river flow regimes and effective discharge · effective discharge functional-equivalent discharge q...
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Eawag: Swiss Federal Institute of Aquatic Science and Technology
Stefano Basso | Riccardo Sprocati Alessandro Frascati | Marco Marani
Mario Schirmer | Gianluca Botter
River flow regimes and effective discharge
Photo: FOEN
EFFECTIVE DISCHARGE
FUNCTIONAL-EQUIVALENT DISCHARGE qf [Doyle and Shields, 2008]: the constant value of discharge resulting in the
same amount of sediment transport determined by the overall hydrologic regime over long time scales.
Sediment rating curve
Photo: Anja Bretzler
TIME
WA
TE
R
FL
OW
q
S
ED
IME
NT
F
LO
W
qs
SE
DIM
EN
T
FL
OW
q
s
WATER FLOW q
qqs
Time series of sediment and water flows
EFFECTIVE DISCHARGE
FUNCTIONAL-EQUIVALENT DISCHARGE qf [Doyle and Shields, 2008]: the constant value of discharge resulting in the
same amount of sediment transport determined by the overall hydrologic regime over long time scales.
Sediment rating curve
Photo: Anja Bretzler S
ED
IME
NT
FL
OW
qs
WATER FLOW q
fsssss qdqqpqq
0
)(
Average sediment flow due to the underlying flow regime
qf
sq
EFFECTIVE DISCHARGE
FUNCTIONAL-EQUIVALENT DISCHARGE qf [Doyle and Shields, 2008]: the constant value of discharge resulting in the
same amount of sediment transport determined by the overall hydrologic regime over long time scales.
Photo: Anja Bretzler
What is it used for?
Lifespan of reservoirs
Channels design / river restoration
Models studying long-term evolution of rivers
OBSERVED EFFECTIVE DISCHARGE
18 catchments 4 seasons
Water & suspended sediment flow data
Every river shows a different value.
Why? Climate, basin morphology, sediment features, flow variability, …
How do these factors interact?
EF
FE
CT
IVE
DIS
CH
AR
GE
(P
ER
UN
IT C
AT
CH
ME
NT
AR
EA
) [c
m/d
]
CATCHMENT #
WORKING HYPOTHESIS
COEFFICIENT of VARIATION
of DAILY FLOWS CVq
FUNCTIONAL-EQUIVALENT RATIO (EFFECTIVE RATIO)
q
qR
f
f
The river flow regime
is a key driver of the
effective discharge
EF
FE
CT
IVE
RA
TIO
R
f [
-]
[Botter et al., WRR 2007, 2008]
CLASSIFICATION of NATURAL FLOW REGIMES
= frequency of effective rainfall; = hydrograph recession rate k
kCVq
[Botter et al., PNAS 2013]
Streamflow pdf ~
River flow regime
Effective ratio
Effective discharge
Sediment flow pdf
Streamflow pdf
Sediment rating curve
[Basso et al., GRL 2015]
AN EXPLANATORY FRAMEWORK
AN EXPLANATORY FRAMEWORK
k
Function of the flow regime
(persistent/erratic)
1
k
kk
q
qR
f
f
Climatic control (effective rainfall frequency)
Landscape control (hydrograph recession rate)
PERSISTENCY INDEX
Landscape control (exponent of the sediment rating curve, sediment related features)
PERSISTENT: flows vary weakly
around their mean
ERRATIC: sequence of
very high and very low flows
AN EXPLANATORY FRAMEWORK
Distinct streamflow dynamics imply different
effective discharge
AN EXPLANATORY FRAMEWORK
CLIMATE CONTROLS ON EFFECTIVE DISCHARGE
Low rainfall frequency High ET
Low
High CVq
High qf
Elm Fork (TX)
Photo: FOEN
For details see: Basso et al., Climatic and landscape controls on effective discharge, GRL 2015.
www.catchsolutions.org