An Enroute Controller experienced a heavy/complex traffic period when departure traffic from a sporting event were assigned other than published procedures due to weather complication/s.

Narrative

I was working the RADAR position at combined Sectors. An annual sporting event ended and aircraft began departing southbound instead of westbound or southwest bound as they normally do after this event. The aircraft were re-routed without any coordination or with any noticeable 'in trail spacing' in place. The complexity and volume increased quickly and most aircraft came into my airspace on headings or deviating for weather. The frequency was heavily congested with pilots questioning their routes and requesting their original routes; which added to the confusion. A BE33 was northbound at 110. An E120 was southbound and I climbed him through the BE33. Conflict Alert activated and I turned both aircraft and called traffic. It was completely unacceptable; and in my opinion; completely unsafe for traffic to ever reach this volume in any sector. It is my understanding that; over the past few years; we have come up with 'special event' departure routes that would alleviate this subject volume. If weather made these routes unusable; someone; other than controllers or even FLMs; should have made sure safe alternatives were in place; and that everyone involved was aware of them.