Question
I have a slight hill around 2-3 feet high at its peak, at the foot of the hill is a sidewalk that leads right to my pool. The hill keeps washing dirt into the pool at heavy rainstorms. I was thinking of building a wall out of railroad ties (landscape timbers) with drainage rocks behind it to prevent the mud slides. How would I go about doing this the right way, and how much drainage rock would I need?

Answer
Hello Dan, sorry if I couldn't get back to you sooner.

By far the best solution would be, yes to terrace the slope, either with walls or landscape timber and then to add what is called a 'French drain'. A French drain system is simply a flexible plastic tube with holes that captures water and then lets it run off from your terraces. The trick is clearly to install the tube with a slope (to allow the water to run to a run-off point or a water collection tank etc.

The tube should be set into a trench no more than 2ft wide and 3ft deep but before laying the tube in you must line the trench with a nylon fabric (the one that builders use). This will prevent soil from entering the trench while still allowing the water to pass.

Then, place a layer (around 5" deep) of gravel (around 3" in diameter) and lay the tube in, cover it with more gravel to a depth of around 2' and fold over the remaining nylon to seal the top of the gravel and cover with soil or, even better with sand. This will drain water effectively and I would install one on every terrace, in order to drain the area well.

Thanks for any bonus points in advance.

Kind regards

Jonathan Radford www.jonathanradfordgardens.com