Letaba Catchment = 13 670 km²
Mean annual precipitation (MAP) = 612 mm
Mean annual evaporation = 1 669 mm
Mean annual runoff (MAR) = 574 million cubic metres (range from 100 to 2 700 million cubic metres)

Mean annual runoff (MAR) in the Letaba Catchment varies from more than 10% of the mean annual precipitation (MAP) in the wet mountainous zone to less than 2% in the drier parts of the catchment. More than 60% of the MAR in this catchment derives from only 6% of the area.

More than 20 major dams have been constructed in the Groot Letaba River catchment. The Tzaneen Dam on the Groot Letaba River and the Middel Letaba Dam are the two largest dams in the Northern Province. Other large dams in the catchment include the Ebenezer, Magoebaskloof, Nsami and Modjadji Dams.

As mountain and foothill streams, the Groot Letaba, Letsitele, Thabina, Debengeni and Magoebaskloof rivers have very diverse in-stream habitats. The river channels contain steep bedrock and fixed boulder rapids with cascades and occasional waterfalls. Cobble riffles occur in lower gradient sections. Deep pools are present in all river sections. These perennial rivers rise in the Great Escarpment Mountains.

The Klein Letaba, Nsama and Molototsi Rivers are typical sandy lowveld rivers, with deeply incised river channels. Wide sandy runs are interspersed with occasional gravel riffles. Bedrock dykes cross these rivers at infrequent intervals, occasionally causing deep pools on their upstream sides. River flows vary considerably during a single annual cycle.

Below the confluence of the Groot and Klein Letaba rivers, (at the KNP border) the Letaba River channel takes on the characteristics of the Klein Letaba River. The Letaba River passes through a steep confined gorge just before joining the Olifants River near the Mozambique border.

Groot Letaba Headwaters

The Groot Letaba headwater streams originate in the Drakensberg Escarpment, descending in long runs with an occasional riffle or pool. Bank sides are of gentle slope. Riparian vegetation is sparse. The natural grasslands have been replaced by commercial forestry. About 45% (more than 20 000 ha) of the total area of ecoregion 2.15 in the Letaba Catchment comprises plantations. Less than 5% is undeveloped grassland.

Broederstroom

Riverbanks of the Broederstroom slope gently.

Siltation originating from forestry roads is a serious problem. An improvement in the management of timber felling practices, especially during the rainy season, would reduce wash-off of soil into the river.

Predatory trout have destroyed the indigenous fish populations in the Broederstroom.

Sandmining for building purposes has disrupted the river channel and riparian zone of the Broederstroom.

Politsi River

Erosion in the riparian zone from bridge construction works. Agriculture, forestry and informal settlements encroach on the riparian zone. Alien plants include bugweed, pines and eucalypts.

Debengeni River

Groot Letaba River

The sharp descent from the Central Highlands to the Lowveld makes this an area of incised streams and numerous waterfalls.

Bridge construction has disturbed bank vegetation, causing erosion. Bramble, lantana, bugweed, pines and other alien plants abound in this region.

Forestry and River Health

Alien trees need plenty of water, therefore plantations are typically located in the high rainfall regions of a catchment. Plantations and stream sources often coincide and special attention needs to be paid to river health in these areas. The main forestry-related impacts on river systems are streamflow reductions and erosion and siltation associated with roads and harvesting activities.

Plantations cover 3.5% of the Letaba Catchment (30 577 ha eucalypts and 17 851 ha pines) and forestry is an economically and socially important industry. Since the early 1990’s, the industry has recognized the need for an environmentally sensitive approach to forestry-related activities and has played a pioneering role in incorporating environmental strategies as part of the business.

Forestry management recommendations

The forestry industry’s management recommendations with positive consequences for river health include:

Politsi River below Magoebaskloof Dam, Letsitele and Thabina rivers

Downstream of the Magoebaskloof Dam, the Politsi River enters the gently sloping Lowveld. A waterfall in the Letsitele River marks the transition from ecoregion 4.03 to ecoregion 4.04. Forestry plantations take up 30% of the total land cover of ecoregion 5.05 in this area and 64% of the area upstream of Tzaneen Dam. Subsistence farming covers 35% and commercial farming 7% of ecoregion 4.04. Ecoregion 5.05 in the Thabina and Letsitele catchments comprises 36% subsistence farming and 22% commercial farming (nearly 45% of the latter is under irrigation).

Politsi River

Letsitele River

Small weirs allow abstraction for agricultural purposes.

Letsitele River

Alien plants invading the riparian habitat include peanut butter cassia, castor-oil plant, sesbania, ageratum and large cocklebur.

A rail bridge and small weir dominate this stretch of river and solid waste pollution occurs. The river is used for irrigation and washing of clothes.

Despite these impacts, the water quality and in-stream habitat is good.

Thabina River

No water is released from the Thabina Dam for ecological purposes. The seepage from the dam, the tributaries and the runoff that feeds the Thabina River downstream of the dam appears to be sufficient to maintain the in-stream habitat in good health.

Molototsi and Nsama Rivers

The Molototsi River is a seasonal stream. The river is mostly a small trickle that disappears into the sand before it reaches the main river, but it experiences occasional heavy flooding during the summer months.

