Plan Interpretation, Documentation and Certification
Reading the drawings
A drainage set normally includes a site plan, drainage plan, sections and details, plus specifications and consent conditions. Read them together. Establish the scale, north point, the datum, and whether levels shown are ground level (GL), invert level (IL), obvert or finished floor level (FFL). Reduced levels should be traced from a known benchmark to the connection point to check the design grades actually work.
Symbols matter: gullies, inspection openings, rodding eyes, junctions, boundary traps, downpipes and pump chambers are drawn differently and are easy to misread under time pressure. Schedules give pipe sizes, materials and gradients; details give bedding, encasement and penetration information.
Managing information
Real projects generate RFIs, variations, shop drawings and as-builts. Any change to the consented design may need a variation or an amendment to the consent - building something different and hoping is not an option. Keep a document register, record instructions in writing, and photograph work before it is covered.
Certification
Certification closes the loop: producer statements (design, design review, construction, construction review), Records of Work for work not requiring consent, inspection records, test results, as-built plans and O&M manuals. The building consent authority then issues the Code Compliance Certificate; specified systems, where present, feed into the compliance schedule and building warrant of fitness.
Traps
Mixing datums between drawings. Reading an invert level as a ground level. Applying a superseded standard edition. Missing a consent condition (sediment control, inspection timing, trade waste). Assuming the as-built matches the design without checking.
Rule of thumb: before you dig, add up the falls shown on the plan and compare them with the levels at the connection - if the numbers do not reconcile, raise an RFI rather than discovering it in the trench.