AWWA WQTC62507

This paper reports on the implementation of a three-dimensional hydrodynamic model topredict the fate of turbidity and particulates through a drinking water reservoir. This workoffers the potential to develop turbidity reduction strategies based on the nature of flowsthrough the reservoir enabling cost-effective improvements in aesthetic water quality.Melbourne's protected catchments supply disinfected but unfiltered water to over 3 millionpeople. This water has a reputation as being one of the world's most pleasant and safe, buthas higher sediment loads in the distribution system than filtered water.Silvan Reservoir is an essential part of Melbourne's water supply system. The averagedetention time in the reservoir is approximately 3 months. However, given the complexnature of the reservoir, short-circuiting is highly likely and the effects of this on turbiditylevels 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-dimensionalhydrodynamics and water quality model. The main objective of the modellingwas to determine the main source of the turbidity measured at the outlets so thatmanagement and operational efforts can be appropriately focused. The models have ahigh data requirement and their development required the installation of temperaturegauging on inflow streams and high-resolution thermistor chains and meteorologicalsensors in the reservoir. An extensive field experiment was also undertaken to track theinflowing water paths and to validate the models.The data collected indicated that circulation in the reservoir is controlled by two things: astrong daily internal wave signal, which causes large vertical excursions of the watercolumn 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 hourswith a dilution of about 100 times indicating that although some mixing is occurring, aportion 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 thanthe in-situ generation and that this turbidity is made up of slow settling particles. Thefaster settling particles, which are generated during storm events, cause turbidity spikes atthe inlets but do not affect the outlet turbidity levels. This implies that the strategy forharvesting water from the catchments into Silvan could be reviewed based on turbiditylimits and may allow for an increase in yield.Various management scenarios were modelled with the ultimate outcome being to reduceturbidity at the outlets and optimize detention times. The results will be used to optimizeoperation of the reservoir and focus further investigation works. The model will be used toassess the implications of future management and operational scenarios as they arise. Includes table, figures.

Product Details

Edition:

Vol. - No.

Published:

11/01/2005

Number of Pages:

8

File Size:

1 file , 650 KB