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5 Spatial patterns of flow and reactions

4 Reactive transport model - MIN3P

Water & Earth System ScienceCompetence Cluster

Water & Earth System ScienceCompetence Cluster

WESSWESS

Nico Trauth, Christian Schmidt, Uli Maier , and Jan H. Fleckenstein

Influence of varying hydraulic conditions on hyporheic exchangeand reactions in an in-stream gravel bar

1 Introduction

Contact: Nico TrauthHelmholtz Centre for Environmental Research - UFZ,Permoserstraße 15, 04318 Leipzig, Germany,nico.trauth@ufz.de | +49 341 235 1983

is licensed under the GNU General Public Licence (GPL) - www.openfoam.com

, Schmidt, C., Vieweg, M, Maier, U., Fleckenstein J.H., (2014), Hyporheic transport and biogeochemical reactions in pool-riffle systemsunder varying ambient groundwater flow conditions. Journal of Geophysical Research-Biogeosciences.

References:

OpenFOAM

Trauth, N.

®

Mayer, K. U.

Paraview

, Frind, E. O., and Blowes, D. W., (2002), Multicomponent reactive transport modeling in variably saturated porous mediausing a generalized formulation for kinetically controlled reactions. Water Resour. Res., 38(9), 1174, doi:10.1029/2001WR000862

- An end-user tool for large data visualization." The Visualization Handbook 717 (2005): 731.

2

Helmholtz Centre for Environmental Research - UFZ, Department of Hydrogeology, Leipzig, Germany

3 CFD simulations

6 Influence of stream discharge and ambient groundwater flow

7 Summary

Solute transport and consumption

?

?

?

?

Solute influx corresponds to HEFLosing and gaining conditions reduce RTand extent of HFC / reactive zones

reduced O and NO consumption

NO consumption increases with discharge:

The higher the discharge, the larger is theHFC and the "reactive fringe" of DNSolute consumption correlates with MRT

→ 2 3

3

Lat. > Long (Q < 1.2):high HEF, long RT

Lat. < Long (1.2< Q > 3.5):low HEF, short RT

ISGB inundated (Q > 3.5):high HEF, shortest RT

∆ h [m]

Str

eam

dis

charg

e [m

³/s]

Median residence times [hours] of HEF

-0.4 -0.2 0 0.2 0.4 0.6

0.5

1

1.5

2

2.5

3

3.5

4

4.5

1

2

3

4

5

6

7

∆ h [m]

Str

eam

dis

charg

e [m

³/s]

Hyporheic exchange flux [m³/d]

-0.4 -0.2 0 0.2 0.4 0.6

0.5

1

1.5

2

2.5

3

3.5

4

4.5

0

50

100

150

200

250

300

∆ h [m]

Str

ea

m d

isch

arg

e [

m³/

s]

O2

consumed by AR [mol/d]

-0.4 -0.2 0 0.2 0.4 0.6

0.5

1

1.5

2

2.5

3

3.5

4

4.5

0

5

10

15

20

25

30

35

Hyporheic exchange flux

Neutral conditions

Gaining conditions

?

?

?

?

?

?

?

hyporheic flow cell (HFC)

Large i HFCextentsReactive zones restricted to HFC

Upwelling groundwater exfiltrates at thestreambed (green areas)

Stream water infiltrates at the streambedfeeding the groundwater (red areas)Large reactive zones exist, also beyond theHFC extent

Stream water infiltrates at the small channeland exfiltrates at the large channel, forminga

n- and exfiltration areas and

Small reactive zones, restricted to the HFCextent

Losing conditions

Hyporheic exchange flux of ISGB? Stream water infiltrates at small

channel and exfiltrates at largechannel, forming a hyporheic flowcell (HFC)

Neutral conditions (

Gaining conditions

Losing conditions

Δ

Δ

Δ

h = 0)

( h > 0)

( h < 0)

?

?

?

?

?

?

Large in- and exfiltration areas andHFC extentsReactive zones restricted to HFC

Upwelling groundwater exfiltratesat the streambedSmall reactive zones, restricted tothe HFC extent

Stream water infiltrates at thestreambed feeding thegroundwaterLarge reactive zones exist, alsobeyond the HFC extent

Orientationof HEF flow paths

AR

DN

AR

DN

Natural in-stream gravel bar

In- and exfiltration areasat the streambed

? In-stream gravel bar (ISGB) at theSelke river in central GermanyExtent: 20 m x 7 m (low discharge)

Survey of morphologySlug tests, freeze coring forStage / discharge measurementsHead, EC, O time series in the

streambed sediments

?

?

?

?

?

K

2

GPS-

AR

DN

Bottom pressure across bedform

Flume discharge vs water level

flow direction

Model parameters:? surface water discharge: Q = 5 to 35 m³/ssurf

? slope: sl = 2 % (const)? inflow / outflow at bottom boundary : q = +2.5 to -2.5 m/dbot

? hydraulic conductivity porous media: K = 5x10 m/-4

s (const.)

