Selecting and designing a river conservation system

In addition to selecting broad priority catchments for river conservation, specific rivers to best achieve biodiversity targets and maintain persistence for each river ecosystem within the planning domain were also selected. A distinction was made between rivers selected for achieving biodiversity targets; and those selected for achieving longitudinal connectivity across the landscape: Only intact main rivers and tributaries were selected to achieve biodiversity targets, whereas any river (irrespective of its integrity) could be selected to maintain longitudinal connectivity across the landscape.

2.4.2.6.1. Rivers selected to achieve biodiversity targets

Figure 14 shows the protocol used to select rivers to achieve biodiversity targets. Only intact main rivers (i.e. A or B class rivers; Table 3) and tributaries (i.e. river segments with natural land cover ≥ 75%; Table 3) were selected to achieve biodiversity targets. Priority was first given to achieving targets in intact main rivers, as there is higher confidence in the integrity data of main rivers, which incorporates both land cover impacts as well as cumulative downstream impacts of large dams, numerous weirs and pollution points. If targets could not be met in main rivers alone, then river segments with percentage natural land cover ≥ 90% were first selected. Only if biodiversity targets had still not been achieved, were tributaries with natural land cover ≥ 75% selected.

An iterative selection approach was followed to select rivers to achieve biodiversity targets. At each iteration complementarity in target achievement across ecosystems was considered to ensure efficiency in conservation design. The order of the iterations was determined by the proportion of national range of each ecosystem within the freshwater planning domain - river ecosystems with higher proportions were selected first, because their conservation depends the most on activities within the planning domain. Where choices existed, each river was evaluated in terms of connectivity to the river system as a whole. Longer river reaches which connect to river systems with best integrity were favoured.

Choose river signature

Select main rivers with PESC A or B

Target achieved?

No Yes

Select tributary with >90% natural habitat

Target achieved?

No Yes

Select tributary with >75% natural habitat

Target achieved?

No Yes

Check options outside grasslands

Figure 14: Protocol used to select rivers to achieve both representation and persistence of river ecosystems within the freshwater planning domain

2.4.2.6.2.Rivers selected to maintain longitudinal connectivity

Rivers vital for achieving longitudinal connectivity and maintaining functioning river ecosystems were selected irrespective of their integrity. However, any connecting river that was not intact did not contribute towards achieving biodiversity targets. Connecting rivers in a moderately modified state (e.g. C class main rivers) can be viewed as functioning conduits for achieving longitudinal connectivity across the landscape. Transformed rivers selected for their importance as conduits across the landscape are likely to be inefficient for achieving longitudinal connectivity in their current state; rehabilitation of these rivers needs to be considered. For example, some transformed rivers may only require implementing recommended ecological flow requirements.

The resulting conservation design, depicting rivers which contribute to biodiversity targets and rivers which need to be managed to achieve longitudinal connectivity between selected tributaries is shown in Figure 15.

2.4.2.6.3. Assessment of target achievement

Of the 42 river ecosystems in the river planning domain, 30 can achieve their targets in intact main rivers and tributaries, with 11 of these being able to achieve targets in intact main rivers alone, an additional 16 in both intact main rivers and tributaries whose percentage natural land cover ≥ 90%, and a further 3 through selecting main rivers and tributaries whose percentage natural land cover ≥ 75% (Figure 16).

Twelve river ecosystems within the river planning domain cannot fully meet their biodiversity targets (Figure 7), although 7 of these can achieve over half their biodiversity target. Four of the remaining 5 river ecosystems which cannot even achieve half of their biodiversity target within the freshwater planning domain (Karoo 6, Lower Vaal and Orange valleys 3, Karoo 7, and Lower Vaal and Orange valleys 6), have the majority of the national range outside of the domain in areas where there are likely to be good opportunities for their conservation. However, there is cause for concern over the one highveld river ecosystem (Highveld 6), which is largely confined to the grasslands domain, and cannot meet even half of its biodiversity target. Rehabilitation of rivers containing this river ecosystem should be investigated if a representative sample of this ecosystem is to be conserved within South Africa.

Figure 15: Rivers selected for conserving river biodiversity in the freshwater planning domain. Representation rivers are intact main rivers and tributaries which contribute towards biodiversity targets. Process rivers are main rivers and

tributaries that are not intact, but which have been selected because of their importance in achieving longitudinal connectivity across the landscape.

16 12 11 3 0 2 4 6 8 10 12 14 16 18 M MT90 MT75 Not achieved Target achievement Nu mb er o f e c o s ys te m s

Figure 16: Target achievement for river ecosystems in selected rivers.

“M” denotes the number of ecosystems whose targets could be met within intact main rivers only, “MT90” are ecosystems whose targets were achieved by selecting intact main rivers and tributaries whose percentage natural land cover ≥ 90%; and “MT75” are ecosystems where targets where only achieved through selecting intact main rivers, and tributaries whose percentage natural land cover ≥ 75%. Ecosystems whose targets were not achieved are also shown.