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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,[email protected] | +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
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