Boring Tunnels to make Sahara Green again
Qattara Depression is in Egypt. Its deepest point is about 130m below the sea level. The idea was using that as an advantage firstly brought in 1912. The multiple different project proposals were considered: Using the elevation distance as a hydro plant or divert Nil river to establish freshwater Qattara Lake. That would make this part of the Sahara Desert habitable. However, the cost of building a canal or tunnels was extreme. The proposed solution to use 213 nuclear bombs (every 1.5 millions of TNT) for the land extravasation was quickly discarded.
However, we could use the advance in the water deseliation and reduce the cost of tunneling. Would be the project commercially viable nowadays?
Boring the tunnels
With the increasing population and water scarcity in Egypt, there is no option to divert freshwater from Nil river as one of the options. So we will need to use the Mediterranean seawater. The shortest distance would require digging a tunnel. The tunneling cost seems quite high. However, we see some innovation coming. The Boring Company founded by Elon Musk stated that the cost will be below $10 million per mile ~ 6mil. USD per kilometer through a number of improvements and innovations.
The minimal required length is about 55 km (34miles), which is close to the existing project of the company: Washington D.C. to Baltimore Loop. As there is no extra cost of environmental risk related to tunneling or an issue with the dirt disposed in the desert. As we would be boring multiple tunnels in parallel, let’s assume extra 10% additional efficiency. So we could build one tunnel for ~300 mils USD.
Could the cost of tunnels paid by themselves by producing electricity? Perhaps, but let’s rather use the energy for water desalination. So we built a lake with freshwater rather than Sahara Sea. So instead of super salted swamp, the green vegetation could be planted around.
Make an electricity / Clean water
How much clean water would be needed? Each water tunnel would have a diameter of 3.6 m, which provides about 10m2 area. That should allow a flow of 70m3 of water every second. That is 250.000 m3 per hour, 6 million m3 per day (~we do build these sizes today) which is about 2 km3 per year. The descent water flow could be used to produced electricity in s hydropower plant, which would be about 40–50 MW depending on the lake water levels.
If we decided to convert all the electricity to create the freshwater by desalination, we need about 1kWh for each m3 with nowadays technologies. That would mean that we could 50.000 m3 per hour using just the electricity from the hydro plant. That is less than we would need, so some additional solar panels with at least 200MW would be required. About 400MW and some batteries would be more practical as using solar as a source of energy. With abundant power, we could desalinate water during the day, store it reservoir, and use it during the night. No large batteries would be needed. With the solar panels as cheap as 0.08 USD/kWh, we would need about 32 mils USD.
To round it up to cover the cost of the desalination pumps and other equipment, we are at the cost of the initial investment of 500 mils USD per tunnel.
So how many tunnels we will need? That pretty much depends on how large a Lake we would decide to make. So let’s flood about half of the depression.
The size of the Lake matters
With the Qattara Lake about 60 meters below sea level, the size will be 12.100 km2 and volume of 227 km3 [link]. With the lake of that size, the net evaporation was estimated to be 5mm/day — 700m3/s. That is about the continuous flow of 10 water tunnels to achieve the equilibrium of the intake and vapor water. Qattara Depression would start filling with water and quickly form a small Qattara Lake, which would gradually spread. We could pump about 20km3 of water every year. Eventually, the new technologies for the reduction of water vapor could be used. A modular floating cover stops evaporation by preventing the dry ambient air from contacting the water in the pond.
However, even without any vapor, it would take 10 years to reach the target water level. The process will slow as the size of the lake increase, so let’s say that we will dig 10-12 tunnels to make sure that we will achieve the lake volume goal within 20 years. That makes the initial investment of about 5 billion USD.
It is a surprisingly low cost! Egypt has more income from Suez Canal transit fees each year. Let’s summarized the key benefits of a fresh lake of this size.
Qattara Lake Benefits
- The lake with its final size will have about two thousand kilometers of straight coastal line, which could be a smart model! If we make 1 km habitable, that would create more area than occupies Cairo, the capital city with almost 10 million people. Just the increase in the value of the land would pay for the project multiple times.
2. Qattara Lake will have up to 60 meters depth. Large and deep lakes which are heated more slowly than the land by day and cooled more slowly than the land by night. Hence moderating the climate of a region in the same way as oceans.
3. If the evaporation would be reduced by some of the floating covers, there will be more water spare for the irrigation of greenhouses, etc. Also, blocks of fish could be cultivated in the lake immediately. That would create an excellent source of nutrition for millions of people. And as the economic progress, more tunnels could be built to provide extra water for plants.
4. Not only that residential areas could be green using available freshwater. But Egypt made an interesting success with using sewage effluent to grow a forest in a desert close to Ismailia. The same process could be replicated here all around the lake. That would allow creating a tropical forest in a large area all around the lake.
5. In the longterm, the water would be preserved in the area. As the map below shows, the costal area receives about 200 millimeters of precipitation per year, which is much more than further out in the desert area. By introducing the inner Sahara Lake, we can expect that the zone with higher precipitation will expand. New rain would create fast loop watering plants and reduce the net vapor. So more water will be available for expanding the vegetation.
Make Sahara Green Again
In the past, Sahara was green with savannas, many animals, and freshwater lakes during the African Humid Period. It was caused by a stronger West African Monsoon, which led to increased moisture import. The climate models indicate that changes from a dry to a green Sahara and back have threshold behavior, with the change occurring once a certain level of insolation is exceeded due to the Earth’s precession.
Could we make the Sahara green by manpower for a reasonable cost? I believe so. Elon Musk want’s to colonize Mars. Let’s see if we could colonize a piece of dessert on Earth first. We have all the required technology. The cost of doing that would be just a fraction of the cost.
