Is this a variation for the contractor?

A project has been awarded to a contractor (design & build - FIDIC) to construct a water treatment plant & he, at his technical proposal to tender, had noted the finished ground level (FGL) of the intake being +16.0 MSL & as well as in the priliminary design report (the existing was around 15 MSL & was initially a paddy field just behind the embankment of the reservoir). Now the client wants to get this raised to +17.5 MSL saying what contractor proposed wasn't esthetically good & would be susceptible for flooding (there is, in fact, no flooding situation as the premises located just at the downstream of the sluice & the possible floods would definitely cater the reservoir & the spillway of it. The maximum downstream water level that could raise at a worse case is + 16.02 MSL & the canal embankment (in between the premises & the canal & the canal runs outside the premises) protects the flow. Contractor is willing to raise provided that a variation is issued whereas the client says that this is not a variation under design & build contract. What's your openion?