Download River Regulation / Dam Construction – Effects on Rivers and Streams.

River Regulation / Dam Construction –
Effects on Rivers and Streams.
HISTORY AND BACKGROUND
 Large scale river regulation started 5000 years ago –
to tame the flow of water and for storage purposes.
 Between 1900-1940 technology to build dams in N.
America, Europe, S.E. Asia – E.g. the Hoover Dam
– Colorado River (1936).
 Between 1950-1980 peak activity in dam building.
 From 1980-Present day, dam building has slowed to
Apprx.500/yr worldwide.
 Estimated that at present over 60% of total
streamflow is regulated.
TYPES OF RIVER REGULATION
 Irrigation ditches/canals and drainage tunnels
 Aqueducts
 Canals
 Impoundments (reservoirs)
 Dams
DAMS AND IMPOUNDMENTS
 Great variability in dams re; size, purpose and
operation. These factors influence the impact on the
river ecosystem.
 Water supply impoundments and irrigation dams
need great storage capacity – to cope with demand
and drought.
 Flood control reservoirs – small pool of water to
maximise storage capacity.
DAMS AND IMPOUNDMENTS:
Hydroelectric dams water storage to meet
regional/seasonal/hourly demands. 2 types –
1. “Run-of-the-river” – low height and has
low adverse effects. 2. “peaking”
hydropower dams – water flows through
turbines to meet regional energy demands
and has serious effects for aquatic life.
EFFECTS OF DAMS (PHYSICAL &
BIOLOGICAL)
 Physical changes downstream – flow, temperature
regimes and water clarity (deep release dams most
adverse effects) – therefore changes in physical and
chemical conditions, resulting in changes in animal
and plant life of the river.
 Water quality changes downstream – depends on
how long water kept in reservoir or if surface/deep
water released from dam.
 Dams break the natural upstream/downstream
connectivity and periodicity of flow in rivers.
EFFECTS OF DAMS (PHYSICAL &
BIOLOGICAL)
 Presence of reservoirs/dams affects the flow regime
of the river and hence transport of fine sediments
and fine particles on the streambed is altered.
Inflowing sediments settle out in reservoir depleting
storage capacity.
 High discharge dams cause scouring of fine particles
and armouring of streambed (surface substrate
becomes tightly compacted) as well as changes in
Channel form, bank erosion, cutting down of
streambed. Elimination of plants & fauna.
EFFECTS OF DAMS (PHYSICAL &
BIOLOGICAL)
 Low discharge dams – reduced flow – increased
algae/phytoplankton blooms develop and greater
abundance of higher plants e.g. aquatic moss –
favours midges and oligochaetes. Mayflies shift
from lotic to lentic species.
 Reservoirs/dams impede the upstream/downstream
migration of fish. E.g. salmon & eels. Damage of
fish by water pressures and turbines.
EFFECTS OF DAMS (PHYSICAL &
BIOLOGICAL)
 Decrease in species richness of benthic invertebrates
but an increase in abundance – due to altered
physical/chemical environment below impoundment
and a reduction in habitat heterogeneity.
EFFECTS OF CANALS AND
IRRIGATION DITCHES AND
AQUEDUCTS
 Loss of channel structure and instream habitat due to
altered flow – effects benthic invertebrates and
fishes dependent on floods to trigger spawning.
 Water diversion (aqueducts) drain rivers and basins
e.g. Aral Sea in Central Asia, since 1960 lake level
dropped 15m, volume decreased by 60% and
salinity level tripled – 24 native fish species
disappeared.
 Canals have physical uniformity – they facilitate
invasion by non-native species and loss of native
species.
CONCLUSION
 Dams and other forms of river regulation
have many negative effects on rivers and
streams, causing changes in community
structure and ecosystem function. The
naturally free-flowing and continuous river
course is transformed into an unnatural,
uniform “river segment”. The argument in
favour of dams and many river regulation
schemes is that it brings huge human and
economic benefits.