I tried to get it as level as possible and you're right, the trestle maintained that over the drainage swale from our backyard. I did find over the next few years that a ground level layout was prone to people walking on the track and all kinds of debris, leaves and sticks mainly, falling on it and difficult to remove. Eventually I built the elevated railway which worked a lot better and was easier to use and maintain. Sadly it only lasted about a year and a half as we moved from Ontario down to Columbus.