Sunday Rant – 2613

[date Sun, Jun 30, 2013 at 9:10 AM]


“A pessimist sees the difficulty in every opportunity; an optimist sees the opportunity in every difficulty” – Sir Winston Churchill

Go Calgary, go!

Some great pictures of volunteers in black and white:

Another week of flooding in Alberta. The math of weather meets the complex geological reality of the earth’s surface. Is there opportunity to be had?

Let me analyze…………….

Basic measurement origins:

One of the numbers I remember hearing in the days leading to the Calgary flooding was “70mm of rain in a 3 hour period”. I got thinking about that, and what it meant. I was schooled in Imperial and Metric systems. The above link betrays my preference: the human story of Imperial measure is older and more pragmatic than the “scientific” metric measurement system (base 10). The first thing I did was a quick mental calculation……. let’s see….. one inch is 2.54 cm……. roughly 2.5…… 3 X 2.5 is 75….. that is just under 3 inches of water in 3 hours, or an inch per hour give or take. (It’s closer to 2.7559 inches, but the extra fractions make the math headach-y.)

So, what does that mean? When you pour 3 inches of water into a glass, it doesn’t look like much, and certainly isn’t threatening. Three inches of whiskey on the other hand, can be quite alarming…. or welcome, depending on your point of view. What does it mean?

Sticking with my favorite Imperial measure, 3 inches of water on a square foot would be 12 X 12 X 3 cubic inches of water, or 432 cubic inches of water. How much is that? The Imperial gallon, which Canada so callously abandoned, is 277.42 cubic inches. The U.S. gallon, which the American people have stood by through thick and thin, is somewhat less at 231 cubic inches (approx. 3.785 litres), but I’m using Imperial. I also fly the Red Ensign on Canada Day, but that is another fettle kettle…. The Imperial gallon of water weighs 10 pounds by the way…. that’s how it got it’s volume.

This means that 70mm of water in 3 hours was a little more than 1.5 Imperial gallons of water per square foot, never mind the time for now…. What does this mean in “real” terms that can be related to daily life? Let’s see……… a mile is 5280 feet, and a square mile is 27,878,400 square feet….. times 1.5…. which is 41,817,600 gallons….. times 10 pounds….. equals 418,176,000 pounds of water. Just under a half billion pounds……

Now we’re getting somewhere. My house is about 1,200 square feet. That means 1,200 X 1.5 X 10 = 18,000 pounds of water. Holy shit! that’s 9 tons of water! Starting to get an image in my noggin that I can actually relate to daily life. If I filled my house with water to the depth of 3 inches, it would take approx. 1,800 Imperial gallons. I have trouble carrying two 5 gallon water jugs into the house for my water cooler. I can carry one OK, but it’s a lop-sided load. Two is a better load, but I can’t open the door….. I digress.

If it is raining 70mm in 3 hours, approximately a BILLION POUNDS of water is going to be deposited on every 2.5 square miles. Multiply that by how many square miles? Sheesh! Big big numbers.

Where does the water go? The extremes of land are rock (a hard place) and sand (a sponge). Other variables include vegetation (how much drinky can a sunflower drink?), animal use (water the horses Myron, or we’ll have a flood!), and existing bodies of water. How much water can the “dry land” absorb? How much water can the water table accept before the table is above ground? Can you drown a tree? You can certainly sweep one away in a flood as a consequence of very large numbers (as demonstrated above). Enter the “delta” – how much absorption is possible over a given time period.

This is getting complicated again. The point however, is that heavy rain makes ground water numbers and lake / river / creek / pond / sea numbers. There is a lot of water on Earth.

Enter the dragoons (an army of data). Here is a table for gallons per hour (gph) for common schedule 40 pipe –

Assume Gravity to Low Pressure. About 6f/s flow velocity, also suction side of pump Assume Average Pressure. (20-100PSI) About 12f/s flow velocity Assume “High Pressure” PEAK flow. About 18f/s flow velocity*
Sch 40 Pipe Size ID
(with minimal pressure loss & noise)
(with minimal pressure loss & noise)
(with minimal pressure loss & noise)
(with minimal pressure loss & noise)
(with significant pressure loss & noise)
(with significant pressure loss & noise)
1/2″ .50-.60″ .85″ 7 gpm 420 gph 14 gpm 840 gph 21 gpm 1,260 gph
3/4″ .75-.85″ 1.06″ 11 gpm 660 gph 23 gpm 1,410 gph 36 gpm 2,160 gph
1″ 1.00-1.03″ 1.33″ 16 gpm 960 gph 37 gpm 2,220 gph 58 gpm 3,510 gph
1.25″ 1.25-1.36″ 1.67″ 25 gpm 1,500 gph 62 gpm 3,750 gph 100 gpm 5,940 gph
1.5″ 1.50-1.60″ 1.90″ 35 gpm 2100 gph 81 gpm 4,830 gph 126 gpm 7,560 gph
2″ 1.95-2.05″ 2.38″ 55 gpm 3300 gph 127 gpm 7,650 gph 200 gpm 12,000 gph
2.5″ 2.35-2.45″ 2.89″ 80 gpm 4800 gph 190 gpm 11,400 gph 300 gpm 17,550 gph
3″ 2.90-3.05″ 3.50″ 140 gpm 8400 gph 273 gpm 16,350 gph 425 gpm 25,650 gph
4″ 3.85-3.95″ 4.50″ 240 gpm 14,400 gph 480 gpm 28,800 gph 700 gpm 42,000 gph
5″ 4.95-5.05″ 5.563″ 380 gpm 22,800 gph 750 gpm 45,000 gph 1100 gpm 66,000 gph
6″ 5.85-5.95″ 6.61″ 550 gpm 33,000 gph 1100 gpm 66,000 gph 1700 gpm 102,000 gph
8″ 7.96″ 8.625″ 950 gpm 57,000 gph 1900 gpm 114,000 gph 2800 gpm 168,000 gph

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