Groundwater Flow Modelling for Selected Parts of Port-Harcourt and Obi-Akpo Local Government Areas in Rivers State, Nigeria

Abstract

Aim: There is a need to develop steady and transient state models for the hydro-geological system of Port Harcourt and Obio-Akpor areas to understand the groundwater system of the area. Study Design:  Port Harcourt and Obio-Akpor. Place and Duration of Study: Port Harcourt and Obio-Akpor, between April 2011 and April 2021. Methodology: Thirty-eight boreholes were selected randomly within the studied areas and examined to obtain their physcio-chemical properties which include borehole locations, chemical properties, water level, discharge, aquifer transmissivity, specific yield, and storativity. The data obtained were used to develop a base map for the groundwater model. A mathematical model (MM) was developed from estimated initial conditions (hydraulic conductivity and recharge). The MM was excited and its response was used to derive a Modular Three-Dimensional Finite Difference groundwater flow model. Groundwater Modelling System version 10.06 software was used to simulate and predict the groundwater flow. Root-Mean-Square=Error (RMSE) analysis was used to assess the relationship between computed and observed hydraulic heads. Results: The mean values of aquifer transmissivity, specific yield, and storativity from the field data were 0.0600m²/min; 0.11596m³/min, and 0.00040, respectively. The developed base map spread between 4.4601ºN, 7.0498ºE, and 4.8156ºN, 7.5098ºE. The estimated hydraulic conductivity and recharge were 0.00004m/day and 0.00054m³/day respectively. However, based on Modular Three-Dimensional Finite Difference groundwater flow model,  the hydraulic and recharge were 0.00055m/day and 2.27520m³/day, respectively. Conclusion: The developed model for the selected parts of Port- Harcourt and Obi-Akpo has low sensitivity values compared with the estimated initial values for hydraulic conductivity and recharge. Results generated from the model cannot be used to predict future recharge and drawdown for the studied domain area but can serve as a baseline for further studies.