Design Requirements & Compliance
8Code and authority requirements that set the design envelope.
WSA 02 Gravity Sewerage CodeWhat the code covers, and how it relates to authority supplements.Local Water Authority RequirementsSupplements, standard drawings and asset standards that modify the code.Minimum and Maximum Pipe GradesHow grade is set between self-cleansing and velocity limits.Minimum Cover RequirementsCover to the pipe crown, and what drives the minimum.Pipe Sizing and Capacity CriteriaSelecting a diameter against design flow, depth and grade.Self-Cleansing RequirementsVelocity and shear stress criteria, and which flow condition to check.Maintenance Hole Spacing and LocationsWhere access is mandatory, and what sets the maximum spacing.Clearances to Other ServicesSeparations, crossings and the alternatives where space is tight.
Hydraulic Design
7Flow estimation, capacity, depth and the hydraulic grade line.
Design Flow EstimationDry weather flow, peaking factors and infiltration allowances.Manning's EquationDischarge and velocity in steady uniform flow.Partial-Flow HydraulicsCircular segment geometry, depth ratio and the Q and V maxima.Flow VelocityMinimum, maximum and where velocity is actually evaluated.Hydraulic Grade LineWater surface, pressure line and how to build the profile.Surcharge ConsiderationsCauses, consequences and what to check when the pipe runs full.Hydraulic Design AssumptionsThe assumptions to record, and how to show sensitivity.
Pipe Design & Installation
7Materials, structure, bedding, loading and groundwater.
Pipe Material SelectionHow material choice interacts with strength, durability and constructability.Pipe Structural ConsiderationsFlexible and rigid behaviour, loads and the checks that matter.Trench Bedding and EmbedmentSupport conditions, embedment material and the zones around the pipe.Backfill RequirementsBackfill zones, material selection and settlement control.Pipe LoadingThe load cases a buried sewer is designed for.Groundwater ConsiderationsUplift, dewatering, infiltration and chemical attack.Pipe BuoyancyUplift on an empty pipe and the resistance available.
Maintenance Hole Design
7Sizing, configuration, drops, structure and access.
Maintenance Hole SizingInternal dimensions driven by access, benching and pipe penetrations.Depth and ConfigurationDepth measurement, cone and slab options, and level adjustment.Inlet and Outlet ArrangementsBenching, channel shape and the angles at which pipes enter.Internal DropsDissipating energy where inlets enter well above the outlet.Structural ConsiderationsWall, base and cover slab loads for a buried structure.Groundwater and FlotationUplift on the structure, and the resistance that prevents it floating.Access and Maintenance RequirementsCovers, steps, ladders, ventilation and safe entry.
Technical References & Examples
5Methods, worked examples, standard details and documentation.
Calculation MethodologiesThe standard sequence for sizing and checking a gravity sewer reach.Worked Design ExampleA short capacity and part-full check for a DN225 pipe.Typical Engineering DetailsThe standard details a sewer design package normally needs.Technical Notes and DocumentationWhat a sewer design report and drawing set should record.Design Best PracticesPractical habits that make a sewer easier to build and maintain.
These references summarise Australian engineering practice and point to the source documents. They do not replace WSA 02, the current Australian Standards or the local water authority's requirements, and no clause numbers or compliance limits are reproduced. Project-specific requirements and current standard editions must be checked before use in design.