Kestani

The unfortunate demise of hundreds of Kenyans during the intense flooding in April and May of 2024 rekindled my interest in the role of nature-based solutions in mitigating similar tragedies. Nature and its elements, such as plants, soils, and water, provide us with essential Ecosystem Services (ES) in the same way that Human Capital and Produced Capital support our economic activities. Ecosystem services include flood control, air purification, food and construction material, and intangible or cultural services such as beauty, relaxation, and health restoration. 

Unlike buildings, the efficiency of ecological systems is heavily pegged on the connectivity of natural environments. For starters, a facile route to understanding Green Infrastructure is contrasting it with Grey Infrastructure. Green Infrastructure encompasses a network of natural systems—such as forests, wetlands, and urban green spaces, that utilises nature to provide essential services like flood control, heat mitigation, improving air and water quality, climate regulation, and improved community well-being. This system is useful in addressing localized floods (from overwhelmed drainage systems) and riverine floods (from overflowing rivers). It can be integrated into urban planning to create livable, sustainable environments while also supporting wildlife through green corridors.

On the other hand, Grey Infrastructure involves traditional structures like dams, seawalls, pipes, and culverts and is primarily designed for stormwater management. Stormwater engineers generally focus on designing and maintaining systems that control rainfall runoff. While grey infrastructure channels water through engineered solutions, Green Infrastructure mimics natural processes to manage rainfall at its source.  A key distinction therefore is that Green Infrastructure leverages nature’s systems to slowly infiltrate water into the ground, while grey infrastructure often tries to control it or direct it into designated channels. Additionally, Green infrastructure is multifunctional, with elements of the physical environment as well as human activities such as recreation in the resultant spaces.  Nonetheless, Grey and Green Infrastructure have complementary roles that should be optimised. Both approaches have an element of connectivity, a critical issue poorly articulated in the case of Green Infrastructure.

Connectivity of Green Infrastructure often implies the connection from one green space to the next, but it has another often-forgotten dimension—the vertical layering. Even within the same space, there are three critical layers: above-ground, ground level, and underground. 

1. Above ground 

Imagine the beauty of encountering a high-spirited swarm of butterflies fluttering gracefully between tall buildings and perching on office windows. The unexpected burst of nature amidst the concrete jungle not only captivates passersby from below but also creates a reconnection with nature and natural processes for those working indoors. 

Green roofs, rooftop gardens, and vertical gardens contribute to vibrant urban ecosystems, adding a touch of nature to concrete jungles. They offer numerous environmental benefits, such as reducing urban heat islands, improving air quality, providing insulation, and managing stormwater runoff. They also create habitats for wildlife: insects like bees and butterflies can benefit from the diverse plant species that often grow on elevated spaces. Furthermore, these spaces can support small mammals like squirrels and bats, offering them a refuge and a place to forage. As pollinators, birds and insects are fundamental to the health of ecosystems; they are not just essential to the natural world but also to human food production and overall ecological balance. The above-ground layer is thus a key component that is often ignored.

2. Ground level

The ground level of Green Infrastructure is what we interact with most. Here, Landscape Architects have to tussle with the functionality of the natural environment (such as stormwater reticulation), access and movement of people, recreational aspects such as children play areas, community gathering and events, and aesthetics.  

Green Infrastructure can serve as a corridor that connects different habitats, allowing species to move and interact, which is vital for maintaining genetic diversity. Native plants are especially important as they offer food and shelter for local wildlife, such as birds, insects, and small mammals. Balancing biodiversity is critical for the equilibrium between different species within an ecosystem, ensuring that no single species dominates to the detriment of others. Disruptions in the availability of plants as food and shelter for animals, which in turn help with pollination and seed dispersal as well as disruptions to the prey-predator balance, can lead to the decline or extinction of species and the degradation of the ecosystem. Habitat loss, pollution, and the introduction of invasive species are the main felons responsible for this destruction.

