Jun
24
Selling Dominica’s Water: Is There Enough? A Rough Analysis
June 24, 2009 | Posted by Michael "Aquadoc" Campana
3 Comments
The other day I returned a call from a fellow who wants to sell Dominica’s fresh water – 37B gallons per year, to be exact. That is about 114,000 acre-feet per year (140 MCM).
Dominica is a rugged, volcanic island nation in the Caribbean Sea. Its area is about 754 square km (290 square miles) with a population of about 73,000.
The water he wants to sell is not desalted water – it’s all fresh water, from streams (365!) and aquifers (my contact said it was ‘runoff’). The water will be shipped out in supertankers or bags to whomever wants to purchase it. By my calculation, 37B gallons would fill 440 average supertankers (assuming a capacity 2 million barrels or 84M gallons per tanker). So that’s about 10 supertankers per week headed for wherever needs it.
My contact said it would help the world’s water crisis. I pointed out that although 37B gallons is a lot of water, it’s literally a drop in the bucket on a global scale. But it certainly could relieve short-term problems, such as coastal cities undergoing dry times.
And, oh yeah – he mentioned about $3B in annual profits.
He said that China and Venezuela are also interested in the island’s water, which has apparently piqued the curiosity of the U.S. Department of State.
So does Dominica have enough water? It is one of the wettest islands in the Caribbean. Here’s the rainfall and temperature plot from the World Travel Guide for the capital, Roseau, located on the drier southwest coast of the island:
If you add the rainfall numbers up you get over 2000 mm (2 meters or almost 80 inches) of rain per year.
I don’t know the water budget of the island, but the Wikipedia entry says that the wetter, east side of the island gets as much as 500 cm (almost 200 inches) of annual rainfall, with mountain slopes receiving 900 cm (almost 360 inches!). The drier west side gets about 180 cm (70 inches).
So let’s do some back-of-the-envelope calculations. Let’s assume that the average annual rainfall over the entire island is (500 cm+ 180 cm)/2 = 340 cm = 3.4 m.
Distribute that amount over 754 square kilometers (754,000,000 square meters) and you have 2.6 B cubic meters (rounded).
So, since over the long term, P = ET + R (precipitation = evapotranspiration + runoff) we can calculate the long-term average runoff if we know the ET. I will assume that on average, 2/3 of the P is ET and 1/3 is R (global continental averages from G. Hornberger et al., 1998, Elements of Physical Hydrology, Chapters 1 and 2 – not great approximations for a tropical island). That means that the average annual runoff is about 1.1 meters per year, or about 0.9B cubic meters. In other units the average annual runoff is about 900,000,000 cubic meters or about 730,000 acre-feet or about 238B gallons!
So my friend wants to take about 16% of the total runoff for export. Is that going to be a problem?
The answer: I don’t know for sure. Dominica does have a heckuva lot of fresh water, but don’t forget that the island’s environment and the near-shore marine ecosystem are adjusted to this amount. So what happens when you remove 16% of this fresh water each year? That’s the question that must be asnwered before this project proceeds.
Keep in mind that my figures are very crude and I’m using a steady-state budget to evaluate an inherently transient situation. I’m just trying to illustrate a point: there is a lot of fresh water on Dominica but we still need to be concerned about withdrawing some of that water. Adverse effects could result not only on the terrestrial (land-based) ecosystems but also near-shore marine ones.
“What is done in the dark will appear in the light.” – Caribbean proverb
No related posts.
Related posts brought to you by Yet Another Related Posts Plugin.
Comments
3 Comments so far
Subscribe
[...] About This News Article… The article Selling Dominica’s Water: Is There Enough? A Rough Analysis is syndicated for use on our Water Pollution Blog. The original content can be found here. [...]
I think your numbers are quite fair, based on an eye-balling of some Budyko-type data.
As for the implications… I doubt terrestrial ecosystems will be bothered. Aquatic ecosystems and geomorphology might be, depending on what parts of the hydrograph are siphoned from and when, and where along the reaches. As for coastal ecosystems, the rain would have fallen there anyway, so it’s just the nutrients and sediment that might be lacking, and this could be ameliorated somewhat provided the material is returned to the river after being pumped into the bottling facility.
Thanks, Daniel.
By ‘terrestrial’ I meant ecosystems on the island, whether they are aquatic, riparian, or whatever. I should have been more explicit and simply said ‘land-based’. True terrestrial ecosystems may be impacted because the SW-GW relationships may be changed, water tables changed, etc. This will be exacerbated if they decide to pump GW.
Near-shore ecosystems will be impacted because the SW flow into the sea will be reduced, which could cause problems to an ecosystem adjusted to a certain amount of fresh water input from the land.