Drying out swampy land in spring

My new house has a SW facing back garden in the area of Niagara Falls & Lake Ontario. Canada. My problem is I have a public walkway behind my garden that is 4 feet higher than my garden. I know I have to build it uo, but how do I di it effectively. Right now its just grass, but when the snow melts for about 4 feet into the garden it is a muddy swamp. Please help on suggestions what is the best solution. Thankyou