Subsistence farming is the main land-use in the Molototsi (36%) and Nsama River catchments (32%). Urban developments comprise 6,5% and 5% of the total catchment areas respectively.

Nsama River

During this survey, the Nsama River in ecoregion 5.03 was dry and no fish or invertebrate index scores are available.

Nsama River

Rural communities and their cattle impact on water quality, especially during the dry season. Washing, agriculture, cutting of trees and overgrazing within the riparian zone and other poor land-use practices all contribute to the problem.

Molototsi River

The Modjadji Dam, which stores water for domestic use, restricts flow downstream. The dam management programme does not include water releases that benefit the river ecology. This loss of flow is detrimental to the next 20-30km of river.

The Modjadji Cycad Reserve overlooks the Modjadji Dam.

Overgrazing, vegetation cutting and other poor agricultural practices occur in the catchment.

Molototsi River

Environmentally unsustainable land-use practices result in accelerated erosion.
Alien invasive plants occur within the riparian zone.

Pools in seasonal rivers are important sanctuaries for fish. Rivers such as the Klein Letaba and Molototsi rivers retain very few permanent pools of water throughout the dry season. In addition, these rivers have few flowing tributaries.

Klein Letaba River

The Klein Letaba tributaries like the Soeketse and Koedoes rivers are wide, dry and sandy ditches for most of the year. The Middel Letaba Dam is situated in the Middel Letaba River.

Subsistence farming takes up 35% of the total land-use in ecoregion 5.03 in the Klein Letaba Catchment and 20% in ecoregion 5.02 upstream of the confluence with the Nsama River. There is no commercial farming and less than 8% subsistence farming downstream of the confluence with the Nsama River.

Klein Letaba River

Sand mining destroys natural habitat and is unsightly.

Agriculture consists of small-scale farming by rural communities and large commercial banana, papino, paw-paw and mango plantations upstream from Giyani. The commercial fruit farms are fed by the Middel Letaba Canal irrigation scheme.

Klein Letaba River

The eastern area of this ecoregion around the Klein Letaba River has the potential to be incorporated into the Kruger National Park.

Soutini-Baleni, a geothermal wetland, is a Natural Heritage Site on the Ivory Route.

Downstream of Soutini, the river has more permanent water. The river is close to natural with exceptionally good indigenous vegetation and almost no human impacts. A small salt works, fed by a natural geological fault, thrives.

Overgrazing in the riparian zone contributes toward donga erosion.

In the Kruger National Park

The very sandy reaches of the Letaba River support only a narrow riparian vegetation band. The riverbed in ecoregion 5.01 is sandy with increasing occurrences of bedrock downstream. The Letaba River in the KNP forms multiple channels of up to 300 m wide. In ecoregion 5.07 and 6.01 the Letaba River flows through a series gorges and ravines. These could form significant fish barriers if water flows were to drop below a certain level.The very sandy reaches of the Letaba River support only a narrow riparian vegetation band. The riverbed in ecoregion 5.01 is sandy with increasing occurrences of bedrock downstream. The Letaba River in the KNP forms multiple channels of up to 300 m wide. In ecoregion 5.07 and 6.01 the Letaba River flows through a series gorges and ravines. These could form significant fish barriers if water flows were to drop below a certain level.

Letaba River

This part of the Kruger National Park is a wilderness area with Shimuwini being the only tourist camp. Tourism impacts are therefore minimal.

The Klein Letaba carries high sediment loads because of erodible soils and poor land management in the catchment. At the confluence of the Groot and Klein Letaba Rivers the gradient decreases and lower flow rates allows sediment to settle, aggravating the natural sand deposition on the Letaba River bed. Impoundment and abstraction, mainly for agriculture, reduce the flow of the Groot Letaba River, causing further settling of sediment.

In response to the lack of water brought in by the Groot Letaba, the Kruger National Park administration has had to build dams to provide water for game and to create habitats for fish, mammals, birds and reptiles.

The setting of Ecological Reserves for rivers gives the KNP management the confidence to cease all dam building practices.

A decision was made not to repair all the flood-damaged dams in the KNP, e.g. the Black Heron Dam is modified into a low flow guaging weir with fishladder and Shimuwini Dam completely removed.

There have been no recordings of the tiger fish in the Letaba River outside of the Kruger National Park since 1990. This temperature sensitive species dies at temperatures below 15°C. Dam walls obstruct migration towards warmer waters during cold spells.

KNP in collaboration with Northern Province Environmental Affairs and private sponsors has recently begun reintroducing tiger fish into selected Northern Province dams.

Letaba River

Many matumi, sycamore fig and jackalberry trees occur along the river. Natal mahogany is also present, but some distance away from the river edge.

Both dams in this area, the Mingerhout Dam and the Engelhardt Dam further downstream near Letaba Camp, have good fishways.

This is a wilderness area, with only a few hiking trails. The river is in a near natural state.

Very little riparian vegetation is present and the terrestrial vegetation grows right up to the rocky edges of the river. Most fish species found here are large and predatory. Crocodiles are abundant within the KNP.

This section will form part of the Gaza-Kruger-Gonarezhou Transfrontier Park.