good question beerbelly - I automatically put surge but now think it is serge as 'sudden increase' i.e. surge is reported in 'serge' - i.e. rough stuff.
Have you solved 11d - Das! it sounds like rain - ?u?e
sorry I didn't realise 11d had been discussed further down the consensus is 'rule' - em rule meaning the same as em dash and rule meaning the same as reign which sounds like rain. Personally, I think this is a terrible clue. Dash with an explanation mark after it led me to think of expletive such as damn, darn etc.