Modelling and hydraulic Management of a boreal reservoir system for mitigating nuisance agents in a public water supply – akershus, norway
The numerical model CE-QUAL-W2 was used for exploring hydraulic measures to minimize the water quality problems experienced by the water works at Aurevatn reservoir, Baerum municipality, serving sixty thousand inhabitants with potable water. The dystrophic nature of the reservoir water is reflected by high values for colour and total organic carbon. The composition of phytoplankton is made up of cyanobacteria, chlorophytes and chrysophytes in moderate concentrations. Problematic contamination of the raw water originates from the development of cyanobacteria. Primary concern has anabaena lemmermannii, producing extracellular substances including geosmin and microcystin. A controlled suppression of the noxious organisms is pursued, and this initiated the requirement for the studies here reported. A number of simulations were tried. The results were interpretable in terms of interacting influences between hydraulic management and microalgal development. An adoptable operating strategy for the system of reservoirs was devised. The implications for an expedient water management are stated. The most important efforts were to use bottom water intake from the upstream reservoirs, and to keep high water level both in Lake Aurevatn and the upstream reservoirs. Effort to remove algal rich surface layer by increased flow over the dam might lead to negative results.