Contents
of June 2004
EDITORIAL
Upsetting the balace of nature
UPFRONT
News
IDENTIFYING INVADERS
The Mexican Poppy and the
Pearl Acacia
BOOK
REVIEW
TREE OF THE ISSUE
Wilna Stones chooses the Pigeonwood
FEATURES
Simple
refurbishment of a collection of buildings and open spaces
Freedom
Park: a landscape narrative of South Africa’s history and heritage
Woodlands to contain pollution in
goldfields
Green soldiering
Environmentally sound river crossings
-----
EDITORIAL
Upsetting the balance of nature
The
fascinating world of figs that is covered in the splendid book published by Umdaus Press,
reviewed on page 12, tells the story of the slow death of a group of Namaqua figs (Ficus
cordata) growing up against some low rocky cliffs near Griquatown. The authors of the book
‘Figs of Southern and South-central Africa’, John and Sandra Burrows, report
that these figs with their branches adhering to the vertical rock faces are tragically
dead or dying – and the cause of their demise is the dassie.
They tell of
how an imbalance in nature has been created by man as he has populated the area and
brought in his sheep and goats. He has over the years systematically eliminated any bird
or animal that has preyed upon his livestock – jackal species, the Caracal and, most
importantly, the Black Eagle. The main food source of the latter is the dassie. Control of
the dassie population in the area is non-existent and the massive increase in their
numbers has left this highly palatable fig totally vulnerable. The authors say that, at
the time of their visit, the cliffs were swarming with dassies devouring every new shoot
the fig trees put forth. The figs were virtually denuded of leaves, and slowly but surely
dying.
The authors
make the observation that unless the predators are allowed to return, the dassies will
kill off the whole population of figs and then turn to another less favoured food source:
“…and so the environmental decline will continue. Ironically, the sheep and
goats will, in the end, suffer the most since the dassies will successfully compete for
the same grazing and browsing. A sobering example of man upsetting the Balance of
Nature.”
Another
story about the balance of nature is playing itself out on Table Mountain where a high
court decision has dismissed the legal action by the ‘Friends of the Tahr’ who
are averse to the eradication of the estimated population of 100 Himalayan Tahrs on Table
Mountain. The Cape Peninsula National Park (CPNP) will now go ahead with the complete
removal of the Tahr population, in conjunction with the NSPCA. The removal, over the
estimated period of a year, of this alien invasive species will pave the way for the
re-introduction of the original indigenous inhabitants of the Mountain –
Klipspringer, Grey Rhebok and Grey Duiker.
CPNP manager
Brett Myrdal says that the re-introduction of these indigenous antelope species will
result in a vast enhancement to the ecology of the Mountain. He points out that the Tahr
and the Klipspringer cannot co-exist on the Mountain, as the latter is a much heavier
animal (50-100kg) and eats everything in sight, out-competing the former. The lightweight
Klipspringer (8-12kg) is a discrete, selective browser and a positive force in the ecology
because many of the insects that feed on its dung are needed as pollinators. He says for
the full restoration of the Mountain, the Klipspringer needs to play its role.
Apropos of
the recent winning of the World Cup Bid, Neil Fraser, executive director of the Central
Johannesburg Partnership, in one of his recent Citichat newsletters encourages
environmental departments countrywide to follow the South Korean example. At the 2002
games, their Ministry of Environment saw the event as an opportunity to realise a
“Green World Cup” because “environmental conditions are widely used as a
yardstick for measuring the quality of life”. He says the massive crowds in Seoul
watching giant TV screens were seen to be collecting their own refuse and civic groups put
up posters encouraging the citizens to grow flowers and plant trees. He also sees this
large sporting event as a wonderful stimulus for inner city regeneration.
This issue
has an article on a simple urban refurbishment project where, as our editorial contributor
Leigh Darroll says, “No fancy stuff” was involved (page 16). Chris Brooker
discusses simple techniques to protect the riparian zone (page 32). Military activities
are related to destruction, whereas environmental concerns protect and cherish: the two
are, however, certainly not incompatible and no training areas on military bases are
planned without initial impact assessment studies and an environmental officer in
attendance during exercises involving explosives, to ensure that impact is kept to the
minimum. Environmental education and training is on the increase and the determination of
the Department of Defence to foster “green soldiering” is illustrated in the
article on the course at SAS Saldanha (page 30). - Carol Knoll
-----
UPFRONT
The importance of housing to urban regeneration
Brickfields
in Newtown is the biggest residential development to happen in the Johannesburg inner city
since the 1970s. Initiated by the Johannesburg Housing Company, this project has been made
possible by a public-private partnership: a partnership committed to the regeneration and
development of the city. Situated at the foot of the Nelson Mandela Bridge, Brickfields
will deliver a total of 1 400 new housing units. It is set to change the cityscape and the
economic and social fabric of Johannesburg.
The new
housing development is sited on Johannesburg’s original brickfields. History tells us
that the area of the city today known as Newtown was first settled soon after gold was
discovered on the Witwatersrand in 1886. The land, formerly part of the Braamfontein farm,
was acquired by the then ZAR government because it included the Fordsburg Spruit, which
would provide a secure water supply for the burgeoning mining camp. The soil surroun¬ding
the stream was rich with clay deposits and here the first bricks with which Johannesburg
was built were made. These were the original brickfields, where enterprising brick-makers
dug clay pits and built drying ovens to supply bricks for mine buildings and the
fast-growing mining town.
By 1896,
however, the brick-makers had lost their land, in spite of protests. It was taken over to
provide a holding and distribution yard for the new railway that was bringing in machinery
and equipment for the mines.
Later, when
the market was moved out of the city and other developments took away Newtown’s
economic raison d’être, the area declined and suffered through years of neglect. It
is only in the past decade, in spite of numerous earlier plans and proposals, that action
has been taken to rejuvenate this key quarter of the Johannesburg inner city.
Identified
by the Joburg Metro Council as an area of strategic importance for the city, and by Blue
IQ as one of its 11 mega-projects aimed at boosting the economic infrastructure of
Gauteng, New¬town is already seeing the benefits of a more than R400 million investment
– from provincial and local government, the private sector and civic agencies. Nelson
Mandela Bridge, the new Metro Mall and Mary Fitzgerald Square have become new landmarks in
the city, and a host of smaller interventions have restored some of Newtown’s urban
vitality. JHC’s own housing developments in this area have contributed to an
upgrading of the environment and the quality of life the city can offer.
The
development of Brickfields, linking into this regenerative momentum, will establish
another new landmark. Reclaiming what had become a derelict, inaccessible and largely
unused though prime city site, and putting it to new use, Brickfields will contribute
further to the transformation of Johannesburg.
Housing, and
the presence of an economically active resident population in the city, are essential to
urban regeneration. International experience bears testimony to this. In its early
planning of Brickfields, JHC sought the expertise of professional consultants from as far
afield as Toronto and Singapore, to bring the benefits of best practice to this
development in Johannesburg. With further input from local consultants, Brickfields has
been conceived as a primarily residential development, with provision for mixed use.
It is
planned in three phases, to be built over three years, and is designed to provide
affordable, good quality housing, for a mixed income tenancy. About 35% of tenants will be
within the national housing subsidy band – earning a monthly income below R3 500, and
the balance will include individuals, couples and families in consecutive income bands
ranging up to R12 000 a month. One, two and three-bedroom apartments will cater to the
needs of the targeted tenancy. The whole development will comprise a complex of low to
medium-rise buildings, clustered around green courtyards and protected open spaces where
children can play safely. Parking will be provided for tenants and, at street-level, there
will be space for shops and small businesses to serve the needs of tenants and the larger
urban community.
Landowners
prosecuted for invasive plants
The joint
initiative between the National Department of Agriculture, the National Prosecuting
Authority, the City of Cape Town, the Working for Water programme and the Santam/Cape
Argus Ukuvuka Campaign to deal with invading plants on the Cape Peninsula continues.
Over the
December period, Ukuvuka launched its extremely successful awareness campaign to inform
landowners about their legal obligations in dealing with invasive plants and fire risk.
Information was made available on the Conservation of Agricultural Resources Act, the Veld
and Forest Fires Act and the local Community Safety Bylaw. The awareness campaign drew
attention to invasive species that are particularly aggressive, infesting landholdings
falling within the declared Protected Natural Environment, and included one-on-one
communication with many offending landowners in a systematic fashion.
This was
followed in the New Year by the launching of prosecutions in terms of the Conservation of
Agricultural Resources Act against those landowners who still failed to deal with invasive
plants occurring illegally on their properties. A number of criminal summonses have now
been issued.
The National
Prosecuting Authority, with support from the Ministry of Justice and Constitutional
Development, has provided critical assistance, advocating that laws that are on the
Statute books should be applied, and that those who are being prosecuted are indeed
breaking the laws of the country.
The first
landowner accused of having invasive alien plants on his property appeared in the
Simon’s Town court on Friday, 16 April 2004. Although the accused sought a
postponement of three months, the case was remanded to 21 May 2004 for further
particulars. The Magistrate was firm in warning the accused that he would not receive a
further postponement. In the other instances where summonses have been issued, the
landowners are also due to appear in court in the course of May.
The
prosecutions are likely to generate public debate. It
will be necessary to emphasise the very real ecological problems created by invasive
plants, such as seed pollution, wildfire, impacts on biological diversity, erosion and
water security and to publicly reaffirm the commitment of government to dealing
effectively with the problems created by invasive plants. Failure to address infestations
inevitably leads to far greater costs in the future, as the plants spread and grow.
Prosecution of negligent landowners is therefore in the public interest.
