The South African State of Rivers Report: uMngeni River and Neighbouring Rivers and Streams

Water quality in this resource unit is generally Good.

Riparian habitats are degraded by invasive trees such as wattles, gums and pines but are in good condition.

Instream habitat is Good, although the large number of farm dams have modified water flow, which in turn affects downstream habitats.

Invertebrate condition appears close to Natural. Fish are in good condition but lower down are only in Fair condition due to the impact of aliens (trout, carp and bass) and invasive indigenous catfish. For most biota the upper reaches of the uMngeni and Lions Rivers are in better condition than downstream towards Midmar Dam.

The Sharptooth catfish (barbel) although indigenous to KZN, never originally occurred upstream of Howick Falls. today it is an alien species in Midmar Dam and upstream.

Damage to wetlands is widespread (see page 15).

Plantation forests contribute to excessive sedimentation and destabilisation of riverbanks. These trees (as well as invasive alien plants) also use a lot of water, over-shade the river and displace indigenous vegetation.

The construction of Midmar Dam transformed what used to be a large natural wetland. There are also numerous farm dams in the catchment. See p. 30 for more detail about the impact of dams on river health.

Agriculture, in particular dairies, piggeries and maize production, impact moderately on river health through excessive nutrient input into rivers.

The interbasin transfer of water from the Mooi River to the uMngeni system is a potential threat to the health of both river systems through flow alteration and genetic mixing of biota.

This is the main water catchment for the KwaZulu-Natal (KZN) Midlands, providing high quality potable water right down to Kloof and the Inanda valley.

Wetlands contribute to the sustained provision of water through dry periods and even maintained supply during the dry early 1980s and 1990s.

Water is used for pasture irrigation, forestry and other forms of dryland agriculture.

Value of conserving rare and endangered habitats and species, e.g. wattled crane of the uMngeni vlei and the endemic mountain malachite dragonfly. Also present is the rare plant Hydrostachys which grows in waterfalls in this area.

The river and the many dams in the area provide for sport and recreation. Indigenous (the KZN yellowfish is a demon to catch!) and exotic fish e.g. trout in cool headwater streams and dams, are popular catches here. Midmar Dam is a hub for water sports including the famous Midmar Mile that draws thousands of swimmers.

Prevent further loss of wetlands and protect existing wetlands.

Plantation forests should continue to be managed sensitively, and options for new plantings restricted.

Continued alien plant management, in and outside of the riparian zone. Recent improvements in the management of plantations and alien plants by forest companies and Umgeni Water are commendable.

Piggery and dairy effluents and sediment and nutrient loads from lands under maize and pasture should be managed.

Pollution from the growing Mphophomeni settlement requires management.

Water savings through water demand management can be redirected to maintain and improve river health and thus river-based goods and services.

Proper fire management is needed, as excessive burning can negatively affect wetland vegetation, damage mist belt forests and impair the soil's ability to absorb rainwater.

TROUT IN THE UPPER UMNGENI RIVER

Brown trout (introduced here in 1890) are found in the upper uMngeni River while rainbow trout (used for recreational angling) are found in dams of the upper catchment. Although breeding takes place in some streams where suitable gravel beds exist, reproduction in the streams is limited and populations are generally maintained by the annual introduction of trout reared in hatcheries.

Trout, being an alien predator, adds a new component to the aquatic ecosystem. The most obvious impact on the uMngeni resulting from trout angling has been the construction of more farm dams. Trout prey on indigenous animals but the impact appears to be minimal. Frogs are preyed on both as adults and as tadpoles although a large portion of the frog population is inaccessible to fish predators. The indigenous Natal mountain catfish is preyed on by trout but they occur in streams that are too small for trout and their cryptic lifestyle reduce their vulnerability. Crabs and aquatic insects are a notable item in the trout diet. Some species are more subject to predation than others, but anything more than a local reduction in abundance seems unlikely. In the uMngeni River, trout are nowhere present in large numbers and the measurable effect on invertebrate prey is likely to be minimal.

The presence of trout is the subject of an ongoing controversy as many feel that trout have no place in South African rivers.

WETLANDS IN THE UMNGENI CATCHMENT

Wetlands in this catchment are most abundant upstream of Midmar Dam, and those in the headwaters are known as "the uMngeni sponge". Some of these wetlands are formally conserved (protected by KZN Wildlife) and they are important breeding areas for the threatened wattled crane.

