The builders move a large amount of gravel from the slope above to fill in the area behind the retaining wall. Whenever possible ... temporary channels dug into the hillside, a wooden sluice ...

I needed a retaining ... t build the wall more than 48 in. high—a taller wall requires special engineering. Do the digging ...

A casual glance might lead you to believe that farmers carve them into hillsides, using the dug-up rock to build the retaining walls and the excavated earth to level the terraces. Well ...