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<small{|style="float: left;"|{{Language-title />box|english_link=Conventional_Gravity_Sewer|french_link=Réseau_d’égout_gravitaire_conventionnel|spanish_link=Alcantarillado_Convencional_por_Gravedad|hindi_link=coming soon|malayalam_link=coming soon|tamil_link=coming soon | korean_link=coming soon chinese_link=Coming soon | indonesian_link=Coming soon | japanese_link=Coming soon }}<!-- table at top of page with logo, picture, Application level, Management level, and input-output tables -->|}

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The '''Conventional Gravity Sewer system is designed with many branches. Typically, the network is subdivided into primary (main sewer lines along main roads), secondary, and tertiary gravity sewers are large networks (network at the neighbourhood and household level). Conventional Gravity Sewers do not require onsite pretreatment or storage of the wastewater. Because the waste is not treated before it is discharged, the sewer must be designed to maintain self-cleansing velocity (i.e. a flow underground pipes that will not allow particles to accumulate). A self-cleansing velocity is generally 0.6–0.75m/s. A constant downhill gradient must be guaranteed along the length of the sewer to maintain self-cleaning flows. When a downhill grade cannot be maintained, a pump station must be installed. Primary sewers are laid beneath roadsconvey blackwater, greywater and must be laid at depths of 1.5 to 3m to avoid damages caused by traffic loads. Access manholes are placed at set intervals along the sewer, at pipe intersections and at changes in pipeline direction (vertically and horizontally). The primary network requires rigorous engineering design many cases, stormwater from individual households to ensure that a self(Semi-cleansing velocity is maintained) Centralized Treatment facility, that manholes are placed as required using gravity (and that the sewer line can support the traffic weight. As well, extensive construction is required to remove and replace the road abovepumps when necessary).'''

{{procontable | pro=- Stormwater and greywater can be managed at The conventional gravity sewer system is designed with many branches. Typically, the same time. <br> - Construction can provide short-term employment to local labourers. | con=- A long time required to connect all homes. <br> - Not all parts and materials may be available locally. <br> - Difficult and costly to extend as a community changes and grows. <br> - Requires expert design and construction supervision. <br> - Effluent and sludge network is subdivided into primary (from interceptorsmain sewer lines along main roads) requires , secondary treatment and/or appropriate discharge. <br> - High capital tertiary networks (networks at the neighbourhood and moderate operation costhousehold level). }}

===AdequacyDesign Considerations===Conventional gravity sewers normally do not require onsite pre-treatment, primary treatment or storage of the household wastewater before it is discharged. The sewer must be designed, however, so that it maintains self-cleansing velocity (i.e., a flow that will not allow particles to accumulate). For typical sewer diameters, a minimum velocity of 0.6 to 0.7 m/s during peak dry weather conditions should be adopted. A constant downhill gradient must be guaranteed along the length of the sewer to maintain self-cleansing flows, which can require deep excavations.

Because they carry so much volumeWhen a downhill grade cannot be maintained, Conventional Gravity a pumping station must be installed. Primary sewers are only appropriate when there is a centralized treatment facility that is able laid beneath roads, at depths of 1.5 to 3 m to receive avoid damages caused by traffic loads. The depth also depends on the groundwater table, the wastewater lowest point to be served (ie.eg. smaller, decentralized facilities could easily be overwhelmeda basement)and the topography. The selection ofthe pipe diameter depends on the projected average and peak flows. Commonly used materials are concrete,PVC, and ductile or cast iron pipes.

PlanningAccess manholes are placed at set intervals above the sewer, at pipe intersections and at changes in pipelinedirection (vertically and horizontally). Manholes should be designed such that they do not become a source ofstormwater inflow or groundwater infiltration. In the case that connected users discharge highly pollutedwastewater (e.g., constructionindustry or restaurants), operation onsite pre- and maintenance require expert knowledge. Conventional Gravity Sewers are expensive primary treatment may be required before dischargeinto the sewer system to build reduce the risk of clogging and, because the installation load of the wastewater treatment plant. When the sewer also carries stormwater (known as a combined sewer), sewer line is disruptive and requires extensive coordination between overflows are required to avoid hydraulic surcharge of treatment plants during rain events. However, combined sewers should no longer be considered state of the authoritiesart. Rather, construction companies local retention and the property owners, infiltration of stormwater or a professional management separate drainage system must be in placefor rainwater are recommended.The wastewater treatment system then requires smaller dimensions and is, therefore, cheaper to build, and there is a higher treatment efficiency for less diluted wastewater

