Mpumalanga Biodiversity Conservation Plan Handbook - bgis-sanbi

Engineering/construction/earth moving : causes
accelerated soil erosion, turbidity (suspended
solids) and sedimentation;
Structures such as bridges, causeways, weirs and
dams: can change the natural erosion and sedimentation
characteristics of a river, causing local and
downstream channel modification.
All questions about development and the need for water and
its impact on water supplies must be referred to the
Department of Water Affairs (DWAF). National Water Quality
Standards are set by DWAF and return flows (of effluent) from
any development are subject to these. The process of
determining the ‘ecological reserve’ flow, developed by
DWAF, is an essential tool in managing water use so that rivers
can survive as ecosystems. There are also internationally
accepted standards set for structures like bridges, culverts and
dams and all such developments should be subject to these.
The most visible aspect of riverine biodiversity is the presence
of prominent vegetation along the river line. This is not
always a reliable indicator of river health. Alien plants and
‘enriched’ water can confuse the picture for the untrained
eye. More accurate assessment of river health requires
multiple sampling for dissolved chemicals and in-stream
biological indicators to provide a true reflection of the
condition of a river.
DEVELOPMENT GUIDELINES FOR RIVERS
Any proposed development likely to impact on a river’s ecological
drivers can potentially alter its functioning. Therefore, all
such developments are subject to a full EIA. Impact assessment
requires knowledge of the appropriate ecological reserve flow.
This is determined by DWAF and involves setting standards for
the quantity and quality of water required to satisfy present and
future human needs and to protect aquatic ecosystems.
A1. WATER EXTRACTION:
No significant amount of water may be extracted from a river
for public, private or commercial purposes, without a water
use license provided by DWAF. This applies to direct extraction
from a river or a dam, whether on private or public land.
Water use licences are controlled by Water and Irrigation
M P U M A L A N G A
Boards located in every catchment. Allocations are made
Biodiversity
according to the possession of ‘water rights’, which are
officially allocated so as to be shared between public and
private users of water. Water for human consumption has
priority in the allocation of water rights, and may not be
exchanged with rights for other uses such as irrigation.
CHAPTER 6 - LAND-USE GUIDELINES
A2. FLOW-CONTROL OR IMPOUNDMENT
STRUCTURES – DAMS AND WEIRS:
Surface water in Mpumalanga is already over-committed to
various forms of development and human consumption. All
our major rivers are impacted by water extraction and dam
construction, leading to severely reduced flows in lower
reaches. Because of this, all proposals for dams require
detailed planning and strict adherence to formal EIA
procedures, including serious consideration of alternatives.
Large public development structures will go through a full EIA
process with mandatory public participation. Small farm
dams, however, are often thought to be too small to justify
impact assessment. Historically farm dams were subsidised
by the state, being considered good water conservation
practice. Subsequent study has shown their cumulative effect
has been to reduce stream-flow dramatically as well as several
other negative impacts. In many areas small farm dams are
being deliberately breached to correct this error. All farm
dams and weirs are subject to EIA legislation.
A2.1 FISH PASSES:
Any structure that obstructs or modifies the flow in a
river or creates a sharp increase in water velocity may
require a fish pass to allow for upstream (as well as
downstream) movement of fish. Fish passes are gently
inclined, sometimes stepped, shallow channels that
allow fish to swim upstream to breed. Specialised
expertise is required to design and build fish passes.
These structures should be compulsory wherever movement
of fish up or downstream is necessary. This is
particularly important in the identified priority subcatchments,
important aquatic corridors and in the
lower reaches of rivers. These corridors are identified
on the Aquatic Biodiversity Map as critical movement
links to retain some connectivity in our fractured river
systems.
A3. IN-STREAM ENGINEERING -
CHANNEL OR BANK MODIFICATION:
Wherever engineering works will disturb water courses or
when structures such as road and rail crossings,have to be
built through them, special measures must be taken to
ensure minimal disturbance, limiting obstruction to fish
movement or restriction of the channel. This provision must
take into account a generous assessment of expected flood
volumes as there is every indication that flood peaks (and
droughts) will become more extreme as global climate
change proceeds. Design specifications for such structures
must be based on South African conditions and information.
Imported specifications may be from less extreme climates
and have inadequate margins to accommodate extremes.
CONSERVATION PLAN HANDBOOK 53
LAND-USE GUIDEINES