Many of the catchment's wetlands have been destroyed by human activities and the state of the remaining wetlands varies greatly. Some are in good condition while others are degraded and their original functions impaired. Currently, the most significant threats to wetlands here are cultivation, artificial drainage, dams and urbanization (especially in the Pietermaritzburg and Durban areas), alien plant invasion, overgrazing and too frequent burning. At the highest altitudes, approximately half of the original wetland area has been lost, while below this the loss has been greater than 60%.

The continued loss and degradation of uMngeni wetlands is serious given their positive impact on river health by purifying water, controlling erosion and regulating water flow through the catchment.

Forestry companies in the area are contributing to wetland restoration by removing exotic forest trees planted within wetland areas in the catchment.

RIPARIAN WEED CONTROL

A study by Umgeni Water in the iMpofana catchment (below Michaelhouse School) showed how effective the removal of alien vegetation is in improving water yield. Thus, leaving these trees to grow and spread would cause a substantial decline in future water yield.

Alien plants require ongoing management but their removal is cheaper than investing capital in infrastructure such as pumping schemes or new dams. There are also numerous other benefits. Since the project started in 1999, it has provided income to more than 160 rural families and it has been used as a vehicle to educate children about environmental concerns. Trade has also been generated through new micro-enterprises such as fire-wood and charcoal production. Other benefits include reduced soil erosion by improving indigenous vegetation cover, improving the status of wetlands and increasing the area for stock grazing.

Since the start of this project, the Department of Agriculture has grouped alien invasive plants according to their potential impact. For example, a Category 2 invader such as black wattle, may only be grown under controlled circumstances.

ALBERT FALLS RESOURCE UNIT

Below Midmar Dam, the uMngeni plunges over the 111m high Howick Falls and into the uMngeni Valley where remnants of Midland forest can be seen. The Karkloof tributary then joins before the uMngeni flows into Albert Falls Dam. Approaching Albert Falls, the uMngeni meanders through grassed farmland, where the riverbanks are treeless or invaded by woody alien plants. Below the falls, the river traverses deeply dissected terrain, which forms the western edge of the Valley of a Thousand Hills. At Nagle Dam, the river is still at a high elevation (400m above sea level) despite being a mere 50km from the coast. The main land use types here are forestry in the west and north and cultivated land, especially sugar cane, and feedlots in the Wartburg area. A large part of the area is hot, dry valley bushveld used for subsistence agriculture. The population of the area is only 68 900.

Water quality in this resource unit is Good although only Fair at iMpolweni.

Riparian habitat in the upper reaches is badly affected by agriculture and forestry although better in the Umgeni Valley Nature Reserve. In the lower bushveld reaches, riparian habitat is Good despite vegetation encroachment into the river channel.

Instream habitat of the Karkloof River is Good and even Natural in the lower reaches. In the uMngeni River, the influence of dams (altered flow pattern and water quality) is noticeable and instream habitat here is only Fair.

Invertebrates of the uMngeni and Karkloof are in Good condition and even Natural in the lower reaches of the latter.

Fish scores show the same trend but reflect the presence of invasive species (trout in the upper Karkloof, and bass at several places). Some indigenous fish are also alien here, like the Mozambique and redbreast tilapia. The fish in the lower uMngeni are only in Fair condition due to the regulation of the river by dams.

Water releases from Albert Falls Dam are particularly "unnatural" as flows tend to be highest in the dry winter months, and low during summer. This flow pattern can disrupt ecological processes (see p.30). At Nagle Dam, bypass gates can be used to mimic a more natural flow pattern.

A considerable portion of the Albert Falls and Nagle catchments (in the upper reaches) are under plantation forests and invasive alien trees which reduce the flow of water to the river.

Cattle feedlots below Albert Falls Dam introduce excess nutrients to the river system.

Effluent discharges from Howick impact on the uMngeni River. Considerable impacts also emanate from the iMpolweni area where poor land management and inadequate sanitation contribute to turbid, nutrient-rich waters.

Tourism and recreation especially around Howick Falls, is based largely on and around the river. Msinsi Holdings offer a tourist package based on the river and the two large dams that includes game viewing, water-skiing, sailing, canoeing, angling and birding.

Environmental education at Umgeni Valley Nature Reserve and tourism in various game reserves (e.g. Albert Falls, Game Valley) centre around the uMngeni and Karkloof rivers.

