From crisis to case study: Cape Town's struggle with sewage and urbanisation dynamics

Those who follow my work will know that I have been acutely interested in state failure as a concept. Way back in 2008 I posed a question at an academic conference held at Unisa, about whether South Africa would become a failed state, citing global water scarcity data that placed us in the highest risk category. That data is all about the number of people per unit of water, but it also deals with the capacity of the state to respond to changes that cross various thresholds of concern.

For this article, there are two specific issues that are colliding in the context of water, so an analysis of what is happening can help us answer the question about whether South Africa is a failing state. These two issues are population dynamics and sewage management. We will focus only on these two issues, to answer the question about the institutional capacity of the state to respond. 

Population dynamics can be understood by the following key statistics. The current population is 64 million people, which translates to a population density of 53 people per km². Two-thirds are urbanised, placing a massive strain on infrastructure in towns and cities. When we became a democracy in 1994, the population was just over 40 million, so a characteristic of our democratic transition is all about the arrival of 24 million new people in urban areas that were never designed for such a population density. To make matters more complex, influx control was abolished in 1994, so in addition to normal population growth, we have seen major changes to migration patterns. 

We can consequently think of the population issue as a composite of natural growth plus migration from internal and external sources. Translating this to sewage management, this means that an additional 4,800 megalitres per day are needed when compared with 1994. We arrive at this number by allocating 200 litres per person per day for domestic use, the majority of which ends up as either grey or black water, both of which typically go down the drain into a sewer. A megalitre is a million litres, so that’s a big number.     

We know from the Green Drop Report that over 90% of our wastewater treatment works are dysfunctional in one way or another. About 40% are totally dysfunctional, with the rest on a spectrum ranging from partial failure to impaired functionality. Therefore, we can say that we have a sewage crisis that has the capacity to overwhelm the state’s ability to respond. We also know that all water infrastructure in South Africa is designed on an indirect reuse model. This means that treated sewage effluent is discharged into aquatic ecosystems, from which our drinking water is also abstracted. For this reason, our sewage discharge standards must be exceptionally high, because in most cases, it will become drinking water soon. The Blue Drop Report is all about drinking water quality, and it tells us that there is an alarming trend across the entire country, showing a steady deterioration in both chemical and microbiological terms. One reason for this is the deterioration of our sewage works.   



Now let us look at Cape Town where we see several wastewater treatment works, many of which are extremely big. On the map, the size of the circle indicates the volume throughput of each plant. Each of these wastewater treatment works are under severe pressure, and all discharge partially treated effluent into an aquatic ecosystem of which there are three distinct types – rivers, wetlands/lagoons and the ocean. 

With respect to the rivers, it is apparent that other municipalities also discharge their effluent into the same river that eventually flows through the greater Cape Town area. This means that water quality in Cape Town is dependent on the capacity of other municipalities to cope. 

Regarding wetlands and lagoons, we need look no further than the plight of the large natural wetland that exists between Somerset West and Stellenbosch, and the Milnerton Lagoon, which is severely contaminated by sewage. 

Regarding the ocean, it gets very interesting, because there are three Marine Outfall Pipelines located at Green Point, Camps Bay and Hout Bay. These three pipelines discharge around 53 million litres of raw untreated sewage daily into the oceans adjacent to some of the best tourist beaches in the country. The only “treatment” that this sewage undergoes is maceration, which converts the solid pieces into paste that is then injected directly into the ocean.  Some of the solids such as condoms and feminine hygiene products are mechanically removed before maceration, but this process is not an exact science, so many of these make their way into the ocean. The interesting aspect is that the flow through the Marine Outfall Pipelines is only 5% of the total volume of effluent produced daily by all wastewater treatment works in the area. 



This is where it gets interesting, because sewage is made up of freshwater, but it is discharged into a saltwater environment. The chemistry and physics of water are relevant, because freshwater is less dense than saltwater, so the plume naturally rises to the surface where it is supposed to dilute itself. Dilution is a complex process, because freshwater and saltwater are typically separated by what is known as a halocline. This separation persists for long distances, potentially measured in terms of tens or even hundreds of kilometres. It is this plume that is clearly visible to drones or aircraft flying over the discharge points. The diagram, obtained from the City of Cape Town, illustrates how the Marine Outfall Pipelines are supposed to work. The expanding plume is exposed to UV sunlight that destroys bacteria, but the sun only shines half the day, turbidity of the water reduces the penetration of the UV spectrum,  and the wind blows the surface plume in directions other than the prevailing ocean current, often directly on to the beaches adjacent to the point of discharge.  



Maps used for environmental management purposes indicate the point of discharge of each Marine Outfall Pipeline and define the precise locations from which sampling must take place to ensure the health and safety of humans using the beaches. Each pipeline has its own map. The map shown here is for Hout Bay, which has 16 sampling points. The other pipelines have a similar number of sampling points, the most being for Green Point. Note that the Hout Bay Marine Outfall Pipeline discharges into a large bay, so if the wind changes direction to become a westerly, then the plume will be dispersed into the bay, and remain there for as long as the wind prevails. This holds true for all three Marine Outfall Pipelines, but the Camps Bay and Hout Bay pipelines are the most sensitive to this. 

Regarding the flow from each pipeline, the most interesting is Camps Bay, because it has peaked at 60 megalitres per day, but it has a design capacity of 40 megalitres per day. All of the Marine Outfall Pipelines have a daily pulse to them, which is monitored by meters. In all cases the pipelines are generally in a good condition, but all are hydraulically overloaded, so the discharge plumes are significantly larger than the design parameters used when they were originally engineered. All are significant contributors to beach pollution, so they require increasingly robust monitoring and telemetry systems making them an ideal candidate for migration to a digital platform capable of artificial intelligence and machine learning type of interventions using real time data. 



Cape Town is therefore an excellent example of the capacity of the state to cope with rapid changes to the system driven by population growth and migration. How it copes will determine the future prosperity of the citizens and the investment inflows from outside of the Western Cape. These challenges are massive, but soluble, which is why Cape Town will become a major case study for governance in the face of growing competition between people for a dwindling natural resource. DM