Tunisia – Page 33 – Not Your Average Engineer

November 28, 2004November 15, 2021

Sand Encroachment

The far south of Tunisia hasn’t always been a sandy wasteland. Once it was a savanna stretching from present day Morocco to the Nile River. Today, it’s a combination of sand and dry land. Somewhere along the way, several thousand years ago, the land underwent a radical change from productive grasslands to sands devoid of life. Whether it be purely as a result of climate change or maybe as a result of over grazing by wild animals or even domesticated livestock or perhaps a more systematic abuse of resources no one at the moment can say. It is clear though, that this process is ongoing and without human intervention, will continue to claim more land every year.

Fighting against desertification is nothing new. People have been battling the sands of the desert for thousands of years. In the desert oases of Tunisia, palm frond fences have been employed since the founding of the first palmeraie to check the advancing sand. With time and persistence, humans have fought and won battles against the desert in hundreds of oases, pushing the cultivated land farther and farther from the water source. A key portion of this effort has been controlling the sand.

In recent years, this effort to control the sands of the desert has been broadened beyond the oasis to the rest of the south of Tunisia. Along most of the major and secondary roads, sand fences have been installed, with good success, to check the advancing sands. In some places, the sand drifts caught by these fences are over 30 meters high and still growing. To keep these artificial sand dunes in place, it requires constant vigilance on the part of the local authorities. Every time one of the fences gets buried under the sand, another fence must be installed at the top of the dune. There may be ten fences below the visible fence!

Efforts to control desertification don’t stop with sand fences. In Libya, for many years, hundreds of thousands of hearty trees have been planted in the desert, pushing back the unusable land and opening vast swaths of country to the possibility of cultivation in the future. In Tunisia, traditional check dams designed to capture scare water during the infrequent but violent rainstorms have been beefed up and improved to keep more land wetter longer. In Morocco, at the edge of the great sand sea, I watched as front end loaders and dump trucks were used to dig out part of a village from the steady advance of the sand dunes. Each country and each region fights wars against the sands in different ways.

Looking out over vast expanses of sand dunes and finding a place where the sand parts and a little bit of the dead earth beneath is revealed makes me wonder just what might lie out underneath the sands of the Sahara. Walking between the dunes in Morocco revealed artifacts dating back several thousand years including such exotic finds as seashells and bits of coral from the red sea. I have a feeling that one day, if the sands can be pushed back far enough, whole lost civilizations will emerge out of the dunes. Let’s hope history doesn’t repeat itself and the sands and desertification are held at bay. Otherwise, one day, all of North Africa will be one big sand sea.

November 28, 2004November 15, 2021

Desert Agriculture

Motoring through the southern half of Tunisia I got a chance to see firsthand the arid conditions of agriculture. Aside from the common oasis of greenery in a sea of brown and tan, Tunisia doesn’t have much in the way of water resources. Unlike in the arid climate regions of America where deep bore wells are used to draw water to the surface for industrialized agriculture, Tunisia employs a more environmentally friendly approach of dry land farming. Throughout the southern deserts, every single dip, ditch, creek, ravine, or low spot on any sort of a slope is blocked by stone and earthen check dams. Behind these dams, hundreds of years of patience have created level patches of soil. Within this soil, the crops of the south are grown.

Some crops are planted at a specific point during the year and allowed to lie dormant until proper moisture rains down in a brief and highly infrequent deluge from above. Other crops are planted and come up on their own accord in spite of the dryness. These check dams actually hold water back underneath the soil where hearty plants can tap into the moisture during dry months. The other category of plants is planted only after it has rained and the earth is humming with water. Palms and other trees grow in these small beds of plenty tapping into the deep underground water supply year round.

These patches of cultivation in an otherwise sea of brown are the soul result of human intervention in an otherwise eroding landscape. Across the south of Tunisia, the ground is hard and parched. When rain does come, it comes in such copious amounts that the earth isn’t able to absorb the moisture. Instead, it runs off in huge torrents, cutting deep ravines and channels across the landscape. To harness the water and erosional soil, dams of all sizes, from tiny to immense, have been built over the centuries. Only through the continued tending of humans have these dams remained in place. In several locations, where maintenance of the dams has fallen by the wayside due to people moving on to bigger cities or to more profitable things, I saw breached dams with deep water cut trenches burrowing through the once productive soil behind the dams.