Rural people particularly in the Mpolweni catchment utilize the river extensively for recreation, drinking water (in places), fishing and for plant products from the riparian zone.

Good quality water used by forestry and agriculture, the latter especially just below Albert Falls Dam, in the eastern section and in parts of the Karkloof catchment.

Angling is very popular in this resource unit, not only in the two large dams, but also in the rivers (see p.33). Albert Falls has been considered one of the world's top bass dams.

The river carries water to Albert Falls and Nagle dams which are the main supply reservoirs for the greater Durban area, supplying more than 400 million litres of water per day for mainly domestic and industrial purposes. The river between the two dams carries water from Albert Falls dam, a storage reservoir, to Nagle dam, from where the water is piped to Durban.

Define desirable river health below Midmar, Albert Falls damsand from this determine the amount, quality and flow pattern of water needed to maintain the river ecosystem so as to provide desired river-based goods and services (i.e the ecological Reserve).

Water demand management by agriculture and forestry and pollution control.

Minimise overgrazing in the iMpolweni district to reduce excessive sediment input to the river.

Minimise effluent pollution from the Howick area.

Accommodate the passage of young eels past dam walls.

EXTINCTION IN THE KARKLOOF RIVER

The Karkloof mist-belt forests, with their giant yellowwood trees, have over the years been heavily harvested and cleared for agriculture and plantation forestry. These magnificent forests, of which a few pristine patches still exist, were associated with streams of unquestionable quality and reliability. The upper reaches of the Karkloof River, were in the 1950s found to contain a rare burrowing mayfly, Ephemera mooiana, which has only ever been found here and in the Mooi River above Rosetta. In these rivers it burrowed into the hard mud banks beneath the water. Unfortunately, with the removal of indigenous forests and the conversion of the grasslands to agriculture, it appears that this species may now be extinct. An extensive search for this rare mayfly by a student from the University of Natal together with Umgeni Water, has proved fruitless.

A RARE CRUSTACEAN OF THE UMNGENI RIVER

Potamonautes dentatus (left) is a river crab found in the uMngeni River, discovered here in 1992. This large species favours fast-running water and can sometimes be seen climbing the vertical cracks in the waterfall rocks at Albert Falls waterfall.

A VERY RARE AQUATIC PLANT

Hydrostachys polymorpha is a small fern-like plant that grows in fast currents, clinging to the rocky substrate of waterfalls and rapids. Hydrostachys is sensitive to changing temperatures (especially below dams) and excessive silt in the water. It is found fairly widely in the upper reaches of the uMngeni (especially the Karkloof tributary) and neighbouring rivers.

REEDS

The reeds on the river between Midmar and Albert Falls Dams are often assumed to be Phragmites australis (syn.P.communis), but on careful study, have proved to be mostly the more tropical relative P. mauritianus which seems to have greater preference for oxygenated, faster flowing water than does P.australis [NOTE: P. australis is widespread in KZN, from Drankenensberg to coast, and is likely also to be present, but probably not admired].

UPPER UMSUNDUZE RESOURCE UNIT

The uMsunduze is one of the major tributaries of the uMngeni River. It rises near Elandskop on the road to Bulwer (1 500m above sea level) and flows eastward to Henley Dam, Edendale and Pietermaritzburg. The river then flows into the hot, dry Edendale valley, where the river gradient is high and the substrate rocky. Pools are few and small in size and the water tends to be highly turbid from soil eroded fro the catchment.

The main land use types here are subsistence cultivation and rural developments with urban areas in the vicinity of Edendale and Imbali. The human population of the area is 278 200. There is also a small area of plantation forestry in the middle of this resource unit.

Water quality is Fair, but spoiled by turbidity and faecal contamination, the latter particularly bad in the lower reaches.
In the upper reaches the riparian habitat is heavily exploited mainly by stock and by people collecting wood and also due to excessive burning of vegetation during winter (annual fires are probably not a natural occurrence). In the lower reaches there are also impacts from alien vegetation.
Instream habitat in the upper portion of the area is Good which allows for healthy fish and invertebrate populations. In the lower reaches instream condition is Poor mainly due to the impact of Henley Dam and water quality issues.
Invertebrates up and downstream of Henley Dam suggest that the river is in Good condition. Species diversity is good, and many sensitive organisms are found here.
The fish scores are higher in the upper reaches due mainly to the presence of the Natal mountain catlet which used to occur in the lower reaches as well. Unfortunately bass have invaded both sections.