Contact Ukuvuka. Tel: (021) 762 7474. Email: info@ukuvuka.org.za
Greenkeeper of
the year award environmental aspects
Golf Matrix
has announced its sponsorship of an annual award to the Greenkeeper of the Year. An award
of this nature is long overdue in South Africa. John Deere will award the winning
greenkeeper with an overseas educational trip to the value of R 30 000. Three commendation
awards will also be made. Site visits to top entrants will be carried out by a member of
the judging panel and a member of the local Greenkeeper’s Association, and finalists
will be required to make a presentation to the panel.
One of the
most important roles played by today’s greenkeeper is environmental stewardship and
one of the categories which will be evaluated for the Award is the greenkeeper’s
knowledge of and planning for environmental complexities which could impact on the golf
course. The Audubon award, which is made to greenkeepers in the USA for their
environmental stewardship abilities, looks at a number of environmental criteria along the
lines of the list below.
•
Water conservation:
use of effluent; a weather station to control the irrigation system; an appropriate
irrigation system; and the type of grass used (drought resistant or less water
consumptive).
•
Integrated Pest
Management: use of environmentally sound pesticides and limiting pesticide use to curative
spraying to lessen impact on water and soils.
•
Appropriate fertiliser
programme designed to maintain turf health but to have least impact; the use of organic
fertilisers.
•
Habitat creation: the
conservation of and provision of appropriate habitats to encourage wildlife; the
conservation of a rare faunal species.
•
Planting of
appropriate largely locally indigenous vegetation to encourage wildlife; botanical
conservation, particularly if unusual/uncommon plants occur in the wild areas of the
course.
•
Wetland conservation
or creation – conserve and improve natural wetland areas for both water filtration
and wildlife habitat.
•
Programme to eradicate
and control invasive plant species.
•
Composting to reduce
and re-use clippings and other biodegradable waste.
•
Oil disposal and
recycling.
•
Storage of pesticides.
•
Environmental
Management System in place.
•
Environmental vision,
strategy, policy of the club.
For further
details about entry requirements contact Rowan Garmany of Golf Matrix. Tel: (011) 397
7445/6/7. Email:rowan@golfmatrix.co.za
Centre for
sustainability in mining and industry
Wits School
of Mining Engineering, BHP Billiton, Lonmin and AngloGold have formed a partnership to
establish the Centre for Sustainability in Mining and Industry. Initial pledges by mining
companies of funding of R900 000 per annum for five years has allowed this initiative to
proceed.
According to
the Director of the proposed Centre for Sustainability in Mining and Industry, Dr Daniel
Limpitlaw, the Centre will aspire to gain recognition as a centre of excellence and as a
global leader in the provision of education and training in the field of Safety, Health,
Environment and Community Studies (SHEC). Provision of short courses will involve
academics from across a variety of disciplines at Wits, other South African Institutions
and some of the best academics and practioners globally.
The concept
of the centre results from the recommendations of the Global Mining Initiative and the
Mining, Minerals and Sustainable Development (MMSD) project, which stressed the importance
of sustainable development in the mining industry.
“Mining
companies have a responsibility to manage the impacts of their activities. This is also in
the companies’ interests, as it assists in the management of their risk profile.
Mining activities can impact on the health and safety of employees, on the present and
future well-being of the communities within which mines operate, as well as on the
environment. Sustainability is not only of concern to the mining industry, but also to a
range of industrial sectors,” commented Daniel Limpitlaw.
Contact Prof
Huw Phillips, Head of Wits Mining. Tel: (011) 717-7403. Email:
sustainability@egoli.min.wits.ac.za
Safeguarding the
future of wildlife in UK forest
Being one of
the most innovative country parks, the Kielder Forest has always been greatly regarded.
Managed largely for timber, the estate also prides itself on the provision of many
conservation and recreational benefits. Now, its enterprise has been highlighted by being
the winner of the first conservation award given by the Northumberland Wildlife Trust in
northern England. A pre-emptive approach to tackling conservation issues has both ensured
the future of red squirrels and restored a number of peat marshes to their former glory.
UK energy company power sponsored the awards that placed the government agency at the top
of the business category.
Forest
Enterprise has supervised the installation of 10,000 dams to raise water tables, clearing
some spruce and conifer crop regeneration along the way. Realising the importance and
value of wildlife, Kielder has been working closely with Tyneside-based Newcastle
University and other partners to help increase the red squirrels within the forest.With a
computer model devised by the university, experts have been able to take a closer look at
the habitat requirements of this colourful creature.
It is
thought that grey squirrels have been largely responsible for falling numbers of the red
variety since their introduction from North America more than a century ago. Moving across
the forest from north and south, grey squirrels are capable of passing on the fatal
parapox virus to their red counterpart. Listed as a priority species by the government,
every effort is being made to protect the UK’s red squirrel heritage. Being home to
12 000 red squirrels, the commitment to amend forest blueprints across Keilder has been
welcomed by conservation agencies and scientists across the globe.
Conservationists
believe the scale of the Kielder scheme in drawing together scientists and land managers
over such a large area is unique. Rolling hills, vast open areas and rivers add diversity
to the forest that, at 595 square kilometres, is the largest in England.
Website: www.wildlifetrusts.org Email: kielder.partnership@tynedale.gov.uk
WasteArt 2004
Enviroserv
is showcasing the work of top South African artists in the inaugural EnviroServ WasteArt 2004 Expo which will be held from 23-27 June at
Nelson Mandela Square (previously Sandton Square), in Sandton. This five day art event
will comprise the work of artisans and crafters exhibiting their wares made from re-cycled
waste materials and the works of 13 of our top artists including: Walter Oltmann, Richman
Buthelezi, Retief van Wyk, Jan van der Merwe, Carla Wasserthal, Wilma Cruise, Antoinette
Murdoch, Dianne Victor, Gordon Froud, Bongi Dlomo, Patrick Mautloa, Fiona Kirkwood and
Stephen Maqashela. These unique pieces made from waste by the famous South African artists
will be auctioned and the proceeds will be placed into a Trust Fund to assist in
developing emerging artists in South Africa.
Website:
www.wasteart.com
Global carbon market: trade fair and conference
This
world-first event, devoted to the currently much discussed topic of emissions trading and
the emerging CO2 market, took place in Cologne, Germany, in the second week of June 2004.
The event was intended to promote transparency in its role as an information forum and to
provide a platform for the exchange of information among market leaders, service providers
and buyers, sellers and intermediate traders of emissions rights. Technology for reducing
emissions was on display.
The aim of
emissions trading throughout the EU is to meet the industrial nations’ obligation to
make a significant reduction in emissions of greenhouse gases by 2012, in accordance with
the Kyoto Protocol agreement concerning climate change. The system provides for the
assignment of emission allowances which can be traded between the companies involved. The
system also enables the companies to receive certificates for projects aimed at reducing
emissions in developing countries. Point Carbon, The world’s leading independent
provider of analyses, news, market information and prognoses for the CO2 market, estimates
that as early as 2005 the annual trade volume of emission rights and certificates will
amount to ±10 billion euros.
Website: www.carbonexpo.com
-----
IDENTIFYING INVADERS
The Mexican Poppy and the Pearl Acacia
UGF’s
regular column to help with the identification of invasive alien species and their
control.
Argemone
ochroleuca
The
White-flowered Mexican Poppy is a very spiny, grey-leaved, robust, herbaceous annual with
creamy-white, poppy-like flowers, which is classed as a Category 1 weed in South Africa,
where it is widely distributed, meaning that regulations require it to be eradicated. Very
similar in appearance – except that it has bright yellow flowers and green leaves
– and also a Category 1 weed is Argemone mexicana, the Yellow-flowered Mexican Poppy,
which is largely found in KZN, the Mpumalanga lowveld and Limpopo.
Both these
plants are South and Central American in origin and in South Africa they invade disturbed
land, riverbanks and riverbeds, where they are competitive. They proliferate along
roadsides and in abandoned lands forming dense stands but also grow in cultivated lands.
They are both poisonous and an irritant to the skin. According to the Briza Publication
‘Poisonous Plants of South Africa’, Argemone seeds are known to have caused
human fatalities in the north-western parts of the Cape as a result of wheat
contamination. The plant’s bright yellow sap has narcotic properties. The seeds
contaminate sheep’s wool.
The peak of
their flowering season lasts for five months from September to January but very often they
produce flowers throughout the year. Their spiny capsules dry out, split and release a
multitude of small black seeds which spread far and wide.
There are
post-emergent foliar herbicides registered for the control of the Mexican poppies, which
are more effective when the plants are small, but shallow digging over of the soil can
also be temporarily effective.
Acacia podalyriifolia
Commonly called the Pearl Acacia, this small evergreen tree is listed as a
Category 3 invader in South Africa. It is Australian in origin and invades disturbed areas
such as roadsides and urban open space, and water courses: its invasive status being that
of a potential transformer, meaning that it has the potential to replace a natural
vegetation layer but is not yet having a marked effect. It seeds and establishes easily
and is common in the large urban metropoles of Johannesburg, Durban and Cape Town –
being most abundant in KZN. As a Category 3 invader, regulations require that the species
is no longer grown, planted or sold but if it is already in existence as a mature tree, it
need not be removed but must be controlled.
It has been
cultivated for ornamental purposes in South Africa, as it makes a very showy display in
gardens and it provides a nectar source for the honey industry. The silvery grey foliage
with its oval-shaped leaves is much favoured by the cut-flower industry and is a lovely
contrast to the bright yellow sprays of puff-ball flowers. The only method of control, as
yet, is by pulling out saplings by hand and strip-barking mature specimens.
-----
BOOK REVIEW
Figs of southern and south-central
Africa
Authors:
John and Sandra Burrows
Photographer:
John Burrows
Pen-and-ink
illustrations: Sandra Burrows
In his
forward to this exceptional book, Professor Braam van Wyk of the Department of Botany at
the University of Pretoria says that the book “…embodies both in words and
pictures all the lofty attributes associated with great scholarship”. Yet it is a
book for both layman and scholar, providing insight into the many and varied attributes of
this vitally important group of trees in Africa.
