It should be possible to write a validation query to check if the lowest vertex of a River reach bank line does not lie below the ground level of the storage area it overflows to. With an implicit link between the river reach and the left and right storage areas it overflows to, the query would be easy:
Object type: river reach
SELECT WHERE min(left_bank.Z) < left_node.ground_level;
SELECT WHERE min(right_bank.Z) < right_node.ground_level;
