Water Journal : Water Journal September 2012-1
rural pipeline management refereed paper technical features 76 SEPTEMBER 2012 water The red dots in Figure 5 are sites in the WMP system where a hydraulic model, running at high demand conditions, indicates pressure could fall below acceptable levels (< 20 m WG) under high demand periods. It shows that a relatively small deterioration in Hazen- Williams friction factor (reducing from C = 130toC=120)inWMPsystemNo3and No 4 resulted in a substantial increase in the number of locations where low pressure could occur. This water quality risk study was used as the basis to pursue further investigations on the management of the WMP including: • Ways to monitor for changes in hydraulic performance and possible sediment scour events. Possible monitoring methods were identified across the system, and recommendations were made for hydraulic monitoring based on existing infrastructure and instrumentation as well as water quality monitoring to better quantify the risks identified in the initial study; • Continuation of research work into Bryozoa and other forms of biofouling with Victoria University; • Better understanding of the impact of heavy storms impairing water quality and ways to minimise impacts; and • The impact of stratification of reservoirs on water quality and the means to overcome them. Other Unintended Consequences This rural pipeline network has generally resulted in customers across the region being supplied with better quality water from a more reliable source. There has also been a substantial reduction in water losses due to cessation of evaporation and infiltration losses that occurred from the open channels that were used to supply the area. However, there have been some unintended consequences with the operation of the system: Changes to water quality characteristics within the new pipe network Drinking water supplies at towns within the WMP that have disinfection as the only treatment barrier experienced a significant rise in concentrations of haloacetic acids (HAAs). The source was traced to the new piped supply from Lake Bellfield, and the different mix of dissolved organics it contained compared to the previous channel-fed supply. By supplying the water directly from the reservoir in a pipeline, the degradation of organic compounds (due to UV degradation and compound volatility) was reduced. Changes to the operation of the disinfection system have been made to maintain the concentration of disinfection by-products within the ADWG values. The WMP is designed for future demands. This, and the fact that at the time of commissioning the region was in the grip of a prolonged drought, meant that stocking rates and, hence, water demands were relatively low compared to design demand values. Long detention times in the DN600 MSCL section of the pipeline from Lake Bellfield, combined with the soft water conditions, caused pH increases up to 11. A simple carbon dioxide dosing system has been installed at the Taylors Lake end of this pipeline to reduce the pH to a range between Figure 5. Output of hydraulic model showing effect of increased pipe friction at peak demand (red dots indicate low pressure). Figure 6. Colour and turbidity in Lake Bellfield at and after a storm event (January 2011).
Water Journal November 2012-1
Water Journal August 2012