Naivasha Geophysical field experiment
Early November 2018 the 3rd and final geophysical field experiment was executed in Naivasha, Kenya, on the geological volcanic sediments on the premises of the Kenya Agricultural and Livestock Research Organization (KALRO) Dairy Research Institute farm, near Lake Naivasha. The geophysical methods applied included:
- conventional VES soundings and HEP profiling,
- ERT (of KenGen),
- TDEM with two instruments: Zonge (of KenGen) and WalkTEM (of ABEM/Guideline Geo Sweden), and
- AMT (of KenGen).
A number of organizations were involved in the Naivasha experiment, including: AMREF Health Africa, ABEM/Guideline Geo Ltd, (Sweden), Jos Hansen & Soenne Ltd, KALRO, KenGen, Ministry of Mines, NIA, Tullow Oil Plc., students and researchers of the universities of Nairobi and Eldoret, Kenya Water Institute (KEWI), and World Vision Kenya, besides the organizing experts of SamSam Water and Wiertsema & Partners, both from the Netherlands. Together they sent 39 participants to the on-the-job training trajectory in Naivasha, of which 5 were women.
A special mention has to be given to the participation of NOEVA Benin, another VIA Water project evolved around geophysics in Benin. Their representative Fabrice Lawson came to Kenya for knowledge exchange with ISGEAG, which worked very well and lead to similar conclusions on conventional techniques (VES, ERT), while NOEVA Benin and its partner IRT France now purchased the ABEM/Guideline Geo WalkTEM technique for application in Benin. On the other hand, ISGEAG learned from the opportunities of the Magnetic Resonance Sounding (MRS) method as tested in the coastal zone of Cotonou, Benin.
Main findings of Naivasha experiment
Main findings from the field experiments in Naivasha are as follows:
- Integration of and between the different geophysical methods, and combining this with existing borehole and geophysical survey data (so called ‘conceptual puzzling’) introduces spectacularly better results;
VES (one-dimensional; 1D), reasonable resolution to approximately 60 – 70 m bgl. Increased risk is when a long spread of the AB (>400 m) is being applied, which leads to blurring of the lateral changes in the geology;
HEP profiling is only appropriate to identify lateral changes in the top 30m of the soil. HEP profiling is, thus, dominated by the top soil layers (lithology), depending on presence of clays, and rarely says anything about deeper structures (as often mistakenly thought). That is why HEP is only interesting for shallow boreholes (up to 30 m bgl);
ERT (or CVES; 2D) can provide reasonable insight up to approximately 100 - 15000 m depth depending the cables and set up in use, if correctly applied and interpreted, itcan provide good indication of possible anomalies, such as fracture zones and salt water intrusion;
TDEM (especially WalkTEM)(1D) gives a good resolution up to 150 to 200 m bgl (when a loop size of 40 x 40m is being applied). When applying a larger loop size depths of 350 to 400 m bgl or more can be reached, but results in a decrease of the resolution. From the two instruments used (Zonge and WalkTEM), the WalkTEM was exceptional in its use. It is practical to use, and easy to learn to work with by operators without the need for specialized knowledge or experience of TDEM and geophysics. First inversions (interpretation of the raw data to a layer-model) is directly visible on the screen while being in the field; this is an important advantage of the WalkTEM;
AMT (1D).because of the use of low frequency natural sources (solar wind and lightning) the exploration depth is over 500 meter, however the resolution is poor. The setup is small but complicated, calibration is needed as well as good skills. Inversion can be improved in respect to true resistivity and layer depth with TDEM soundings, with the so-called ‘shifts’ When also additional information is available (borehole logs) the inversion can be constraint and further improved with dedicated software.
A final ISGEAG workshop was held at the KenGen office in Naivasha on November 6 & 7, 2018. Day 1 focused on applied geophysical methods and the importance of interpretation, while Day 2 sparked a lively discussion around the question 'How can the ISGEAG results lead to improved groundwater exploration in Kenya?'. The workshop attracted a variety of persons from several disciplines, including water consultancies, mining consultancies, educational institutions, NGOs, and private sector. It was proved to be very successful and profound discussions on geophysical prospecting as well as the groundwater exploration in general were held. ABEM / Guideline Geo Sweden was available and gave a presentation focused on their geophysical solutions. The ABEM representative in Kenya (Jos Hansen) really helped the ISGEAG project to increase the amount of attendants. Also, Fabrice Lawson, a geophysicist of NOEVA Benin attended and gave an inspiring presentation on his experience with the MRS method in the coastal zone of Greater-Cotonou, Benin.
One very clear message that came from this workshop was the all participants established that more research and education is needed in the field of geophysics and groundwater exploration, since there is a profound lack of quality education and curricula in these fields in Kenya.
