Erosion and Flood Control: A Surveyor’s Perspective
Lagos is dominated by its system of islands, sandbars, and lagoons. The islands are connected by bridges, and the land is low-lying. According to LagosGeoinfo, Lagos lies on a coastal plain with an average elevation of less than 15m above sea level. The land slopes gently from the interior to the sea. Water bodies and wetlands cover over 40% of the total land area of the state with lagoons and creeks consisting of 22 % of its area. An additional 12% is subject to seasonal flooding.
Perennial flooding in Lagos has left many homeless and destroyed lives and property in millions of dollars, which is a dent to the ultra-modern city concept of Lagos. According to the National Emergency Management Agency (NEMA) data, more than 2 million people were directly affected by flooding nationwide in 2020.
Beyond Lagos’ vulnerability to climate change, poor drainage systems and clogged street gutters in large swathes of the city are believed to have escalated its flooding challenges.
It was due to this that a webinar was organized and held online by 6 pm on Saturday, the 26th of October, 2024, tagged “Erosion and Flooding Control: A Surveyors Perspective.
The organisers were the Building Collapse Prevention Guild Amuwo Odofin Cell led by Bldr. Chubike Okafor. The speaker for the day was Surv. Ogonna Roberts Agwu. A vastly experienced registered surveyor and a host of a radio show “The Bench Mark” on Traffic radio 96.1fm where he advocates and enlightens the public on how environmental challenges can be resolved through professional Surveying practice.
We had scores of professionals of the Built Environment in ⁷ it was filled with intense professional interaction, opinions, and solutions on how the menace of Erosion and Flooding could be curbed.
Key take-home points were:
1. Regular bathymetric survey is the study of the depths and shapes of underwater terrain, such as the ocean floor. Hydrographic surveys are deployed for this. Hydrographic survey is the science of measurement and description of features that affect maritime navigation, marine construction, dredging, and offshore operations. This gives us the predictive advantage through data to determine and accommodate any potential disaster that might occur through flooding by ensuring our rivers and lagoons can handle such volumes generated through floods.
2. The need for flood alert systems for monitoring sea level and giving early warninga in the event of an excessive rise in the sea level.
3. Systematic Dredging of lagoons, lakes, and rivers as a system of flood control by creating more volumes in the existing lagoons and water bodies.
4. Construction of Dykes on flood plains to serve as flood brakes and water collection points.
5. Clean up and evacuation of structures obstructing the flood plains.
6. Enforcement of a good percentage of green and open areas in all upcoming developments.
7. Systematic tree planting exercises.
8. Systematic drain design and construction that are interconnected with primary, secondary and tertiary channels in the metropolis.
9. Desilting of channels to ensure free flow of water.
10. Determination and establishment of building floor design levels for sectors of every metropolis to guide planning authorities on finished floor levels to assign to upcoming developments.
11. Clearly defined evacuation plans and routes in case of floods.
12. Marked out land portions dedicated as potential resettlement camps for displaced persons from submerged lands.
13. Dam monitoring using structural deformation techniques to ensure the structural health and safety of all existing Dams.
14. Regular Bathymetric survey of the downstreams before the dam spillways are opened to ascertain their capacity to receive large volumes of water.
15. Construction of Buffer dams to compliment existing major dams.
16. Regular desilting of existing Dams to enhance free flow of water.
17. Reforestation and afforestation.
Reforestation and afforestation can be effective nature-based solutions for flood risk management in Pakistan. Planting trees and restoring forest cover can help to reduce the runoff and soil erosion, regulate water flow, and improve soil structure. Reforestation can also provide other benefits such as carbon sequestration, biodiversity conservation, and livelihood improvement.
18. Wetland restoration.
Wetland restoration can help to mitigate flood risks in Pakistan. Wetlands act as natural buffers against flooding by absorbing and storing water, reducing peak flows, and filtering pollutants. Restoring degraded wetlands can provide multiple benefits such as improving water quality, enhancing biodiversity, and providing recreational opportunities.
19. Sustainable land management.
Sustainable land management practices can help to reduce flood risks in Pakistan. These practices include soil conservation, terracing, contour farming, and crop diversification. Sustainable land management can help to reduce soil erosion, increase soil water holding capacity, and improve crop productivity. These practices can also help to reduce the impact of floods on agricultural lands and improve the resilience of farming communities.
20. Green infrastructure.
Green infrastructure can be an effective nature-based solution for flood risk management in Pakistan. Green infrastructure includes natural or engineered features such as green roofs, rain gardens, and permeable pavements. These features can help to reduce runoff, increase infiltration, and improve water quality. Green infrastructure can also provide other benefits such as improving urban aesthetics, enhancing biodiversity, and reducing the urban heat island effect.
21. Enforce recycling of plastic and no degradable waste.
22. Safe and efficient waste management and disposal systems.
We believe strongly that this webinar doesn’t end here and have pledged as a group to be change agents starting from our local governments to the State and the National spectrum. The responsibility not only lies with government in creating the polices that will establish and put systems in place but on the support and involvement of the Private sector that includes Built environment Professionals and community stake holders to for there to be any success. Practical lines of actions include:
– Establishment of a Partnership with the Public and Private sector that will be focused on Erosion and Flooding Control by the Lagos State Government. This relationship already exists with other parastatals of the Lagos as regards building collapse, waste management etc therefore erosion and flooding should not be left out.
– Stakeholders meetings at Local Government Areas and Development areas to identify and address the causes of erosion and flooding locally.
– Creating empowerment among the youth by supporting recycling initiatives that will drastically reduce the pollution blocking our drainages and lagoon
– Invest and research into the huge hydro-electric power potential of the State to make it energy self-sufficient.
Change starts now!
