Outfall Off Research Articles

Considerations for Storm-Water Outfalls off Exposed Coasts

There is a worldwide movement for coastal municipalities in developed countries to replace whole series of storm drains with far fewer storm-water outfalls that discharge well offshore. Such an extended-length pipe, passing into the surf zone along an exposed coastline, is far from easy to plan, support with data, design, install, and operate. This paper is intended to school drainage engineers in these matters.

BOD–DO modeling and water quality analysis of a waste water outfall off Kochi, west coast of India

Water quality scenarios around an offshore outfall off Kochi were simulated using MIKE21 water quality model, assuming a high Biochemical Oxygen Demand (BOD=50 mgl−1) effluent discharge. The discharge is introduced into the model through an outfall located at a distance of 6.8 km from the shore at a depth of 10 m. Three scenarios were simulated with different discharge rates such as 2, 5 and 10 m3 s−1, with BOD load of 8640, 21,600 and 43,200 kg day−1 respectively. Model simulations were carried out to estimate the assimilation capacity of the waters off Kochi for the three discharge rates. The results show that for 10 m3 s−1 effluent discharge, the initial BOD of 50 mg l−1 reduced to 3.33 mg l−1 at the outfall after 48 h. High BOD values were confined to an elliptical area of ∼8 km2 around the outfall. Based on this, the assimilative capacity of the waters off Kochi in terms of BOD can be estimated as 38,000 kg day−1. It is suggested that offshore waters could be used as a feasible alternative to the Kochi backwaters for the disposal of treated effluent.

Discussion: An unusual marine outfall off central California, USA

Discussion: An unusual marine outfall off central California, USA

An unusual marine outfall off central California, USA

An unusual marine outfall off central California, USA

An unusual marine outfall off central California, USA

An unusual marine outfall off central California, USA

An unusual marine outfall off central California, USA

An unusual marine outfall off central California, USA

An unusual marine outfall off central California, USA

This paper concerns Monterey Bay, California, where two prohibited wastewater discharge areas were established in 1971 following sewage pollution incidents. Several south Bay municipalities were forced to close their own treatment plants and outfalls, with the sewage being piped to a central coastal location for combined discharge. Eleventh-hour limitations on coastal access resulted in the outfall's having an unusual Z configuration, with the middle leg perpendicular to some directions of storm wave approach. Construction of the outfall was halted by the El Niño storms of 1982–1983 that destroyed half the trestle and removed countless tons of armour rock. After more difficulties, the pipe was completed in 1984, but then suffered damage from a strong earthquake in late 1989. A year later the outfall was repaired in an extraordinary inside-the-pipe operation. In 1995 and 1996, duckbill valves were placed, in 30 m of water, over all operating diffuser ports. This was done because of impending wastewater reclamation for crop irrigation, and virtual outfall shutdown at certain times. The latest concern has involved the adequacy of diffuser rock protection.

An unusual marine outfall off central California, USA

This paper concerns Monterey Bay, California, where two prohibited wastewater discharge areas were established in 1971 following sewage pollution incidents. Several south Bay municipalities were forced to close their own treatment plants and outfalls, with the sewage being piped to a central coastal location for combined discharge. Eleventh-hour limitations on coastal access resulted in the outfall's having an unusual Z configuration, with the middle leg perpendicular to some directions of storm wave approach. Construction of the outfall was halted by the El Niño storms of 1982–1983 that destroyed half the trestle and removed countless tons of armour rock. After more difficulties, the pipe was completed in 1984, but then suffered damage from a strong earthquake in late 1989. A year later the outfall was repaired in an extraordinary inside-the-pipe operation. In 1995 and 1996, duckbill valves were placed, in 30 m of water, over all operating diffuser ports. This was done because of impending wastewater reclamation for crop irrigation, and virtual outfall shutdown at certain times. The latest concern has involved the adequacy of diffuser rock protection.