It is the
extensive experience in the field that makes this book so special: the authors travelled
70 000 km, at their own expense, to find the figs in their natural habitats – they
followed their dictum of not writing about a plant without first seeing it growing in the
wild. The depth that this has brought to their study, particularly in the details of
ecological aspects, insight into problems with nomenclature and wonderful clear habitat
photographs and line drawings, could not have been achieved without these long and often
difficult journeys, undertaken over a ten year period. As the science of botany grows in
importance in this age of growing environmental awareness, so the realisation of the need
to move away from the dried herbarium specimen and into the field increases.
Prof van Wyk
adds that this is “…a book that will foster an awareness of nature and the need
to conserve it…”, while the authors impress on the reader the vital need to
value diversity in the words: “the one resource that is the raw material for
evolution and man’s continued existence on earth is diversity”, and thereby
justify their inclination to move away from “lumping plants together” under a
species ‘complex’. They are of the opinion that “the best way to accentuate
diversity is to maintain a broad range of species, even when they may be closely related
to one another”.
They
emphasise the importance of this in relation to an Environmental Impact Assessment
exercise where, for example, a group of figs that may disappear under the property
developer’s bulldozer is being evaluated under the large Ficus thonningii complex.
Labelling them as Ficus thonningii which is extremely widespread may mean that the loss of
a few trees could be justified. This could, however, result in missing the rarity and
restricted habitat of the particular fig that is being evaluated. The authors have
“…upheld species rather than lost them to a sweeping lumping exercise”.
In his
specialist chapter on ‘Growing Figs’, horticultural consultant Geoff Nichols
says: “this genus of trees is probably the most productive of all our tree genera for
the requirements of wildlife”, while another specialist contributor Duncan Butchart,
in his chapter on ‘Figs, Birds and other Wildlife’ says: “…there is
such a host of creatures – from bats and butterflies to hornbills and duikers –
that interact with figs, that the trees can truly be regarded as ecosystems in their own
right”. The third specialist chapter deals with the fascinating relationship, one of
obligate mutualism (neither can survive without the other), between figs and the fig wasps
that are their specific pollinators.
The
hardiness, large size and longevity of many fig species (Van Wyk feels they radiate a
sense of immortality) is another aspect that makes them special and these characteristics
relate to their choice of a highly suitable habitat. Figs known as rock-splitters start
life in a rock crack, sending roots down the crack or over the rock surface until they
reach soil level. Growing on rocks or cliffs protects the fig from fire and frost, and
there is good soil moisture from runoff trapped at the base of rocks. Terrestrial figs
that germinate in the soil, in the manner of most flowering plants, are often fire
resistant. Stranglers start life when a seed is deposited in the crotch of a tree by a
bird or bat. The roots extend down the host tree until they reach the soil and the
expanding network of roots can over time kill the host plant. The fig is left as a
free-standing tree, its trunk a cylinder of roots. The forest strangler fig has the
advantage of being situated high up in the canopy from the start of its life, where it is
able to access adequate light to compete well with other species, can easily present its
fruit to seed dispersers and is out of the reach of browsing animals.
The book
describes the value to man of each fig species. Every part of Ficus sycamorus, for
example, has economic value to the local tribes – the wood, the bark, the latex which
is used as bird lime, the fruit which is eaten fresh or dried and used to make brandy, and
the leaves which are cooked as a vegetable. Bark cloth is made from Ficus natalensis. An
extraordinarily large specimen of Ficus ingens was used as a shelter from the lions that
used to prowl the area near Rustenberg – in 1829, the records say that 17 huts were
built in the spreading branches of what is called ‘The Inhabited Tree’.
The book
also deals with some exotic figs and other species in the fig family, aside from the genus
Ficus, and it is interesting to note that the exotic White Mulberry, Morus alba, which is
a declared Category 3 invader in South Africa, under the regulations of the Conservation
of Agricultural Resources Act, is described in some detail – particularly concerning
its important economic value as the host plant of the silkworm in the production of silk.
The authors say that it appears that the Indian White Mulberry variety, Morus alba var
indica, is the serious pest of river banks in the summer rainfall regions of South Africa.
With its value to sericulture, it seems strange that Morus alba has not been declared a
Category 2 invader.
Contact Alex Fick at Umdaus Press. Tel: (011) 880 0273.Fax: (011) 788 1498. Email: afick@iafrica.com
Red Data Book of
the Mammals of South Africa
The
Endangered Wildlife Trust (EWT), the Conservation Breeding Specialist Group of the
IUCN’s Species Survival Commission, the Vodacom Foundation and over 30 other
participating organisations have published the ‘Red Data Book of the Mammals of South
Africa: A Conservation Assessment’. At the launch Dr John Ledger, immediate past
president of the EWT, commented that the book was the finest national red data book
produced anywhere in the world. He said that this new book represented a quantum leap
forward in SA’s efforts to conserve its mammalian biodiversity and to meet its
obligations in terms of the Convention on Biological Diversity.
IUCN Red
Data Books were initiated by Sir Peter Scott in 1963, as a means of documenting and
highlighting biodiversity losses at species level, and have since become important tools
globally for guiding the conservation activities of governments and conservation
organisations.
The book
covers 295 terrestrial and marine species and subspecies of mammals, which have been
assessed within SA’s borders, excluding Swaziland and Lesotho. GIS-based distribution
maps are included for all the terrestrial species. It also makes recommendations for
strategic conservation and management of threatened species and their habitats.
Ten
‘critically endangered’ mammals which have the highest risk of extinction have
been identified in South Africa, including the Black Rhinoceros – arid ecotype, five
Golden Mole species and the Riverine Rabbit. Seven of these ten critically endangered
mammals are endemic (found nowhere else in the world). There are 18 ‘endangered’
mammals, 33 of which are endemic to SA, and these include the African Wild Dog, the Indian
Ocean Bottlenose Dolphin (migratory subpopulation), Hartmann’s Mountain Zebra, the
Oribi, three more Golden Mole species and the Southern Elephant Seal. Amongst those
considered to be ‘vulnerable’ are the Cheetah, the Lion, the Black Rhinocerous,
the Cape Mountain Zebra, the Bontebok, the Pangolin, the Sperm Whale and Roan and Sable
Antelope. The South African Hedgehog and the Brown Hyena are ‘near threatened’
species, while there are 53 species that are ‘data deficient’.
Primary
threats which are impacting negatively on many mammals include habitat loss and land
transformation through deforestation, agriculture, timber planting and urban and
industrial development. Poisoning, pollution and hunting have also been listed as
potential impacts. The book includes a Gap Analysis of species which occur within
SA’s Protected Areas and those which do not occur at all within these areas. All
SA’s mammals have been reviewed in order for these assessments to serve as a useful
indicator of biodiversity trends.
The book is available free of charge on CD from the Endangered Wildlife Trust.
Contact Yolan Friedmann of EWT and CBSG. Tel: (011) 486 1102. Cell: 082 990 3534. Email:
cbsgsa@wol.co.za
-----
TREE OF THE ISSUE
The Pigeonwood
Wilna Stones
has worked for Polokwane Municipality for eight years, where she is employed as a senior
horticulturist in the Business Unit: Environmental and Waste Management. She has chosen
Trema orientalis from a single experience that she has had with the tree growing on what
is known loosely as the city square in Polokwane in Limpopo province. She feels that this
tree which is not commonly utilised horticulturally has a great deal of potential and
needs to be highlighted. She is planning to start growing it in the municipal nursery.
Wilna chose
the Pigeonwood because it is a particularly beautiful tree and a fast grower – its
function in its natural habitat is as a pioneer on forest margins, and riverbanks in the
bushveld. A couple of the tree books call it one of the fastest growing of South
Africa’s indigenous species and it germinates easily from seed. Wilna feels that it
will work well to plant it in conjunction with slower growing species, as the Pigeonwood
will grow large quickly (it reaches about 15m in height) and give protection to the more
tardy growers that will come into their own more slowly.
She likes
the fact that it is single-stemmed and has a smooth, whitish trunk. She visualises a
grouping providing a striking effect with the light-coloured, tall, straight stems in a
parkland area. The shade that it provides is not too dense and this means that plants such
as Dietes and Clivia do well under its canopy. She also loves its deciduous nature because
this makes the seasonal changes more evident. It attracts birds and butterflies:
“There are always birds around the tree on the city square in Polokwane,” she
comments. It is, in her opinion, an ideal tree for parks and city squares.
The natural
distribution of Trema orientalis in South Africa is along the KZN coast, through Swaziland
and up into the bushveld areas of Mpumalanga and Limpopo provinces. Its shiny green,
three-veined leaves are similar in appearance to those of Celtis africana, except that the
Pigeonwood’s leaves have serrations along their entire margin. It serves as a larval
host plant to two of the Charaxes butterflies. Its bunches of small black berries also
attract fruit bats.
According to
Piet van Wyk’s ‘The Trees of the Kruger National Park’, Trema orientalis
prefers deep, well-drained, slightly acid soil and moist conditions. It grows in warmer
areas and is frost sensitive.
-----
Simple
refurbishment of a collection of buildings and open spaces
44
Stanley Avenue - no fancy stuff
Following an
intense clean up but with minimal further intervention in terms of refurbishment, the
collection of buildings and open spaces that constitute 44 Stanley Avenue in Milpark,
Johannesburg, have been transformed into a successful retail and commercial node. Its
honesty, simplicity and human scale are among the qualities that make it so attractive.
As Brian
Green, the man who made this transformation happen, says: “There’s no fancy
stuff…no glamour…nothing neo…” in this upgraded cluster of buildings.
“There’s nothing here that’s not needed. We debated the water reservoirs,
but without them the place would have been rather harsh.” He describes 44 Stanley
Avenue as “accommodating, inclusive, comfortable”.