When <br>{{procontable | pro=- Less maintenance compared to Simplified and Solids-Free Sewers <br>- Greywater and possibly stormwater is also carried by the sewer (called a Combined Sewer)can be managed concurrently <br>- Can handle grit and other solids, sewer overflows are required. Sewer overflows are needed to avoid hydraulic surcharge as well as large volumes of treatment plants during rain events. Infiltration into the sewer in areas where there is a flow <br>| con=- Very high capital costs; high water table may compromise operation and maintenance costs <br>- A minimum velocity must be maintained to prevent the performance deposition of solids in the Conventional Gravity Sewer.sewer <br>- Requires deep excavations <br>Conventional Gravity Sewers can be constructed in cold climates - Difficult and costly to extend as they are dug deep into the ground a community changes and grows <br>- Requires expert design, construction and maintenance <br>- Leakages pose a risk of wastewater exfiltration and the large groundwater infiltration and constant water flow resists freezing.are difficult to identify}}

===Health Aspects/AcceptanceAppropriateness===Because they can be designed to carry large volumes, conventional gravity sewers are very appropriate to transport wastewater to a (Semi-) Centralized Treatment facility. Planning, construction, operation and maintenance require expert knowledge. Construction of conventional sewer systems in dense, urban areas is complicated because it disrupts urban activities and traffic. Conventional gravity sewers are expensive to build and, because the installation of a sewer line is disruptive and requires extensive coordination between authorities, construction companies and property owners, a professional management system must be in place.

This technology provides Ground shifting may cause cracks in manhole walls or pipe joints, which may become a high level source of hygiene groundwaterinfiltration or wastewater exfiltration, and comfort for compromise the user at performance of the point of usesewer. However, because Conventional gravity sewers can be constructed in cold climates as they are dug deep into the waste is conveyed to an offsite location for treatment, ground and the ultimate health large and environmental impacts are determined by the treatment provided by the downstream facilityconstant water flow resists freezing.

===MaintenanceHealth Aspects/Acceptance===If well constructed and maintained, sewers are a safe and hygienic means of transporting wastewater. This technology provides a high level of hygiene and comfort for the user. However, because the waste is conveyed to an offsite location for treatment, the ultimate health and environmental impacts are determined by the treatment provided by the downstream facility.

===Operation & Maintenance=== Manholes are installed wherever there is a change of grade or alignment and are used for routine inspection and sewer cleaning. Debris (e.g., grit, sticks or rags) may accumulate in the manholes and block the lines. To avoid clogging caused by grease, it is important to inform the users about proper oil and grease disposal. Common cleaningmethods for conventional gravity sewers include rodding, flushing, jetting and bailing. Sewers can be dangerous because of toxic gases and should only be maintained only by professionals , although, in well-organised communities, the maintenance of tertiary networks might be handed over to a well-trained group of community members. Proper protection should always be used when entering a sewer.

* ASCE (1992). Gravity Sanitary Sewer Design and Construction, ASCE Manuals and Reports on Engineering Practice No. 60, WPCF MOP No. FD-5. American Society of Civil Engineers, New York. (A standard design text used in North America although local codes and standards should be assessed before choosing a design manual.) * Tchobanoglous, G. (1981). Wastewater Engineering: Collection and Pumping of Wastewater. McGraw-Hill, New York, US.(Book)

* Tchobanoglous, G., Burton, FLU. and Stensel, HDS. EPA (20032002). Wastewater Engineering[https: Treatment and Reuse//nepis.epa.gov/Exe/ZyNET.exe/P10053D9.TXT?ZyActionD=ZyDocument&Client=EPA&Index=2000+Thru+2005&Docs=&Query=&Time=&EndTime=&SearchMethod=1&TocRestrict=n&Toc=&TocEntry=&QField=&QFieldYear=&QFieldMonth=&QFieldDay=&IntQFieldOp=0&ExtQFieldOp=0&XmlQuery=&File=D%3A%5Czyfiles%5CIndex%20Data%5C00thru05%5CTxt%5C00000021%5CP10053D9.txt&User=ANONYMOUS&Password=anonymous&SortMethod=h%7C-&MaximumDocuments=1&FuzzyDegree=0&ImageQuality=r75g8/r75g8/x150y150g16/i425&Display=hpfr&DefSeekPage=x&SearchBack=ZyActionL&Back=ZyActionS&BackDesc=Results%20page&MaximumPages=1&ZyEntry=1&SeekPage=x&ZyPURL Collection Systems Technology Fact Sheet]. Sewers, Conventional Gravity. 832-F-02-007. U.S. Environmental Protection Agency, Washington, 4th EditionD.C. Metcalf & Eddy, New YorkUS.(Good description of the technology, including more detailed design criteria and information on operation and maintenance)