We're preparing to get a dairy cow and calf, and wondering if we can feed grass during the cold/rainy season, or if having cows tromping around in the wet will destroy our grass even with a quick rotation. We're on the wet side of Vancouver Island, BC, west coast north america. Zone 8, very little snow, but pretty wet from October to the end of May.
Hey! I used to live in the San Juans, which isn't that much different a climate..... Do you have any hill sides? I pastured a few cattle higher up slope and only went down slope during the drier times. You will have to have some sort of sacrifice spot I think, as that's inevitable.
Another thing I did was scythe down lots of feed in an area I knew would be too wet for cattle and then move it to hanging drying racks ala Newman Turner in a place which was up slope and drier. This reduced haying time and I was only moving about 300 bales worth 500 feet. This kept the softer ground from plugging and allowed me to strip graze the ricks.
I'm assuming your probably getting a Jersey or other smaller breed. They tend to be lighter than a holstein..... that helps. It also helps to keep them moving around and not in one area too long. Moving smaller amounts twice a day is preferable to moving once in a bigger area. It also helps prevent mastitis and other woes if you can keep those teats out of the mud. I fought a few muddy places on my last farm where the cows had to cross between fields and except during the winter when the ground was frozen and 1 or 2 times during the summer, there was a muddy patch. Not ideal.
The other thing is to stockpile forage in areas around the place and then graze into the winter. There will be a high wastage feed-wise, but the organic matter put down will help the soil in years to come and should improve the structure so that impaction becomes less of an issue with light winter grazing in the future.
Island grazing is hard though because the soil can be thin, full of clay and no where for the water to go as it's all on rock. Good luck!