Birch fly aka blackfly

Hi,

Since moving to our new house two years ago I have been bitten every summer by what I have now identified as birch fly (aka blackfly). They were first heard of in Speyside a few years ago I believe, but no-one I've spoken to in my area has ever come across them. I have lived in this area in the west of Scotland since 1979 and have never had this problem. Midges and  horsefly yes, but never blackfly. We live next to a small spate river where a small hydro scheme has just been completed earlier this year. Will this make a difference to numbers of these horrible little things? The generator shed and concrete outflow is about 100m away. I never feel them bite just find congealed trickles of blood or small subcutaneous haemorrhages around my ears and hairline mainly. The dog is a magnet for them. Next day the bites itch like mad and swell up and take days to disappear. I find taking a Loratidine tablet (once daily antihistamine, non drowsy) helps keep the itching and swelling to a minimum. Does anyone know of a repellent that works against these flies? I've tried all the usual including tropical strength mossie repellent but with no effect. Will be interested to hear any thoughts on this. Thanks