Modelling of pollution dispersion

1
Modelling of pollution dispersion in natural
stream during dry period
Yvetta Velísková Institute of Hydrology SAS,
Racianska 75, 831 02 Bratislava,
Slovakia e-mail veliskova_at_uh.savba.sk

2
(No Transcript)
3
(No Transcript)
4
(No Transcript)
5
Environmental problems
Water pollution
Mathematical and numerical modelling
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

6
(No Transcript)
7
(No Transcript)
8
Dead zone model - scheme

• the mass transfer across the main flow and dead
  zone interface is proportional
• to the concentration difference across them and
• to the discharge velocity

9

• 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.

10
numerical models

• condition for application
• range of input data
• rate of precision
• etc.

two-dimensional model
11
Hydrodynamic approach
influence of dead zones
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, ex, ey, ez - 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

12
Model MODI

• 2-D simulation model for determination of
  pollutant transport in natural
• (non-prismatic) channels
• based on the solution of advection-diffusion
  equation
• simulates under conditions of steady flow in
  non-prismatic channels
• possibility of simulation
• arbitrarily situated unsteady sources of
  pollution
• influence of dead zones
• self-purification effect

• 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)

13

• 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)

14
dz eps Amz Vmz T
15
dz 0,03 Amz Vmz T
16

• Conclusion
• 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
dead zone
17

• Conclusion
• there are existed the dead zone models 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.
  

18
THANK YOU FOR YOUR ATTENTION
www.ih.savba.sk E-mail veliskova_at_uh.savba.sk