Detail of garden trenches at Tupou Bay. Like stone rows, trenches may have several purposes. One may have been to mark the boundaries of a garden plot; these examples are spaced at an average of 13 m along the base of the slope—a smallish plot-dimension. If the spaces between the lines were small plots, the function of the lines was also to drain the soil, so that it became more suitable for kūmara or yam. On the flat slopes at the foot of the hill, the trenches may have served to concentrate seepage to create the right conditions for the growth of taro. This would explain the number of trenches. The largest trenches are about 150 m long and about 1.5 m wide.