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)

stefano.basso@eawag.ch

Photo: FOEN

For details see: Basso et al., Climatic and landscape controls on effective discharge, GRL 2015.

www.catchsolutions.org