Wepener
4.8 WATER USES
4.8.1 Domestic water use
The water resources of the Caledon River Basin are locally important to sustain water supplies for many small and medium sized towns in South Africa and Lesotho. The Caledon River is used for various water uses including irrigation, and municipal and industrial use in two local municipalities namely, Dihlabeng and Mantsopa. According to the South African census of 2011, Dihlabeng municipality (six towns) has a total population of 128 704 people, while Mantsopa (5 five towns) has 51 056 people (Statistics South Africa, 2013).
The Lesotho capital, Maseru, relies on direct river abstraction (40 000 m3 d-1) from the Caledon River when the flow is high enough (i.e. > 2 m3s-1) and on storage in off-channel reservoir (Maqalika) at other times. The reservoir is used when the river flow is low or when the river water is too turbid. The abstraction is meant to meet the capital’s water demand, mainly for wet garment industries and the population of about 432 000 people. There are also other smaller towns such as Teyateyaneng, with 250 000 people (Bureau of Statistics Lesotho, 2006) which rely on the Caledon River for water. According to the water utility in Lesotho, Water and Sewage Company (WASCO, 2013) the minimum water allocation target set by the Lesotho government is 30 litres per capita per day; however, some social classes use up to 80 litres per person per day or more. There are also very small and scattered rural settlements located in the highlands of Lesotho. There are no developed water distribution facilities or reticulation systems in most of these villages and the water they use is mainly from natural springs and boreholes. The water is used primarily for domestic purposes.
The Caledon water resources are important even beyond the catchment. There is an inter- basin transfer scheme abstracting water from the Knellpoort and Welbedacht dams to Magaung municipality which comprises the cities of Bloemfontein, Thaba-Nchu, Botshabelo and others, and is located in the Modder River Basin in the north-western part of the Free State province and to the west of the Caledon River Basin. The Caledon-Modder scheme transfers about 5.6 *
88 106 m3 per annum, mainly for municipal purposes and supplies more than 747 430 people with potable water (discussed further in section 4.9 below).
4.8.2 Reservoir Infrastructure
There are seven major artificial reservoirs constructed within the boundaries of the Caledon River Basin on both sides of the international border (Table 4.3). The reservoirs have diverse storage capacities, ranging between 4 and 130 * 106 m3. While the majority of these reservoirs are located across tributaries (Leeu, Rietspruit and Phuthiatsana Rivers) of the main Caledon River channel, only Welbedacht and Maqalika dams receive water from the main channel as instream and off-channel reservoirs, respectively. Amongst the reservoirs in the basin, the Knellpoort dam presents a unique case, being both an instream and off-channel reservoir in that it simultaneously intercepts flow of the Rietspruit River and receives pumped water from the Caledon River. The main aim of these impoundments is to secure a more stable and reliable water supply for nearby urban centres and for industrial and irrigation purposes. Table 4.3 provides a brief summary of the reservoirs located within the catchment.
Table 4.3 List of large dams in the Caledon basin Reservoir River Storage Capacity
(106 m3)
Quaternary
Newbury1 Leeu 5.6 D23C
Armenia1 Leeu 13.0 D23C
Knellpoort1 Rietspruit 130.0 D23H
Welbedacht1 Caledon 9.6 D23J
Maqalika2 Caledon 3.7 D22H
Metolong*3 Phuthiatsana 63.7 D22J
*Under construction.
Sources: 1 DWAF (2013); 2Letsie (2005); 3Metolong Authority (2013).
There are also many small and moderate sized farm dams (Figure 4.9) in the basin which have a direct impact on the total runoff of the river. Midgley et al. (1994) list a total of 53 impoundments with a combined storage capacity of approximately 202 * 106 m3, compared with the river’s estimated mean annual runoff of 1 244 * 106 m3. There is no doubt that small and large impoundments offer some sort of socio-economic benefit, but they impact significantly on the hydrological regime of the watershed which might complicate studying and understanding the contemporary and future hydrological characteristics of the Caledon River.
89 The impacts of small farm dams on the hydrological regimes have been reported by many researchers including Schreider et al. (2002), Hughes and Mantel (2010), and Nathan et al.