Overgrazing by stock has led to poor grass cover. This leads to rapid run-off of rain, poor infiltration, rapid and high flooding with soil erosion , incision of the river and turbid water.

Many informal settlements lack adequate waste services, leading to faecal and nutrient pollution. Sewer surcharges in the lower reaches compound the issue.

Industrial effluents and illegal discharges are few but occur nevertheless.

Henley Dam (now decommissioned as a supply dam) does impact on water quality. Water passing over the dam is unnaturally low in nutrients and has phytoplankton not normally found in local rivers. This encourages the occurrence of invertebrate species adapted to filtering phytoplankton, which are not natural in this area.

Dilution and transport of pollutants from the urban/peri-urban areas.

Water to support small-scale agriculture in the upper portion of catchment, with emphasis on stock watering.

Recreation and subsistence fishing.

Reeds from the riparian zone.

Cultural and in particular spiritual activities.

The river is used for clothes washing.

Measures to minimize immediate human health hazard from faecal contamination e.g. complete provision of potable water and sanitation.

Upgrading and improved management of sewerage systems

Control of stock numbers and overgrazing to reduce land degradation.

Reduce frequency of veld fires.

TOO MUCH WATER, TOO LITTLE WATER
As is the case in many parts of South Africa, the uMngeni River catchment is subject to wide fluctuations in flow, ranging from crippling droughts to raging floods over the space of a few years. The last twenty years have seen these in extreme proportions, with two of the most severe droughts in recorded history (early 1980s and 1990s) interspersed by two extreme floods, cyclone Domoina in 1984 and the September 1987 floods. The latter had the greatest impact on the uMngeni River.	We must appreciate that while these changes in river flow are inconvenient to society, they are essential for the maintenance of the natural ecosystem. The plants and animals associated with this river evolved to cope with these cycles and any change will mean that some species will be lost or their numbers and dynamics altered. One of the worst things we do to the uMngeni River, is to regulate its flow so that it is uniform all year round, and from year to year. In this case hardy pioneer species characteristic of the uMngeni would be replaced by less adaptable species, many of which may be alien imports from rivers which have a more constant flow. Species diversity is reduced, and the whole ecosystem becomes impoverished. As a result, the risk of the breakdown of ecosystem functions and resulting failure to deliver desired goods and services to people, becomes greater.	Management of the uMngeni River becomes difficult as it must balance the needs of society for a constant flow of water, with the needs of the environment which requires that some of the variability of the system be maintained.

PIETERMARITZBURG RESOURCE UNIT

This resource unit is dominated by the urban sprawl of Pietermaritzburg (altitude 750m), a mix of formal city, residential and industrial suburbs and informal housing developments. Here the uMsunduze River enters a canalised reach (an 'artificial' river) at Camps Drift. It then passes through the city in an incised narrow channel and is joined by small tributaries before picking up treated effluent from Darvill wastewater works. Large parts of Pietermaritzburg used to be floodplains and wetlands but the river system is now a shadow of what it was. The total population of the area is 239 500 people.

Water quality in the region is Poor mainly due to faecal contamination and declines as the river passes through the city. Interestingly, the effluent from Darvill Wastewater Works often improves the quality of the river water.
Of concern is the Poor health of both the instream and riparian habitats. Extensive canalization (particularly at Camps Drift) has significant impacts on the river's natural flow pattern. Because of Poor water quality (eutrophic and turbid water) habitat is Poor for the natural fauna and flora.
The decline in the health of the invertebrates from Good to Poor over a few kilometres, shows the magnitude of urban impacts. In the lower reaches of the city, only the toughest invertebrates survive, and then in great quantities due to the abundance of organic "food" (i.e. pollutants).
Fish health is Good, as most of the indigenous species in the area are resilient to pollution. However, alien species abound, especially in the Camps Drift impoundment, where carp and bass are common. The weirs on the river are mostly impassable to migrating fish.

Urbanization and high population densities, including areas with minimal sanitation services. The extensive network of sewers discharges its contents into the river at times.

City street storm water discharges can be as polluting as sewage discharges. The large surface area of paved ground and rooftops increases run-off during storm events.

Legal and illegal discharges from factories are a major problem, particularly on the Baynspruit tributary, which drains the Willowton Industrial area.

