DEPARTMENT OF
GEOLOGY AND GEOPHYSICS, FEDERAL UNIVERSITY,
INTRODUCTION
The report
highlights the result of geophysical survey made at Bishop Court in Onwe Road,
Abakaliki, Ebonyi State. The survey aimed to located aquiferous unit for a
groundwater borehole.
GEOLOGY
The area lies within the Asu
River Group and comprises shale interbedded with siltstone, thin beds of
hard
splintery metamorphose mudstone and granite that are highly jointed, fractured
and faulted, clays and overburden `~overlie the area.
TABLE 1: SCHLUMBERGER ELECTRICAL DATA SOUNDING SHEET
AB/2(m)
|
MN/2 (m)
|
Apparent Resistively (ohm-m)
|
2
|
603.1462
|
|
3
|
447.5779
|
|
6
|
1
|
490.8668
|
9
|
400.8721
|
|
9
|
335.1996
|
|
15
|
217.168
|
|
25
|
4
|
81.70575
|
40
|
52.01427
|
|
50
|
40.9571
|
|
75
|
42.70032
|
|
75
|
38.46008
|
|
100
|
20
|
30.51497
|
150
|
42.33405
|
|
200
|
42.24827
|
A total of 14
station data points were acquired as shown above. The apparent resistivity at each station was
generated by multiplying the resistance with the geometric factor (K-) for Schlumberger
electrode array. The data was curve matched and interpertated manually and
automated using computer aided techniques and combination of software –
Winglink and IP12 Win.
The investigation area is located
in a hydrogeological complex terrain underlain basically by the Asu River Group
sediments. These comprise mainly the Abakaliki Shale Formation with the
associated siltstone, limestone and silicic sandstone. Groundwater exploration in this area is thus
difficult due to the low permeability of this rock unit. This low permeability makes
this unit an aquitard. This situation is similar to that in basement terrain.
RESULT AND DISCUSSION
From the geo-electric sounding data (Fig
2), apparent resistivity curves were made from which a geo-electrical
distribution (Table 1) and geo –
electrical section figure 3 were prepared. Depth to water table was met at 40m while depth to ground
water head was interpreted to be 52m.
RECOMMENDATION
Following the interpretation of the VES
curve, depth to aquifer was met at 40m. We therefore recommend a borehole depth
of 52m.