Challenges of Groundwater Development and Supply in the Niger Delta, Nigeria

Some problems of groundwater development in the Niger Delta ranging from negligence to geological peculiarities are examined to highlight the importance and application of geologic knowledge and research for decision making and averting failure in groundwater development for provisional use. Although the geology and hydrogeologic properties of the aquifer system in the Niger Delta immensely favors groundwater development, there are several recorded cases of failed groundwater development projects poor water quality, dry boreholes and boreholes with surprisingly low yield which could have been avoided. This is due to the perception that since groundwater is prolific, geologic and locational peculiarities can be ignored. This research has highlighted the importance of the knowledge of the hydrogeology of the different geologic units as significant factor in the success of groundwater projects through the correlation of past research of geologic units and groundwater potentials, quality and challenges with the present projects implemented in some of the locations. Cases where groundwater projects are executed with wrong exploration options and without consideration of the peculiarity of the geologic units of the project area, including engagement of incompetent contractors, and negligence to the existing regulatory framework for groundwater development in Nigeria are presented. In order to promote sustainable groundwater development and management in the Niger Delta, this research highlights and recommends the pragmatic use of geologic information including various technical, institutional, regulatory and management measures which have the capacity to avert challenges in groundwater development for provisional use.

Impact of Dredging on Coastal Infrastructure: Case Studies from Okrika and Port Harcourt, Niger Delta

Sand excavations in river beds have compromised the safety of several bridges in recent years. Large scale sand mining from river beds is now common in the Niger Delta, due to the necessity of reclaiming land for development purposes and to meet construction needs in the region. There is currently no regulation as to where sand can be mined in river channels because of the lack of adequate understanding of the risks to coastal infrastructure involved with its abstraction. The phenomenon of bridge Abutment and bank failure induced by excessive dredging of sand river bed is considered. Two types of instability were distinguished, one relating to the equilibrium slope of the riverbed and the other riverbank instability. An empirical relationship in the form Xs = 3Htan(90 - α) has been developed through analysis, supported by examples that a minimum distance of 94 m (for sand river beds) from a bridge should be observed for sand abstraction in order to guaranty the safety of bridge foundation. For clay riverbeds, slightly shorter minimum distances can be considered safe. The study further shows that the capacity of sand borrowing in river channels to generate bank instability is dependent on the composition and stratigraphy beneath the river bed.

Evaluation of Factors of Soil Resistivity in the Niger Delta

Soil conductivity is responsible for its aggressive behavior to metallic objects either in contact or buried in the ground. Rapid deterioration and eventual rupture of pipelines leading ultimately to crude oil spillages have been of economic as well as environmental concern. Although many factors contribute to soil resistivity, these relationships have hardly been quantitatively expressed. This paper explores the factors affecting soil resistivity firstly by matching the spatial regional distribution with each of the identified factors of influence, including ground elevation soil type, depth to water table and undrained strength. 183 Vertical Electrical Sounding VES with the ABEM SAS 1000, using Schlumberger electrode configuration were carried out along a pipeline route to generate resistivity distribution across a linear alignment that traverses three geomorphic sub-environments in the Niger Delta Region. The apparent resistivity values averaged over depths of 3 m and 10 m were plotted against the co-ordinates using Surfer-16 and overlaid on Google earth Pro to produce a spatial distribution with enhanced location visibility. The results show that apparent resistivity is influenced by depth to water table with lower values in areas of shallow water table occurrence. Furthermore, it is shown that changes in resistivity below the water table are more due to variation in soil type. Within a soil type above the water table, soil resistivity increases monotonically with depth until the depth of probe extends to a different soil horizon. Results of this study provide guidance as to what ground resistivity to expect in different part of the delta as well as provide valuable information to assess the risks to assets either as a means of prioritizing maintenance or of improving design for new installations in the Niger Delta Region.

Analysis of Hydrological Characteristics: A Case Review of the Niger Delta

This paper reviews the significant contribution of hydrologic continuity in the development, evolution and fate of the Niger Delta. Formed from the aggregation of sediments from a drainage catchment area of over 2 million km2, the Niger Delta has evolved into a prolific sedimentary basin with a dense network of rivers and creeks. The ecological system is in a fragile state with fresh and saline water ecosystems maintaining a dynamic equilibrium. Rainfall typically varies from 2500 - 4000 mm per year compared to average annual evaporation of about 1500 mm, resulting in net antecedent moisture. Over 70% of the rainfall occurs in 4 months between May and September, creating a potential for flooding. Water level varies from less than 1.5 m in the estuaries to about 8 m at the apex of the delta, with Nun River having a slightly higher elevation compared to Forcados River, implying that canals connecting both rivers at the same reach would experience water movements from Nun to Forcados River. Similarly, water level gradients vary across the stretch of the rivers from 8.6 to 9.5 × 10-5 (cm/km) between Onitsha and Asamabiri, 7.5 to 7.7 × 10-5 (cm/km) on the Forcados River downstream of Asamabiri, and from 7.4 to 7.6 × 10-5 (cm/km) on the Nun River. At peak flood, about 23 × 103 m3/sec of runoff enters the Niger Delta. At the same time, about 16 × 103 m3/sec discharges from the estuaries into the ocean in a semi-diurnal tidal flow leaving a surplus that accumulates to cause flooding. The delta thus acts like a sponge, absorbing the shear amount of flow and releasing slowly stored water through at least twenty-one outlet estuaries into the Atlantic Ocean. The shear amount of discharge overwhelms the capacity of the network of distributaries and predisposes the delta to flooding. Assessment of the capacity of the rivers to evacuate pollutants showed that rivers to the west of Brass which are fed by Forcados River exhibited relatively stronger flux efficiencies prior to 1998 but are presently weaker compared to rivers fed by Nun. The rivers to the east between New Calabar and Imo Rivers exhibited very weak ebb tide asymmetry or net upstream flow largely because these rivers receive little or no freshwater influx from upstream sources. Flood and erosion are the major hydrological hazards in the region.