Impoundment of the river at Camps Drift has extensively altered its nature.

Mowing of riparian vegetation and canalization reduces the river's ability to recover from flooding, increases flow velocities and results in damage to river morphology within and downstream of the resource unit.

Large alien trees (e.g. at Alexandra Park) and other invasive alien plants in the riparian zone shade natural vegetation, destabilise the banks and alter the instream habitat.

Transport and assimilation of domestic and industrial pollutants.

Informal domestic water use especially from the small tributaries entering the uMsunduze.

Recreational and subsistence fishing.

Adequate river flow and sufficient water of adequate quality to support contact recreation like canoeing (e.g. Dusi canoe marathon); threatened at times due to poor water quality. Swimming is no longer safe here.

The river forms the focal point of an open space outdoor and parkland facility - Alexandra Park and Camps Drift. The full potential of this facility is spoiled by poor water quality.

River-based educational activities are widespread.

Reduction in pollution from sewers, informal settlements, city streets, illegal discharges and the wastewater works and reduction in solid waste (litter).

Control of water weeds and alien weeds in the riparian zone, including removal of large alien trees, unless where serving an important function (e.g. shading in Alexandra Park).

DUSI CANOE MARATHON

In January each year, the Dusi canoe marathon starts at Camps Drift in Pietermaritzburg and ends at Blue Lagoon in Durban, with some 3000 paddlers participating. The total exchange of money on this event in direct costs i.e. equipment and accommodation, is R20 - 30 million. The marketing value is approximately R100 million, giving an indication of the economic value of a sporting event which relies heavily on adequate river flow and good water quality. The Dusi marathon has redirected much of its income to developments in the rural parts of the catchment.

Unfortunately the event is threatened by faecal contamination and by water hyacinth choking the river near the estuary.

DRAGONFLIES AND RIPARIAN VEGETATION

Dragonflies are familiar to us as the pretty aerial creatures associated with streams and ponds. Young dragonflies (larvae) live underwater in the weed or mud and are highly sensitive to stream conditions such as flow, water temperature and amount of sunlight on the water.

Most species avoid heavily forested areas, except where there is dappled sunlight on the bank and water. Invasive alien plants in the riparian zone over-shade the banks, making the habitat unsuitable for most dragonfly species. Local biologists recently found that the removal of invasive alien plants has a dramatically positive effect on dragonfly abundance. Within one season of alien plant removal, dragonflies return. Dragonfly abundance and diversity can thus provide an indication of both instream and riparian vegetation health.

Several local communities make use of the rivers for cultural and religious purposes (Hindu ceremony on the Townbushstream.)

Dragonflies are also sensitive to altitude. The species found at Albert Falls are quite different from those at Midmar. Pietermaritzburg lies in between and has dragonfly species from both higher and lower elevations. This dual recruitment combined with a variety of habitats makes the National Botanical Gardens at Pietermaritzburg a dragonfly hotspot of 30 or so species.

INANDA RESOURCE UNIT

Below Nagle Dam, the uMngeni River is joined by the uMsunduze tributary and continues in an easterly direction. Towards Inanda Dam, increasing air temperatures and more unpredictable rainfall results in riparian grassland being partly replaced by indigenous tree and shrub thornveld dominated by indigenous acacias. Apart from farmlands around the uMsunduze, this resource unit is dominated by the rural Valley of a Thousand Hills, a vigorously undulating landscape with hills and valleys. A large rural population lives here, and many are directly dependent on the uMngeni River. The total population of the area is 152 000.

In the valley bushveld region, the uMsunduze River water quality is Poor, reflecting the impacts of the upstream city of Pietermaritzburg. The uMsunduze River thus reduces river health of the uMngeni River. Aquatic weeds flourish because of high nutrient levels, in particular in the uMsunduze River (see page 23).
The riparian zone of this river is in a Good condition despite intensive utilization in parts, especially in the lower reaches.
Instream habitat of the uMsunduze River is Fair. With the combination of poor water quality (caused primarily by excessive nutrients, toxic pollutants and high silt loads), the river habitat is unsuitable to the more delicate plants and animals. The instream habitat of the uMngeni River is in Good condition.
Invertebrates of the uMsunduze are in a Fair condition, reflecting the poor water quality coming from the city. The river is home to large numbers of hardy species such as benthic algae and midge larvae (Chironomids).
The fish in the area are fairly tolerant and have done well despite the poor water quality. Aliens include carp, bass and redbreast tilapia. Invertebrates and fish of the uMngeni River are in Good condition.

