Date: 202107
Local time of day: 0601-1200
Location: ZDV.ARTCC, CO
Aircraft: Any Unknown or Unlisted Aircraft Manufacturer
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Airspace: Class A ZDV
ATC / advisory: Center ZDV
Second aircraft: Commercial Fixed Wing
Reporter organization: Government
Reporter function: Enroute
Reporter qualification: Air Traffic Control Fully Certified
Human factors: Communication Breakdown; Workload
Anomaly: ATC Issue All Types; Conflict Airborne Conflict; Deviation / Discrepancy - Procedural Published Material / Policy; Inflight Event / Encounter Weather / Turbulence
Detector: Person Air Traffic Control
Result: Air Traffic Control Issued Advisory / Alert; Air Traffic Control Issued New Clearance; Air Traffic Control Provided Assistance; Air Traffic Control Separated Traffic
Contributing factors: Weather; Procedure; Human Factors; Company Policy
Primary problem: Ambiguous

Narrative: For the east arrival push into DEN; beginning around XA:00 and lasting until sometime after XB:30; Sector 9 and Sector 16 became over-saturated and unsafe. The numbers in these sectors had been forecasted to be well over MAP (Monitor Alert Parameter) numbers for some time prior to the sectors going red. Management and TMU were alerted to the upcoming situation.Compounding the very high volume was the complexity in the sectors. Denver Approach restricted our arrival gate to one route with 5 miles in trail. ZMP was asked by TMU to provide us 2 routes with 10 miles in trail per route. ZMP offloaded arrivals from the LAWGR arrival to the AALLE arrival to help accomplish this despite the fact that LAWGR was the only arrival we were permitted to use going into approach. Sector 9 was then tasked with rerouting all AALLE arrivals and blending them with the existing LAWGR stream. While trying to accomplish this they had a high volume of deviating overflight traffic due to weather on the southern boundary of the sector.Sector 9 did the best they could but began to fall behind. This resulted in a Denver feed entering Sector 16 that was falling apart at the boundary of sectors 16 and 9. Sector 16 also had a volume issue that was alerted well prior to the over-saturation. Sector 16 then became overwhelmed with trying to manage the volume of traffic while also trying to reestablish the Denver arrival sequence.The safety of the NAS was severely compromised due to a lack of planning when it was obvious early on that traffic volume was going to be well over the limits of these sectors during a highly complex time. Aircraft should have been routed around or below these sectors to alleviate unnecessary volume and complexity. Some aircraft were routed around the sectors and the answer from TMU and management about the oversaturation was 'there could have been more airplanes; but we routed some around.' This answer is unacceptable. More effort should have been made to make sure the volume and complexity did not get to the point where controllers were overloaded and unsafe.In the end; multiple Denver arrivals ended up being routed to the northwest arrival gate because the controllers on Sectors 15 and 16 could not get them sequenced in. This increased workload for Sector 33 who also had his own traffic to handle. Sector 16 had to refuse hand-offs and point-outs due to saturation.When Center is restricted by TRACON to one route for arrivals; all involved Centers need to be under the same understanding. It increases workload and complexity to change aircraft to another arrival for stream balancing for both pilots and controllers. The aircraft that were switched to the AALLE arrival in ZMP airspace were subsequently switched back to their original arrival and re-sequenced upon entering ZDV airspace.When the TFMS alerts Management and TMCs that a sector will be well over negotiated safe MAP numbers for a session; a plan needs to be put in place. Aircraft need to be rerouted or sent to an altitude to avoid overloaded sectors. The high volume in sectors that were already being asked to handle a higher than normal complexity due to weather and sequencing or rerouting constraints became very unsafe. TMCs in conjunction with management should have made sure that the volume in those sectors never exceeded limits.




Synopsis: ZDV Center Controller reported the Monitor Alert Parameter numbers for two sectors became over-saturated and unsafe.