modelling of pollution dispersion in natural stream during dry period
DESCRIPTION
Modelling of pollution dispersion in natural stream during dry period. Yvetta Velísková Institute of Hydrology SAS, Racianska 75, 831 02 Bratislava, Slovakia e-mail: [email protected] . Drought consequences environmental economic social. reduction of water quality. - PowerPoint PPT PresentationTRANSCRIPT
Modelling of pollution dispersion
in natural stream during dry period
Yvetta Velísková
Institute of Hydrology SAS, Racianska 75, 831 02 Bratislava, Slovakia
e-mail: [email protected]
Drought consequencesDrought consequences
•environmentalenvironmental
•economiceconomic
•socialsocial
reduction of water quality
H
X1 X2
X
Y
Hh
Hb
H 2
B
H 0
D 0
HPV
H
X1 X2
X
Y
Hh
Hb
H 2
B
H 0
D 0HPV
Environmental problems
Water pollution
determination of transport, dispersion and self-purifying characteristics of channels, optimum location of outlet structures in streams, delineation of
mixing zones, prediction of spreading of accidental contaminant waves, etc.
determination of pollutant distribution in natural streams in which the bed stream roughness, as results of flow conditions during low flows, forcefully impacts on a
flow structure
Mathematical and numerical modelling
Mathematical models
of natural processes
energy and
matter conservation law
non-uniform velocity distribution (low flow condition)
pollutant distribution changes caused by trapping and slow release of pollutant from eddies that are trapped behind roughnesses
in an open channel DEAD ZONES
Dead zone model - scheme
the mass transfer across the main flow and dead zone interface is the mass transfer across the main flow and dead zone interface is proportionalproportional
•to the concentration difference across them and to the concentration difference across them and
•to the discharge velocityto the discharge velocity
The influence of dead zones was formed to the equations, which represent the conception:
• transported mass – pollutant from the main flow (with the concentration C) gets into a side or a bottom dead zones as into a mixing tank;
•after that pollutant is mixed within the tank volume and then
•is exported back to the main flow zone with concentration CDZ .
The residence time of the fluid in the tank depends on
•the mass exchange coefficient between the dead zones and the main flow
and also
•on ratio of interfacial area to the dead zone volume. DZDZDZ CCkDt
C
..
numerical models
•condition for application
•range of input data
•rate of precision
•etc.
( B>30h )
two-dimensional model
Hydrodynamic approach
z
ch
zy
ch
yx
ch
xz
cwh
y
cvh
x
cuh
t
chzyx
c - mass concentration of pollutant [kg.m-3], h - depth [m], t - time [s], x,y,z - longitudinal, transverse and vertical coordinates [m], u,v,w - depth-averaged longitudinal, transverse and vertical velocities [m.s -1], εx, εy, εz - longitudinal, transverse and vertical dispersion coefficients [m2.s-1]
Input data:• geomorphological characteristics of river, • data connected with discharge and water level regime • dispersion characteristics at simulated part of river• data about pollution sources
+ influence of „dead zones“+ influence of „dead zones“
Model MODI:Model MODI:
• 2-D simulation model for determination of pollutant transport in 2-D simulation model for determination of pollutant transport in natural natural
(non-prismatic) channels(non-prismatic) channels
• based on the solution of advection-diffusion equationbased on the solution of advection-diffusion equation
• simulates under conditions of steady flow in non-prismatic channelssimulates under conditions of steady flow in non-prismatic channels
• possibility of simulation:possibility of simulation:
arbitrarily situated unsteady sources of pollutionarbitrarily situated unsteady sources of pollution
influence of “dead zones”influence of “dead zones”
self-purification effectself-purification effect numerical solution ADQnumerical solution ADQ
stream-tube stream-tube conceptionconception
Input data:Input data:
•geometric characteristics of cross-sections and velocity profiles in selected location of computed part of stream
