The effect of the pool and riffle on transport in rivers
One-dimensional steady flow pollutant transport models assume that the river reach modelled has a uniform cross-sectional shape which manifests as a constant average velocity in the model equations. Rarely do rivers meet this criterion. Their channels are seldom uniform in shape, but rather alternat...
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ftcanadathes:oai:collectionscanada.gc.ca:MWU.1993/4044 2023-05-15T15:26:06+02:00 The effect of the pool and riffle on transport in rivers Halket, Ian Rasmussen, Peter (Civil Engineering) Doering, Jay (Civil Engineering) Cicek, Nazim (Biosystems Engineering) Lobb, David (Soil Science) Steffler, Peter (Water Resources Engineering, University of Alberta) 2010-07-26T16:18:49Z http://hdl.handle.net/1993/4044 en_US eng http://hdl.handle.net/1993/4044 Water Quality Modelling 2010 ftcanadathes 2014-03-30T00:50:28Z One-dimensional steady flow pollutant transport models assume that the river reach modelled has a uniform cross-sectional shape which manifests as a constant average velocity in the model equations. Rarely do rivers meet this criterion. Their channels are seldom uniform in shape, but rather alternate in a quasi-periodic manner between pool and riffle sections. This bedform sequencing imparts a corresponding variation in the average cross-sectional velocity which is not accounted for in constant velocity transport models. The literature points out that the pool and riffle planform may be the reason for the sometimes poor predictions obtained from these models. This thesis confirms that the fluctuation in average cross-sectional velocity caused by the pool and riffle planform does have a marked effect on transport in rivers. The pool and riffle planform promotes an enhanced decay of a pollutant when a first order biochemical reaction is simulated. This effect becomes more pronounced as flow declines. The reason for this is that travel time in a pool and riffle channel is greater than for a uniformly shaped channel. Current one-dimensional models assume a uniform channel and therefore overestimate the velocity of a substance moving downstream. To show this an equation is developed that describes the variation in average cross-sectional velocity along a pool and riffle channel. The parameters of the equation can be easily evaluated for any river. The equation is incorporated into a mass balance analysis and a new form of the river transport model is derived. Analysis shows that the transport of a substance in a pool and riffle channel is governed by travel velocity which is different from the average cross-sectional velocity used in the traditional advection model. Replacing average velocity with travel velocity provides a simple fix for the traditional model. The new transport model is tested on the Athabasca River with excellent results. The variable velocity model successfully simulates the DO dynamics on a 550 kilometre stretch of the river. This suggests that the model has good potential for simulating pollutant transport in other rivers. Since analysis shows that the effect of the pool and riffle planform on contaminant transport is magnified at low flow levels, the model has good potential for use in determining TMDLs for contaminants, because these regulatory levels are set for low flow conditions. Other/Unknown Material Athabasca River Theses Canada/Thèses Canada (Library and Archives Canada) Athabasca River |
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Open Polar |
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Theses Canada/Thèses Canada (Library and Archives Canada) |
op_collection_id |
ftcanadathes |
language |
English |
topic |
Water Quality Modelling |
spellingShingle |
Water Quality Modelling Halket, Ian The effect of the pool and riffle on transport in rivers |
topic_facet |
Water Quality Modelling |
description |
One-dimensional steady flow pollutant transport models assume that the river reach modelled has a uniform cross-sectional shape which manifests as a constant average velocity in the model equations. Rarely do rivers meet this criterion. Their channels are seldom uniform in shape, but rather alternate in a quasi-periodic manner between pool and riffle sections. This bedform sequencing imparts a corresponding variation in the average cross-sectional velocity which is not accounted for in constant velocity transport models. The literature points out that the pool and riffle planform may be the reason for the sometimes poor predictions obtained from these models. This thesis confirms that the fluctuation in average cross-sectional velocity caused by the pool and riffle planform does have a marked effect on transport in rivers. The pool and riffle planform promotes an enhanced decay of a pollutant when a first order biochemical reaction is simulated. This effect becomes more pronounced as flow declines. The reason for this is that travel time in a pool and riffle channel is greater than for a uniformly shaped channel. Current one-dimensional models assume a uniform channel and therefore overestimate the velocity of a substance moving downstream. To show this an equation is developed that describes the variation in average cross-sectional velocity along a pool and riffle channel. The parameters of the equation can be easily evaluated for any river. The equation is incorporated into a mass balance analysis and a new form of the river transport model is derived. Analysis shows that the transport of a substance in a pool and riffle channel is governed by travel velocity which is different from the average cross-sectional velocity used in the traditional advection model. Replacing average velocity with travel velocity provides a simple fix for the traditional model. The new transport model is tested on the Athabasca River with excellent results. The variable velocity model successfully simulates the DO dynamics on a 550 kilometre stretch of the river. This suggests that the model has good potential for simulating pollutant transport in other rivers. Since analysis shows that the effect of the pool and riffle planform on contaminant transport is magnified at low flow levels, the model has good potential for use in determining TMDLs for contaminants, because these regulatory levels are set for low flow conditions. |
author2 |
Rasmussen, Peter (Civil Engineering) Doering, Jay (Civil Engineering) Cicek, Nazim (Biosystems Engineering) Lobb, David (Soil Science) Steffler, Peter (Water Resources Engineering, University of Alberta) |
author |
Halket, Ian |
author_facet |
Halket, Ian |
author_sort |
Halket, Ian |
title |
The effect of the pool and riffle on transport in rivers |
title_short |
The effect of the pool and riffle on transport in rivers |
title_full |
The effect of the pool and riffle on transport in rivers |
title_fullStr |
The effect of the pool and riffle on transport in rivers |
title_full_unstemmed |
The effect of the pool and riffle on transport in rivers |
title_sort |
effect of the pool and riffle on transport in rivers |
publishDate |
2010 |
url |
http://hdl.handle.net/1993/4044 |
geographic |
Athabasca River |
geographic_facet |
Athabasca River |
genre |
Athabasca River |
genre_facet |
Athabasca River |
op_relation |
http://hdl.handle.net/1993/4044 |
_version_ |
1766356658687049728 |