Field assessment of numerical impacts of coastal sewage disposal on fish larvae relative to natural variability

Sewage disposal in aquatic environments can have significant impacts on assemblages of organisms. There have been few field investigations on effects of sewage disposal on fish larvae. Data on abundances of larvae, current velocities and the size and shape of sewage plumes from point-source shoreline outfalls off Sydney (Australia) indicated that alongshore currents could transport large numbers of fish larvae into plumes, potentially affecting their health. Assemblages of fish larvae in surface sewage plumes differed to those in distant shelf (control) waters, but no such impacts were detected for assemblages in subsurface (20 m depth) waters beneath plumes. No predictable negative or positive numerical responses of fish larvae to sewage disposal were detected. Abundances of fish larvae fluctuated greatly in space and throughout time, and responses appeared to vary between taxa, outfalls and sampling periods. However, the large inherent level of natural spatial and temporal variability in abundances of larvae confounded the detection of possible impacts. Future field investigations need to focus on effects of sewage disposal on the health and condition of fish larvae. Designs for future field-based studies are discussed.

Trophically-based assessment of the impacts of deepwater sewage disposal on a demersal fish community

The impacts of sewage disposal on the demersal fish community were identified after approximately 2 years of operation of a deepwater outfall off Sydney, NSW Australia. Gut-content analyses were used as a basis for identifying groups of fish with dietary similarities. Similar results from multivariate analyses (Bray-Curtis dissimilarity measure and MDS) identified 8 trophically-similar groups of fish. The majority of the fish comprising these groups consumed organisms in the soft-bottom community. Only 5 of the 8 trophic groups identified could be analysed in detail as individuals comprising the remaining groups were not caught in sufficient numbers near the outfall. Asymmetrical analyses of variance showed that the numbers of individuals and species in one particular trophic group increased significantly following the commissioning of the Bondi deepwater outfall. However, the proportional representation of individuals in the 5 trophic groups examined did not change. Five hypotheses are advanced to account for the observed impacts. Of these, hypotheses centred around increased habitat complexity and a numerical response to increases in prey abundance warrant further investigation. Directions of future research and the limitations of various designs to assess environmental impacts are discussed in light of these results.

Organochlorine compound and trace metal contaminants in fish near Sydney's ocean outfalls

Sydney's inshore sewage outfalls were significant contributors to organochlorine contamination of inshore sedentary fish such as red morwong. Diversion of the sewage to deepwater outfalls has resulted in marked declines in the concentrations of these compounds in inshore red morwong. Apart from lead, however, similar trends did not occur for concentrations of trace metals. A wide variety of trace metals and organochlorine compounds were found in the flesh and/or livers of a variety of fish species caught at sites associated with the present deepwater ocean outfalls off Sydney. Fish caught at locations remote from Sydney also contained a wide variety of trace metals although organochlorine compounds were usually at lower levels. The mean contaminant levels in all species of offshore fish were generally found to be low when compared to the Australian National Food Authority's Maximum Residue Limit (NFA MRL). No fish analysed was found to have levels of an organochlorine compound above the MRL and no fish was found to have levels of zinc or lead above the MRL. When detected, fish with levels of a trace metal above the MRL appeared to be distributed throughout New South Wales, independent of the deepwater ocean outfalls off Sydney. There is no evidence as yet that the commissioning of the deepwater outfalls has led to an increase in levels of contaminants in the fish examined to the extent that they are of concern relative to the NFA MRLs.

Recent temporal trends in sediment metal concentrations near a large wastewater outfall off Orange County, California

Temporal trends in sediment metal concentrations near a large wastewater outfall in southern California were evaluated with respect to changes in effluent metal concentrations and mass‐emission rates (MERs). During 1985 to 1992, metal concentrations and MERs in the County Sanitation Districts of Orange County effluent decreased by approximately 30% to 90%. Relatively smaller but statistically significant changes in metal concentrations in sediments adjacent to the outfall also occurred during this period. At nearfield sites, significant decreases in sediment concentrations were apparent for a subset of the metals that were more highly enriched in the effluent relative to background sediment concentrations. Changes in effluent concentrations of Cd, Cu, Cr, Ni, and Zn explained 48% to 62% of the variance in the corresponding metal concentrations in sediments immediately adjacent to the outfall. Appreciable but relatively smaller decreases in sediment metal concentrations occurred at other shelf locations. Correlations between effluent and sediment metal concentrations generally were weaker at greater distance from the outfall.

