1.5 Niger

Near the town of Gotheye, conventional investigations have been performed and, based on the information obtained until then, 7 boreholes had been drilled to a depth of 150 m. The total obtained yield was about 150 l/min which was only a third of the 450l/min, required for the supply of this town. As the necessary water quantity could not, in the opinion of the responsible hydrogeologists, be reached, an alternative had to be searched for. It was planned to take the water of the Niger river flowing close to the area and to treat it appropriately for public use. That implied high expenditure as well as operational and maintenance costs for the water treatment, which might be avoided if sufficient and suitable ground water was available. Before this time-consuming and expensive solution was adopted, an opportunity came up to conduct an investigation of the area by means of the dowsing technique.

The GTZ expert Schröter was asked to visit the area where he inspected the available boreholes and their environment by means of the already described method and tried to determine to what extent water bearing fractures might already have been hit. According to his subjective assessment, he found that this had only occurred in two of the seven borehole sites. But even these 2 sites he considered being badly positioned as other, neighboring points along the supposed fracture would provide a higher yield.

The best of the seven original locations provided 80 l/min at a depth of 144 m, but just missed a better developed fracture situated in a relatively permeable zone. After a short investigation, Schröter located a point barely 40 m from that site which he considered to be much better and which would hit the fracture zone more accurately. Furthermore, he predicted that the new location had to be drilled to a maximum depth of only 90 m to obtain a yield of 300 l/min. A little later, drilling took place at this point and water was actually already found at a depth of 54 m. Provisional pump tests verified the high expected yield of 250 l/min at a depth of 60 m. Later long term pump tests, though, revealed a decline of the water table so that this well cannot yet be considered as being definitely successful. In particular, the well could not yet be considered as completed, because the borehole was not drilled down to the proposed depth of 90 m. A perfect technical construction of this borehole up to the depth advised by Schröter may well provide the initially predicted and necessary yield. Nevertheless, the participation of the dowser brought about an unexpected and remarkably good result from the start.

1.6 Yemen

This time the aim was to establish a water supply scheme for approximately 17,000 inhabitants of the Yemenit town of Al Wasitah and its neighboring desert communities. Two hydrogeological studies from 1985 and 1988 formed the basis of the investigations [14, 15]. At this time, a single well in Al Hamidah yielding 3 l/sec and several shallow dug wells were known in this area. The latter ones are situated in the Wadi Ayyan and produce water for approximately four months, especially in the monsoon season. The mean annual precipitation is about 300 mm, of which more than 60% evaporates and 30% flows away, so that only 10% is available for ground water recharge.

Lime and sandstone, as well as rock of volcanic origin characterize the region. The Wadi apparently lies on an extended fault with strike angles of 20-30 degrees and is covered by 100 m thick layers of sediments of limited permeability. The surrounding formations are practically impermeable, so that the water catchment area of the Wadi is limited by its own extension.

Hydrogeological studies considered drillings into the rock basement to be unpromising and recommended the establishment of three deep wells in the Wadi area where the sediment layer exhibited maximum thickness. Detailed geo-electrical soundings indicated drilling depths up to 100 m, down to the hard and impermeable rock basement, in order to most efficiently exploit the aquifer which was believed to lie in the lower sediment layers. On account of the limited permeability, a distance of 200 m between drilling points was considered to be sufficient. As the actual water demand amounted to 12 l/sec, a target yield of 15 l/sec was envisaged. To provide the demanded quantity it was estimated without further model calculations that two wells would certainly be necessary. A third well should be built to serve as a standby.

The location of the drilling points followed the above mentioned combined procedure. Initially, topographic features had been utilized to roughly define an area in which geo-electrical investigations were conducted at 11 sites by means of the Schlumberger/Wenner method. Schröter then located some promising points by means of the dowsing technique. His three finally selected points were incontestable according to the interpretation of geo-electrical measurements.

Schröter recommended drilling to a depth of 65–70 m and expected the principal inflow with a yield of more than 10 l/sec between the depths of 25 and 55 m. In all cases, water influx was indeed observed, actually in the ranges 22–29 m and 51–57 m for borehole 1, up to 60 m for borehole 2, and 12–35 m and up to 57 m for borehole 3. The yields amounted to 8, 13 and 25 l/sec, respectively, however with varying strong drawdowns. Especially for borehole 1 a comparatively small specific influx occurred for a drawdown of as much as 51 m. Unfortunately, in this case the major water bearing zone had not been utilized at the beginning of the drilling procedure since appropriate filter casings were not employed. Water was observed only after some modifications of the plain casing had been performed, so that it is possible that the quoted yield is not the available optimum. It must be appreciated, though, that already well number 3, which was drilled and developed first, delivered by itself more than the totally required water quantity.

In this project area, as in many others, the dowsing technique proved itself practically useful and sufficiently reliable. The impression should be avoided, though, that in the present case the unconventional technique, combined here with classical procedures, would be indispensable for a project success. On account of the estimated considerable spatial extension of the aquifer, conventionally located drilling spots might have been successful with high probability. For example, due to some practical considerations, drilling site 2 was slightly relocated from the initially determined point and was nevertheless a success. However, the drillings revealed quite different underground conditions and the observed two higher yields could not have been attained anywhere in the area; the limited ground water recharge and permeability renders successful drillings difficult, in principle.

In view of later discussions to explain the dowsing effect, a test is relevant which was carried out near Al Bayda. Within a program put into effect by KFW (Kreditanstalt für Wiederaufbau, Germany) regarding urban water supply, geo-electrical investigations were conducted in a wide, extremely arid area at an altitude of 3000 m. A few sites were also investigated by means of the dowsing technique. Water was not to be expected. Schröter determined two sites where he predicted a fracture zone extending down to 150 m. The subsequent geo-electrical measurements at this site allowed a resolution up to only 35 m and were interpreted as follows: the feature represented not a pronounced fracture zone, but only a slightly weathered one with loose materials.

Later, a drilling was carried out at one of these two points: from the drilled material it became clear that there was indeed a fractured zone up to the final depth of 150 m; as expected, no water was present. This result strengthens the supposition th at dowsers do perceive geological fault zones, but in fact, not actually the accumulation of water (as a chemical substance). This important conclusion will be discussed in part III and should be examined more thoroughly in further experiments.