The economic and societal benefits of large scale submerged drainage

Abstract

All around the world, peatlands suffer from the negative effects of land subsidence. In the Netherlands, the peatlands are mostly used for dairy farming. Submerged drainage and pressure drain infiltration are two technical innovations with the aim to reduce the land subsidence and at the same time have a positive impact on the dairy farming.

These techniques are only tested on a scale of a plot or several plots, hence the focus was on a small scale level. Only for some individual effects, an analysis of large scale use is made. Therefore, in this master thesis a multi criteria analysis (MCA) of large scale use is presented. As a case study the Lange Weide polder is used and six alternatives are determined. The alternatives consist out of different combinations between submerged drainage, pressure drain infiltration and water-level strategies. To assess the different alternatives the following criteria are determined: agricultural effects, greenhouse gas emissions, storage requirements, investment costs and water consumption. The outcome of the MCA is used to give a policy advice about the large scale use of submerged drainage and pressure drain infiltration.

The first three criteria of the MCA are strongly influenced by the land subsidence, and the outcome of the subsidence equation is based on the clay thickness and the Average Deepest Groundwater table (ADG). Hence, it is important to provide the most accurate method in determining the clay thickness and ADG as possible. In order to gain the most accurate input data about the clay thickness different (interpolation) methods are analysed with the principal of validation. The ADG is determined using the outcome of the two existing models.

Kriging with the nearest 5 data points was the most accurate method in determining the clay thickness. The ‘karteerbare kenmerken kaart’ was most suitable to determine the ADG, because the Hydromedah method had unexplainable deep ground water levels. With this input data and the effect of an alternative the subsidence for 2010-2050 is modelled. After the addition of the different criteria, the five alternatives with submerged drainage and/or pressure drain infiltration had a higher score than the alternative without technical investment. The two alternatives with a combination of submerged drainage and pressure drain infiltration had the highest score.

The MCA showed that the large scale use of submerged drainage and pressure drain infiltration is social and economic beneficial. Therefore the policy advice is given to encourage the large scale use of these techniques.