Metal contamination of sediments associated with deepwater ocean sewage outfalls, Sydney, Australia

The New South Wales Environment Protection Authority has recently completed a programme to evaluate the impact on near-shore shelf sediments, following the commissioning of three new deepwater sewage outfalls off Sydney, Australia. These outfalls discharge a total of around 1300 ML day −1 of primary treated sewage derived from domestic and industrial sources. The study compared three locations that were close to the outfalls (likely impacted) and three locations far from the outfalls (likely non-impacted). Four zones were sampled within each location to provide estimates of spatial variability. Three samples of surface sediment were collected from each zone at six monthly intervals over a three year period which encompassed the commissioning of the outfalls. The results of the study suggest that, associated with the commissioning of the three deepwater outfalls, there has not been a significant effect on the concentration of trace metals in the sediments surrounding the outfalls. The concentrations of trace metals in the whole sediment generally were close to the world-wide background levels quoted in the literature, and generally reflected the distribution pattern of the sedimentary fines (< 62.5 mm). When compared to a number of sediment quality guidelines, the concentrations of trace metals were found to be below a level considered to have the potential to cause biological effects or (in the case of As, Ni, Cr) at a level that could be tolerated by the majority of benthic organisms.

Assessing impacts of deepwater sewage disposal: A case study from New South Wales, Australia

To overcome the problems of beach pollution Sydney Water constructed three deepwater sewage outfalls off North Head, Bondi and Malabar. The outfalls were commissioned over the period September 1990–July 1991. A 5-year multi-disciplinary environmental monitoring programme was set up to assess the impacts on the demersal fish and soft-bottom macro-invertebrate communities. Assessment of impact was based on an asymmetrical analysis of variance which provided an a priori orthogonal contrast between a single outfall and multiple control sites sampled before and after commissioning. Impacts were detected in both communities, included several commercially and recreationally important species of fish, and occurred with the greatest frequency in the soft-bottom community. The results are summarized, and several examples are presented and show that the direction and magnitude of the impacts varied among outfalls and taxa. The results are then discussed in terms of the needs of future monitoring and the implications for the assessment of human-induced impacts in other parts of the world.

Current monitoring for environmental pollution studies by acoustic Doppler current profiling

NOAA’s National Ocean Service (NOS) has been measuring and predicting coastal currents for over 100 years. In earlier times, measurements were made with current poles, or propeller-type current meters. In the late 1980’s, acoustic Doppler current profilers (ADCPs) were widely adopted. In Tampa Bay, 10 ADCPs (RD Instruments) were deployed in bottom-mounted platforms; a towed ADCP provided spatial contours of current speed. A real-time system provided 6-min averages of current to mariners and environmental managers. This system, still in place, provides vital information for tracking land cleanup of pollutant spills. Recently, an ADCP was added to a conventional current meter array deployed by NOAA/AOML at a wastewater outfall off Miami, Florida. The ADCP measurements compared well with earlier observations and facilitated assessing the effects of mooring motion and bio-fouling. Analysis of ADCP profile data revealed a near-linear velocity gradient from surface to bottom, enabling interpolation of velocity profiles from earlier measurements. ADCP backscatter intensity provided a rough estimate of suspended material. Future applications include mapping the three-dimensional circulation around point sources of pollution. Such maps provide environmental managers with data for effective effluent disposal management at minimum cost.