Not only do these dams provide agricultural land, but they also control the torrential downpours which periodically strike the southlands of Tunisia. Without such places for the water to be slowed down, huge torrents would rush down the dry riverbeds, washing out roads, houses, communication lines, everything. Recognizing the value of the dams, the Tunisian government has a program to revitalize and expand the dam system to help control the flood waters and encourage agriculture on the marginal lands of the desert.

This isn’t the first time I’ve seen such dams in use. On the east side of the high atlas mountains in Morocco, I also saw such a system in place and still actively used by the Berber tribes who reside in the mountains. Conditions there were so extreme as to warrant planting individual dwarf wheat plants about ten inches apart to make the most of limited amounts of rainfall. When I visited one such agricultural operation outside the small village of Amassen, the wheat plants were already ready to harvest in the beginning of July and only stood about five inches tall. I haven’t seen such extreme agriculture in Tunisia, but no doubt, in some areas, it once existed. Since independence, such subsistence agriculture has, it appears, fallen by the wayside in favor of more profitable and leisure inducing enterprises.

As more and more high production agricultural land in Tunisia is taken up by tourism and industry, Tunisian farmers will be forced onto more and more marginal land until even the driest of locations are being farmed. Maybe moisture farming, like Luke Skywalker’s uncle and aunt practiced, isn’t too far off in the future.

November 28, 2004November 15, 2021

Oasis Water Systems

Throughout the four oasis complexes we visited on our trip to the south, the level of sophistication of irrigation and irrigation control impressed me. In all of the oases, a complex system of water management has been in use for several thousand years. This is evident especially in the larger Gabes oasis complex where the bus got up close and personal with a roman aqueduct which passes water over the road and another roman aqueduct which passes water under the road. These two aqueducts have effectively limited the size of vehicles which can use that particular road through the oasis for some two thousand years. They have also provided irrigation for large swaths of greenery.

In the oasis of Chebika utilizes a dam to retain water in a narrow gorge in the mountains above the alluvial fan of greenery. This dam appears to be a recent construction, but similar methods of storing water for lean times no doubt have been used in the mountain oases for quite a while – if not by a dam that retains water in the liquid form, then by earthen berms designed to capture water runoff from the particularly strong and rather infrequent rain storms which, from time to time, hit the deserts of Tunisia.

The oasis of Tamerza employs a series of canals and pipes to carry water throughout its palmeraie. Little has changed here, aside from the plastic pipes now being used, since the oasis was carved out of the desert landscape. Probably before the water was so heavily exploited, the natural swimming hole at the bottom of the cascade in Tamerza was a bit deeper and a bit cooler, but having the choice between an entire oasis that can support several thousand people and a cool refreshing swimming hole, it seems that the local populace decided on the less invigorating of the two.

Tozeur’s oasis has been operating at its current state since the 1200’s when Ibn Chabbat, Tunisia’s famous engineer, designed the irrigation system. The same channels, canals, and dams which he devised to supply the ten square kilometer oasis with all of its water are still in use. Some of them have been upgraded from the original stone and wood linings to concrete and metal, but otherwise, the whole system has been running with minimal maintenance for about 800 years.

Recent years have seen the amount of water available to oasis agriculture decrease substantially. In Gabes, the various non-agricultural uses of water have increased greatly. Phosphate processing uses water. So does the new city. So does the zone touristique. Everyone is water hungry. Unfortunately, as is the case in many places, the traditional agricultural practices loose out. From what I gather, each section of the oasis used to get two or three days of water per week – now they get water every 45 days or so. To adapt to this, beds that used to be 20 meters long have been divided into 10 or even 5 meter sections. Originally, the watering practices consisted solely of flood irrigation. Now, people use a combination of flood irrigation, made more efficient by smaller beds, drip irrigation, and direct injection of water to the root level via pipes stuck in the ground next to the root balls of trees during planting. The oasis at Gabes has managed to cling to is precarious existence in this manner, but continued growth of industry, tourism, and the city are increasing the threat to the oasis.

An interesting bit of wisdom imparted on Lucas and I by our host dad, Ahmed, struck both of us as very true and very interesting. The only reason such large and complex oases exist is that humans decided to use the water from a spring to build oases out of the desert. It’s a daily battle with sand, heat, and drought to keep the palmeraies alive. Even a few days interruption in vigilance against the sands of the more sandy deserts and the entire palmeraie could be lost. Take humans out of the equation, and every oasis in Tunisia would shrink to but a few palm trees and some small bushes clustered around a little spring surrounded by desert. The peoples of the oases of Tunisia not only are the benefactors of the greenery but are also the architects and caretakers. Humans and the oases they live in are bonded together. Take one away, and the other will succumb to the sands of the desert.