Abstract
Abstract. The term "Environmental Flows (EF)" may be defined as "the quantity, timing and quality of water flows required to sustain freshwater and estuarine ecosystems and the human livelihoods and well-being that depend on these ecosystems". It may be regarded as "water for nature" or "environmental demand" similar to crop water requirements, industrial or domestic water demand. The practice of EF is still limited to a few developed countries such as Australia, South Africa and the UK. In many developing countries EF is rarely considered in water resources planning and is often deemed "unimportant". Sri Lanka, being a developing country, is no exception to this general rule. Although the country underwent an extensive irrigation/water resources development phase during the 1960s through to the 1980s, the concept of EF was hardly considered. However, as Sri Lanka's water resources are being exploited more and more for human usage, ecologists, water practitioners and policymakers alike have realized the importance of EF in sustaining not only freshwater and estuarine ecosystems, but also their services to humans. Hence estimation of EF has been made mandatory in environmental impact assessments (EIAs) of all large development projects involving river regulation/water abstraction. Considering EF is especially vital under the rapid urbanization and infrastructure development phase that dawned after the end of the war in the North and the East of the country in 2009. This paper details simple tools (including a software package which is under development) and methods that may be used for coarse scale estimation of EF at/near monitored locations on major rivers of Sri Lanka, along with example applications to two locations on River Mahaweli. It is hoped that these tools will help bridge the gap between EF science and its practice in Sri Lanka and other developing countries.
Highlights
The term Environmental Flows (EF) may be defined as “the quantity, timing and quality of water flows required to sustain freshwater and estuarine ecosystems and the human livelihoods and wellbeing that depend on these ecosystems”
FDC heights (Hx) at all 17 percentage categories for Ullapane was estimated in this manner (Fig. 3(a)) by solving equation (1) for Hx with Ax = Aullapane. This simulated natural FDC was converted to a monthly time series by using the spatial interpolation technique of Hughes and Smakhtin (1996) considering that flows at any particular month in Peradeniya and Ullapane occur at similar percentage points on their respective FDCs due to their close proximity to each other
Once the decision on whether to downgrade, upgrade or maintain the current ecological condition of the river is made, the relevant FDC may be translated into a flow time series which may be maintained as EF
Summary
The term Environmental Flows (EF) may be defined as “the quantity, timing and quality of water flows required to sustain freshwater and estuarine ecosystems and the human livelihoods and wellbeing that depend on these ecosystems”. In other areas, when flow regimes of rivers/streams are altered due to dams/water abstractions upstream, sufficient flow at the right times needs to be maintained in the river/stream for the maintenance of aquatic ecosystem services downstream. At times this streamflow requirement may include social and cultural components in addition to the environmental component, e.g. in the case of the holy River Ganga in India (O’Keeffe et al 2012). It is hoped that these tools will help ensure healthy ecological functioning of the heavily developed rivers like Mahaweli, and other less developed ones (forming the majority of the total of 103), the resources of which are under pressure, especially due to the rapid urbanization and infrastructure development activities initiated after the end of the war in the North and the East of the country in 2009
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