•quantity and location of pollutant sources
•coefficients of transverse dispersion
•self-purification coefficient
•diffusion coefficient with “dead zones” and the interfacial area between the main flow and “dead zones” (the volume of “dead zones”)
0
2 0 0
4 0 0
6 0 0
8 0 0
1 0 0 0
1 2 0 0
d i s t a n c e [ m ]
1 0
2 0
3 0
w i d t h [ m ]
0
5
1 0
1 5
2 0
2 5
3 0
3 5
4 0
4 5
5 0
5 5
6 0
6 5
7 0
7 5
8 0
8 5
9 0
9 5
t= 1000s
0
2 0 0
4 0 0
6 0 0
8 0 0
1 0 0 0
1 2 0 0
d i s t a n c e [ m ]
1 0
2 0
3 0
4 0
w i d t h [ m ]
- 2
0
2
4
6
8
1 0
1 2
1 4
1 6
1 8
2 0
2 2
2 4
2 6
2 8
3 0
3 2
3 4
3 6
t= 2000s
1 0 0 0
1 2 0 0
1 4 0 0
1 6 0 0
1 8 0 0
2 0 0 0
2 2 0 0
d i s t a n c e [ m ]
1 0
2 0
3 0
w i d t h [ m ]
0
2
4
6
8
1 0
1 2
1 4
1 6
1 8
2 0
2 2
2 4
2 6
t= 4000s
•the mass exchange coefficient between the dead zones and the main flow
(from 0.003 m2s-1 to 0.03 m2s-1),
•the interfacial area of dead zones
(from 10% to 30% of active part) and
•their volume (from 20% to 50% of active part)
0
1
2
3
4
5
6
7
0 1000 2000 3000 4000 5000distance [m]
co
nc
en
tra
tio
n [
mg
/l]
T1=1000s T2=2000s T3=3000s T4=4000s
0
1
2
3
4
5
6
7
0 1000 2000 3000 4000 5000distance [m]
conc
entr
atio
n
[mg/
l]
T1=1000s T2=2000s T3=3000s T4=4000s
dzl1020T1 dzl1020T2 dzl120T3 dzl1020T4
dz eps Amz Vmz T
0
2
4
6
0 1000 2000 3000 4000 5000distance [m]
con
cen
trat
ion
[m
g/l]
T1=1000s T2=2000s T3=3000s T4=4000s
dzl1020T1 dzl1020T2 dzl1020T3 dzl1020T4
dzh1020T1 dzh1020T2 dzh1020T3 dzh1020T4
dz 0,03 Amz Vmz T
0
1
2
3
4
5
6
7
0 1000 2000 3000 4000 5000distance [m]
co
nc
en
tra
tio
n [
mg
/l]
T1=1000s T2=2000s T3=3000s T4=4000s
0
2
4
6
0 1000 2000 3000 4000 5000distance [m]
con
cen
trat
ion
[m
g/l]
T1=1000s T2=2000s T3=3000s T4=4000s
dz1020T1 dz1020T2 dz1020T3 dz1020T4(dz interface area volume time )
0
2
4
6
0 1000 2000 3000 4000 5000distance [m]
con
cen
trat
ion
[m
g/l]
T1=1000s T2=2000s T3=3000s T4=4000s
dz1540T1 dz1540T2 dz1540T3 dz1540T4
0
2
4
6
0 1000 2000 3000 4000 5000distance [m]
con
cen
trat
ion
[m
g/l]
T1=1000s T2=2000s T3=3000s
T4=4000s dz3050T1 dz3050T2
dz3050T3 dz3050T4 dz3050T5
0
2
4
6
0 1000 2000 3000 4000 5000distance [m]
co
nc
en
tra
tio
n [
mg
/l]
T1=1000s T2=2000s T3=3000s T4=4000s
dz1020T1 dz1020T2 dz1020T3 dz1020T4
dz1540T1 dz1540T2 dz1540T3 dz1540T4
dz3050T1 dz3050T2 dz3050T3 dz3050T4
dz3050T5
ConclusionConclusion
drought - a period of abnormally dry weather sufficiently prolonged for the lack of water to cause serious hydrologic imbalance in the affected area.
It is a period of unusually persistant dry weather that persists long enough to cause serious problems such as
•crop loss or damage,
•water supply shortages,
•soil erosion
• reduction of water quality, because low water flows change conditions in a natural stream, reduce dilution of pollutants and so increase contamination of water.
low flow roughness
dead zone
ConclusionConclusion
there are existed the dead zonedead zone modelsmodels which divide the flow into two distinct zones: the main stream, in which advection-diffusion equation could be applied, and well mixed separation zones along the bed and banks
the mass transfer across the main flow and dead zone interface is proportional to the concentration difference across them and to the discharge velocity
this idea and conception was successfully applied into the two-dimensional dispersion model MODI
the results of numerical experiments show that the curve of mass distribution modifies its form and its peaks delay; this decrease and shifting of pollutant distribution curve depends on the values of the dead zones parameters (with increased time the shifting and decreasing grow)
It is very important to give higher attention to prediction and solution of ecological accidents also in future, because
from the outputs of climate scenarios it is clear that occurrence of minimum discharges at streams would be more and more frequent,
the industry and land-use of regions near streams would mean possibility of new pollutant sources and
from point of view of environment it is necessary to know how we can solve such problems.
