Prediction of flow duration curves in ungauged basins - Runoff Prediction in Ungauged Basins: Synthesis across Processes, Places and Scales - page 136

Figure 7.1. Definition of flow
duration curves (FDC). (Left) Daily
hydrograph based on measured
daily runoff of the Kamp River at
Zwettl in Austria, juxtaposed against
the long-term (period-of-record)
FDC (red line). (Right) Quantiles of
the annual FDCs, with long-term
FDC (red line).

20.0

10.0

5.0

2.0

1.0

0.5

0.2

0.1

1980 1985 1990 1995 2000 2005 0 50 100 150 200 250 300 350

Days per year exceeded

Q

WUA 0 1 Duration Power, P 0 1 Duration

Energy, E

Habitat duration
curves Power duration

curve

Figure 7.2. Two illustrations of the utilisation of FDCs: (Left) Construction of two habitat duration curves from FDCs and a rating curve for
weighted useable area (WUA), an indicator of habitat suitability for specified wildlife species: the higher the value the higher the suitability.
The two habitat (WUA) duration curves are for the natural scenario (blue line) and for an altered scenario characterised by upstream human
abstraction, Q h (red line). (Right) Construction of the power - duration curve based on a typical power - runoff relationship (area under the
power - duration curve is a measure of the hydroelectric power that may be produced over the period of interest).

ecological habitats. FDCs are also used to determine the
optimum allocation of water for different human uses, and
for the environment (Alaouze, 1991 ), and for the purpose
of evaluating the impact of alterations in flow regimes. In
this respect, Vogel et al . (2007b ) introduced the concepts
of eco-deficit and eco-surplus, both indicators estimated
based on the FDC.
Figure 7.2 presents two different applications of the
FDC, the first one for setting design standards for envir-
onmental flows (left) and the second for hydropower
production (right). Both involve the construction of
appropriate water resource indices, relating to habitat con-
ditions or hydropower potential respectively, through the
combination of the FDC with a rating curve for the index
of interest (Vogel and Fennessey, 1995 ; Bonta and Cle-
land, 2003 ). Figure 7.2 (left) illustrates the construction of

two habitat duration curves, one for the natural scenario
(blue) and the other for a control scenario that accounts
for water extractions upstream (red). The water resource
index in this case is the total habitat area (weighted
useable area, WUA). The rating curve that connects
WUA to runoff, which can be derived via simulation
based on ecological considerations is shown (Milhous
et al., 1990 ). The construction of a power - duration curve
is also shown ( Figure 7.2 , right), highlighting the within-
year variability of the amount of hydroelectric power that
can be produced. Once again, a key component in this
construction is the relationship between hydropower and
runoff, which are the design characteristics of a particular
type of hydropower scheme.
Finally, since the FDCs are a key signature of runoff
variability, they can also be used for evaluating rainfall -