This paper reports on the implementation of a three-dimensional hydrodynamic model to
predict the fate of turbidity and particulates through a drinking water reservoir. This work
offers the potential to develop turbidity reduction strategies based on the nature of flows
through the reservoir enabling cost-effective improvements in aesthetic water quality.
Melbourne's protected catchments supply disinfected but unfiltered water to over 3 million
people. This water has a reputation as being one of the world's most pleasant and safe, but
has higher sediment loads in the distribution system than filtered water.
Silvan Reservoir is an essential part of Melbourne's water supply system. The average
detention time in the reservoir is approximately 3 months. However, given the complex
nature of the reservoir, short-circuiting is highly likely and the effects of this on turbidity
levels at the outlets has been largely unknown.
Two different numerical models were used to simulate water flow in the reservoir:
DYRESM, a one-dimensional hydrodynamics model; and, ELCOM-CAEDYM, a three-dimensional
hydrodynamics and water quality model. The main objective of the modelling
was to determine the main source of the turbidity measured at the outlets so that
management and operational efforts can be appropriately focused. The models have a
high data requirement and their development required the installation of temperature
gauging on inflow streams and high-resolution thermistor chains and meteorological
sensors in the reservoir. An extensive field experiment was also undertaken to track the
inflowing water paths and to validate the models.
The data collected indicated that circulation in the reservoir is controlled by two things: a
strong daily internal wave signal, which causes large vertical excursions of the water
column followed by horizontal transport; and, the off-take depths, which set the stratification.
The models have shown that the fastest inflow-outflow travel time is approximately 3 hours
with a dilution of about 100 times indicating that although some mixing is occurring, a
portion of the inflow water is reaching the outlet with very little to no detention. The models also show that turbidity at the outlets is dominated by the inlet turbidity rather than
the in-situ generation and that this turbidity is made up of slow settling particles. The
faster settling particles, which are generated during storm events, cause turbidity spikes at
the inlets but do not affect the outlet turbidity levels. This implies that the strategy for
harvesting water from the catchments into Silvan could be reviewed based on turbidity
limits and may allow for an increase in yield.
Various management scenarios were modelled with the ultimate outcome being to reduce
turbidity at the outlets and optimize detention times. The results will be used to optimize
operation of the reservoir and focus further investigation works. The model will be used to
assess the implications of future management and operational scenarios as they arise. Includes table, figures.
| Edition : | Vol. - No. |
| File Size : | 1
file
, 650 KB |
| Note : | This product is unavailable in Ukraine, Russia, Belarus |
| Number of Pages : | 8 |
| Published : | 11/01/2005 |