Str

eam

dis

charg

e [m

³/s]

∆ h [m]

NO3

consumed by DN [mol/d]

-0.4 -0.2 0 0.2 0.4 0.6

0.5

1

1.5

2

2.5

3

3.5

4

4.5

2

4

6

8

10

In the hyporheic zone (HZ) importantbiogeochemical reactions of stream andgroundwater solutes occur with crucialimpact on nutrient cycling in fluvialsystems. Solutes that infiltrate into the HZare transported advectively by h

Computational FluidDynamics (CFD)

yporheicexchange flux (HEF) and show residencetimes (RT) that are controlled by streamhydraulics, streambed morphology andpermeability, and ambient groundwaterflow.In this study, we investigate how streamdischarge and ambient groundwater flowcontrol HEF, RT, solute transport andreactions in the HZ of a natural in-streamgravel bar (ISGB). We use three-dimensional

simulations coupled to areactive transport groundwater model.

[m.a.s.l]

x [m]

y [

m]

Q = 0.178 m³/s

h = 0.003 msurf

Δ

Q = 3.63 m³/ssurf

Δh = 0.017 m

r)

15 20 25 30 35 40

10

15

20

25

x [m]

y [

m]

-2 0 20

500

1000

1500RTD of HEF

log(hours)

0 100 2000

100

200

300RTD of GW-SW

hours

0 100 2000

100

200

300RTD of SW-GW

hours

15 20 25 30 35 40

10

15

20

25

x [m]

y [

m]

0 100 2000

100

200

300

400RTD of GW-SW

hours

0 200 4000

50

100

150RTD of SW-GW

hours

-2 0 20

500

1000

1500RTD of HEF

log(hours)

90

270

180 0

-2 0 20

500

1000

1500RTD of HEF

log(hours)

0 100 2000

100

200

300

400RTD of GW-SW

hours

0 200 4000

50

100

150RTD of SW-GW

hours

90

270

180 0

15 20 25 30 35 40

10

15

20

25

x [m]

y [

m]

-2 0 20

200

400

600

800

log(hours)

0 20 40-1

-0.5

0

0.5

1RTD of GW-SW

hours

0 100 2000

200

400

600

800RTD of SW-GW

hours

90

270

180 0

15 20 25 30 35 40

10

15

20

25

x [m]

y [m

]

-2 0 20

500

1000

log(hours)

50 100 1500

200

400

600RTD of GW-SW

hours

0 20 40-1

-0.5

0

0.5

1RTD of SW-GW

hours

90

270

180 0

15 20 25 30 35 40

10

15

20

25

x [m]

y [

m]

0 100 2000

20

40

60

80RTD of GW-SW

hours

0 100 2000

50

100

150

200RTD of SW-GW

hours

-2 0 20

500

1000

1500

2000

log(hours)

90

270

180 0

90

270

180 0

Orientation of HEF Orientation of HEF

RTD of HEF

Aerobic respiration

Denitrification

x

z

y

z

Orientation of HEF

RTD of HEF

Field site

0.92

Velocity

0.8

0.6

0

0.4

0.2

2.93

Velocity

2.0

0

1.0

Low discharge Q=0.18 m³/s

High discharge Q=3.63 m³/s

?

?

Discharge: 0.18 to 5.0 m³/sValidation to rating curve

Coupled to groundwatermodel

y

x z

y

x z

x

y

[m.a.s.l]

x [m]

y [m

]

y

x

Aerobic respiration (AR)

Denitrification (DN)

CH O + O CO + H O

5CH O + 4NO + 4H 5CO + 2N + 7H O

2 2 2 2

2 3 2 2 2

→

- +→

Subsurface flow

Hyporheic exchange flux and RT

Solute transport and reactions

?

?

Steady state simulations

neutral, losing, gainingconditions

Variation of groundwater headsimply

: h= -0.4 to +0.4 mΔ

?

?

?

Losing and gaining conditionssignificantly reduce HEF and RTVariation with stream discharge: Effect ofpredominance of lateral or longitudinal

head gradients across

the ISGB and the resulting flow-througharea.Different hydraulic system for completelyinundated ISGB

(∇ ∇Lat. / Long.)

Upstream head boundaryInflux of groundwater solutes:

O = 2 mg/l

NO = 100 mg/l

DOC = 0 mg/l

2

3

-

Hydraulic head distributionfrom CFD model

Influx of stream water solutes:O = 10 mg/l

NO = 10 mg/l

DOC = 18.66 mg/l

2

3

-

Dow

nst

ream

hea

d

boundar

y

Hydraulic head distributionCFD code:

Flowdirection

Flo

wdire

ctio

n

Flow direction

y

x

z

x

y

x

y

x

z

Subsurface flow pathsand reaction rates

y

z

20 30 40 50 1020

HEF In- / exfiltrationGaining flow pathsLosing flow paths

x-z crossection

Reactio

n ra

te

Inundated

Hig

hL

ow

∇ ∇Lat. Long.<

∇Long.

∇ ∇Lat. Long.<

∇ ∇Lat. Long.>

∇Lat.

y-z crossection

Flow direction Flow intoplane