Predicting Oil Slick Migration at a Pipeline River Crossing on the River Niger Using Hydraulic Geometry

Understanding oil slick migration in rivers is important for effective spill response because rivers provide essential services for household purposes e.g. fisheries, water supply, transport, socio-cultural activities and recreation. Rivers constitute the second most important source of household water supply in Nigeria. Yet, rivers are major receptors of oil pollution. This paper focuses specifically on oil Pipeline River crossing upstream of Lokoja (on the Niger River) to demonstrate likely oil slick migration trend, herein referred to as oil travel time (OTT). An OTT describes the average time it takes lead oil plume to arrive at a downstream destination. The primary objective of this paper is to facilitate timely warning for water and environmental managers through OTT prediction; and, provide valuable information for contingency planning, monitoring and impact assessment. Method applied is the Hydraulic Geometry (HG) model using historic mean daily discharge MDQ (m3 s-1) (1980-2008), hydraulic characteristics: width w (m), mean depth d (d), mean velocity v (m s-1) and 3% ‘differential oil-water velocity' of wind speed (m s-1) at Lokoja. Results suggest that any spilled oil at the pipeline river crossing is likely to hit key receptors (e.g. water reservoir ~34km downstream) in 4 hours during high flow and takes ~9 days to reach Onitsha (~240km downstream) during low flow. This prediction is based on at-a-station HG using logarithmic regression (R2 = 0.8447). Power regression was also used but had weaker R2 value of 0.6175; hence the former appears more reliable. The absence of adequate data for other cross-sections downstream of the lower Niger River makes downstream HG less useful in this study. There is urgent need for more data points and systematic survey along the lower Niger to enhance downstream HG OTT prediction. This study represents the first known attempt to predict OTT in Nigerian Rivers using historic intermediate environmental data, though there have been a number of studies on marine/coastal oil spill incidents. This level of analysis is expected in every EIA where oil transport pipeline crosses rivers/streams. It is hoped that the results and the models used in this study would form useful basis for impact assessment in the ongoing efforts to explore oil at the inland river basins of Nigeria known as Nigerian Frontier Inland Sedimentary Basins (NFISB).