(2005). Similarly, hydrological changes of rivers brought about by large dams, such as those in the Caledon basin, have been investigated (Maingi and Marsh, 2002; Magilligan and Nislow, 2005; Graf, 2006).
Figure 4.9 Distribution of farm dams and other impoundments, both represented by black shaded areas, in parts of the Caledon River Basin. Quaternary catchments and river network are shown by red and blue lines, respectively.
4.8.3 Water Development Projects
There are two major water development projects designed to supply the Bloemfontein area through an inter-basin transfer scheme, and an additional scheme that supplies the Lesotho capital of Maseru. The other water developments projects are much smaller and designed to supply either local municipalities with domestic water or irrigation schemes. These include many privately owned farm dams.
90 4.8.3.1 Caledon-Modder River Government Water Scheme
The Caledon-Modder River Government Water Scheme (CMRGWS) was commissioned in 1974 to transfer potable water from the Caledon to the Modder River through a 115 km long pipeline in order to meet the water demand of Bloemfontein and neighbouring urban areas. To achieve this, the 32-metre high Welbedacht dam was constructed with an original storage capacity of approximately 115 * 106 m3. Severe siltation in the Caledon reduced the dam’s capacity to about 16 * 106 m3 some 20 years after completion (DWAF, 2012). The transfer pipeline has a discharge capacity of about 1.16 m3 s-1. Because of the high sediment content, the water was first treated at a purification plant, located downstream of the dam, before being transferred. The plant has average and maximum capacities of 1.68 m3 s-1 and 1.85 m3 s-1, respectively.
4.8.3.2 Novo Transfer Scheme
As silting reduced the storage capacity of the Welbedacht Dam from 115 million m3 to about 10% of that, the water demand of Bloemfontein and other towns could no longer be satisfied.
The Novo transfer scheme was therefore inaugurated in 1988 and was expected to deliver water with the maximum capacity of 150 million m3 by the year 2030. The scheme comprises the construction of the Knellpoort Dam on the Riet River (tributary to the Caledon), with a maximum storage capacity of 137 million m3.
The 50 m high dam was completed in 1988. The dam also receives water from the Caledon River, as off-channel storage, through a pumping facility at Tienfontein. Water from the Caledon is delivered through a 2 km long canal to the Knellpoort Dam from the Tienfontein pumping station which is equipped with four pumps with a combined maximum pumping capacity of about 3.7 m3 s-1. The transfer channel was designed to trap and minimise siltation of the Knellpoort Dam to avoid a similar situation to that of the Welbedacht Dam. From the Knellpoort Dam, water is then pumped into the Modder River. Figure 4.10 gives a schematic view of the Novo transfer scheme. Slabbert (2007) investigated the potential impacts that the Novo water transfer scheme might impose on the integrity of the both the Caledon and the Modder Rivers.
91 Figure 4.10 The Novo water transfer scheme (Source: DWAF, 2012).
4.8.3.3 Maqalika Reservoir
The Maqalika reservoir is located on the outskirts of the Lesotho capital, Maseru, and collects the runoff of the Mejametalana stream which drains a 44 km2 catchment. The sole purpose of the dam was to supply the rapidly developing city with a stable potable water supply. With a 25 m high zoned clay core embankment, the reservoir initially had a maximum storage capacity
92 of 3.7 million m3 which is however, dwindling because of the high rate of sedimentation (Letsie, 2005). Maseru was previously supplied by water pumped directly from the Caledon River to the nearby water treatment facility. However, during dry seasons, the flow can be very low, thus failing to meet the city’s water demand. The construction of the Maqalika reservoir was aimed at stabilising the supply. The reservoir was constructed in 1983 as a temporary measure to ease the ever-increasing water demand of Maseru, and was intended to be operational till 1995, while more sustainable alternatives were being sought. The reservoir is still being used at the moment. During high flows in the Caledon River, water is pumped into the reservoir, which is located less than 100 m away (Figure 4.11). Caledon water inevitably adds more sediment to the already silted reservoir resulting in a decreased capacity.
Figure 4.11 Arial view of the location of the Maqalika Reservoir and the Caledon River.