Tackling Flooding and Groundwater Pollution

The recent flooding in some parts of Lagos State, Nigeria has once again reminded us of the need to adhere to fundamental and mitigation measures required to tackle flooding and groundwater management and sustainability in Nigeria. While some professionals have called on residents of the affected flooded areas and environs to put water consumption from their boreholes on hold until treated of possible contamination from the recent flooding, it is important to stretch this further to the present and future challenges of groundwater with respect to flooding.

Flooding evolves new challenges, especially in this era of climate change, global warming and excessive environmental degradation. Several developed countries, like the UK and USA, suffer flooding from time to time. The UK, for instance, loses valuable asset to flood almost on a yearly basis. In addition, there is possible groundwater contamination. This is because excessive water recharge via infiltration (that is, the downward movement of water into the soil), leakage, indiscriminate industrial discharge, the blocking of drainages, et cetera, can cause raging floods and flush pollutants and contaminants into rivers and streams over time. Aquifers are also fed into these water bodies by these recharge media.

In Nigeria, the possibility of groundwater contamination through flooding is very high, hence the advice to temporarily stay away from borehole water in flooded areas. This, indeed, is good advice, as the possibility of having contaminated water from boreholes within these flooded areas and environs remains high.

Flooding is common within watershed areas. The recent flooding in Lagos State is a typical example. But what are some of the possible problems associated with flooding, using Lagos State as a case study?

In addition to possible pollutants being transported to the groundwater through flooding, Lagos State is a watershed that is geologically and geographically plain and near the sea level. Hence, excessive water influx from the ocean, in addition to rainfall, discharges, leaks and other forms of water recharge can reduce both surface water and groundwater flow. This can cause waterlogging, flooding and/or the weakening of soil components, which can lead to subsidence and, in turn, cause the collapse of buildings, roads and other engineering designs. There is also the possibility of saline intrusion, whereby saline (salt) water from the oceans and lagoons migrate into the freshwater aquifers in the inland areas. This can lead to the contamination of drinking water sources.

It is important to note that saline intrusion occurrence can be high in coastal aquifers due to the hydraulic connectivity between groundwater and seawater. As salt water has higher mineral contents and water pressure than freshwater, storm surges or flooding (in addition to navigation channels, which are common in Lagos, as it hosts the majority of Nigeria’s sea ports) can trigger it to push inland beneath the freshwater, leading to groundwater contamination.

The degree, nature, structure and extent of groundwater contamination and pollution in an area post-flood times are prone to be high, if international standards governing groundwater resource management and sustainability are not adhered to during water exploration and exploitation. This makes one to ask how much of groundwater protection, principles and practice (GP3) are applied in our day to day groundwater resource exploration and exploitation. What happens to our water protection zones, safeguard zones, source protection zones and groundwater vulnerability (the susceptibility of groundwater resources to pollution from various activities, be it natural or anthropogenic)?

In dealing with groundwater pollution and contamination, the hydrological, geological and soil situations of water source need to be put in check. These and more will entail the potability (and not just portability) of the water we consume, and can be achieved through many ways, including adequate research, data acquisition and professionalism. There is the need for Nigeria to step-up water research and water data acquisition by professionals, to produce detailed and accurate information, including flood measurements, river/ocean gauges, precipitation forecast, et cetera, for efficient future predictions and planning of water resource.

There should be a water allocation policy and practice, to guide how much water abstraction is needed at a given time in a particular area, for a specified need (industrial, agriculture or domestic), as this can reduce flooding threats. It is also important to make use of water-saving measures such as rainwater harvesting and sustainable drainages. There should be the construction of standardised drainages, which are (alongside other water channels) to be kept unblocked at all times by users. This is essential in areas with rapidly increasing urbanisation, as in Lagos, where concrete pavements, roofs, deforestation et cetera can increase rapid runoff, which can, over time, increase the recharge rate and induce flooding. There is also the need for Environmental Impact Assessments (EIAs) of developmental projects and events with respect to water pollution and flooding. Vital projects such as waste water impact assessments and water quality and quantity assessments should not be neglected.

It is important to note that accurate past and present flood measurements, such as the amount of rainfall that caused the recent flooding, its nature and extent of damage can help save lives, property and the environment in the future. Considering the present climate change challenges and increasing global warming, there is need to understudy the rise in sea level of the Atlantic Ocean. This is because a continuous sea rise in the ocean will directly feed the lagoon with excessive water, which can overflow and flood surrounding areas.

In addition, adequate implementation of water policies is needed for qualitative groundwater resource. Although, several efforts have been made by governments to implement different water policies, including those within the most recent MDGs/SDGs projects, there is a need for full enforcement of groundwater protection, principles and practice (GP3) in areas associated with land reclamation and landfill in Lagos State. These practices will help to define zones suitable for borehole locations, thereby preventing indiscriminate borehole drilling, with respect to pollution sources.

This article is written by Precious Onyinyechi Odika

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