Master of Engineering (Hons.)
Amino, Nobushige, Destratification of a potable water supply reservoir, Master of Engineering (Hons.) thesis, , University of Wollongong, 1990. http://ro.uow.edu.au/theses/2553
The origin of the most sources of water supply and requirements for farming is the rain, which becomes surface water and ground water. The water sources will be classified roughly into three types, namely, river water, lake water and ground water.
Quantity and quality of water sources are basic factors in water supply planning. Planned intake must be possible throughout the year and the water quality must satisfy the needs and requirements of drinking water. These desirable qualities are not to be changed in the future, and further water in future works of expansion. Treatment methods are determined based on water quality of the water source, and layout of water supply facilities are determined based on the location of the source. Water is an important part of our life. One can survive without food for less than a month, however without drinking water one can only survive for less than a week. Thus drinking water especially clear water, is vital for everyone. Nearly 100 % of drinking water comes from surface reservoirs in NSW. Australia. The general management of a reservoir not only includes the the catchment area, water circulation and water usage but water quality.
In the summer months, the heat from the sun stratifies the water in a reservoir resulting in the bottom layer becoming poor in oxygen or de-oxygenation. Stratification of reservoirs, or the formation of water layers, as a result of many factors including heat from the sun. The denser water forms at the bottom, so that no mixing occurs. The outcome is three distinctly different layers of water by depth ; EPILIMNION is the top layer, it extends from the surface to the level where the temperature is relatively constant with depth. THERMOCLINE is the layer with rapidly changing temperature by depth. HYPOLIMNION is the layer between the thermocline and the reservoir bottom.
Consequences of stratification are : Depletion of oxygen in the hypolimnion Increased concentration of iron and manganese in the hypolimnion. Increased algal (marine plant) blooms in the hypolimnion. Possible generation of hydrogen sulphide. Unpleasant tastes and orders. High colour and turbidity. Low temperature releases.High zooplankton numbers. High numbers of aquatic insects. Water quality fluctuations.High zooplankton numbers. High numbers of aquatic insects. Water quality fluctuations.
De-oxygenation of the hypolimnion may lead to the release of the elements such as iron(Fe) and manganese(Mn), and phosphate and ammonia nutrients from bottom sediments. These releases have important consequences such as "dirty water" to the consumer may cause corrosion of pumps, and nutrients for example may further increase phytoplankton (free floating microscopic plants) production, thus accelerating degradation of water quality. They also may cause taste and odour problems for water supply authorities, produce surface scums, which interfere with recreational use of the water. This phenomenon is a worldwide one. affecting the quality of water everywhere, including Australia. Drinking water in NSW, especially in the Illawarra Region, has the same problems caused by excess of iron and manganese in water which give water a metallic taste and colouration.
The WHO (World Health Organisation) report in 1984 on drinking water gives the following guidelines of Iron and Manganese.
Although iron is an essential element in human nutrition, drinking water is not considerd to be an important source. At levels of about 0.3mg/litre, iron stains laundry and plumbing fixtures and causes an undesirable taste in beverages. The precipitation of excess iron gives an objectionable reddish-brown colour to the water. Increases in the concentration of iron in water during distribution may be due to either corrosion of iron pipework or disturbance of existing deposits." and At levels exceeding 0.15 mg/litre, manganese in water supplies stains plumbing fixtures and laundry. At higher concentrations, it causes an undesirable taste in beverages. In common with iron, its presence in drinking water may lead to the accumulation of deposits in the distribution system. Even at a concentration of 0.05 mg/litre, manganese will often form a coating on pipes which may slough off as a black precipitate."
The levels recommended by NHMRC and AWRC (1987) are 0.30 mg/L for iron and 0.10 mg/L for manganese. However, recent work done in Australia by Sly et. al(1988) suggests that the levels set by NHMRC and WHO are high for manganese concentration and it is suggested that levels of manganese concentrations should be kept as low as 0.02 mg/L to avoid Mn related dirty water problems.