Water flow is affected by the dams upstream. Inanda Dam wall blocks fish migration. Some estuary species would have been present here but are now absent due to Inanda Dam wall.

In the area of the "Thousand Hills", the natural vegetation including that of the riparian zone has been much depleted during the 1900s as a result of over-utilization by a large local population. The area also suffers severe invasion by alien plants. The result is increased erosion and sedimentation of the river, and bank instability both of which reduce river health.

Excessive nutrients and pollution in the uMsunduzeRiver from The upstream city of Pietermaritzburg.

Overharvesting by subsistence fishermen.

Aquatic weeds are found throughout this resource unit, including water hyacinth, water lettuce, Kariba weed and parrots feather (see page 23)

Sand mining.

The instream purification of polluted water is a major service provided by the river, in particular the uMsunduze.

Supply of large amounts of good quality water via Inanda Dam to the city of Durban. Also extensive use of water by rural people for riparian agriculture and stock and game watering.

Sand mining from the river bed is an important activity in the middle reaches.

Scenic river environment and adequate river flow support a small but potentially much larger tourism industry. The river itself supports vibrant canoeing activity. Inanda Dam and Resources Reserve is only 45 minutes' drive from Durban and is an extremely popular site for jet skiing, power boating, yachting, fishing and self-guided hiking trails.

Riparian and wetland plants harvested for craft weaving, e.g. ikhwane and imizi.

Unfortunately this area has also lost valuable products - important indigenous medicinal plant species such as Siphonochilus aethopica and Stangeria eriopus have been eliminated.

Manage flow releases from Nagle and Inanda dams to meet river-based needs downstream.

Consider the installation of eelways to allow juvenile migrating eels to climb the dam walls.

Minimise overgrazing and resultant sedimentation of the river.

Management of pollution and eutrophication, in particular of the uMsunduze River.

Control the spread of aquatic and terrestrial alien plants.

RIVER AND SELF-PURIFICATION

Rivers have an extraordinary ability to purify themselves. Self-purification takes place as the water tumbles over rocks and sand, where huge numbers of invertebrates live together with a coating of microscopic algae, bacteria and other forms of life. These algae and bacteria absorb the nutrients and pollutants contained in the water. Some of the invertebrates in turn, feed on these organisms, while some bacteria convert toxic ammonia to less noxious forms. The activity of all these creatures scrubs, cleans and filters every millilitre of water, converting pollutants into animal and plant bodies, which in turn feed the next level on the food chain. These processes provide a service that is not visible and seldom appreciated. If rivers are abused to a point where these purification processes are damaged, the consequences for all users of the river could be extreme. The uMsunduze River is a prime example of a river where these processes play a very important purification role, producing a more acceptable water quality by the time it joins the uMngeni.

AQUATIC WEEDS

Within the uMngeni catchment, Inanda Dam and the uMngeni River upstream from the dam suffers the highest incidence of aquatic plant invasion.

Aquatic alien plants become problematic when their rampant spread is encouraged by excessive nutrients, particularly from urban runoff, sewage and agricultural fertilizers. The mild climate of KwaZulu-Natal also encourages rapid growth. Water hyacinth, water lettuce, Kariba weed, red water fern and parrot's feather have all been found at various places and times within the uMngeni and uMlazi rivers. These plants clog the water surface, deplete oxygen, foster mosquitoes, disrupt rivers' self-purification processes and may lead to a loss of aquatic species, with an associated loss in resource use and value. They also evapotranspire large volumes of water. Water supplied from water bodies covered with alien plants often requires sophisticated, expensive treatment.

ALGAL BLOOMS

Algal blooms develop when water nutrient levels are high enough to support rampant growth. The nutrients mainly responsible are phosphorous (mostly from detergents and fertilizer) and nitrogen (from sewage and fertilizer. One way to minimise problems associated with algal blooms is to maintain river health by preventing excess nutrients from entering rivers and thus dams.

Algal blooms sometimes impart high costs to water consumers. The cost of removing just the taste and odour imparted by algae at times of a severe bloom (e.g. approximately once in 24 months on Nagle Dam), is significant. Millions of Rands worth of chemicals have to be kept at the water-works year round, just in case these algae get out of hand.