As a
cameraman, Green has an eye for beautiful places and spaces. As an entrepreneur, he
recognised the potential of the site. Driving past it daily from his offices at the
neighbouring Media Mill, he liked what he saw – a loose collection of low-key
buildings and outdoor spaces, pedestrian bridges and stairways linking them – even
though at that time the site was derelict and barricaded. A property of about 8 000m2,
with more than 4 000m2 under roof, just abandoned.
He first
gained access to the site about two and half years ago, after putting a proposal to the
owners, Old Mutual Properties, that it could be restored and adapted to new use for a
fresh mix of quirky tenants that Green himself undertook to sign up. For its part, Old
Mutual Properties agreed to cover the minimum costs of a restoration to safe
functionality, and to sell the property to Green and his business partner, Mark Bachelor
from Sedgeley Developments, for a nominal sum. The restoration and sale of the property
were contingent on Green securing a threshold tenancy of 1 000m2, about a
quarter of the total lettable area.
Green
commends Old Mutual Properties for their willingness to consider an out-of-the-blue,
unconventional proposal. This is not common practice for major property owners and
developers. Through negotiation, the parties were able to find a meeting ground between
entrepreneurial enthusiasm and corporate convention, which opened the way for the renewal
of 44 Stanley Avenue.
From
Green’s perspective, the tenant mix was crucial. “You’ve got to have the
right people and the right products. I sought out entrepreneurial start-ups, individually
owned enterprises, people who are passionate about what they do. The restaurant
overlooking the main courtyard was critical in terms of tenancy; it’s key to the
vitality and the pace of the place.” Before refurbishment began in May 2003, Green
had booked tenants for more than 2 000m2.
The cleaning
of the buildings was the first major undertaking. Roofs were repaired and re-waterproofed;
walls were resealed and newly painted only where necessary – drawing from the
original palette of colours in evidence on the buildings; services were restored to
working order; stairways and bridges were checked for safety and stability. Beyond that,
the interventions have been minimal. All the built structure has been retained virtually
unchanged, with some additions to extend existing spaces.
Green says
that they did consult an architect initially to look at the upgrade but this route was
abandoned when it started to feel too fussy and formal. “We wanted to keep the loose
grain and comfortable informality of the relationships between the buildings and the open
spaces.”
By August
2003, the first tenant had moved in and others opened for business as refurbishment
progressed. This overlap (and the general chaos one might imagine accompanied it) spawned
an interactive process involving the tenants also in decisions on things like shading and
signage and other details.
Abutting the
street edge along its northern boundary, 44 Stanley Avenue presents itself as a row of
single and double-storey buildings with three access routes leading into the site –
at the eastern edge, a driveway that accesses on-site undercover parking for tenants;
towards the western edge a service lane closed by steel gates; and, centrally, a
pedestrian thoroughfare which leads into the main courtyard.
The sunlight
in the courtyard and the sight of people seated on the raised verandah of the restaurant
overlooking it, draw one in from the street, through the covered walkway. Shops of
differing scale and nature surround this courtyard. At the southeast corner, another wide,
open walkway leads to other outlets and on to the parking garage. Steel stairways lead up
to office suites in the three-storey building that forms the southern edge to the site.
From the main courtyard, a covered thoroughfare leads westward between buildings to a
secondary courtyard – more small shops, a craft studio for children, restaurants, a
bar, and a small office building.
Two
pétanque courts have been newly built in the western courtyard. Concrete reservoirs in
each courtyard introduce water. Olive trees (Olea europaea subsp. africana) and Wild
Irises (Dietes grandiflora) establish a restrained consistency of planting, with aloes in
giant concrete pots and leopard trees along the southern walkway.
Green says
that there are still some corners that need attention. Space has been taken up by 28
tenants and a maximum of 32 can be accommodated. He knows what he wants to add to the mix
that has already made 44 Stanley Avenue ‘a destination’ in retail-speak.
For Green,
the measure of the precinct’s success can be counted in the number of people crossing
the central courtyard at any time – it’s an interactive space, a meeting place,
and the looseness of the buildings around it makes for different approaches and exit
angles – the space is dynamic.
Neighbourhood renewal
One of the most positive aspects of this renewal on Stanley Avenue is its
location. Green sees it as a stepping-stone to the CBD and points out that renewal is now
happening in a broad swathe more or less aligned along Empire Road, from Constitution Hill
westward. In his view, people are pulling back from the northern suburbs towards the city
again.
Other
renewal and reuse projects in Milpark confirm this. Some years ago, the first
refurbishment and conversion of old and mostly derelict buildings to new use in the area
established the Media Mill – now home to the Mail & Guardian, amongst an eclectic
mix of tenants. More recently, the same architects cum developers who were responsible for
that project, Jonathan and Lorien Gimpel, turned their attention to the old Atlas Bakery
on the corner of Frost and Owl Streets nearby. This building, now Atlas Studios, has been
refurbished and adapted to house film production studios and associated production
services and facilities.
In addition,
The Refinery, a former industrial building that occupies the corner of Owl and Stanley
Streets and is wedged between the Media Mill and 44 Stanley Avenue, is being refurbished
and converted to residential use by entrepreneurial developer Ricci Polack.
Green says
these later projects have all happened at around the same time, though not in any planned
way. “None of us are property developers in the formal business sense,” he says,
“but more in a social sense, with a view to creating places where people want to
be.” He adds that the synergy of the Media Mill, Atlas Studios, The Refinery, and 44
Stanley Avenue is now impacting on the neighbourhood and is motivating further upgrading.
For Green,
the next project is in the city centre itself. He’s already identified the site and
determined new uses for the building that are in line with what he believes the city needs
and the kind of places people want.
Report by
Leigh Darroll
-----
Freedom
Park: a landscape narrative of South Africa’s history and heritage
A dedicated
heritage precinct on a site of significant ecological value in Pretoria
Freedom Park
is an ambitious project that will see the development of a dedicated heritage precinct on
the Salvokop hill outside Pretoria. Intended as a centre of knowledge it aims to create a
deeper understanding of South Africa and all its people through the narration of the
country’s pre-colonial, colonial, apartheid and post-apartheid history. It will
retell South Africa’s story, to dispel the many myths and prejudices that have
concealed its true history and distorted the richness of its cultural heritage.
Beyond
acknowledging the past, Freedom Park will celebrate the achievement of democracy and stand
as a beacon of hope for the future. It is envisaged to become a place of pilgrimage,
renewal and inspiration for South Africans and all humanity.
Freedom Park
is a cabinet-approved Legacy Project and the Freedom Park Trust, set up to manage the
project, is led by Dr Mongane Wally Serote. Former president Nelson Mandela is the
patron-in-chief of the Trust. The first phase of the project was formally handed over to
President Thabo Mbeki in March 2004.
The site
Freedom Park is located on Salvokop, a 52 ha site immediately south of
Pretoria. The koppie is situated at the interface between urban areas to its north and
natural areas to its south.
The hill was
chosen for its symbolic historical and cultural significance. The location of Freedom Park
in view of the Voortrekker Monument, which lies to the southwest, was intentional –
to juxtapose that history with the processes of moving forward as a united nation. The
crest of Salvokop also offers open views to Church Square, the Union Buildings, the
neighbouring hills of Klapperkop and Skanskop, and locally to Salvokop Village which lies
at its northern base. These view lines function as important connectors to the past and
the future and have been emphasised in the development framework.
Documentation
issued by the Freedom Park Trust highlights the significance of high ground, rock, hills
and mountains in African culture. “Essentially, the rock is our home… in the
mountains African people listened to the voice of silence. Mountains and hills served as a
seat of governance for many of the royal kraals. Mountains were considered sacred by some
groups who used to go there to pray for rain, or to bury kings in the caves…
believing that the ancestors reside there… a step to the heavens and to our
humanity.”
The development
framework – a landscape response
Newtown Landscape Architects (NLA) became involved in the project early in 2002
when the Freedom Park Trust appointed the firm on the basis of its response to an
invitation for landscape proposals for the site.
A
development framework had already been prepared for the site by a consortium of architects
and urban designers, involving GAPP, MMA and Mashabane Rose. Landscape architect Graham
Young of NLA says that their first task was to review the existing framework and, on the
basis of a preliminary ecological survey of the site, they put forward a landscape
development concept which proposed a revised approach to the development.
The
ecological survey recognised Salvokop – a natural quartzite ridge – as a site of
significant ecological value, a fact which was confirmed, with greater detail, by the
later Environ¬mental Impact Assessment. It is characterised by thickly wooded savannah on
its northern and eastern slopes, giving way to high¬veld grassland on its southern
slopes, where there is also a small forest of Protea caffra.
From this
survey, the landscape architects identified the more and less ecologically sensitive zones
of the site, and so defined those areas where development should be excluded or limited,
and others, less sensitive or already disturbed, where built impacts could be better
accommodated.
A
consequence of this review was that the proposed conference centre, parking area,
administrative and information buildings, were moved from the southeast to the north of
the hill. Here there is also a more direct interface with the urban edge of the site, and
the more natural aspect of the southern slopes – looking out to the bowl of valleys
and hills south of Pretoria – is retained.
Importantly
too, the integrity of the natural profile of the hill is retained. Young points out that
this is in line with the City of Tshwane’s framework, which identifies the ridges
surrounding Pretoria as natural gateways into the city, (as it is with the provincial
policy on protecting ridges – see UGF Sep/Oct 2002).
The
principal elements of Freedom Park include a Garden of Remembrance, a museum, and a
memorial and gathering place. The Landscape Development Concept locates these elements in
response to the sensitivities of the site.
From this
concept, a masterplan was prepared, with the first phase of development programmed to
include the parking area, an information centre, the upgrading of the service ring road at
the base of the hill, and the isivivane – the first of a series of planned
contemplative places in the Garden of Remembrance.