Whether it’s a serene river meandering through a lush valley, a cascading waterfall plunging into a pool, or the gentle ripples of a brook, the sight and sound of moving water evoke a sense of peace and tranquility. The quality and articulation of water resources in landscape design thus determine their effectiveness for recreation. Riverfront open spaces such as parks leverage the scenic and ecological benefits of riverine environments. For some rivers, the spaces afford a setting for land-based activities such as picnics, walking, and cycling, and water-based activities like kayaking and fishing. The Active, Beautiful and Clean (ABC) project launched in  2006 in Singapore is an example of efforts at improving the functionality of Green Infrastructure along rivers. According to the INAS website, the program “aims to achieve a synergistic integration of waterways with their surroundings and the lifestyles of urban residents…Multiple benefits have already been observed, including draining and treating stormwater, enhancing biodiversity, enhancing the living environment, and improving water quality.” The relaunch of the Nairobi River cleanup in September 2024 is another example, whereby the Kenyan government aims at regenerative activities including cleaning up, planting trees along the river corridor, and affordable housing for families living along the corridor.

Green Infrastructure projects do not have to be massive to be effective. Rain gardens are some of the small components of Green Infrastructure that are an effective and aesthetically pleasing solution for managing stormwater runoff in urban areas. These shallow depressions with a mix of grasses, and flowering perennials are designed to collect and percolate water from rainwater from roofs, driveways, or streets and also help filter out pollutants, reduce erosion, promote biodiversity, and recharge groundwater. 

3. Underground

Subsurface conditions have immense but often understated impacts on the success of green infrastructure. For example, water percolation is crucial in regulating drainage, replenishing groundwater supplies, and maintaining soil health. The percolation rate depends on the soil’s texture and structure. Soil compaction reduces percolation while the presence of organic matter improves it. 

In urban settings with sidewalks, parking lots, and roads, Landscape Architects are faced with a duality of ensuring the application of soils that allow water percolation and root growth, while at the same time having the strength to handle the foot and vehicular traffic above. Without proper consideration, trees can damage sidewalks, curbs, underground pipes, and other public properties. At the same time, when roots are deprived of space to grow and extend, they form superficial roots near the surface increasing the chances of tree fall and damage to pavements. The CU-Structural Soil Developed by Cornell University, CU-Structural Soil is an example of a patented mix designed to foster tree root growth while bearing the load of urban infrastructure.

Soil microorganisms are an important ingredient in aiding the breakdown of organic matter, the release of nutrients for plants, and improving soil structure by binding soil particles together. Researchers have suggested that Mycorrhizal Fungi and plants have a symbiotic association where plants provide carbohydrates produced through photosynthesis to the fungi, while the fungi in turn form networks, which extend far beyond the plant roots, helping the plant absorb water and nutrients more efficiently. The fungi have other benefits such as helping plants to resist diseases and pests by strengthening their immune systems and also help bind soil particles together, improving soil structure, and reducing erosion. Mycorrhizal fungi can be added to degraded habitats to help plant communities establish by transferring soil or plant material with mycorrhiza to new areas.

Conclusion

Green Infrastructure can offer a memorable tapestry of nature’s grace when designed to cater for services beyond stormwater management. The network of open spaces offers many a chance to enjoy a unique blend of physical exercise and the calming beauty of nature through walking and cycling among other activities. 

Vertical layering, in addition to its multifunctionality, is a complication that seeks to be resolved with a high level of sophistication. An integrative decision-making approach is thus important: Landscape Architects, hydrologists, and other professionals must work together to ensure proper consideration for all these layers and functionalities. Additionally, a monitoring and maintenance plan that includes the control of invasive species must be put in place to ensure the effectiveness of the systems.

The spaces discussed here vary in size, character, and ownership. Public parks, forests, and riverine spaces are often public spaces managed by government agencies, while green roofs, rooftop gardens, and vertical gardens are often owned by private corporations and institutions. The vision for green infrastructure thus needs to be promoted to and supported by all these stakeholders. Some of the spaces might be minute in size, but their value as connection points can make or break the entire system.