Nemyar, I think the problem may be that you're waiting too long to start building the dam. Especially with a runner, you don't need to use him for farming except to top up the food supply to maybe around 400-500... you should put him on building the dam as soon as you have enough tech points to get engineering.... (you shouldn't need to buy the coconuts first). Getting the dam built is the important thing so you can get crops. Put everyone you can spare on getting the dam built.