For someone designing storm water to minimize contaminants, the most important thing to track in your diagram is the level of contaminants. Above is a simple, bounded diagram of storm water with contaminants coming in.
One possible start to designing a new system is to look at the 'clouds' outside your usual design of the infrastructure. In the wider world, how and why are things coming in to your system? Can you manipulate them somehow before they become inputs?
You might be able to think of a way of doing that...
You might be able to design a physical intervention that prevents the contaminants coming in from source or you might be able to legislate or educate for behaviour change.
Or we can work at removing the contaminants once they are in the system.
The reed beds here can be diagrammed in a lot more detail. What parts of the system could you make even more visible?
On the other hand, if you are designing the storm water for flood control, you need to track volume in your diagramming:
The first step is to extend your thinking by looking into the clouds at either end of the system. We start with in - where is the water coming from? That is the subject of the second diagram below.
We know reasonably well what we can do about reducing the volume of water coming in to the infrastructure system; build permeable paving, use green roofs or collect roof water for use inside the building. Using the technique of connecting the loops, we connect outputs to places where they are more useful - within the buildings and to the groundwater.
As an example of bio-mimicry in design, lets look at a garden with plants. If we track what happens to water going through a planted garden, this is something like what happens:
It does not take too much thought to spatialize this diagram of a garden and turn it into a Landscape device, a rain garden.
Remember the groundwater reservoir can become 'full' - the level of the water table gets so high that it is higher than the ground level - a flood. The diagram of what is happening now looks like this:
When the groundwater & river are full, they can no longer accept water from the permeable surfaces or the network of pipes. So all the water that would have gone into the river or groundwater lies on the surface - a flood.
Because all these overflows act like multiple reinforcing loops, this means once the system has reached its limits, failure is compounded exponentially. This type of failure is called a 'catastrophic' failure of a system (even if the event is not catastrophic in a social sense).
To summarise the steps to take in re-designing your system:
1) Track the element that you most want to manage in your stock flow diagram
2) Research the cloud - the external system that feeds that element in to your system
3) Can you modify that element somewhere in the cycle before it enters the system?
4) Look at the outputs - can you connect them up to something useful rather than dumping them? Can they be useful inputs in to another system? Or can your own system use them somehow? Think of the methane that used to escape in to the atmosphere now being used to power the landfill
5) Can you introduce a balancing (or reinforcing if appropriate) loop into the system? These might be making a harmful activity more difficult, more expensive or more visible somehow.
6) Bio-mimicry: Draw a diagram of how this process is handled in nature. Replicate this process in your design