Marine Outfa
711
Part C | 32
32. Marine Outfalls
Peter M. Tate, Salvatore Scaturro, Bruce Cathers
Marine outfalls are used to discharge treated liquid
waste to the environment. Not all contaminants in
liquid waste can be removed by treatment. A properly designed, constructed, and operated marine
outfall effectively dilutes the discharged waste
which then substantially reduces the concentration of contaminants in the wastewater. In turn,
this reduces the risk to biota and human users of
the marine environment. An introduction to some
of the main aspects of marine outfalls is provided.
Five areas are covered, commencing with the
main influences associated with the decision to
build a marine outfall. Included is an overview
of the wastewater treatment process. Near-field
numerical modeling is described and it is demonstrated how this tool can be used to assist with
the design of a marine outfall. Outfall hydraulics
is discussed, detailing a range of features including head losses, manifolds (or diffusers), seawater
intrusion, and air entrainment. A very brief summary of the construction of a marine outfall is
provided. The final area covered describes environmental monitoring that should be undertaken
to confirm the putative impacts associated with
a marine outfall.
32.1 Terminology ........................................ 712
32.2 Governance ......................................... 713
32.2.1 Drivers for a Marine Outfall ........ 713
32.2.2 Wastewater Treatment ............... 714
32.2.3 Data Collection
for Outfall Design ...................... 715
32.3 Predicting Near-Field Dilutions ............ 716
32.3.1 Physical Models......................... 717
32.3.2 Positively Buoyant Jets
and Plumes .............................. 717
32.3.3 Negatively Buoyant Jets ............. 718
32.3.4 Model Validation ....................... 718
32.3.5 Far-Field Numerical Modeling .... 721
32.3.6 Data for Running the Models...... 721
32.3.7 Conceptual Design
for Positively Buoyant
Discharges ................................ 722
32.4 Hydraulic Analysis and Design .............. 723
32.4.1 Governing Hydraulics ................. 723
32.4.2 Diffusers – Hydraulic Design ....... 725
32.4.3 Flow Variability ......................... 729
32.4.4 Hydraulic Integration ................. 730
32.4.5 Air Entrainment......................... 732
32.4.6 Sedimentation .......................... 733
32.5 Outfall Construction ............................. 734
32.5.1 Construction Materials .............. 734
32.5.2 Construction Methods ............... 734
32.5.3 Some Considerations ................. 735
32.6 Environmental Monitoring ................... 736
32.6.1 Change Versus Impact ................ 736
32.6.2 Pre- and Post-construction
Monitoring ............................... 736
32.6.3 Long-Term Monitoring ............... 738
32.6.4 Summary .................................. 739
References................................................... 739
Work presented in this chapter concentrates on the
discharge of wastewater to the environment through
marine outfalls. Marine structures are required for intakes for drinking water (e.g., extraction of some types
of minerals, cooling of thermoelectric power equipment, desalination plants) and water for industrial or
commercial use (e.g., flushing of toilets). The focus
here is on marine outfalls; marine intakes are not considered further.
The primary objective of this chapter is to provide
practitioners with an overview of the fundamentals of
marine outfalls and to outline some initial considerations to help those new to the subject area. Understandably, the present chapter does not cover all areas in detail; the focus is on the design and monitoring aspects
of marine outfalls. Information on some of the problems drawn from experience with marine outfalls is provided and reference material with additional detail is
identified.
711
Part C | 32
32. Marine Outfalls
Peter M. Tate, Salvatore Scaturro, Bruce Cathers
Marine outfalls are used to discharge treated liquid
waste to the environment. Not all contaminants in
liquid waste can be removed by treatment. A properly designed, constructed, and operated marine
outfall effectively dilutes the discharged waste
which then substantially reduces the concentration of contaminants in the wastewater. In turn,
this reduces the risk to biota and human users of
the marine environment. An introduction to some
of the main aspects of marine outfalls is provided.
Five areas are covered, commencing with the
main influences associated with the decision to
build a marine outfall. Included is an overview
of the wastewater treatment process. Near-field
numerical modeling is described and it is demonstrated how this tool can be used to assist with
the design of a marine outfall. Outfall hydraulics
is discussed, detailing a range of features including head losses, manifolds (or diffusers), seawater
intrusion, and air entrainment. A very brief summary of the construction of a marine outfall is
provided. The final area covered describes environmental monitoring that should be undertaken
to confirm the putative impacts associated with
a marine outfall.
32.1 Terminology ........................................ 712
32.2 Governance ......................................... 713
32.2.1 Drivers for a Marine Outfall ........ 713
32.2.2 Wastewater Treatment ............... 714
32.2.3 Data Collection
for Outfall Design ...................... 715
32.3 Predicting Near-Field Dilutions ............ 716
32.3.1 Physical Models......................... 717
32.3.2 Positively Buoyant Jets
and Plumes .............................. 717
32.3.3 Negatively Buoyant Jets ............. 718
32.3.4 Model Validation ....................... 718
32.3.5 Far-Field Numerical Modeling .... 721
32.3.6 Data for Running the Models...... 721
32.3.7 Conceptual Design
for Positively Buoyant
Discharges ................................ 722
32.4 Hydraulic Analysis and Design .............. 723
32.4.1 Governing Hydraulics ................. 723
32.4.2 Diffusers – Hydraulic Design ....... 725
32.4.3 Flow Variability ......................... 729
32.4.4 Hydraulic Integration ................. 730
32.4.5 Air Entrainment......................... 732
32.4.6 Sedimentation .......................... 733
32.5 Outfall Construction ............................. 734
32.5.1 Construction Materials .............. 734
32.5.2 Construction Methods ............... 734
32.5.3 Some Considerations ................. 735
32.6 Environmental Monitoring ................... 736
32.6.1 Change Versus Impact ................ 736
32.6.2 Pre- and Post-construction
Monitoring ............................... 736
32.6.3 Long-Term Monitoring ............... 738
32.6.4 Summary .................................. 739
References................................................... 739
Work presented in this chapter concentrates on the
discharge of wastewater to the environment through
marine outfalls. Marine structures are required for intakes for drinking water (e.g., extraction of some types
of minerals, cooling of thermoelectric power equipment, desalination plants) and water for industrial or
commercial use (e.g., flushing of toilets). The focus
here is on marine outfalls; marine intakes are not considered further.
The primary objective of this chapter is to provide
practitioners with an overview of the fundamentals of
marine outfalls and to outline some initial considerations to help those new to the subject area. Understandably, the present chapter does not cover all areas in detail; the focus is on the design and monitoring aspects
of marine outfalls. Information on some of the problems drawn from experience with marine outfalls is provided and reference material with additional detail is
identified.