Pongolapoort Dam, also referred to as Lake Josini, was the largest dam in South Africa when it was constructed. It serves mainly as a source of irrigation water. Prior to construction of the dam, the area was the first formally recognized conservation area in Africa, leading to other conservation areas, including the Kruger National Park, one of Africa's greatest wildlife conservation parks. The lake is flanked by private wildlife reserves, with wildlife and birdlife abounding in the area. There is little information regarding its environmentally-related management challenges, although there are some concerns regarding minimum environmental flow requirements in its river system. Nevertheless, it may not exhibit serious transboundary issues requiring possible GEF management interventions.

TWAP Regional Designation Eastern & Southern Africa   Lake Basin Population (2010) 334,110
River Basin Maputo Lake Basin Population Density
(2010; # km-2)
Riparian Countries South Africa, Swaziland Average Basin Precipitation
(mm yr-1)
Basin Area (km2) 6,982 Shoreline Length (km) 167.7
Lake Area (km2) 128.6 Human Development Index (HDI) 0.61
Lake Area:Lake Basin Ratio 0.164 International Treaties/Agreements Identifying Lake No

Josini/Pongolapoort Dam Basin Characteristics

(a)Josini/Pongolapoort Dam basin and associated  transboundary water systems

(a)Josini/Pongolapoort Dam basin and associated transboundary water systems

(a)Josini/Pongolapoort Dam basin and associated  transboundary water systems

(b)Josini/Pongolapoort Dam basin land use

Josini/Pongolapoort Dam Threat Ranking

A serious lack of global-scale uniform data on the TWAP transboundary in-lake conditions required their potential threat risks be estimated on the basis of the characteristics of their drainage basins, rather than in-lake conditions. Using basin characteristics to rank transboundary lake threats precludes consideration of the unique features that can buffer their in-lake responses to basin-derived disturbances, including an integrating nature for all inputs, long water retention times, and complex, non-linear response dynamics.

The lake threat ranks were calculated with a spreadsheet-based interactive scenario analysis program, incorporating data and information about the nature and magnitude of their basin-derived stresses, and their possible impacts on the sustainability of their ecosystem services. These descriptive data for Josini/Pongolapoort Dam and the other transboundary lakes included lake and basin areas, population numbers and densities, areal extent of basin stressors on the lake, data grid size, and other components considered important from the perspective of the user of the data results. The scenario analysis program also provides a means to define the appropriate context and preconditions for interpreting the ranking results.

The Josini/Pongolapoort Dam threat ranks are expressed in terms of the Adjusted Human Water Security (Adj-HWS) threats, Reverse Biodiversity (RvBD) threats, and the Human Development Index (HDI) score, as well as combinations of these indices. However, it is emphasized that, being based on specific characteristics and assumptions regarding Josini/Pongolapoort Dam and its basin characteristics, the calculated threat scores represent only one possible set of lake threat rankings. Defining the appropriate context and preconditions for interpreting the lake rankings remains an important responsibility of those using the threat ranking results, including lake managers and decision-makers.

Table 1. Josini/Pongolapoort Dam Relative Threat Ranks, Based on Adjusted Human Water Security (Adj-HWS) and Reverse Biodiversity Threats,
and Human Development Index (HDI) Score

(Estimated risks: red – highest; orange – moderately high; yellow – medium;
green – moderately low; blue – low)

Adjusted Human Water Security
(Adj-HWS) ThreatScore
Relative Adj-HWS Threat Rank   Reverse Biodiversity (RvBD) Threat Score Relative RvBD Threat Rank   Human Development Index (HDI) Score Relative HDI Rank
0.85 23 0.52 37 0.61 27

It is emphasized that the Josini/Pongolapoort Dam rankings above are discussed here within the context of the management and decision-making process, rather than as strict numerical ranks. Based on its geographic, population and socioeconomic assumptions used in the scenario analysis program, the calculated Adj-HWS score for Josini/Pongolapoort Dam indicates a moderately high threat rank compared to other priority transboundary lakes.

