Civil Engineering Reference
In-Depth Information
Box 1.3: Managing for variable flows and water quality
The Mara River is a typical example of the inter-relationship between
consumptive use, ecosystem services, and human benefits. The Mara
River runs from Mt Kilimanjaro through a coffee-growing area, Masai
Mara Nature Reserve, an agricultural area in Tanzania and ends up in
Lake Victoria, which flows into the upper Nile basin. Environmental
flow assessments have been completed for both the Kenyan and
Tanzanian parts of the river, but are somewhat limited by available
data. The challenge for water resource planning is to balance water use
for native animals, which are a major tourist attraction and income
generator, and for human use including potable water, irrigation and
cattle grazing. While maintaining a minimum water flow is a typical
objective in most water plans, in Masai Mara Nature Reserve hippo-
potamuses (a tourist attraction) need 1.5m depth of water in pools for
their health (Figure 1.6 in colour plates). Nutrient levels in the river run
high from: wildebeest deaths while crossing the river during migration,
wild and domestic animal use, agricultural run-off, and tourism facil-
ities (although waste treatment for the latter are licensed). The Mara
River, along with other streams, contributes to the nutrient load of
Lake Victoria which has massive growth of the invasive water hyacinth.
A major driver for Australia's water reform was the 1991 toxic algal bloom
in over 1000 km of rivers in the Murray-Darling Basin, which affected stock,
domestic, tourism and recreational use of water (Figure 1.7 in colour plates).
Further motivation for addressing the land-water nexus was identification
of a potential three-fold increase in the area affected by dryland salinity
from the current 5.7 million hectares (NLWRA 2000). Salinity had already
had impacts on water quality, native vegetation, and lifespan of road, rail
and urban infrastructure. Similarly, a decline in the Great Barrier Reef off
the coast of Australia has been partly attributed to nutrient and sediment
run-off from the adjacent mainland. This has resulted in a $AUD200m
collaborative Reef Rescue Program with farmers and graziers to reduce diffuse
contaminants into the Reef World Heritage Area.
Degradation has also prompted reform in other developed countries. In
2005, the province of Alberta in Canada announced it would no longer
accept applications for new allocations from the Bow, Oldman, and South
Saskatchewan River sub-basins because of river degradation. At that time, 22
of the 33 main Alberta rivers were suffering moderate environmental effects
from increased water stress caused by water extraction for consumptive use,
five were suffering heavier environmental effects, and three were environ-
mentally degraded. Of note is that about 75 per cent of all allocated water is
used for irrigation, a large percentage of which is used to produce relatively
