Nature Based Solutions
Learn about Nature Based Solutions piloted in Nairobi's and Dar es Salaam's informal settlements
Rainwater harvesting
What...
Rainwater Harvesting (RWH) does just that, it harvests rainwater off rooftops or other surfaces into tanks or other storage structures. Any stored water is then possible to use (but maybe not for drinking depending on the cleanness of the surface and system).
Why...
In informal settlements RWH can add to water security and water access, it can also contribute to reducing flooding as it captures rainwater that would otherwise add to overground flows.
How...
RWH from roof surfaces is typically done via gutters that direct rainwater to storage tanks. In informal settlements guttering is often not easy - In Kibera the R.U.NBS project saw structurally independent gutters installed (drawings and images here). To measure the effectiveness of this NBS the volume of water collected daily or weekly can be measured. Regular inspection and cleaning of collection systems and filters are needed.
To read more about the process how to design NBS like rainwater harvesting with community members click on read more.
Filter Drains
What...
Filter drains are also known as 'French Drains'. These drains are small trenches lined with a geotextile and filled with gravel, runoff water can infiltrate (soak) into the gravel and be drained away via a perforated pipe system.
Why...
The gravel in the filter drain provides some filtering of the runoff, trapping sediment, organic matter and oil residues that can be broken down by bacterial action over time. The runoff rate can be reduced, and runoff storage is also provided. Stored water can also pass through the geotextile membrane and infiltrate (soak) into the ground (taking some pressure off the watercourses).
How...
In the assessment of the suitability a filter drain solution the outflow is critical, is the purpose of the drain to let water flow out into a watercourse? Will the drain be at the right height to allow for this and will the falls of the drain meet the flow rates needed..?
A simple filter drain can be made lining a trench with geotextile (R.U.NBS project used woven rice bag as lining), placing a perforated pipe 6" from the bottom, backfilling the trench with gravel, and covering with geotextile.
To read more about the process how to design NBS like filter drains with community members click on read more.
Permeable Paving
What...
This is paving that allows surface water or runoff to soak between the paving into the ground or a storage structure (this could be gravel) reducing water runoff.
Why...
The surface and the sub-grade need to be designed with the permeability function in mind. Water may infiltrate directly into the subsoil where conditions are suitable. Alternatively, water can be held in a reservoir structure under the paving for reuse, infiltration, or delayed discharge.
How...
The permeable paving can be gravel, concrete, or plastic webbing, concrete blocks designed for the purpose or porous asphalt
To read more about the process how to design NBS like permeable paving with community members click on read more.
Raingarden
What...
Rain gardens, also called 'Bioretention' facilities, can look just like a planted garden but will also be able to treat, store and soak stormwater runoff.
Why...
A rain garden can enliven any space but they can also help to cool down hot areas (transpiration and shade), they can help to treat, store and help soak water.
How...
Rain gardens can be very simply constructed and planted. The correct species of plants need to be selected depending on how much the garden will be flooded or wetted among other factors. The outflow from the garden does need to be considered carefully.
As with other gardens the plants need to be maintained to keep the best health. At one of the R.U.NBS project sites, St Johns a community school in Kibera, the school gardening club will look after the planted areas and measure the effect of the rain garden on the schoolyard.
To read more about the process how to design NBS like raingardens with community members click on read more.
Infiltration Tank
What...
A void created or constructed, usually underground, to capture stormwater and hold it to allow for it to infiltrate into the ground.
Why...
The capture and detention of stormwater help to reduce the volume of water flowing into watercourses, and therefore can help to reduce the risk of flooding downstream. Less surface water runoff can also translate to less erosion and a more stable ecosystem. The water captured in the tank can be used for watering plants or washing down surfaces but is usually not potable.
How...
To construct a simple detention tank below ground a suitable site is the first step, the tank needs to allow for water to flow into it and the future use of the area around the tank should be considered (tanks are structures and can collapse or cause collapse of other structures - seek engineering advise to avoid this). Detention tanks can be built to be watertight or to allow some infiltration into the surrounding ground. The use of the water can help to determine if waterproofing is needed or not. For example, if the ground is contaminated but the water is to be used the tank should have a waterproof lining, if the ground allows infiltration but the water is to be used then there should be a waterproof lining, or if the ground water quality is saline but you want to keep the stormwater fresh then use a waterproof lining.
To read more about the process how to design NBS like infilitration tanks with community members click on read more.
Planting
What...
Simply planting and establishing ground cover vegetation for numerous positive impacts it can have.
Why...
Plants contribute to cooling the local micro-climate and provide a habitat. Plants roots can assist with erosion control and support ground infiltration of water. Plants can improve water quality by absorption and transpiration of water.
How...
Planting vegetation to ensure it can establish and thrive is critical. Plants rely on varying levels of adequate water, soil, sunlight and air flow. Some plants can be quite sensitive whereas others are incredibly hardy, recharge and planning ahead of planting is always the best way to get good results.
To read more about the process how to design NBS like planting with community members click on read more.
Biogas Reactor
What...
What... A biogas reactor (or anaerobic digester) is an anaerobic treatment process that produces (1) a digested slurry (digestate) that can be used as a fertilizer and (2) biogas that can be used for energy. Biogas can be generated from human waste and means that toilets might not just produce waste, but actually produce a product. Biogas is a mix of methane, carbon dioxide, and other trace gases which can be converted to heat, electricity or light through burning.
Why...
Where there are no sewer lines or if sewer lines are compromised an off-grid option for the treatment of sewage that may also produce a product in the process, might be the solutions. The biogas reactor protects ground and surface water from contamination by human waste; it saves energy resources such as firewood, electricity, and canister gas for cooking; and it provides nutrient-rich water for plant irrigation thus contributing to food security and saves freshwater consumption for garden irrigation.
How...
A biogas reactor needs to consider these processes in the design: Primary treatment: (digester, settler) - Sedimentation and floatation process. Secondary treatment: (ABR, AF) - To remove dissolved and colloidal substances from wastewater by microorganisms. Tertiary treatment: (PGF, VSF, PP, Vortex) - To remove specific substances from wastewater using biological, chemical, and physical treatment methods.
To read more about the process how to design NBS like DEWATSs with community members click on read more.
Riverbank stabilisation
What...
As rivers have lost their natural surroundings their capacity to be life-giving watercourses has been undermined. This solution looks to imitate natural rivers and the vegetation layers with strong and branched root networks that would have managed erosion.
Why...
We are seeing more intense and sudden flooding events in cities and urban areas due to rapid urbanisation, componded by climate change. By stabilising riverbanks we can contribute to reducing the risk of flooding and limit the impacts of pollution, both of which have negative impacts on our environment and on people. Stabilised banks are protection against soil erosion, and improve drainage functions.
How...
CCI in Dar es Salaam constructed riverbank stabilization by combining sandbags with planted vegetation layer which controls erosion, the flow capacity has been considered to design a river profile that minimises flooding. Riverbank stabilisation has also been done in Kibera, by KDI, using planted riprap and gabions.
To read more about the process of how to design NBS like riverbank stabilisations with community members click on read more.
