The transfer, storage and release of water colour in a reservoired catchment

Abstract

In recent years discoloured water has become a matter of growing concern to water resource managers. Discoloured water is a major source of consumer complaints and is expensive in capital and recurrent costs. The treatment of water discolouration is believed to be associated with a number of health issues, such as Alzheimer's disease. In particular, discoloured water, upon chlorination, is believed to produce carcinogens. The principal aim of this research has been to consider and manage water colour within an entire reservoir catchment system; Thornton Moor Reservoir, the study area, has experienced some of the highest values of colour in the Yorkshire Water Region, and has been an area of significant concern and cost to Yorkshire Water Services. Apparently homogenous subcatchments can produce marked differences in the colour of runoff data. This research has involved an investigation into the relationship between the subcatchment tributary water colour and catchment morphology. The relationships established were used to generate a predictive model for water colour such that areas of high water colour could be identified without intensive sampling. The initial phase of this study considered the transfer network involved in bringing the colour from the catchment to the reservoir. This has involved an analysis of the spatial and temporal variation of water discolouration within the catchment. The consistency of the spatial variation of water colour between the tributaries has been utilised to develop a management protocol which is presently being implemented at Thornton Moor in order to minimise the level of discolouration, whilst maintaining water supplies. Edwards (1987), describes the reservoir as the second line of defence in the protection of water supplies in direct supply reservoirs. No research to date has considered the role of the reservoir in the storage, transmission and release of discoloured water. Empirical evidence at Thornton Moor Reservoir suggests that for the majority of the year, the reservoir operates as a buffer to colour; however at certain times of the year it appears actively to increase the colour entering the treatment works. In considering the entire catchment system, it has been possible to develop a transferable staged approach to catchment management