Could it not also be "This part is the shallowest,..."?
That would be, "Bagian ini yang paling dangkal/terdangkal..."
I don't think that 'shallowest' is the correct form. It can be changed to MOST SHALLOW.
ada vs adalah?
this is the most shallow part
I wrote "This is the most shallow part. The deepest part is there." But I'm pretty sure my answer should be accepted. Probably rejected because I refused to make a run-on sentence in English.