Impact of ISGEAG
The exact impact – direct or indirect, and now or in 5 years’ time – of the ISGEAG project is hard to estimate. There are, however, some signs indicating that a change has been brought about:
- Growth in hydrogeological conceptual thinking of ISGEAG participants;
- Urgency and better understanding of (coastal) fresh-salt situation created;
- the Kajiado, Kwale and Naivasha study outcomes contributed to more effective hydrogeological advice;
- Successful demonstration of ABEM/Guideline Geo Sweden’s WalkTEM and its purchase by various VIA Water partners.
All ISGEAG final and technical reports can be found back on the website of SamSam Water.
Some of the main lessons that are learned during the ISGEAG project include:
- During the project it appeared difficult to get the Kenya Water Resources Authority (WRA) involved into the ISGEAG project. Being the regulatory body and potential ‘game changers’ in groundwater exploration and exploitation, they play a pivotal role in groundwater management. It was learned that (financial) incentives are needed to get WRA and their technical officers involved. The project plan should have incorporated WRA involvement and renumeration for this from the beginning. It has been difficult to contact WRA officials and get the right persons involved;
In kind contributions are not to be expected from local partners due to the socio-economic state of Kenya and most of these organizations (no budget). Project budgets needs to anticipate more on this;
Memorandums of Understanding (MOUs) with project and involved partners should be signed well in advance of starting the fieldwork mission, to avoid discussion points about input and fees;
The three geophysical field experiments provided training to a total of 110 participants. Out of this 110 only 11 were women (10%), ranging from managerial positions at Kenyan national companies to hydrogeology or geophysicist students. This low percentage can partly be explained by the fact that this is still a very technical and male dominated field of work;
Before the start of the fieldwork, the field location should be visited for reconnaissance and social grounding by a field hydrologist, a social worker and local community leaders to create local buy-in, put people at ease, and not cause local suspicion and unrest;
With the WalkTEM system it is proved that a higher resolution can be achieved. The ABEM WalkTEM system proved to be very successful, especially in Kwale but also in Kajiado and Naivasha, it is an easy to use sounding system with a high resolution combined with a relative small transmitter loop (spread).
Post-ISGEAG continuation options
Geophysics and groundwater exploration remains a very specialized fields of work. For an outsider it is often hard to comprehend which methods are being used and how indications and characterization of underground water are being established. The Kenyan groundwater exploration sector and geophysical consultants make good use of this fact, and use the basic amount of information and tools to provide the minimum of hydrogeological indications. This system and mindset can only change when the ‘rules of the game’ are radically changed. It is therefore advised to develop and improve the standard model report for any hydrogeological related assessment, wherefor ISGEAG introduced a “minimal” reporting standards for consultants.
Focus on the youth as future leaders
A bottom up approach seems to be the only solution, targeting getting young students involved, enthusiastic professors in front of the classroom and establish long term educational programs was one of the outcomes of the workshop. Through learning on the job through internship placements, requests for universities and the private sector (such as ABEM/Guideline Geo, BASE Titanium, KISCOL, KenGen, Tullow Oil and KALRO) to co-operate even more. At the same time building a community of reliable experts that can help each other and overrule the consultancies who do not want to invest in knowledge and sustainability. With or without the Water Resources Authority (WRA), although in the end they have to join at some point.
Urgent issue: Over abstraction of Groundwater
Over abstraction of groundwater in some parts of groundwater is currently already a major problem and will only have a greater and socially disruptive impact in the coming years. Especially around Kwale County this is substantial and growing, having to supply growing populations in and around Mombasa City, the tourism industry, and big mining and agricultural industries in the area. At various locations salinization of boreholes have been confirmed with the TDEM/WalkTEM measurements.
Therefore, further hydrogeological mapping and monitoring of Kwale County groundwater is advised. The results of the WalkTEM, in particular for mapping of salt water intrusion were a real eye-opener for Kwale geologists. There is a good opportunity to better identify and locate locations which pose a risky situation of saltwater intrusion along the coast. Picking up this recommendation and action point should, however be demand-driven and lies with the responsible Kenyan water resources authorities (e.g. WRA, MoWS and County Governments).
If this is going to be picked up, then it is advised to setup a measurement campaign for the entire coastal area as quickly as possible, starting with the geophysical mapping of the coastal zone around Kwale with SkyTEM (an airborne TDEM technique related to WalkTEM). Based on the results, deep probing will have to be carried out at specific locations (TDEM / AMT) as well as investigation of possible deep groundwater exploration (e.g. the Neogene aquifer). Following the results, a monitoring program will have to be set up in the salinization areas. The area otherwise runs great social and economic risks. ISGEAG experts have tried to address these issues at local authorities (WRA), the local companies BASE Titanium and KISCOL, and explore (funding) opportunities for this with international organizations, such as WorldBank, the Netherlands Embassy in Nairobi (EKN), Aqua for All (A4A) and with Vitens Evides International (VEI).