell you I can’t make the call we will have to do an on the ground survey, which will be big dollars. I’m just trying to give you an idea what would happen based on my experience.