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

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.