الفهرس 
chapter 1Only 14 pages are availabe for public view
 |  | from | 117 |  |  |
| | | from | 117 | | |
Abstract
Various approaches for improving ecological systems can be distinguished. The two most important approaches are restoration and
rehabilitation. The number of rehabilitation projects has been increased
considerably during the past decade. This is because of the fact that streams
have been receiving large amounts of pollutants and disposals. Water quality
and its enhancement depend upon the level of dissolved oxygen present. In
fact, the oxygen concentration in surface waters is a prime indicator of the
water quality for human use as well as for the survival of aquatic biota. There
are many different hydraulic structures that have been employed to enhance
self purification purposes such as weirs, spillways, gated sills, ogee crests,
gated conduit outlets, stepped cascade and tainter gates. Self-aeration on
stepped cascades is now recognized for its substantial contribution to the air-
water transfer of atmospheric gases including oxygen and nitrogen. Stepped
cascades are efficient structures to enhance aeration because of the strong
turbulent mixing effect induced, the large residence time and the substantial
air bubble entrainment caused by turbulence fluctuations acting next to the air-
water free surface. Through this interface, air is continuously tapped and
released. There are large numbers of streams have natural stepped cascade that
the water turbulently over the steps forming huge numbers of air bubbles that
entered the water and make it naturally purified. For example, In Egypt, there
is Bahr Wahbi drain that flows in Fayoum, Five reaeration cascades have been
built to reaerate the depleted water along Chicago’s Calumet waterway, and a
two steps reaeration cascade was added downstream of the Petit-Saut Dam in
French Guyana to treat turbined waters which had unacceptably high methane
content.
The aim of this research is to study the influence of stepped cascade with
its different geometry on enhancing the level of aeration efficiency at different
flow rates and determine the most suitable hydraulic structure (stepped
ABSTRACT
Various approaches for improving ecological systems can be
distinguished. The two most important approaches are restoration and
rehabilitation. The number of rehabilitation projects has been increased
considerably during the past decade. This is because of the fact that streams
have been receiving large amounts of pollutants and disposals. Water quality
and its enhancement depend upon the level of dissolved oxygen present. In
fact, the oxygen concentration in surface waters is a prime indicator of the
water quality for human use as well as for the survival of aquatic biota. There
are many different hydraulic structures that have been employed to enhance
self purification purposes such as weirs, spillways, gated sills, ogee crests,
gated conduit outlets, stepped cascade and tainter gates. Self-aeration on
stepped cascades is now recognized for its substantial contribution to the air-
water transfer of atmospheric gases including oxygen and nitrogen. Stepped
cascades are efficient structures to enhance aeration because of the strong
turbulent mixing effect induced, the large residence time and the substantial
air bubble entrainment caused by turbulence fluctuations acting next to the air-
water free surface. Through this interface, air is continuously tapped and
released. There are large numbers of streams have natural stepped cascade that
the water turbulently over the steps forming huge numbers of air bubbles that
entered the water and make it naturally purified. For example, In Egypt, there
is Bahr Wahbi drain that flows in Fayoum, Five reaeration cascades have been
built to reaerate the depleted water along Chicago’s Calumet waterway, and a
two steps reaeration cascade was added downstream of the Petit-Saut Dam in
French Guyana to treat turbined waters which had unacceptably high methane
content.
The aim of this research is to study the influence of stepped cascade with
its different geometry on enhancing the level of aeration efficiency at different
flow rates and ·determine the most suitable hydraulic structure (stepped
ABSTRACT
Various approaches for improving ecological systems can be
distinguished. The two most important approaches are restoration and
rehabilitation. The number of rehabilitation projects has been increased
considerably during the past decade. This is because of the fact that streams
have been receiving large amounts of pollutants and disposals. Water quality
and its enhancement depend upon the level of dissolved oxygen present. In
fact, the oxygen concentration in surface waters is a prime indicator of the
water quality for human use as well as for the survival of aquatic biota. There
are many different hydraulic structures that have been employed to enhance
self purification purposes such as weirs, spillways, gated sills, ogee crests,
gated conduit outlets, stepped cascade and tainter gates. Self-aeration on
stepped cascades is now recognized for its substantial contribution to the air-
water transfer of atmospheric gases including oxygen and nitrogen. Stepped
cascades are efficient structures to enhance aeration because of the strong
turbulent mixing effect induced, the large residence time and the substantial
air bubble entrainment caused by turbulence fluctuations acting next to the air-
water free surface. Through this interface, air is continuously tapped and
released. There are large numbers of streams have natural stepped cascade that
the water turbulently over the steps forming huge numbers of air bubbles that
entered the water and make it naturally purified. For example, In Egypt, there
is Bahr Wahbi drain that flows in Fayoum, Five reaeration cascades have been
built to reaerate the depleted water along Chicago’s Calumet waterway, and a
two steps reaeration cascade was added downstream of the Petit-Saut Dam in
French Guyana to treat turbined waters which had unacceptably high methane
content.
The aim of this research is to study the influence of stepped cascade with
its different geometry on enhancing the level of aeration efficiency at different
flow rates and determine the most suitable hydraulic structure (stepped
Various approaches for improving ecological systems can be
distinguished. The two most important approaches are restoration and
rehabilitation. The number of rehabilitation projects has been increased
considerably during the past decade. This is because of the fact that streams
have been receiving large amounts of pollutants and disposals. Water quality
and its enhancement depend upon the level of dissolved oxygen present. In
fact, the oxygen concentration in surface waters is a prime indicator of the
water quality for human use as well as for the survival of aquatic biota. There
are many different hydraulic structures that have been employed to enhance
self purification purposes such as weirs, spillways, gated sills, ogee crests,
gated conduit outlets, stepped cascade and tainter gates. Self-aeration on
stepped cascades is now recognized for its substantial contribution to the air-
water transfer of atmospheric gases including oxygen and nitrogen. Stepped
cascades are efficient structures to enhance aeration because of the strong
turbulent mixing effect induced, the large residence time and the substantial
air bubble entrainment caused by turbulence fluctuations acting next to the air-
water free surface. Through this interface, air is continuously tapped and
released. There are large numbers of streams have natural stepped cascade that
the water turbulently over the steps forming huge numbers of air bubbles that
entered the water and make it naturally purified. For example, In Egypt, there
is Bahr Wahbi drain that flows in Fayoum, Five reaeration cascades have been
built to reaerate the depleted water along Chicago’s Calumet waterway, and a
two steps reaeration cascade was added downstream of the Petit-Saut Dam in
French Guyana to treat turbined waters which had unacceptably high methane
content.
The aim of this research is to study the influence of stepped cascade with
its different geometry on enhancing the level of aeration efficiency at different
flow rates and determine the most suitable hydraulic structure (stepped