Even though you now have drainage in this area I guess it is still likely to be damp/wet and, at times, it might still get wetter.
I don't know the situation or what you want but would a few small trees be appropriate? Silver birch, Alder, Wych Elm, perhaps. I've heard silver birch prefers dry acid soils but, to me, it looks the deciduous tree that defines the Highlands, so it must be able to cope with quite a bit of wetness.
You have no idea how much I appreciate your advice CM. Especially giving me the the measurements and ground cover. I get totally stumped with kilos and metres. I will get planning. Most of the area is going to be left wild and I do like the idea of a tussocks area, and selected areas for wild flowers. Only a the area where now the pipe enters our burn, will be mowed. This was the area, surrounded by huge banks of male fern, backed by trees, where I had one of my feeding stations. It is the area I got most upset about. I am going to try digging up fern from elsewhere and re-planting it, but of course it will take forever for them to get back to the size of the huge clumps that were removed. On another note, and following Dave's comment, I am toying with the idea of planting trees here and there on the steeper slopes, I have loads of rowan a appearing all over the place - thanks to the jays I think, but I am not sure when the best time for this would be, or even If they will survive being dug up and replanted. I don't want them where they are appearing, get lots of beech and birch also.
On another note, and following Dave's comment, I am toying with the idea of planting trees here and there on the steeper slopes, I have loads of rowan a appearing all over the place - thanks to the jays I think, but I am not sure when the best time for this would be, or even If they will survive being dug up and replanted. I don't want them where they are appearing, get lots of beech and birch also.
Rule of thumb for transplanting is if it's deciduous, then transplant in the dormant period, if it's evergreen then transplant in the growing season (as ever there are exceptions but they are few). Given your location then you've got another couple of weeks before growth really gets going and moving the rowans etc is unlikely to cause them stress, if later than that then probably best to wait until Autumn. The real challenge is drying out before the plant has time to get the new root system going - later transplanting - April, May can be managed if diligent watering is provided, though losses are to be expected. For seed sowing you should be OK till the end of April, again drying out is the main challenge but unless you get a whole week of dry weather before germination that shouldn't be a problem, and with such a large area you are going to have to trust to nature - not exactly a new bit of back lawn you are creating
I have taken on board your advice about the selected species of grasses and the wildflower meadow seed for some of the more open area. I have copied and pasted your advice onto a word doc, so I can refer. Tomorrow Daughter is going to take a series of photos to line up as a panorama so that I can mark out areas to be grass/tussock, areas to be wild flowered and where to put trees and ferns. Might have to wait till the Autumn for the trees and get a move on with the seeds.
I think I have gone mad also. I got so upset about all the frogs and newts etc that must have been living and breeding in all that laying water backing up along the back and I want to build a pond - as if there is not enough water around here! but I am sure they don't use the burns.
If it were me, I would take the opportunity to introduce some selected species to that location before other plants get to take over. I certainly wouldn't though spend £150 on it. My approach would be to go to Emorsgate wildseed.co.uk/species/category/wild-grasses and buy a selection of grasses in single species - even the 1gram packets can contain many seeds so there's a chance of getting good numbers established from a single sowing. The species that stand out to me as probably being suitable are Tall Fescue, Smaller cat's-tail, Red fescue, Sheep's fescue, Wavy hair-grass, Tufted hair-grass, Sweet vernal-grass, Marsh foxtail, Creeping bent and Common bent. Wildflower species could be added depending on cost/appropriateness. Harold's suggestion about hay bales is good and I'd certainly try that. I wouldn't do anything about soil preparation other then raking the area(s) to be sown and then treading in the seed using a board, as protection from birds even if that does reduce germination success. With the variation in elevation - the central dip will presumably stay wetter the the top of the slopes, a range of micro habitats should quickly develop.
Just to let you know I took your advice + advice from Emorsgate, then spent a few days planning the area, by taking photos of the area - joining photos together to get the full length etc and marking which seeds to go where - great fun and managed to get all done within the growing timeframe, bar three lots which should not be planted till autumn. Daughter and I did the sowing on the high ground and in the very wet boggy areas (had a few 'you have been framed' moment) My I ever patient gardener spent a week removing broken branches, rocks old stums etc from the flatter land, raked it all over, we spread the seeds, then he raked the ground again. Oh so pleased with ourselves I also got wild garlic for the wet areas in the slopes beneath the trees, and seeds of some of the plants that were originally in the various areas.
Now I could weep. Drainage did not work, so contractors - sometime - are coming back to do alterations repairs but only up by the really boggy areas. And all that raking and seeding of the biggest flat area? A tourist drove up our drive onto this area, got out took photos, got back in car did a 3 point turn, the wheels spinning in the soft ground and dug big ruts all over it. Never mind, says gardener! Spent a day redoing it all, more seed, more raking. Two days later - 2 cars of tourists drove onto - I don't believe it! Been out and bought that red and white tape and pegged it up all along our road.
Helen - commiserations, it's always a bit missery making when you think some new plant/area is all set to burst forth and then someone/thing procedes to mess it all up. One consolation is that grass seeds are pretty resilient and hopefully losses will be limited, also if you do have losses and are left with significant bare areas you should have fresh seed this summer to support resowing. You can of course rely on natural spread but if there are large bare patches I'd be inclined to take and store summer ripe seed and then sow directly in late August early September and support with additional watering if the weather is particularly dry. And of course you can always but more seed if absolutely necessary. Hopefully not too much harm has been done.
There's an old say along the lines that tourists change the places they visit - while travellers are changed by their travels. There's research that shows that in the UK the maximum distance tourists will walk from their car is less than 100 metres, so any chance they have to minimise walking is taken without any any thought. You culd console yoursel with thoughts of acquiring one of these: www.spanset.co.uk/fileadmin/spanset_uk/pdf/catalogue/62507_Stinger_Brochure.pdf
Thanks again CM, good advice as usual. Love the idea of a stinger! Gardener did not like the idea of the red tape and is busy moving large rocks to line the edge of the road with, personally I think ramming pointed stakes into the ground would be easier, but he is not one to argue with.