Environmental Monitoring and Assessment

, Volume 65, Issue 1–2, pp 231–238 | Cite as

Near Field Dispersion in the Urban Environment - A Hydraulic Flume Study

  • R.W. MacDonald
  • B.J. Coulson
  • P.R. Slawson


The dispersion of material released from a point source immediately upwind of an obstacle array has been examined in a hydraulic flume with a low level of background turbulence. The main purpose of the experiments was to examine the interaction of the plume and the internal boundary layer (IBL) created over the obstacle array. The obstacle array consisted of 11 rows of cubes at 16% packing density in a staggered arrangement. Plume dispersion was measured using flow visualization with Rhodamine dye and also with a thermal tracer technique. During the experiments the source release height was varied between z = 0 and z = 4H, where H is the obstacle height. For the low-level releases, the upper boundary of the plume followed the growth of the IBL over the array. For higher level releases (z/H ≥ 2) the rate of plume growth was much reduced until the point downstream where it descended into the IBL, after which it experienced the intense turbulent mixing within the array. This suggests that the urban lateral spread parameter σy should be a strong function of height in situations where the turbulence level in the ambient approach flow is low. These results highlight the importance of the ambient turbulence even in strongly obstacle-affected dispersion.

dispersion turbulent boundary layer physical modelling urban pollution 


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Copyright information

© Kluwer Academic Publishers 2000

Authors and Affiliations

  • R.W. MacDonald
    • 1
  • B.J. Coulson
    • 2
  • P.R. Slawson
    • 2
  1. 1.Department of Mechanical EngineeringUniversity of WaterlooWaterlooCanada
  2. 2.Department of Mechanical EngineeringUniversity of WaterlooWaterlooCanada

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