The Garden of
Remembrance
The entire site – a natural indigenous garden – constitutes the
Garden of Remembrance. It is intended to become “a national symbol for reparation, a
symbol of healing, a symbol of clean¬sing, a place where the spirits of those who lost
their lives for freedom can rest.”
The
conceptual design for the Garden evolved as an iterative process between the design team
– including the landscape architects and architects – and an advisory panel
established by Freedom Park Trust. The panel included traditional healers, artists and
academics specialising in African culture and indigenous knowledge systems, who provided
information and guidance on cultural matters.
In addition,
the Trust arranged consultative workshops with a broad spectrum of stakeholders. At the
workshops, the concept was presented and explained and feedback obtained from the
stakeholder groups, drawn from across the country and representing youth, women,
traditional leaders, labour, creative artists, veterans, the disabled, the Afrikaanse
Kultuur & Taal Vereeniging, and various religious organisations. Young says that the
Trust has consistently emphasised that the process of developing the concept is as
important as the end result.
The Garden
of Remembrance creates the context in which the various elements will be built and
anticipates further development in the future, as South Africa’s story unfolds.
Anchoring
the Garden of Remembrance will be a spiral pathway, with contemplative spaces along it.
The pathway is seen as a connector along which a symbolic narrative can be expressed and
played out. It will wind up the hill from a position near the proposed administrative
buildings, which will be located on the north side of the hill in line with the extension
of Paul Kruger Street. This main access point to the site will ultimately connect, via
pedestrian routes, to Pretoria Station and the proposed Gautrain Station. (It is worth
noting that a lower alignment than was initially proposed has been adopted for the
Gautrain route where it is to tunnel beneath Salvokop and measures will be taken to
diminish the visual impact of the tunnel at the base of the Freedom Park site.)
After much
debate between the design team and the advisory panel, it was agreed that the pathway,
originally planned to move up the hill in a westerly direction, would be routed in an
easterly direction. East is significant because it is here that the sun rises, marking the
beginning of a new day and, metaphorically, new beginnings in the history of South Africa.
Along a
stretch of the pathway, as it curves up the eastern slope through quite dense bush, it is
envisaged that smoke will be created, evoking a sense of mystery and a reminder of
difficult combative times during the past. However, smoke also signifies the beginnings of
spiritual healing – smoke being indicative of the impepho or incense that is often
burned in traditional or religious ceremonies to signify a holy place and to represent
spiritual cleansing.
Leaving the
wooded area, the visitor will enter a small opening defined by two parallel quartzite
ridgelines. Here the landscape is characterised by natural rock outcrops, stunted
vegetation and fascinating endemic plants. An intimate contemplative space is planned in
this sensitive environment, with a focus of a small ‘shrine’ that will
incorporate a place for burning incense. In the African tradition and on special
occasions, traditional beer – umqombothi – would be drunk here.
Following
the contours, the pathway reaches the isivivane – which has been built on the
southeast slope of the hill. In this location, the isivivane will see the rising sun
through all the seasons of the year.
Isivivane
The isivivane is a sanctuary, “a final resting place for all the people
who fell in the fight for freedom in the eight conflict events that have shaped South
Africa.” These conflicts are defined by the Trust to include: the Pre-colonial Wars;
Colonial Wars; Genocide; Slavery; the Wars of Resistance; the South African War
(Anglo-Boer War); the First and Second World Wars and their impact on South Africa; and
the Struggle for Liberation.
Isivivane
roughly means ‘cairn of stones’, but its deeper meaning translates as
‘monument, memorial, testimonial…fervour, concentration of energy, commitment to
solidarity and oneness of purpose’. These different meanings, as well as other
significant cues and pointers, became apparent through the process of discussion and
consultation on the initial landscape concept and contributed profoundly to its present
resolution.
This
contemplative space has been designed primarily with deference to African symbolism and
belief systems, but also, intentionally, contains universally recognisable symbols of hope
and unity. During the design process, it was agreed that symbolism should not be
translated literally but rather that the imagery should be abstract, simple and devoid of
clutter. If this could be achieved, it was felt that the ensuing aesthetic would be
powerful and evoke strong emotions and a sense of the reverence of the place. Stone, water
and carefully chosen plant materials formed the basic design elements.
African
cosmology gives special significance to stones, boulders and rocks. They represent
mountains and caves, the significance of which has already been noted. According to Credo
Mutwa, “the stones and bones of the earth and some of the mountains are identified as
places where the gods reside. Because they are ancient and timeless, because they have
long been here before us, they carry sacred networks of information.”
The
fundamental layout of the isivivane is derived from an African homestead which
traditionally encompasses the lesaka (burial place) and the kgotla (meeting place).
A wide flat
terrace has been created in the slope of the hill. It is supported by a retaining wall of
packed stone which is reminiscent of the ancient structures at Mapungubwe, Thulamela and
even Great Zimbabwe.
The Freedom
Park Trust describes the lesaka as a circular structure, commonly found in southern
African villages, where generation upon generation are buried. It is a place where the
spirits can come home to rest, a place of the ancestors, and of the cattle who are
mystically linked to the ancestors.
At Freedom
Park, the lesaka is transcribed as a flat circle of stone, edged with brushed concrete.
Around this circle, eleven boulders have been placed; nine of these were selected and
sanctified by each of the provinces and transported to the site – some with soil from
their home ground which was laid beneath them before they were cast into position; the two
larger boulders represent the national and local governments. The story of each of these
boulders is to be conveyed to visitors, although the best means of doing this is yet to be
decided. It is interesting to note that the landscape architects prepared a maquette, to
scale, of the lesaka and each of the boulders, in order to determine the best balanced
positioning for them before they were placed on site by a crane. Contained within the
circle, are stones from countries outside South Africa, symbolic of the exiles who fell
while they sought refuge abroad.
The circular
form is all-important. It is symbolic of unity, equality and wholeness, and it sets up a
dialogue among the boulders placed around it, all at the same level.
A fine water
spray has been designed into the lesaka so that at intervals mist rises up to billow and
drift across it. This ‘smoke’ or impepho emphasises the sanctity of the place
and is again representative of the healing process central to helping the South African
nation recover from its past.
Near the
lesaka, also on the terrace, a lone Acacia galpinii has been planted within the embrace of
a semi-circular concrete bench. This Mologa, or Monkey Thorn, signifies the kgotla. This
tree has its own presence and, in effect, holds the space beneath it. It will provide
dense shade and a place of shelter for visitors who wish to rest and reflect on the
meaning of the isivivane. The kgotla is oriented with a beautiful view across the lesaka
to the valleys and hills south of the site.
Nine Buffalo
Thorn trees (Ziziphus mucronata – Umphafa) have been planted to form, when they are
fully-grown, a green backdrop to the isivivane. The choice of this tree was inspired by
the special reverence in which it is held by the Nguni people. In earlier times, when a
person died far from home (often in battle), the elders of the family would send a party
to ‘fetch the spirit’ of that person and the party would carry a branch from the
umphafa tree. At the place where the person had died, they would call out his name and
announce that they had come to take his spirit home. Similarly, it is said that if another
was with the person when he died, he should carry a branch of the umphafa home from that
place, to take the spirit of the dead person home to rest.
One of the
interpretations of isivivane is that of ‘paying homage to the hospitality of
place’. This relates to a cairn of stones that might be found alongside a footpath
near a village in the countryside. When African people passed a village but could not go
into it, they indicated that they had passed the place by picking up a stone, breathing on
it, then placing it on the heap of stones. This accumulated mound of stones, called
isivivane, was believed to bring good luck to travellers paying homage to the landscape
and all that it contained. An abstraction of this idea is contained in the sloping
packed-stone wall that has been formed between the terrace and the pathway that runs
behind it.
To build on
the significance of rock and water in African healing, a waterfall has been designed into
the packed-stone wall that frames the terrace. Water flows over a trough, down the stone
wall, and into a shallow pool, to remind the visitor that in this place “the spirit
flows and cleanses like water”.
On the way
out from the isivivane, a small ‘spring’ of water bubbles into a bowl carved
into the top of a large boulder placed near the exit. Here visitors can wash their hands
in respect of the place, after paying homage to the spirits of those who rest here.
It is hoped
that the isivivane, as the first built component of the Garden of Remembrance, will inform
the others that follow, in particular in the simplicity and symbolism of its design and in
the restrained choice of materials.
Phase 2
Work on the second phase of Freedom Park, for which a proposal call has been
issued, is expected to begin soon and is planned for completion in early 2008. The main
components of this phase of development are the museum, memorial, an amphitheatre, a
moshate, or presidential guesthouse, and the administrative offices. One of the key
challenges will be to achieve the EIA recommendation that the overall development should
not impose a footprint covering more than 5% of the site.
Salvokop Village
At present, the approach roads to the site through Salvokop Village are being
upgraded. A redevelopment framework for the village has been approved by Propnet (as
owners of the former railway housing), City of Tshwane and the Freedom Park Trust. GAPP
and MMA in association, Newtown Landscape
Architects,
Africon in association with Nkambule and Associates, and Cultmatrix, are also involved in
this project. Karel Bakker of Cultmatrix is the guardian of the heritage aspects of the
project and, while it seems likely that there will be a significant change in the nature
of the village, care is being given to retaining the historical buildings. (See UGF Sep/Oct 2003).
-----
Woodlands to contain pollution in
goldfields
An
intensive research programme into the value of indigenous plants on and around slimes dams
In
recognition of the significant impact of the gold mining industry on the environment,
AngloGold Ashanti Ltd, Harmony (previously Freegold) and Avgold are collaborating with the
University of the Witwatersrand in an intensive research and development programme.
