Just a thought for a new wvw siege :
Have explosives added to the list of siege weapons. how I imagine it working, is you drop the siege in the general area of a bridge (the farther away, the more supplies it takes). where you drop the siege is where the trigger is, and you can press it to blow up the bridge. You can just blow it to slow down an incoming zerg, or you can blow it when the zerg is crossing the bridge for even more mayhem. After the bridge is blown, a worker from a nearby camp will start repairing the bridge and it will be back up when its finished. Defending the worker until the bridge is repaired can be an event also.