Under traditional management regimes there are soil additions each year too, which should be included in the consideration of net losses. These come from the annual cutting back of the vegetated terrace risers by about 2 cm. Not all farmers practise this, but it is common in the low-to-middle-elevation areas. On a terrace 50 m long with a 2 m riser, this will add approximately a further 2 m3 of soil to the terrace below. Some, but not all, of this material will have been trapped as eroded soil passing down the vegetated riser but, nevertheless, the long-term net effect will be to move the whole terrace set back and up into the hillside. Thus, in a situation where the terraces are ditched and where annual additions come from the riser, the net soil losses from the terrace surface, if any, will be very small.