Royal HaskoningDHV1, KWR Watercycle Research Institute2, Province of Overijssel3
Introduction A sustainable drinking-water supply requires durable securing of the resource (Moen & Cramer, 1987). With an increase in spatial pressure, decline in social commitment for planning limitations that arise from the protection of groundwater, the decreasing possibilities to move the abstraction sites and the time-bound demands from the EU Water Framework Directive (EU, 2000), the need to fit the abstraction sites in the environment (surrounding) in a durable manner is increasing (Van den Brink & Buitenkamp, 2006). Especially to ensure the production of safe and reliable drinking water at as low as possible societal costs (LBOW, 2007). To achieve this, cooperation from other stakeholders, such as the municipality, water board and users/residents is essential to illustrate the impact of several land-use functions or spatial development scenarios in this process (Van den Brink e.a., 2014). This situation is especially challenging in the province of Overijssel with 24 groundwater abstraction sites with abstractions ranging from 3 -- 12 million m3/yr, vulnerable Pleistocene sandy soils and increasing spatial pressure from both agricultural and urban areas (Meinardi, 1994). Method REFLECT is a negotiation support system that gives an overview of the impact of several land-use functions on the groundwater quality (Laeven et al., 1999; Van den Brink e.a., 2013). It does this by means of scores given for the impact of land-use and the vulnerability of the abstraction site. The scores for the several land-use functions are determined by a Delphi approach, where experts are requested to judge the impact of land-use on the aspects diffuse pollution, risk of calamities and maintenance. The scores for the vulnerability is obtained by combining the characteristics of the soil, the reactivity of the sediment and the travel times of groundwater from soil surface towards the abstraction wells. By combining these impact scores with the vulnerability map of the drinking water abstraction, risk scores are obtained. REFLECT supports the negotiation process by providing the risk scores for the drinking water abstraction to be able to evaluate the scenario's in terms of stand-still and step forward. Results and discussion REFLECT is used in the province of Overijssel to obtain the risk scores of the actual situation of all drinking water abstractions and to support spatial developments. This instrument provided a transparent overview of the impact of individual land-use changes and areal weighted risk scores. The areal specific overview of risks was used to identify measures aiming at reduction of these risks (Ten Heggeler, e.a., 2010). An example is the identification of farms which were invited to take part in a project to improve their nutrient management resulting both in an increase of the operational result of the farm and a decrease of the loss of nutrients to the groundwater. Knowledge of the impact of land-use changes on groundwater quality helped stakeholders also in developing spatial plans which were harmonizing with the interest of the drinking water abstraction site and creating a step forward in the protection level of the abstraction site. An example is the development of a residential area on former agricultural land within a groundwater protection area in such a way that the impact of land-use on the groundwater abstraction -- expressed as risk score -- is decreased. Conclusion REFLECT is an instrument that fits well within a process driven risk based groundwater governance approach aiming at a sustainable protection of drinking water abstractions by harmonizing land-use functions. The use of a limited amount of land-use types enables the use of the instrument and leaves the necessary space for discussions regarding the need for additional soil protecting measures. However, the stand still and step forward principles as part of the risk based groundwater protection policy of the province of Overijssel require careful communication with the local and regional stakeholders to combine harmonizing land-use changes with increasing social commitment and support. EU (2000). Directive 2000/60/EC of the European Parliament and of the council of 23 October 2000 establishing a framework for Community action in the field of water policy, Official Journal of the European Communities 22.12.2000, L 327. Laeven, M.P., W. Beekman, L.J.L. Drogendijk, P. van Bergen, C. van den Brink (1999). 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