We usually report water quantity information as a volumetric rate (e.g. m3/s); we usually report water quality information as a concentration (e.g. mg/l); and we usually report precipitation as a length (e.g. mm). But we don’t have to.
The mass of water is related to its volume by its density which, conveniently, can be assumed to be unity (1). This means that we could just as easily report water information using the dimension of mass.
Would reporting water information in a different dimension change the way that we understand water?
For example, in Vancouver, BC we use 173.4 m3 of treated water per person per year and we get 1.117 m of rainfall per year. What does this information tell you about our water footprint? There is no intuitive linkage between this data and our dependency on our watersheds. However, I could tell you that we consume 173.4 t (1 tonne = 1000 kg) of water per year and we ‘only’ get 1.117 t/m2 of rainfall each year. This puts our place in the watershed into better perspective. You don’t even need a calculator to ‘see’ that — even without accounting for losses — we need more than 150 m2 of watershed area per person.
That simple insight could change the conversation about water management.
It doesn’t need to be a choice of either/or. We already routinely report water data in different dimensions/units for sediment and water quality depending on the end-use of the data.
The average sediment concentration in the Mississippi River at St. Louis is 324 mg/l. Is that a big number or a small number? Most people do not have any context for evaluating sediment concentration data so it doesn’t contribute to a meaningful understanding of the role of the Mississippi River in landform processes. However, if I report that the sediment load of the Mississippi River is 250,000 t/d and I also provide a bit of additional context that a common railway car has a capacity of 100 t, then a new understanding of the Mississippi River emerges from the data.
Similarly, with water quality data we may report that a stream with a flow of 5.0 m3/s has a total nitrogen concentration of 1.5 mg/l. Those values may be meaningful if I am already an expert in the field of water quality. However, for a watershed stewardship NGO trying to understand the role of agriculture in water quality, these data might be a bit intimidating. However, suppose we were to report that the flow of water is 5 t/s of water and the flow of nitrogen is 7.5 g/s. Even a non-expert can intuitively understand that there is proportionately very little nitrogen in the water but the total quantity of nitrogen can quickly add up. For example, if a bag of nitrogen fertilizer at the local feed store weighs 20 kg then this concentration is equivalent to one bag of fertilizer being dumped in the stream every 44 minutes.
The way we traditionally report water data is not wrong.
There are some very good reasons for the conventions that we have widely adopted. However, in the distant past, when these conventions became entrenched the target audience for water data was primarily engineers. Perhaps there is now room to be a bit more creative in reporting water data. Perhaps, with a bit of innovation we could make the information from our data more meaningful for everyone sharing our watersheds.
Do you know of anyone who has experimented with reporting water data in non-conventional units and dimensions? How did that work out?
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