Programme
leader Isabel Weiersbye of the School of Animal, Plant and Environmental Sciences at Wits
took Carol Knoll on an extensive guided tour of a number of slimes dams in the Welkom,
Orkney and Carltonville areas, on and around which sustainable vegetation trials are
underway. The gold mining industry produces more waste than most other industries combined
– 200 000 tonnes of waste is produced for every tonne of gold that is extracted. In
terms of South Africa’s environmental protection and mining legislation, the polluter
must pay for rehabilitation. Very little is known about the rehabilitation and remediation
potential of South Africa’s indigenous plants – and the overall objective of
this extensive programme, which was initiated in 1996, is to test the performance of
woody, semi-woody and herbaceous indigenous species in the containment of pollution from
gold slimes dams, and their effectiveness as windbreaks, and in dust and hydrological
control, on slimes dams.
The overall
aim of the programme is to develop strategies for the reduction of both wind and water
borne pollution. It is divided into two projects because of different legislative and
research and development requirements: the Sustainable Vegetation of Slimes Dams Project
and the Mine Woodlands Project. The major achievements of the Wits programme to date have
been significant improvements in slimes dam rehabilitation methods for seepage and dust
control – and a significant reduction in the cost of slimes dam rehabilitation.
Another achievement has been the establishment of the Freegold mine nursery which produces
tolerant indigenous plants for the rehabilitation experiments and from which technology is
to be transferred to community nurseries set up by DWAF, along with further capacity
building through training unskilled labour in rehabilitation methods.
Seepage from
slimes dams is acidic, saline and contaminated with various heavy metals and
radionuclides. During the initial stages of the programme, a large variety of indigenous
species that were colonising the polluted soils of mines right across the Witwatersrand
basin were identified, along with growth-promoting micro-organisms related to these
species. The local ecotypes of indigenous plants that are tolerant of both local
conditions and acid mine drainage are being used, together with micro-organisms, in the
indigenous slimes dam and woodland trials. These plants have become tolerant of the harsh
mining environment through a process of natural selection over many years.
Preparation
of the sites in and around slimes dams, in readiness for planting, varies according to the
overall conditions of the specific site. At AngloGold and Avgold, site preparation has
been done by contractor EMPR Services, whereas at Freegold work is carried out in-house,
under the supervision of both Weiersbye and Fractal Forest Africa. Very little
amelioration of polluted soils is necessary for woody plants as they produce quantities of
organic litter from fine roots and leaves which serves as natural compost, reducing
acidity and increasing microbial activity in the soil. Ameliorating the soil pH will also
cause certain metals to go out of solution – in other words, will immobilise these
metals in the rooting zones of the plants and the surrounding soil, stopping further
contamination of surface and groundwater. A super-absorbent is used when tree seedlings
are planted. Amelioration trials have tested dumping garden refuse and/or sludge onto the
slimes as this is very inexpensive, but the high proportion of undesirable alien species
in garden refuse means that this method is not ideal. The trials have indicated that
patches of woody and semi-woody vege¬tation can be established with minimal amelioration
and no irrigation on the tailings.
Mechanical
digging of the tops of slimes dams in preparation for planting is carried out by a 450mm
auger mounted on a 4x4 tractor at the rate of 3ha/day. Holes are squared of manually after
auguring, and compost and any other ameliorants that are considered necessary are
mechanically mixed in by the same augur. Gravel is used to ensure good drainage.
In the
Freegold mine nursery at Welkom, the seedlings are grown in acid slimes with various
supplements and inoculated with mycorrhizal fungi and rhizobia bacteria derived from the
same slimes polluted soils from which the plant originated. These soil organisms are grown
in sterile laboratory conditions at Wits. The mycorrhizae, which are bulked up on the
roots of plants in tunnels at the Freegold nursery, serve to make the plant tolerant of
drought, low nutrients and heavy metal stress by enabling the plant to acquire key
nutrients such as phosphorus. The rhizobia are largely host specific on legumes, even to
the level of ecotype on Acacias, to the extent that the Welkom ecotype of a particular
species will not infect the Klerksdorp ecotype.
The tree
seedlings are planted by hand and, both on and around the tailings dams, are watered for a
few weeks, or until the first rains, to aid establishment. So called
‘micro-catchmenting’ – well planting or planting in swales between ploughed
ridges – is done to capture water and organic matter around the saplings. Pioneer
grassy and herbaceous vegetation rapidly invades the plantings and hand weeding of exotic
invaders is done regularly. Combined ripping and ridging by a specialised plough is done
on clay soils which are subject to hard setting in winter and inundation in summer.
Programme
leader Weiersbye comments that by growing a vegetation type on top of slimes dams that
will utilise all the rainfall – that is a mix of woody (dominating), shrubby and
grassy species – further recharge of seepage will be reduced. This vegetation will
also break the forces of rain and wind which erode the dumps. The woodlands around the
edges of tailings dams are being tested for the capture of seepage to prevent the further
spread of pollutants. The woody plants, both on and around the tailings, will immobilise
pollutants, including certain heavy metals and radionuclides from the seepage, and it is
possible that these will remain bound up in their root systems and on other organic matter
in the slimes or soil. Weiersbye points out the importance of choosing the right
vegetation type and species for the particular site. Trees also serve as windbreaks and
dust traps. Wood¬lands are therefore multi-purpose.
Woody
species also remediate slimes as they produce a lot of leaf litter and have large mats of
fine roots, and as this organic matter composts, so it starts the nutrient cycle. Cycling
of nitrogen and phosphorus is inhibited by acidity and, Weiersbye points out, ameliorating
the pH with organic matter will kick-start nutrient cycling and provide slow release of
nutrients for the plants.
On top of
the slimes dams, the vegetation type should be chosen according to different zones. The
centre of the slimes dam is fine-textured and compacted, wetter and anaerobic, and lends
itself to reedbed vegetation surrounded by sedgelands. Reed¬beds are particularly good at
containing pollutants and the bed will shrink naturally as the water table lowers and the
slimes dam becomes more arid. Around this area, a psuedo-savannah can be created with
plantings of scattered trees, shrubs and forbes and perennial highveld grasses –
using the dryland method. The outermost areas which are better drained have coarser
slimes, where more deeply rooted woody species, planted at varying densities depending on
their water use, are appropriate. The so called psuedo-savannah on the slimes dams should
be reinforced with indigenous nitrogen-fixing legumes such as Indigofera, Sutherlandia and
Acacia spp. Approximately 200 species of forbes with extensive roots such as Ziziphus
zeyheriana, Helichrysum and Protasparagus spp, will be planted on the slimes dam slopes to
increase the sheer strength of slimes and contain erosion.
Weiersbye
says the spacing of trees is important because if they are too close in a low rainfall
area there will not be enough water for them, whereas if they are too far apart, they will
not provide protection for each other and other bird and wind dispersed species that may
be brought in, and which will create islands of diversity and fertility. The patterns of
vegetation are also important: the vegetation should not be too homogenous but there
should be different heights and widths to break up the erosive forces of wind and rain. It
is important to recreate patches of vegetation to instate ecosystems – woody patches,
which use more water, interpersed with grassy patches, is the ideal – although,
Weiersbye says, this seems to be contradicted by some of the tree trials which are planted
in rows to enable data collection.
Inoculation
of the plants with mycorrhizae and rhizobia, in the case of legumes, has proved to be
crucial for survival and growth in slimes. A 90% improvement in tree survival and up to
50% improvement in growth has been observed, with increased nutrient uptake. The infected
trees also come into leaf earlier in spring and are more drought resistant. The oldest
infected trees have survived almost seven years in slimes, including the severe 2003/2004
drought, and are bearing viable seed, whereas most uninfected plants died within 18 months
of planting.
Many
indigenous tree species have been chosen for the trials and the water use, growth and
pollutant uptake of these species are some of the most important aspects being tested. No
exotic species are being planted on slimes dams in the Wits programme but a few Eucalypt
species are being used as benchmarks in trials around slimes dams. These are grown under
controlled conditions because some are listed as Category 2 invaders in the regulations
under the Conservation of Agricultural Resources Act. They will be used to benchmark the
water use of indigenous species because their water use under semi-arid highveld
conditions is known, from work done in the area of silviculture by the CSIR. Their water
use and growth rate on polluted sites is not known and this will be compared with the
water use on general highveld sites. The CSIR, AGES-Geocon and AquiSim Consulting are
sub-contracted to Wits to measure tree water use, develop water balances for slimes dams
under vegetation, and determine the effects of the trees on site hydrology and
geohydrology. AquiSim is also undertaking the radiological risk assessment, whereas Wits
scientists are assessing woodland ecology, nutrient cycling and pollutant cycling.
Maximum
potential evapotranspiration can be obtained from Eucalypts – they remove the highest
possible amount of water that can be removed by vegetation. A CSIR study has already
established that Rhus lancea (the Karee) has a high water consumption rate on acid mine
drainage – almost as high as that of Eucalypts. The latter reach maximum water usage
by three years of age and retain this until 15 years of age, whereas it is thought that
Rhus lancea, because it is slower growing, will only reach peak water use when it is
older. Dendrochronology, micrometeorological and remote sensing techniques are being used
to estimate tree water use and stress on acid mine drainage.
It is
interesting to note that although the indigenous trees have been planted in this harsh
environment, there have been virtually no mortalities on slimes dams. Herbivory is,
however, a problem in the woodlands where duiker and scrub hare feed on the leaves and
ground squirrel damage the roots. Raptor perches have been installed in areas of new
plantings and have worked well in attracting many different birds of prey, including large
Eagle Owls which have knocked down perches and resident Jackal Buzzards. More robust
perches are in the process of being constructed and installed. In more mature woodlands,
the trees themselves serve as perches and roosting sites, and bird dispersed seeds are
adding to the natural colonisation.
Another
aspect of the sustainable vegetation programme is investigation of indigenous plants on
slimes dams for their economic end use value. Possible economic benefits include timber,
fibres, charcoal, gum, tannin and phytochemical production.
