Effect

Flood risk

Costs

Dams

Retention capacity

Space for water

Space for land

Agriculture

Buildings

Potential damage

Nature

Flood risk

1

1

Costs

Dams

-1

1

-1

1

-1

Retention capacity

-1

Space for water

1

1

Space for land

1

1

Agriculture

-1

-1

1

-1

Buildings

-1

-1

1

-1

Potential damage

1

Nature

1

-1

Figure 11.1. Conceptual model for a river basin management system.

in the third cell of the first row and is represented by the value 1. The reverse flow from dams to flood risk (if more dams are built, the flood risk decreases) is represented by the value —1 in the first cell of the third row. As in the notation of system dynamics, positive flows (1) reinforce the original signal, and negative flows (—1) dampen the original signal.

We will not explain the content of the conceptual model in detail here because it serves as an illustration only. However, in order to introduce the reader to the kind of causal thinking represented in this diagram, we will follow some of the causal chains. For example, the size of the retention capacity influences the risk of floods. The risk of floods is an important factor when the number and size of dams to be built are determined. These dams take up land that could be used for agriculture and buildings if there were no dams. Buildings and agriculture produce economic benefits that reduce opportunity costs. The flows connect stocks that are directly related in that there is no other stock in the system through which the flow described would take effect. In other words, the arrows represent only first-order relationships.

Because this description gives rise to different possible interpretations, the background material of each case study contains extensive documentation on the argu ments and discussions raised during the drafting of the system, the interpretations considered, and the relevant scientific literature.

If we want to evaluate the sustainability of the system described in our model, we need to define sustainability by making the inherently normative choice of what is desirable. We proposed to let these judgments be formulated in a stakeholder process. This way, the normativity is made explicit rather than being buried implicitly in the framework underlying an indicator or index.

For the purpose of the QSSI this choice is made for every stock separately, independently of the effects of that stock on other stocks. The choice to attribute a low desired state to agriculture therefore cannot be based on the argument that agriculture reduces retention capacity or has a detrimental impact on nature. Because of this criterion of independence of other stocks, the discussion will not be concerned with the choices that should be made between mutually exclusive stocks.

We add the information on the desired direction of the stock to our model in the form of "+" and "—" (Figure 11.2). These symbols stand for the desired state of each stock in terms of direction independent of the other stocks in the system and also independent of the system consequences of that target. A "+" indicates that a high value for that stock is desired, a "—" indicates that a low level is desired (ceteris paribus).

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