In the early 1990s Inanda Dam became a seething mass of noxious algae, largely due to the rotting vegetation and humus layer drowned by the rising waters. Since then the dam has stabilised and water quality has improved mainly due to upgrades by Umgeni Water at Darvill Wastewater works, that reduced the nutrient load from Pietermaritzburg.

Shongweni Dam (in the neighbouring uMlazi catchment) has also had severe problems, with the main cause being excessive nutrient inputs from Hammarsdale and Mpumalanga. Blooms of, at times toxic, blue-green algae have been common, making this dam unsuitable for domestic water supplies, and of questionable quality for recreation purposes.

LOWER UMNGENI RESOURCE UNIT

From Inanda Dam, the uMngeni River flows from the Thousand Hills with a gentle gradient for 24 km before it flows out to sea just north of Durban. This part of the river is extensively modified, with riparian vegetation and direction of flow significantly altered to accommodate human settlement and activities. Historically the uMngeni River entered Durban bay over a large swampy plain where Durban is now situated. This resource unit is highly urbanized (population 1 314 200). A few smaller rivers are also important here. They include the uMhlatuzana and uMbilo Rivers, which rise in the hills above Durban, draining large areas of urban and industrial development before entering the bay.

Water quality in the uMngeni River is Fair, due mainly to the purification of the water in Inanda Dam. Unfortunately by the time the river enters the sea, water quality is Poor from the large volumes of city pollutants.
Riparian health is Fair, but is no longer subject to frequent flooding, resulting in excessive reed growth and invasion by terrestrial weeds.
Instream habitat (Fair) is affected largely by dam-regulated flows and prevention of the natural supply of sand to the river. This causes silting and closing of the estuary, reducing its contact with the marine environment.
Invertebrates are in Good condition although species composition would probably not resemble the natural diversity, due to the unnatural water quality.

The river and estuary fish populations are in Fair condition. Water quality of the uMhlatuzana and uMbilo Rivers is Poor, due to urban impacts. Habitat integrity, riparian and instream condition of the uMhlatuzana River are Fair, with resulting invertebrate populations also being in Fair health. The fish are in a Good condition. In the lower reaches the riparian habitat quality deteriorates to Poor.
The uMbilo River habitats are in a Fair condition although mixed, with Good health in the middle reaches and Poor health in the lower reaches. The invertebrates in this river were in a Poor class as a result of the heavy pollution load. Fish are in a poor condition in the lower reaches.

Intensive, large-scale urbanization and associated modification of the river course.

Canalisation of the uMngeni, uMbilo and uMhlatuzana Rivers has removed natural habitat in the lower reaches.

High population densities and effluent discharges, excessive nutrients and polluted run-off from streets, factory yards and informal settlements.

Upstream activities, dams and bulk water abstractions alter water quality and sediment dynamics, reduce flow and alter the river's natural flow regime on which many species depend.

Water hyacinth negatively affects the aquatic ecosystem (see p.23).

Sufficient flow and water volume to transport and assimilate domestic and industrial waste.

The estuary is a nursery area for many marine fishes, and provides for sport angling for kingfish, springer and gurnards. Subsistence fishermen also collect fish from the river here and higher upstream. Blue Lagoon with its beachwood mangroves is an important recreational and educational facility.

Sand mining for construction, although since Inanda Dam was built, the supply of "Umgeni Sand" has diminished.

The flood plain of the river has provided valuable land for building although at a high ecological cost.

The river is extensively used for cultural and spiritual activities.

Recreation: the river below Inanda Dam is used for canoeing.

Much of the Durban Metropolitan Open Space System (which includes education and recreation facilities) is based on these rivers.

Management of water releases from Inanda Dam to maintain the services provided by the river and estuary.

Management and minimisation of industrial and domestic pollution.

Control of rampant aquatic weed, in particular water hyacinth.

Restoration of riparian vegetation especially by elimination of invasive alien plants (e.g. triffid weed).

Solid waste disposal, especially in the informal areas, is a priority. Litter of the rivers and bay is a widespread aesthetic and health problem.

UMNGENI ESTUARY

Estuaries, like rivers, provide us with a wide range of opportunities and benefits. They are an important location for recreational and subsistence activities. The health of estuaries is dependent on the provision of freshwater from the rivers that feed them. By protecting river health, we are also protecting estuaries and the benefits that people derive from them.

