In 2012, UNESCO commissioned me and my company RTI to explore and map the potential of groundwater resources of a 36,000 km2 area of north-central Turkana. It was clear then that the prospect of mapping groundwater in the rough and dry remote corner of Kenya would pose a challenge.
Such a task was given greater purpose with the need to find more viable water supplies for the inhabitants of Turkana, one of Kenya’s poorest and most vulnerable populations.
We conducted a geologic exploration campaign of the Turkana Basin in October 2012, which offered me the opportunity to discover the harsh beauty of this landscape.
Bit by bit, I was able to reconstruct a concept of the geologic evolution of this portion of the Rift valley, which is irrigated by the Omo River flowing from the highlands of Ethiopia.
The landscape ‘Lucy’ saw
While exploring for fossils along the empty river beds and rocky plains of the western ranges of Lake Turkana, I began observing characteristics of a paleo-shoreline. There I encountered lacustre fossils which I identified as stromatolites – a 4-million year-old rounded coral reefs (see image below), a feature that the early human ancestor Lucy may have crossed as she was foraging in the upper valley of the Omo river in nearby Ethiopia.
Image (left): Discovery of a stromatolite located up Lagga Kaitio, approximately 8 km west of the shoreline of Lake Turkana. These stromatolites are a member of the Nariokotome of the Nachukui Formation (Harris et al., 1988)
This discovery allowed me to reconstruct the paleo-levels of this lake through the last 4 million years, which was affected by several climatic incidents related to the last four glaciations that affected our planet during the Gunz, the Mindel, the Riss and the Wurm which are well identified and dated in Northern Europe.
Modeling the paleo levels of Turkana Basin was performed with a base layer of SRTM imagery (Shuttle Radar Topographic mission) dating from 2004 and covering a range that extended from Lake Albert and the White Nile to the Eastern ranges of Turkana basin and the Omo River, from 1 to 10 degrees north and from 30 to 38 degrees West, with an accuracy of 5 meters in elevation and 80 m in geographic location.
A secondary dataset included gravimetric data and seismic echographies acquired from the petroleum industry, which provides us added detail to the model of this vast panorama.
Looking back in time
Interpreting these datasets in an integrated fashion led us to understand that the prolific Omo River, during one of the rainy climatic periods several million years ago, was the primary tributary of Lake Turkana, bringing the lake’s level to around 540 m above today’s sea level.
The excess of Turkana waters was then spilling over into the adjacent Lotikipi depression to the west, which during that period was a lake. Today the area is a seasonal swamp.
While Lake Turkana was feeding into Lotikipi Lake, there was also discharge feeding into it from rivers in the south, which originated from the highlands to the southwest near what is today the Kenyan-Uganda border.
From Lake Turkana to the Nile
The sequence of flow was observed to continue: as Lotikipi Lake reached its storage capacity, excess volume was discharging to the North-West along the Kangen, Pibor and Sobat Rivers in present day South Sudan. Ultimately, this water ends up supplying the course of the White Nile intersected around Malakal.
The traces of this hydrological migration system are still visible on Landsat 7 images.
This study has revealed the ancient boundaries of Lake Turkana fed by the Omo River of Ethiopia which was one of the major source of the Nile some 4 million years ago when Lucy was hunting in the Rift Valley.
Today, due to the present climate change and drought progression in the Horn of Africa, the Turkana Lake dried up progressively down to 365 m. Today, Lake Turkana no longer supplies water to the Lotikipi Plains (formerly a lake).
The Lotikipi Lake eventually dried out completely, but the Litokipi Basin Paleo-Lake is permanently replenished underground by discharging rivers and hosts vast quantities of fresh groundwater over a surface of 4,100 km2 as shown by seismic Line TVK-4 (below).
This dry pan of harsh land offers an significant potential of an underground active aquifer which is active today, still exfiltrating groundwater from Kenya towards the Nile Basin in the north, offering new possibilities of groundwater in South Sudan.
Seismic Line TVK-4 showing deep aquifers of the Anam-Natira and Tarash-Nakalale in the Lotikipi Basin extending over 75 km from East to West and 3 km deep .
Seismic line TVK-4 interpreted by RTI-Alain Gachet from seismic lines bought to NOCK in October 2012, clearly shows the Lotikipi Basin along 75 km between Mogilla Hills in the West to Lokwanamur Hills in the East.
Ethiopian highlands to the White Nile
This extensive survey of the Turkana Basin, which was based on a combination of essential inputs such as indications of fossils along the paleo shores of Lake Turkana, Radar Interferometric data and seismic echographies, has revealed the traces of an ancient hydrological system dating from one of the wet climatic episodes a few million years ago.
This ancient hydrological system is observed to begin in the prolific Omo River from Ethiopia Highlands, which fed the Lake Turkana in Kenya, which then filled the Lotikipi Lake, and finally supplying freshwater to the south eastern part of present day South Sudan towards the White Nile.
As a result of this ancient system, today we observe that underneath the vast emptiness of the Lotikipi plain, lies the large Lotikipi Aquifer that might store several hundred BCM of water, whose only source of replenishment remains the discharging rivers from Uganda and Kenyan Highlands.
Today, this Aquifer continues to drain its vast underground supply towards the White Nile through the eastern part of South Sudan which might in return host substantial supplies of freshwater.
Future surveys and drillings in Kenya and South Sudan will confirm these assumptions.
The story of this ancient system continues today.