The population in New Zealand is expected to increase to over five million by the mid 2020’s from the current level of 4.3 million (Statistics New Zealand, 2009). An increasing demand for primary produce as a result may put pressure on marginal land to be farmed. Understanding the economic value of avoided erosion in New Zealand is therefore an important factor in policy making to optimise the soil related activities in the economy. Establishing a methodology for estimating the economic value of avoided soil erosion is the first step in assessing the problem. This study uses the future forest scenarios developed by Scion to identify potential afforestation areas and thereby compare the current erosion/sedimentation status under current land-use (non woody vegetation) with potential future afforestation. The study aims to quantify the incremental public and private net benefits from the change in scenario. The notion has come under different headings in the literature, such as on-site and off-site erosion effects or sediment and soil erosion effects, all of which recognize the importance of separation of effects to avoid double-counting. The separation into public and private benefits and costs in this case, while avoiding double-counting, will also help identify appropriate policy instruments to avoid soil erosion damage using the private and public net benefit framework (Pannell, 2008).