By Greg Odogwu.
In view of the onslaught of climate change in our country, experts and government functionaries are now brainstorming on ways to best increase our cities’ resilience. Just a few weeks ago, three people died in Trademore Estate, Lugbe (Airport Road), Abuja, due to an overnight flooding incident that nobody saw coming. For Lagos, it is a perennial menace; people are now used to it. But the fear is that it would get worse because of the rapidly changing climate.
Recently, the Agricultural Research Council of Nigeria jointly organized a one-day workshop with the University of Nottingham on Blue-Green Initiative for Urban Flood Resilience in Nigeria. Developed by researchers at the University of Nottingham, the Blue-Green City concept is aimed at creating a naturally-oriented water cycle while contributing to the amenity of the city by bringing water management and green infrastructure together. In this way, the initiative generates environmental, ecological, socio-cultural and economic advantages.
The reality is self-manifest. There are increased flooding incidents in Abuja and in other cities of the country because Nigeria is blessed with streams and water bodies that are not treated with respect by the citizens and their leaders. There are vast real estate development models that do not take into consideration the ecological settings in which they are situated. In this way, there are many poorly informed choice of building settlements near rivers and flood plains.
Other causes are development of slums, indiscriminate dumping of refuse, abuse of plans by desperate builders; and overall poor management of water infrastructure, indiscriminate dumping of linear low density polythene, hard density polyethylene. All these are exacerbated when there are no greenbelts to allow water infiltrate naturally into the ground after rainfall.
This is captured in the words of Prof. Garba Sharubutu, the Executive-Secretary of ARCN: “The major factor in the generation of runoff or overland flow is the occurrence of rainfall. However, where runoff is professionally controlled through well-built underground drains or well-constructed wide and deep surface drains, flood will not take place. So, poor planning and not necessarily the amount of rainfall received is one of the causes of flood occurrences in Nigerian cities. Nigeria is a country that is dissected by many rivers, streams and rivulet. The economic allurements of streams and rivers for fishing, irrigation, domestic water supply, recreation exercises like boating and so on attracts Nigerians to encroach and settle near streams or rivers.”
After further research, I think the Blue-Green Concept could be understood by looking at the infrastructural attributes, which has a template already developed by the Department of Environment, Land, Water and Planning of the Victoria State Government of Australia, in a working plan they published as Green-Blue Infrastructure Guidelines.
The term ‘green-blue infrastructure’ refers to the use of vegetation, soils and natural processes in an urban context to simultaneously deliver landscape and water management benefits. For many modern urban centres around the world, there is a very direct and important link between greening and water management, though too often landscape and water planning are considered separately. Healthy trees and vegetation rely on provision of soil moisture to thrive and flourish, while vegetated areas play a key role in absorbing, treating and controlling the excess water in urban areas. When planned and designed well, green-blue infrastructure can help to solve urban and climatic challenges through the provision of ecosystem services that enhance the well-being and prosperity of local communities.
Many Nigerian cities are still at their developmental infancy, which means that green-blue infrastructure could be incorporated. Nonetheless, it requires imagination from leaders who are ready to go the extra mile to fight climate change hands on. For instance, when Nasir El-Rufai became the Minister of the Federal Capital Territory, he came down hard on people who had constructed on Abuja’s green areas, demolishing and reclaiming them. But when he left office, everything went back to business-as-usual.
This means that there should be more imagination and progressive innovation on the part of political leaders. Hard-man tactics are not enough. There are several aspects of Green-Blue City concept that could achieve the same result without demolitions and forceful evictions. On the same hand, our indigenous urban planners and eco-researchers should stand up and be counted in the comity of nations. It is not enough to just copy and paste what has been implemented in other climes. There are peculiar local characteristics that should inform our own practices, and these can only be discovered and adopted through robust research and development.
Elements of the green-blue infrastructure include green roofs, green walls, street trees, gardens, raingardens, swales, parks, sports grounds, urban agriculture, green corridors, ponds and lakes, wetlands, waterways and forests. Green roofs are building roofs which have be partially or completely covered in vegetation which is planted into a growing medium sitting above a waterproof membrane. Harvested rainwater can be used for irrigation. Green walls are a vertical garden on the side of a building which comprises vegetation planted within a growing medium which is attached to the wall. Rainwater or greywater from the building can be used to support plant health.
Street trees planted in growing medium underneath sidewalks which can be designed to be passively irrigated from storm-water runoff from pavements and roads. These can also be designed to enhance storm-water pollutant removal with the inclusion of special filter media. Permeable paving can also be used to channel storm-water into underground soil areas to support trees. Gardens comprise vegetation planted into a growing media (soils). Storm-water can be directed into gardens to provide passive irrigation, or an active irrigation system can be provided, fed by alternative water sources.
Raingardens are garden beds which are designed to capture, detain and treat storm-water runoff as it filters through the underlying filter media before it is discharged at the base of the system either into the surrounding soils or into the local storm-water network. Swales are shallow, vegetated open channels that convey and treat storm-water. The vegetation can vary from mown turf to sedges.
Parks are public open space areas which provide the local community with a range of recreational activities. These could be irrigated using an alternative water supply or designed to provide storm-water detention and infiltration. Sports grounds are large open space areas which support active recreational activities. These could be irrigated using an alternative water supply or designed to provide storm-water detention and infiltration. Urban agriculture is the local production of food products. This can include community gardens which are open to the public, or commercially viable small-scale urban farms. Suitable alternative water sources can be harnessed for irrigation.
Green corridors are linear green spaces that can provide a range of connectivity services including natural habitat and recreational pathways. These areas are typically located along waterways or other easements. Ponds and lakes are open water bodies which are designed to permanently hold water. They can be fed by a storm-water supply or a recycled water supply. Vegetation can be included around the edge or in shallow sections. Wetlands are heavily vegetated water bodies. These systems can either be natural features in the landscape or can be constructed to treat storm-water. They can appear as natural systems or integrated as hard edged features in urban areas.
Waterways are channels that capture and convey flows from catchments. They include streams, creeks and rivers and can be natural or modified systems (e.g. rock edged or even concrete lined). Forests are large areas of dense plantings of trees, shrubs and ground covers. They can be remnant, regrowth or newly created urban forests. Forests play an important part in the water cycle, creating pervious area to absorb storm-water.