Wits has
site offices and field labs at Harmony’s Freegold mine in Welkom and AngloGold
Ashanti’s Vaal River mine at Orkney. Weiersbye heads up a team that includes 10 Wits
scientists and, to date, their 18 post graduate students, four scientists from the
CSIR’s Land Use Hydrology Unit at KZN University and Stellenbosch and five senior
consultants from industry. The programme is jointly funded by AngloGold Ashanti Ltd,
Harmony and Avgold Target Mine (the mines have also seconded staff to the projects), the
Department of Trade and Industry’s THRIP programme, the National Research Foundation
and the University of the Witwatersrand. The DWAF Directorate of Participatory Forestry is
partnering Wits on the project for the purposes of developing community nurseries and has
allocated two foresters to assist.
The limitations of
grassing slimes dams
The Wits programme has done research into the value of the traditional grassing
of slimes dams in comparison to the planting of indigenous vegetation types in a so called
psuedo-savannah on slimes dams. Prof Ed Witkowski, who helped to initiate the Wits
programme, and Weiersbye believe that grassing is an effective but short term solution to
dust control but will not contain seepage or achieve slimes dam closure.
Generally
only 50% of original cover is in evidence three years after irrigation has been stopped.
Furthermore, Weiersbye comments that it is difficult to obtain indigenous grass seeds to
create the kind of diversity that would be preferable to the pasture grasses,
traditionally used in slimes dam rehabilitation. Not only water but large amounts of
fertilisers are needed to establish pasture grasses, and irrigation on slimes is not ideal
as it promotes further leaching of pollutants. Lime and other fertilisers are needed to
ameliorate the substrate and these are expensive.
She says
that the nutrient cycling necessary to get the whole ecosystem functioning and to ensure
that cover is retained cannot be kick-started with grasses, as it can with woody species,
because grasses produce less organic litter and this is lower in nitrogen and phosphorus.
In addition grasses on slimes have a high demand for potassium. Grasses burn regularly and
in the event of fire further nutrient loss is experienced. The ash blows away in the high
wind conditions on slimes dams or is washed down the slopes before it can be of benefit to
the substrate. Pasture grasses are largely without mycorrhizae or have low levels of these
and, once nutrient levels have dropped, they do not have the benefit of mycorrhizae to
help them access the essential elements for tolerating conditions on slimes. Weiersbye
says that the only way to keep grassed slopes in good condition is to make continual
inputs of compost and fertilisers and to intersperse with a healthy population of legumes.
In the past exotic pasture legumes such as lucerne were used. She says that even with all
this expensive care traditional grassed slopes are not necessarily sustainable.
An important
aspect of tailings rehabilitation which is included in the new DWAF guidelines is the
reduction in steepness of the slopes of slimes dams. The angle of the slope should be
reduced by approximately one third. Existing tailings dams have slopes of between 33-35
degrees, whereas the preferred slope is between 15-18 degrees. This, Weiersbye comments,
makes common sense, as this simple change in design will improve stability, enable deep
amelioration of slopes using agricultural machinery, and facilitate vegetation growth. The
first slimes dams to have their slopes reduced during the Wits programme are situated at
Welkom and were grassed by AngloGold and EnviroGreen.
Joane Pim’s trees
In the early days of the Welkom mines, Anglo American employed the renowned
landscape architect Joane Pim who was responsible for the layout of the new town and was a
prolific planter of trees. Another interesting
aspect of the Wits project is that Weiersbye is using data that has been obtained from
Joane Pim’s original trees to tell her about the groundwater quality in the early
days of Welkom. Cores are taken from the trunks of these trees and the tree rings not only
tell the age of the tree but how long ago the pollution plumes reached the tree, and the
rate of movement of the plume can then be estimated. The signature of the water chemistry
is found in the growth rings of these trees. Isotope signatures of oxygen and carbon in
the cell walls of the tree rings, together with the anatomy of the tree ring cells, will
allow estimates to be made of previous water
availability to the tree. The weather history can be determined from these core samples
and they tell how the tree coped with low water availability over the years. This science
of dendrochronology allows for interpretation of how much water and pollutant stress the
tree has coped with over its lifetime.
Chemical
signatures in the foliage of trees have also been used to characterise and track
pollution. The isotope signature in the leaves of certain ‘indicator’ tree
species shows whether the tree is accessing groundwater and what the relative quality of
that groundwater is, so that the exact location of pollution plumes can be determined.
This means that woodlands can be planted exactly where they are necessary.
Social investment
Entire plant production supply chains have been set up, along with
rehabilitation teams, utilising labour sourced from local communities. By the end of 2004,
400 people will have been trained in plant production, tree planting and maintenance.
(Large scale production of tolerant plants in community nurseries, established in
conjunction with DWAF, will be covered in detail in a forthcoming issue of Urban Green
File.) Education of local communities in environmental awareness is another aspect of the
Wits programme.
Every year,
Wits, DWAF and Freegold use Arbor Week to educate about 1 500 Welkom school children about
pollution from gold mining and the use of indigenous plants to rehabiltate areas around
Welkom. Each child plants a tree on a slimes dam every year and each is given a tree to
plant at home. The local schools and Wits also plan to use the trees on the slimes dams
for environmental school projects, with children taking measurements from the trees they
have planted and learning how much dust, water and pollution their trees can contain. In
2001 and 2002, two Virginia schoolgirls won silver and gold medals at the Sci-Fest with
projects about trees on tailings dams.
-----
Green soldiering
Environmental
Maritime Wardens Course at Saldanha
The term
‘green soldiering’ is borrowed from an article written by Colonel Seakle
Godschalk of the military’s Environmental Services as far back as 1996, where he says
that soldiers have a responsibility to protect all the resources that have been made
available to them by the taxpayer, including the land that is used for training and other
military purposes. Environmental awareness has
been promoted within the ranks of the military through a number of programmes that have
been developed over the years, including the presentation of the Department of Defence
Annual Environmental Awards. These have been acknowledging the efforts, in such categories
as ecological management, environmental education, water and energy efficiency and
integrated waste management, made by units or bases in the airforce, army and navy since
the awards were first instated in 1983.
Carol Knoll
visited the Saldanha naval base, SAS Saldanha, to learn more about the Environmental
Maritime Warden’s Course from the dedicated Warrant Officer in charge of the course,
Blackie Swart.
This
environmental course was started at the beginning of 2003 and the entire new intake of
sailors was invited to participate in the course, which is recognised by Cape Nature
Conservation – it is the equivalent of Module A of a Nature Warden’s
qualifications. The Nature Conservation curriculum has been adapted to suit military
needs. The final certificate which indicates that both the practical and theoretical
components of the course, which is accredited by SAQUA, have been successfully completed
is countersigned by Nature Conservation. Swart points out that naval personnel, if they
choose, can go on to complete further modules and become qualified Nature Wardens once
they have completed their naval contract.
The course
is held in a tented camp within SAS Saldanha’s Nature Reserve, which was proclaimed
in 1994 in an agreement between the navy and nature conservation. The bush camp is sited
in a previously disturbed area where its impact will be minimal. Drip trays are placed
under all vehicles, wherever they may be parked and this is a requirement during military
training exercises as well. The toilet facilities comprise hired portaloos, while grey
water from the shower trucks and field kitchens is disposed of through a gutter which
leads into a fat trap. Eco-friendly soap and washing powder is used and the sailors are
encouraged to buy eco-friendly shampoos. All vehicles are restricted to a speed limit of
30km and obliged to use the roads: no forays into the veld will be tolerated.
Swart
indicates that the overall objective of the course is to instil a very real awareness of
the environment and environmental concerns into the new intake of sailors. He believes in
the principle of what he calls ‘Look and actually See what you are looking at’.
A good 60% of the course takes place outside of the classroom environment and Swart says
tackies and lip-ice are essential. This part of the course involves discreet collection of
species from the veld and the intertidal zone for the purposes of identification and to
convey the value of natural resources. The sailors also learn to swim and that they can
live off the resources of the sea.
The seven
principles of ‘leave no trace’ are strictly observed throughout the course. The
course attendees compile their own Code of Conduct which has to include no speeding, no
smoking and no sleeping in class. They learn the importance of travelling and camping in
already disturbed areas and the value of the pristine environment; about the correct
removal of waste ‘what you bring in you take out’; about always camping at least
50m away from a stream or pan; about respecting animals and observing them from a
distance; and about not making a noise in the wild. They are taught not to pick up stones
as they provide habitat for insect and other faunal species.
Swart says
he emphasises the stewardship role – that they are custodians of their environment.
He says the course has philosophical content built into it, along with environmental and
maritime law, and methods of conserving water, agricultural resources and cultural
heritage sites.
The
ecological side of the course has a strong emphasis on the marine environment and involves
the study of food chains, a study of the tides, coastal ecosystems, rock pools, sea birds,
abalone, kelp forests, the dune system and dune vegetation, sea sand and the salt in the
sea, red tide, pollution caused by harbours and its effect, the danger of plastic bags to
marine animals, and oil spills and their danger to penguins. The navy patrols the crayfish
reserve and the students are taught about the high risk of abalone poaching and methods to
guard against this.
Swart says
there is a strong emphasis on soil management. Erosion and methods of erosion control are
part of this component. The sailors are taken to farms in the area where erosion dongas
are in evidence and they need to explain the origin of the erosion and suggest
rehabilitation methods. Veld, game and fire management are further aspects of this broadly
based course.
