Before we started construction, the site was a fairly uniform slope down 9% to the west. The new house foundation was installed across most of the width of the site, set into the slope. Because the foundation acts like a big barrier to the downward flow of water, we need to pipe the rain around the house to avoid a wet basement.
Rain will fall on four major surfaces: the house roof, the PV panels over the garage, the autocourt, and the landscaped yard. The house roof water will be harvested for reuse inside, so it is routed into big rain tanks. But the rest of the rain must be directed to a new raingarden just downhill from the house. The purpose of the raingarden is to collect and then slowly infiltrate all that rain so it does not flow off the site.
The task this week is to install the buried piping, all of which flows to a single catch basin (concrete box) at the uphill end of the rain garden. A backhoe digs the trenches and then the black polyethylene piping is installed. The contractors carefully set the slope of the pipe to assure positive drainage. The trench is then filled with gravel to bed the piping before being covered with dirt and plants. Where the pipe bends underground, vertical pipes called cleanouts stick up to allow for future maintenance.