Analysis of Western Cape dam levels

Western Cape dam levels: 15% by April 2017?

Since the winter of 2014, the Western Cape region has been in the midst of a significant and worsening drought. The winter rains of 2015 and 2016 have done little to offer relief, and as of the beginning of November 2016, the City of Cape Town entered into Level 3 Water Restrictions, and the agricultural operations of the Western Cape continue to face substantial water-related risks. In this piece, I take a look at the historical levels of the major dams in the Western Cape, and what these might mean for the province’s municipal and agricultural water resources in 2017.

The Western Cape is a winter rainfall region and this has significant implications for the use and storage of water resources: water demand (and evaporation) is highest during the dry summer months of the year – the sufficient recharge of the region’s major reservoirs (surface and groundwater) during the winter months is thus critical.

As is evident in Figure 1 below, the total level across the W. Cape’s major dams tends to peak between July and September each year, and reaches its low-point between March and May. During the winter of 2014, the total across the W. Cape’s major dams peaked at 93% in July, and steadily declined to its  minimum point of 40% of capacity in May 2015. Conversely, due to insufficient winter rains, the total peaked at just 72% of capacity in September 2015 – this is more than 20% lower than during the winter of 2014 – entrenching the inertia of a severe drought.

Analysis of Western Cape dam levels

Fig. 1: Western Cape historical dam levels (2014 – 2016) (Source: Western Cape Department of Agriculture, 2016)

 

By March of 2016, the low-point of the total storage of the W. Cape’s major dams was just 28%, more than 10% lower than in 2015. Again, insufficient winter rains in 2016 have not been enough to drive a recovery of the W. Cape’s dam levels, and the total water stored reached its maximum point of just 63% of capacity in September 2016 – 30% lower than the maximum point reached in 2014 (and 10% lower than 2015).

Assuming that the minimum point in stored water resources is generally 40-50% lower than the maximum point reached during the preceding winter (as is roughly evident in Figure 1), in the absence of water restrictions and the unlikely event of any further substantial rainfall, we can assume that the minimum point in the W. Cape’s major stored water resources would likely dip to between 10 and 20% of total capacity (across the major dams) by March – May 2017. These underline scary times, and just how entrenched the current drought actually is.

The impacts of the current drought also vary considerably across different parts of the Western Cape, due to variations in run-off potential (by virtue of the local climate and catchment characteristics) and water demands. This is also clear in Figure 1 for each of the major dams.

In the beginning of November 2016, the City of Cape Town imposed Level 3 Water Restrictions. Level 3 Water Restrictions reflect severe water shortages and are designed to reduce the City’s water demands by 20% (IOL 2016). However, almost 70% of the Western Cape’s water resources are allocated to irrigation agriculture – this where the real impacts of  the drought are being felt. According to the South African Government (end-Oct 2016), “current water restrictions applicable to irrigation water vary from 30% (Berg River system) to 43% in the Olifants River System (Clanwilliam/Vredendal)”, and “on average, on-farm storage dams are at 50% or less”. Importantly, “this implies that farmers already have a 50%+ restriction on their own water resources added to the 30% to 43% restriction from the large government-managed dams” – this will place considerable pressure on agri operations reliant on irrigation over the coming summer months.

But what is clear is that even if the current municipal and agricultural water restrictions can maintain stored water resources above 15-20% of total capacity by the end of summer, if we do not have a higher than average 2017 winter rainfall, the impacts of this current drought in the Western Cape will likely perpetuate and worsen beyond 2017.

 

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References

IOL (2016). Level 3 water restrictions start. [Online] Accessed 09-11-2016 at http://www.iol.co.za/southern-suburbs-tatler/news/level-3-water-restrictions-start-6522831

South African Government (2016). Western Cape agriculture on drought impact. [Online] Accessed 09-11-2016 at http://www.gov.za/speeches/western-cape-agriculture-remains-water-stressed-latest-drought-impact-30-oct-2016-0000

Western Cape Department of Agriculture (2016). Agri-Outlook. [Online] Accessed 09-11-2016 at http://www.elsenburg.com/agri-tools/agri-outlook

1 reply
  1. Doug HS
    Doug HS says:

    Very worrying indeed! Not to mention that many dams cannot drop below 20/30% for hydrological or environmental reasons so that water is simply not available to communities and farms. the other challenge I believe is that 40% of the water in the system is lost to leaks so they are looking at reducing the pressure to reduce this. Too bad if you live on a hill. And the development of new housing continues.

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