A fitting
conclusion to this brief description of the course that has been put in place at Saldanha
is the general overview provided in a paper by Lieutenant Colonel Etienne van Blerk,
assistant director Environmental Co-ordination at the Department of Defence, given at an
international conference in August 2003 and entitled ‘Military environmental
education, training and development – the South African encounter’:
“Defence
in South Africa has a history of environmental care reaching back as far as 1978 when the
first internal policies on the environment were formally adopted. An early focus on nature
conservation or ecological management had made way by 1992 for the more contemporary
strategy of military integrated environmental management. This approach considers the
entire scope of military activities and their associated footprint or impact on all
spheres of the environment, in a quest for sustainable military use of any land, sea or
airspace entrusted to Defence for use in the course of its operations or training.
“Such
an ostensibly pervasive approach understandably presents the department with marked
challenges in the process of ensuring sustained environmental management performance. This
situation is amplified by a rather complex climate that requires compliance with the
prescripts of proliferating environmental legislation, minimising the costs of managing
the environmental footprint caused by all manner of military activities, expansion of
military integrated environmental expertise and instituting the ethic of environmental
stewardship amongst the broadest possible base of soldiers.”
-----
Environmentally sound river crossings
Chris
Brooker discusses simple techniques to protect the riparian zone
“The
riparian zone is an essential part of the river system and an emblem of the artistic soul
of human beings.” Luna B Leopold
Rivers have
many functions. A important one of which is the opportunity that they provide for escape
from the general pressures of life. Sitting under a tree watching the play of light on
water tumbling over stones, marvelling at the powerful roar of a magnificent waterfall,
watching animals and birds that frequent the edges of a river, or simply strolling along
the banks of a stream, rejuvenates the soul.
It is this
quality that gives rivers their greatest value to human kind and without this quality, far
fewer people would interest themselves in the technical aspects of the real functions of
rivers: the conveyance of water and solids, more or less safely to the sea, the
rejuvenation of floodplains with fertile sediment, provision of water for consumption and
their own ecological needs, and the maintenance of riparian strips that are the major
links in the network of corridors that join the undisturbed areas across cities and
countryside alike.
It is these
riparian corridors, the streams and their banks and floodplains that give the rivers their
identity and soul, the value that we prize so highly. And yet we persist in destroying
them.
We squeeze
their edges until they are little more than a single row of trees or bushes trapped by
busy roads, playing field embankments, fences, or the grubby butt ends of shopping centres
or factories, providing no cover for the animals and birds, no filtering for the
stormwater that flows through their undergrowth to the stream, and no resistance or
storage for the floodwater. And we cut across them willy-nilly with ugly bridges, culverts
and embankments, that constrain the rivers, further forcing water into high velocity
chutes – offending our own enjoyment of the place and interrupting the movement of
people and animals alike, up and down the riparian corridor.
Yet it is
not difficult to avoid these impacts – there are really only two rules. Firstly, give
the river room to do its job. Do not squeeze the riparian corridor to the point that it no
longer works. Leave it wide enough to provide cover for creatures. Let it stand out as a
strip of nature in a sterile environment when seen from afar, and let it break sightlines
and create a presence when up close. Do not squeeze the stream itself so tightly that it
has to be constrained and lined with gabions or concrete when its natural morphological
movements threaten buildings and services. Secondly, make sure that crossings do not
interrupt the aesthetic and functional flow of the riparian corridor.
The first
rule is easy to obey – allow the river space. The 100 year floodline is defined in
law as the edge of the river’s corridor and this floodplain can be observed in
practice as the minimum space the river needs. Obeying the second rule needs more thought,
but not necessarily more money.
Make structures
attractive
Bridges and culverts must be visually attractive. Hydraulic forces are high,
and robust structures are needed to resist them, but textures, shapes and shadow lines can
hide the mass. Suspension structures fly. Golden rectangles and arches have been
recognised since ancient times for their beauty of proportion. Use these forms, they cost
no more.
Precast
concrete culverts are ugly, especially when multiple identical barrels protrude from the
face of the embankment in a zigzag pattern. But they can be trimmed flush and the ugliness
can be hidden with variety and cladding, at little additional cost. The shape of a
haunched culvert is close to that of a well-proportioned arch and it can be clad with
artificial stone to create a remarkable replica of a renaissance arch bridge. Where
multiple barrels are needed, vary the width and height of the openings to create visual
interest. Even the industrial utilitarian appearance of galvanised steel arches can be
masked.
Pipe
culverts are horrible, nothing in nature looks like a perfect circular opening and there
is little that can be done to disguise a row of circular orifices. Avoid them!
Opening sizes
The hydraulic contraction of a bridge is the ratio between the flow approaching
directly towards the openings and the total flow in the stream. A low value of this ratio
indicates a high proportion of flow approaching the solid embankment and having to turn to
flow parallel to the face of the bridge, before turning again to flow through the opening.
These multiple changes in direction reduce the hydraulic efficiency of the structure. The
jet of water within the bridge opening is forced to contract more, increasing its velocity
and erosive power. Large volumes of water flowing parallel to the face of the embankment
may cause erosion of the face, particularly close to the opening. Eddies in the trapped
water at the extremities of the embankment cause sediment and other debris to accumulate
and be deposited as the water level drops, increasing maintenance requirements. The water
in these dead zones is at the same energy level as the flow in the main stream but has
little or no velocity head, so its level will be higher than the water level in the main
stream by an amount equal to the difference between the velocity heads – increasing
the flood levels adjacent to the bridge and increasing the risk of the embankment being
overtopped.
In most
instances, the surface of the water flowing through the bridge is drawn down as the flow
speeds up through the opening, with relatively little upstream backwater until the water
surface reaches the soffit of the opening and the inlet becomes submerged. If the
contraction is too high, the opening will create a hydraulic choke, a high backwater with
a rise in water level upstream and the flow through the opening will be forced down
through critical depth, to become a supercritical jet that will end in the formation of a
hydraulic jump. This jet will scour the streambed and the hydraulic jump will dissipate
great amounts of energy by tearing at the bed and banks of the channel. This condition
will be highly detrimental to the stability of the channel and could affect the stability
of the bridge itself.
If the flow
through the bridge is controlled by the upstream water level and this level is allowed to
reach the roof of the opening, the hydraulic conditions change very quickly. The discharge
capacity reduces from being proportional to water depth to the power of 1.5, to being
proportional to the square root of depth, and the upstream water level has to rise much
higher to match any increase in flow. A very high velocity jet of water will be forced
through the opening, which will be potentially damaging to the bed and banks of the
watercourse downstream, but will also block the upstream migration of fish and other
aquatic organisms.
The lesson
here is – keep the opening as wide as possible in relation to the width of the stream
under flood conditions. Do not force the water into a jet through the bridge. And make the
opening either high enough that its entrance is not submerged, or low enough that both the
inlet and outlet are submerged and water flows over the deck.
Keep the corridor open
Many species of fish swim upstream to spawn and many other animals and insects
move upstream to lay their eggs – under various stimuli, the most important of which
is probably flood¬water. The reason for this movement is quite simple, the larvae are not
strong swimmers, mostly drifting at the mercy of the current or attaching themselves to
something solid in the stream. But everything in the water is gradually being swept
downstream by the flowing water – so that if the adults did not migrate upstream, the
entire populations of many species would soon be washed downstream, leaving the upper
reaches of the watercourse depleted. Of course this depletion does not occur in natural
waters because the natural cycle of adults moving upstream and young being swept down by
the current works efficiently – until we interrupt it.
Some of our
fish species (Barbel, Yellowfish, etc) are powerful swimmers and could probably force
their way through, but most small species, such as barbs, minnows, bream, etc, would be
prevented from moving upstream against the high velocity uniform currents in most
culverts. Many fish are capable of short bursts of speed against strong currents and can
move upstream in fast flowing rivers, if there are sufficient resting places where they
are protected from the current by eddies behind boulders or in deeper pools. These resting
places do not exist in engineered culverts – but they could be built into new
structures, or retrofitted into old ones, at little cost.
Vertical
drops, even of low height, represent an impenetrable barrier to most fish and other
aquatic species. These are often incorporated into engineered structures for energy
dissipation or develop morphologically by erosion downstream of culverts. Where possible
steps should be avoided. Concrete blocks or splitters or, preferably, natural boulders,
anchored into place, can serve the same engineering purpose with much less ecological
impact.
Almost all
streams have a deeper channel, known as a thalweg, flanked on one side or both by areas of
shallow water that rise up to the banks. This concentration of water provides for a
diversity of habitats and a path of deeper water, even when flow is low. Most culverts
have flat smooth beds so that flow is equally spread out across their full width and often
over several barrels. The thin, unbroken, film of water flowing over a smooth concrete
base, or several equally sized streams flowing through pipe or egg shaped culverts, does
not provide an inviting or safe environment for aquatic organisms moving up or downstream.
This problem
can be avoided by setting the floor level of one barrel lower than the others to emulate
the thalweg. Small boulders and cobbles can be cast into the concrete surface to create a
diversity of environments, concentrating low flows into the channels between the stones
and creating areas of reduced bed shear, where small creatures can anchor themselves for
feeding or take refuge from the current.
Many
terrestrial animals use the stream banks in the riparian corridor as places of refuge or
routes to move from one part of their territory to another. But this movement is
frequently prevented or made more hazardous by crossings with embankments that extend
right up to the edge of the water on both banks, forcing the animals either to climb the
embankment and cross the road or to enter the water of the stream. If the floor level of
at least one barrel on either side of the stream were set well above base flow water
level, animals moving along the corridor would be able to cross the barrier without
endangering themselves.
A similar
principle applies when people walk along the stream banks – safe and convenient
crossings should be provided. If culvert heights are sufficient, one barrel could be
fitted as a pedestrian walkway. Alternatively, steps or ramps should be provided to ease
the climb up the steep face of the embankment.
River
crossings are unavoidable, but they do not have to be ugly or significantly
environmentally harmful. All it takes is some thought and careful aesthetic and functional
design to create a crossing that is an asset, at little or no additional cost.
Article
by Chris Brooker, PrEng, of CBA Specialist Engineers in surface water management. |
