This problem should be ...

This problem should be consider with the plant design to have average and peak flow for such situation for the plant installation, whatever the peak flow is due to raining water or the process waste water, and normally raining water should by passed the plant if it clean free of debris and mud otherwise should treat to remove such mud and debris by screening and primary settling tanks and then discharged to the surface water streams straight, and no need to inter to the full treatment system. to avoid high hydraluic loads, and  currently I can advice to clean the screen regularly to avoid blocking the screen as well as new investment to add second screen to receive the extra loads due to the rain water then can bypassed by overflowing to surface water without treatment if not not mixed with the waste water otherwise should be go through the treatment plant cycle.