Indentification and quantification of mono-, di- and trihydroxybenzenes (phenols) at trace concentrations in seawater by aqueous acetylation and gas chromatographic—mass spectrometric analysis

A method is described that uses aqueous acetylation with acetic anhydride, solid-phase extraction (SPE) and concentration, and gas chromatographic—mass spectrometric (GC-MS) analysis to identify and quantify mono-, di- and trihydroxybenzenes (phenols) at low concentrations in marine and waste waters. Phenolic compounds in water samples were buffered with NaHCO 3 and directly acetylated with acetic anhydride. Phenol acetates were then extracted using C 18 SPE columns. The columns were eluted and the phenol acetates concentrated and analyzed by GC-MS. Detection of phenols in the ng 1 −1 concentration range can be obtained with 500 ml of sample. A large volume extraction setup is described from which detection limits in the upper pg 1 −1 range may be obtained. The method was applicable to a wide range of phenolic compounds but was not suitable for nitrophenols. Water samples from several coastal environments and wastewater treatment facilities were analyzed for phenols using this method. Phenol, cresols and catechols were the most common phenolic compounds identified. Concentrations ranged from 2.5 to 370 ng 1 −1 for these phenols in seawater sampled in San Diego Bay, in the vicinity of White's Point outfall off San Pedro (Los Angeles area) and outfalls off the Northern coast of California near Eureka.

Coprostanol as sewage tracer in McMurdo Sound, Antarctica

Sediment cores from the vicinity of sewage outfalls off McMurdo Station as well as surface grab samples from different locations in the McMurdo Sound, Antarctica were analysed for coprostanol (5β-cholestan-3β-ol) and epicoprostanol (5β-cholestan-3α-ol) to assess the degree of sewage addition to the Sound. Sediment samples close to the point source contain as much as 3 mg g −1 dry sediment of coprostanol, whereas samples farther from the source, for example from New Harbour and Granite Harbour, contain only trace levels to 40 ng g −1. Coprostanol in the sediments of latter locations most likely originates from seals rather than from sewage outfalls. It appears that sewage particles are very quickly incorporated into the sediment layers close to the discharge point in the eastern Sound. However, significant levels (930 ng g −1) of fecal sterols were detected in Cape Armitage surface sediments, indicating that the sewage plume could also have reached the seawater intake station, situated in between the outfall and Cape Armitage sampling site. These results suggest the need for a sound environmental monitoring and assessment of the existing wastewater practices in the region.

Temporal changes in fish community structure near a sewage ocean outfall, Mokapu, Oahu, Hawaii

The results of a study performed before and after the discharge of an ocean outfall off Mõkapu Point, Oahu, Hawaii, from 1975 to 1979 show large increases in the number of species and abundance of fish around the outfall site. The construction of the outfall afforded new rock substratum for the attachment of algae and sessile animals which attracted large aggregations of fish. During a 1 1 2 year period there were no significant community structure 1–5 km from the outfall when measured by similarity indices. No significant changes in algal biomass occurred between samplings. Similarity indices may be better indicators of fish community change than diversity indices since the former reflect changes in the relative abundance of species in common and large temporal changes in a community structure may occur without changing the value of its diversity index. Morisita's (1959) similarity index has greater sensitivity to the changes in fish community structure than the index derived by Sorensen (1954) due to emphasis on the relative abundance of dominant species.

CONSTRUCTION AND MODEL INVESTIGATION OF STORMWATER OUTFALL

Posford Pavry Sinclair and Knight were commissioned in 1976 to design a new stormwater outfall off one of Sydney's surfing beaches. The location of the outfall was dictated by a previous outfall which had been built in the dry when the beach line was much further seaward but which had been destroyed by wave action when the beach line retreated to the 1976 position (a distance of approximately 50 metres (Figure 1)).

An offshore biomonitoring system for chlorinated hydrocarbons

Uncontaminated intertidal mussels transferred to a tautline buoy system near a major submarine outfall off southern California proved to be useful bio-indicators of water column contamination. Mussel survival exceeded 90%, and specimens maintained for 13 weeks near the polluted bottom (35 m) and the sea surface accumulated DDT above control concentrations by factors of 200 and 20, respectively. Corresponding factors for PCB were 60 and 6.