The Reverse Biodiversity (RvBD) for Josini/Pongolapoort Dam, which is meant to describe its biodiversity sensitivity to basin-derived degradation, places the lake in a much less threatened position, exhibiting a moderately low threat rank, compared to the other transboundary lakes. Management interventions directed to improving the biodiversity status must be viewed with caution, however, since we lack sufficient knowledge and experience to accurately predict the ultimate impacts of biodiversity manipulations and preservation efforts. Further, the RvBD scores indicate the relative sensitivity of a lake basin to human activities, and high threat scores per se do not necessarily justify management interventions. Such interventions may actually increase biodiversity degradation, noting that many developed countries have already fundamentally degraded their biodiversity because of economic development activities. Thus, activities undertaken to address the Adj-HWS threats may actually degrade the biodiversity status and resources, even if the health and socioeconomic conditions of the lake basin stakeholders are improved as a result of better conditions, thereby increasing stakeholder resource consumption.

The relative Human Development Index (HDI) places the Josini/Pongolapoort Dam basin in a medium threat rank compared to the other transboundary lakes in regard to its health, educational and economic status.

Table 2. Josini/Pongolapoort Dam Threat Ranks, Based on Multiple Ranking Criteria

(Scores for Adj-HWS, RvBD and HDI ranks are presented in Table 1; the ranks may differ in some cases because of rounding of figures; Estimated risks: red – highest; orange – moderately high; yellow – medium;
green – moderately low; blue – low)

Adj-HWS Rank HDI Rank RvBD Rank   Sum Adj-HWS + RvBD Relative
Threat Rank
  Sum Adj-HWS + HDI Relative Threat Rank   Sum Adj-HWS + RvBD + HDI Overall Threat Rank
24 27 37 61 34 51 29 88 31

When multiple ranking criteria are considered together in the threat rank calculations, the Adj-HWS and HDI scores considered together place Josini/Pongolapoort Dam in the lower half of the threat ranks. The relative threat is somewhat reduced when the Adj-HWS and RvBD threats are considered together. Considering all three ranking criteria together, Josini/Pongolapoort Dam exhibits an overall medium threat ranking.

Further, a series of parametric sensitivity analyses of the ranking results also was performed to determine the effects of changing the importance of specific criteria on the relative transboundary lake rankings. This analysis involved increasing or decreasing the weights applied to the threat ranks derived from multiple ranking criteria to reassess the relative impacts of the weight combinations on the threat ranks. For example, in determining the sensitivity of the Adjusted Human Water Security (Adj-HWS) and Biodiversity (BD) ranking criteria, the threat rank associated with the first was assumed to be of complete (100%) importance (i.e., rank weight of 1.0), while the other was assumed to be of no (0%) importance (i.e., rank weight of 0.0). The relative importance of the two ranking criteria was then successively changed, with weight combinations of 0.9 and 0.1, 0.8 and 0.2, etc., until the first ranking criteria (Adj-HWS) was assumed to be of no importance (rank weight of 0.0) and the second (BD) was of complete importance (rank weight of 1.0). In the case of Josini/Pongolapoort Dam, the 0.5 and 0.5 weight combinations for three cases of parametric analysis for Josini/Pongolapoort Dam resulted in respective threat rankings of 7th, 19th and 2nd, respectively, among the total of 23 African transboundary lakes in the TWAP study (see Technical Report, Section 4.3.3, pp44-49).

In essence, therefore, identifying potential management intervention needs for Josini/Pongolapoort Dam must be considered on the basis of both educated judgement and accurate representations of its situation. A fundamental question to be addressed, therefore, is how can one decide that a given management intervention will produce the greatest benefit(s) for the greatest number of people in the Josini/Pongolapoort Dam basin? Accurate answers to such questions for Josini/Pongolapoort Dam, and other transboundary lakes, will require a case-by-case assessment approach that considers the specific lake situation and context, the anticipated improvements from specific management interventions, and its interactions with water systems to which the lake is linked. To this end, it is noted that the African transboundary lakes as a group merit special attention in regard to management interventions, with some lakes requiring more immediate attention than others.