Trenches played a big part in World War 1. Spreading from The North Sea to the Swiss Frontier. The Germans hot on the ball, were the first to pick where to put there trenches, this gave them the advantage of building on higher ground, forcing the British and French to live in the worst conditions. The trenches were built only about two to three feet above sea level, so water would often be filling the trenches. So the troops put down "Duck Boards" over the water so they would not be standing in puddles. Often troops got what was called trench foot. Trench foot was an infection of the feet caused by cold, wet and un-sanitary conditions. In the trenches men stood for hours in waterlogged trenches without being able to take off wet socks or boots. The feet would go numb and the skin would turn red or blue. If untreated, trench foot could turn gangrenous and result in amputation.
Back to the trench system, trenches were built in "zigzag" patterns so that if the enemy ever over took the trenches they couldn't shoot straight down the trench and kill the troops easily. The trenches were about 7 feet deep and troops couldn't shoot over them so they had what was called "fire steps", that were about 2-3 feet high, so troops could shoot the enemy without any trouble. They also had sand bags in front of them and in back of the trenches. The front sand bags were so the enemy could not shoot them when they would fire and the back ones were for the trenches behind them. The trench system worked like this: From front to back No mans land, barbwire entanglements, front-line trench, support trench, reserve trench, then long range artillery guns placed about 10 km behind the front-line. Most trenches had "dug outs" about 15m below the ground. Most of the dugouts were to well constructed to be damaged by shell fire.
Much of the land where the trenches were dug was either clay or sand. The water could not pass through the clay and because the sand was on top, the trenches became waterlogged when it rained.