Hello I have just taken on an allotment and having problems with drainage. The water seems to flow from top to bottom and then seems to back up. I thought it would be a good idea to dig a big trench and fill it with rouble and sand to help. I started to dig, managed a 6x2x2 trench. I covered with plastic sheeting to start filling a day or two later. I went back today to find it full of water. I have no idea how to drain it or what to do next. Any help will be great.