ABSTRACT

Sixty (60) geoelectrical sounding data sets. collected from various parts of Abia State of Nigeria, were analyzed using the Resist Software. The geologic formation, mainly the Coastal Plain Sands (or 13cnin loriiiatioii) of tcrtiary-quatcrntiry period, eonsists of line-mcdium-eorse grained Sands occasionally pebbly with localized clays and shale. Groundwater recharge is high and run-oil' is low in most parts of the State. Statistical analyses, have shown that the Coastal Plain Sands span across 72% of the 22') communities investigated in the state and that depth to horcholes range from 60 in to 100 in in Aba, Obingwa and tJkwa LOAs and from 140 to 20 in around Umualiia, lsialangwa and lkwauiio LGAs. Results have further shown that the majority (>80%) of Abia State is overwhelmingly aquiferous and of' great potential and that an increase of about 50 persons in population of a community in the State is accompanied by a unit volume (I m3) draw down of wells due to groundwater use. The data of' eleven Schlumhcrgcr Vertical Electrical Soundings (yES), with a maximum ABI2=500 in, were also specifically analyzed for the Kwa Ibo River watershed for a detailed study. The layer :arameters thus obtained were used to calculate the Longitudinal Conductance (S) and the 'l'ransvcrse Resistance (T) distribution. Assuming a homogenous sandy aquifer and using the existing lithologs and pumping tests dnta, data analysis was done to arrive at the I lydraulic Conductivity (k) and 'l'ransmissivity ('l'r) distribution within the study area. Aquii'er churaeteriintion ol' the ureu ulsc showed that the resistivity range is between 400-1350 rn and wiuifir thickness ranged between 6 m near Usaka I.legu and 325,5rn near Government College Umuahia. From the results obtainc, average aquifer transmnissivity value in most parts of the watershed was observed to he as high as 1722m2/day. xi Groundwater flow modeling was also undertaken to assess the degree of interaction between the Kwa Ibo River and the thick sandy aquifer. The river marked the north and south boundaries, with constant heads near tJsaka Elcgu and (iovcrnmcnt College Umuahia. 'l'he velocity vector near Unmdike, Nialakwu and environs is about (L44ni/day due southeast, showing that the Kwa Ibo River is iniluent throughout its course. 'l'he Kwa Ibo River stage data at Umudike, Ainaworn, Ntalakwu and Usaka Elegu has been used for assigning surface water levels and riverbed elevations in the model. The watershed is modeled with a grid of 65 rows x 43 columns using two layers. Permeability distribution was inferred from pumping tests. A steady state flow simulation WIS carried out and calibrated against the May 198() waler levels using 26 observation wel Is and 123 iterations per run ol the modeL Siiiiilarly, a transient state simulation between he year 1 988 and 1997 showed that groundwater recharge around Umudike was maximum during 1996 and ininaium during 1991. The computed groundwater balance of 55274 iii3/day was comparable to that estimated from field investigations. Results from the modeling show that ahstractTon is 'ess than the groundwater recharge. Based on the above unalyse, potential aquifer zones such as those at Umuohia Olokoro cum Government College Unniahia sub-basin have been idcntifled for regional groundwater development for the entire Abia State