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Drought and the Maritime Sector

Cape Town
Cape Town

By Harry Valentine 2018-01-13 10:30:19

At the present time, two metropolitan regions in the Southern Hemisphere are experiencing drought and facing severe water shortages. The cities are Sao Paulo, Brazil and Cape Town, South Africa, and the maritime sector offers several options for providing potable water to such cities.

Changing Weather Patterns

The cities of Sao Paulo and Cape Town depend on prevailing winds to carry humidity from the ocean toward coastal mountains, where the humidity usually condenses into rainfall. The rainfall flows into storage dams built at high elevation in the mountains. A slight shift in wind direction and a slight increase in local air temperatures results in massive reduction of rainfall. Property owners who live in the low-lying areas of these cities, and many other cities around the world, harvest rainwater from their roofs and store that water in tanks on their property.

Citizens in these cities have also been encouraged to recycle water, such as collecting soapy bath water or laundry water and transferring it into toilet storage tanks that operate on a restricted number of flushes per day. On humid days, electrically-powered water-from-air technology extracts potable water from the humid air and purifies it using UV-radiation treatment. This technology is commercially available and wealthier citizens who live in humid, drought affected regions have invested in such technology. Some commercial establishments use deep level, coastal sea water or deep level cold saline groundwater to operate large-scale water-from-air technology.

Desalination

Desalination of seawater occurs in many coastal cities internationally including at Chennai in India, Tel Aviv in Israel and at several Emirates coastal cities. The Koeberg coastal nuclear power station is located to the north of Cape Town, and plans are underway to desalinate seawater at that location. The availability of thermal energy from the thermo-nuclear power station plus abundance of cold seawater makes thermal desalination a potentially viable option near Cape Town. There are also plans to introduce reverse-osmosis (R-O) porous membrane desalination of seawater at other locations around the Cape Town area.

Authorities in Brazil are evaluating several locations to develop seawater desalination. Brazil’s only nuclear power station is located next to the Atlantic coast and within close proximity to Sao Paulo. There is the option of operating thermal desalination at that location and to use heat exchangers cooled by seawater to condense steam into potable water. 

Over the short term future, the use of desalination ships could supply a portion of the potable water requirements of the populations of Cape Town and Sao Paulo. Also over the short term, the transportation sector could carry water from distant locations.

Flushing with Seawater

Toilets were built into the early wind-powered ships of centuries ago, with effluent being released directly into the sea. The equivalent of flush toilets operated using seawater, with corrosion-resistant plumbing having being made from wood, clay and porcelain. Modern corrosion-resistant plumbing is made from materials such as plastic. Several tall buildings in Hong Kong include duplicate plumbing for seawater to flush the toilets, a trend that is slowly spreading internationally to other coastal cities and including upscale residential areas located on offshore islands where potable water is scarce and expensive.

Water Transportation

Private people in Cape Town have on occasion organized trucks to carry water from distant locations where water was more readily available. There has also been discussion in South Africa about trains of railway tanker carriages carrying water from distant areas where sufficient water is available into Cape Town. 

To move massive volumes of water, maritime tanker ships offer a lower transportation cost for bulk movement than either rail or truck transportation. Brazilian coastal cities such as Belem, Fortaleza and Recife are located close to the Amazon River where water tanker ships could collect potable water.

Historically, the construction of aqueducts made it possible to transport water from rain swept inland locations at higher elevation, to ancient metropolitan areas at lower elevation. Long-distance pipelines represent the modern version of the aqueducts and are long-term investments. There are coastal lagoons in Brazil’s low-lying southern region, while Sao Paulo is located at higher elevation some 900 kilometers (560 miles) to the northeast. A water pipeline would be costly and would consume much energy to push water through the mountainous coastal region. Over the short-term future, tanker ships would represent a potentially viable alternative.

W.I.G. and Airborne Water Transport

Where large bodies of water are available, tanker aircraft pick up water from lakes and rivers and spray the water over burning vegetation as a method to control forest fires. Such aircraft can also be used where large bodies of potable water are located in close proximity to drought stricken agricultural regions. Many of the technical precedents of airborne tanker aircraft can be applied to wing-in-ground (W.I.G.) vessels that could travel at speed above a water surface while also collecting much greater volumes of water than tanker aircraft, through multiple parallel intake pipes. 

The reverse-delta wing design and tandem wing design of some W.I.G. vessels allow them to carry many times the weight of water that conventional airplane flight wings. During emergencies, W.I.G. vessels could carry potable water from the mouth of a large river to a sea plane runway next to a coastal city. The ability of W.I.G. vessels to lift to an elevation equivalent to 40 percent of their wingspan could allow large versions of the technology (60-meter, 200-foot wingspan) to travel above some agricultural areas where sufficient vertical clearance is available, to spray water over the produce.

Conclusions

Changing weather patterns produce periods of drought that sometimes last for several years, as recently occurred in California. Drought could occur almost anywhere. While investment in fixed-location desalination technology has merit, the technology could remain idle and unused for many years after the end of a drought period. 

Mobile desalination technology installed aboard ships allows the technology to visit different regions at different times, in response for the need for potable water. Transportation technology and/or pipelines may be suitable for locations where drought stricken regions are in relative close proximity to large bodies of potable water.

The opinions expressed herein are the author's and not necessarily those of The Maritime Executive.