Conditions favouring growth of fresh water biofouling in hydraulic canals and the impact of biofouling on pipe flows

Biofouling increases frictional resistance and slows the water flow in fresh water canals and pipes. It results in up to 10% reduction in the flow carrying capacity in hydropower canals in Tasmania, Australia. This project investigated the effect of colour on the growth of biofouling in open channels and the impact of biofouling in pipes and penstocks. The effect of substratum colour on the growth of biofouling was studied by submerging mild steel plates painted with four different coloured epoxy coatings in fresh water. The plates were placed in a concrete lined canal for a period of time to allow biofouling to grow. Results show that black was the favoured colour for the growth of biofouling whereas the white plates developed the least amount. The amount of biofouling increases progressively from white to grey to black at the settlement stage of biofouling. However, the effect of colour on the growth of biofouling became less significant when the biofouling was fully developed. It was found that the amount of light also affected the growth of biofouling. Under full sunlight and slow flow conditions(1 m/s), plates with lower total light intensity and lower UV light exhibited higher levels of biofouling. In addition to open channels, biofouling also causes head losses in cooling water pipes and penstocks in hydroelectric power stations. The influence of water quality on the growth of biofouling was investigated by analysing water quality data of eight lakes used for hydroelectric power generation. It was found that power stations with fewer biofouling problems in their cooling pipes use water with a higher pH value and dissolved oxygen level, while having lower water conductivity, water turbidity, iron, manganese, aluminium and nutrients. A new pipe rig was designed and built to investigate the impact of biofouling on pipe flows. Located in the hydraulics laboratory at the University of Tasmania, this consisted of a removable test section that was placed in a purpose built field test rig installed in a hydropower station canal. The pressure drop across the test section and velocity profiles under different flow rates were measured for both clean and fouled conditions. Results show that biofouling increased the head loss along the test section and changed the shape of the velocity profiles. This data did not fit the widely used Colebrook-White equation.