I have created a rule to alert if traffic is over 150Mbps (you need two rules one for in one for out):
SELECT * FROM devices,ports WHERE (devices.device_id = ? AND devices.device_id = ports.device_id) AND (ports.ifOperStatus = "up" && ports.ifAdminStatus = "up" && (ports.deleted = 0 && ports.ignore = 0 && ports.disabled = 0)) = 1 AND ports.ifOutOctets_rate > 19660800
Calculator for reference: http://www.endmemo.com/sconvert/b_smbps.php
EDIT: I just realized you said “over time” not sure if this will do what you want, I’m just trying to help.
EDIT2: Just to clarify this is the key piece here:
ports.ifOutOctets_rate > 19660800