How the Coronavirus is Like a Flood

Flattening the Curve, Slowing the Flow


March 19, 2020

By now most of us have heard of “flattening the curve.” This is the effort to reduce the number of coronavirus (COVID-19) cases that happen all at once, exceeding the capacity of our healthcare system.

Interestingly, the graph of flattening the curve of peak cases is very similar to the graph of flattening the curve of peak flow in a flooding stream.

Slow the Flow

The goal in both cases is to slow the flow. In the case of the coronavirus, it’s to slow, reduce, and spread out the number of cases in order to save lives and not overwhelm or flood our healthcare system, specifically the number of hospital beds available to take care of people (as well as the number of masks, ventilators, tests, nurses, doctors, and other necessary equipment).

In the case of a stream during a storm, the goal is to increase the length of time it takes for rainfall to hit the ground and enter a waterway. The longer it takes, the lower the peak water level in the stream, making it less likely that the stream will flood. Slow it down, spread it out, soak it in.

Here is a graph showing the impact of flattening the curve of coronavirus cases on our ability to care for them:

Flattening the curve of coronavirus cases so that the number of cases doesn’t overwhelm our healthcare system. Graphic from The NY Times, adapted from the Centers for Disease Control.


And here is a graph of what’s called “lag time” showing how slowing (and reducing) rain runoff with, say, plants and trees, lengthens the time it takes for the stormwater to enter the stream and lowers the peak flow:


A graph of the impact of slowing the flow of stormwater runoff on the peak water level of a stream. Courtesy of Slow the Flow.


Do We Have the Hospital Capacity? It Seems We Don’t

Could our Houston area hospitals be overwhelmed by a flood of cases? Yes, they could, according to a recent report by ProPublica. Which is why public officials here and elsewhere have taken such extreme steps to “slow down” our social circulation by shutting down schools and the rodeo, closing restaurants and bars; why conferences and parties are being cancelled, etc.

ProPublica analyzed the impact of cases on local hospitals under different scenarios: more cases faster, fewer cases over a longer period of time, and so on. “It is estimated that about 8% of the adult population would require hospital care,” according to the report. “In a moderate scenario where 40% of the population is infected over a 12-month period, hospitals in Houston, TX would receive an estimated 430,000 coronavirus patients. The influx of patients would require 14,300 beds over 12 months, which is 2.8 times the available beds in that time period. The Harvard researchers’ scenarios assume that each coronavirus patient will require 12 days of hospital care on average, based on data from China.

“In the Houston, TX region, intensive care units would be especially overwhelmed and require additional capacity. Without coronavirus patients, there are only 650 available beds on average in intensive care units, which is 4.6 times less than what is needed to care for all severe cases.”

Slowing Down, Spreading Out, Letting It All Sink In

So think of social distancing as spreading out the flow, slowing it down as it trickles through tall grasses and pebbles, soaking into gardens, swales, and green spaces filled with trees so that it doesn’t overwhelm our system.

Instead of rushing to gather in one place as many people as possible, we pause, stand apart, wait, get out in the sun if we can, and reflect on what more we can do to help.


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