The uMngeni estuary is very different today compared to the 1800's. The estuary mouth appears to have moved between the bay and the sea until it was mechanically redirected by the city engineer in the early 1900s due to concerns of flooding, malaria and damage to reclamation works.

There have also been significant changes in the estuary habitat. Between 1934 and 1984 the estuary has lost many of its intertidal and backwater habitats. Also, salt concentrations extended much further inland historically. Bridge construction, industrial and organic pollution and the damming of the rivers appear to exert the most significant impact on the estuary. Altered flows (due to upstream impoundment) have transformed the previously flood-dependent and permanently open estuary to a temporary open/closed system. In the absence of floods, sediment accumulates, changing the ecology of the system and thus the system's ability to provide a certain range of estuary-based goods and services.

Despite human impacts, the uMngeni remains an important estuary. The remaining 44ha of beachwood mangroves in the estuary support a wide diversity of plants and animals. Studies in the early 1980s recorded 56 fish species, 13 prawn species and 11 crab species. The estuary also provides habitat for juvenile marine fish. The uMngeni estuary also provides a variety of recreational opportunities. But, the uMngeni River will need to be managed carefully in order to maintain a desirable level of benefits from the estuary.

A RARE CRUSTACEAN

The Molweni River, a tributary of the uMngeni at Krantzkloof Nature Reserve near Durban, boasts a freshwater shrimp (Atyoida serrata - large shrimp in photo) only recently found in African waters. It lives exclusively in rocky crevices in torrential water.

UMLAZI RESOURCE UNIT

The uMlazi River originates south west of Pietermaritzburg at 1 500m above sea level. In the upper uMlazi, the main land-use types are agriculture, forestry and small rural and peri-urban settlemements. The river flows through the Baynesfield and Mapstone dams before entering the Tala Valley, an area of intense commercial agriculture and isolated forestry. From here, the river flows into Thornlea Dam, through the Killarney valley and Mpumalanga settlement and into Shongweni Dam. Here the river is joined by the Sterkspruit and Wekeweke tributaries. Below Shongweni Dam, the river runs through steep sided valleys and then through rural areas downstream of Dassenhoek. It then flows through the densely populated areas of Chatsworth, uMlazi town and the industrial zone near Durban airport (historically a large swamp) before flowing out to sea through a concrete canal. The population of the uMlazi catchment is 690 800.

Water quality of the uMlazi is Good, but deteriorates to Poor in the lower reaches.
Riparian habitat is Good in the upper reaches, but invasive alien plants are a major problem especially in the lower reaches, despite control efforts. The riparian zone is also affected by heavy stock grazing.
Instream habitat is Natural in the upper reaches aided by removal of alien plants from the banks. In the lower reaches of the uMlazi and the Sterkspruit below Hammarsdale, the instream habitats are only Fair, largely due to excessive nutrient input.
Invertebrates upstream of Shongweni Dam are in Good condition due to the presence of several pollution sensitive species.
Fish are in Good condition but Fair in the middle reaches and Poor in the sea. The biota of the Sterkspruit are in Poor condition.

Regulation of river flow by impoundments.

Abstraction for irrigation (upper uMlazi) and water use by plantation forests.

Excessive industrial (in particular Hammarsdale and Isipingo) and nutrient inputs (mainly by agricultural activities in the upper catchment and 4 wastewater works in the middle and lower catchments) to the river leading to eutrophication (excessive nutrient enrichment of water).

Rampant aquatic weed growth.

Sand mining for construction purposes.

Rapid urbanization (e.g. Mpumalanga and lower uMlazi), with increasing population densities and inadequate services, leading to increased contaminated runoff and faecal pollution from residential areas (e.g. KwaNdengezi and Dassenhoek) and informal settlements.

Surcharging sewers in the lower catchment.

Canalisation of the uMlazi River in the lower reaches and loss of the original estuary.

Supply of good quality water mainly to formal agriculture and forestry in the upper reaches and Tala Valley; also for small-scale agriculture and rural settlements.

Subsistence and sport fishing in rivers and dams.

Tourism and trade, based on presence of river (and dams), their scenic value and opportunities for water-based activities: e.g. game viewing and canoeing on and around e.g. Shongweni Dam and Resources Reserve.

River-based education activities abound in this catchment.

Assimilation and transport of pollutants from agriculture, the domestic sector and industry.

Sand mining (below Shongweni Dam)