I generally take an exploratory approach at first. Start with qualifying what you believe to be the associated benefits of a management action (e.g., system of dikes; if this a specific dike system, a GIS approach to bounding the agro-hydrologic and social system would be quite beneficial). Determine how these qualified benefits might be measured bio-physically (again, if this is a specific system of dikes, are there hydrologic simulation models available that might simulate the effects of water management on watershed-level crop yields and other beneficial outcomes? For example, where I am located, we often use the SWAT model for these types of simulations: http://swat.tamu.edu/). If these benefits can be measured/quantified it may be possible to develop production functions for these outcomes (e.g., see how the InVest Model does this: http://www.naturalcapitalproject.org/invest/). The production function route is but one way to quantify the direct and indirect economic benefits of managing water tables. There may be benefit transfer opportunities depending upon available data and similar studies. I googled "value of ecosystem services and dikes and Netherlands" and got a number of hits (mostly regarding flood mitigation), yet there may be some studies that align with what you are thinking about doing. If you are thinking not so much about the hydrologic benefits of a dike system and more about the economic development opportunities afforded by expanded water infrastructure (e.g., dikes), there may be various Input/Output models that might be applied to help estimate direct, indirect, and induced effects (e.g., jobs, income, etc) of expanded agronomic or urban capacity due to new/expanded dikes (this document, for example, overviews some I/O possibilities as examined by investment banks: http://www.eib.org/attachments/thematic/economic_appraisal_of_investment_projects_en.pdf).

Context is everything in these types of analysis. If you can be more specific, I (and others) may be able to provide more specific advice.

 Thank for your valuable advice, John. I will ask specific questions later. Could I contact you via email?