Quick, transparent calculators built around New Zealand standards, materials and council guidance. Every tool produces a branded PDF calculation sheet for your job file.
Rational-method peak flow with E1/VM1 runoff coefficients, composite catchments and time-of-concentration helper. Pairs with HIRDS v4 rainfall.
NZBC E1/VM1 · NIWA HIRDS v4Tank volumes to Auckland SMAF, GWRC hydrological control or Wellington's pre-sized approved solutions — with the GD01 orifice sized for 24-hour drawdown.
AUP E10 · GD01 · GWRC · Wellington Water v5Storage volume for a whole development, derived from a depth-duration rainfall table — sweeps every storm duration for the critical one, then sizes an underground tank, an oversized pipe or a dry detention pond with its orifice and spillway.
E1/VM1 rational · GD01 §C5 & §C9 · HIRDS v4Soakpit and trench sizing from the site soakage test — GD07 factors of safety on the tested rate, GD01 storage and 72-hour drain-down equations.
Auckland GD01 §C7 · GD07WQV (volume to treat) and WQF (flow for flow-based treatment) for device sizing — Auckland GD01/TP108 curve number, Christchurch first flush, Wellington Water WSD or the generic Simple Method. Feeds the rain garden tools.
GD01 · TP108 · CCC WWDG · WW WSD · Simple MethodRain garden sizing by the local method — Auckland GD01 (water quality or SMAF), Christchurch's Darcy method or Wellington's 2% rule — with the layer build-up.
GD01 §C3 · CCC Rain Garden Manual · WW WSDRaingarden / bioretention filter-area sizing (Af = WQV·d_f/[k(h+d_f)·t_f]) and groundwater / seepage flow Q = k·i·A — with flexible units (m³/s, L/s, m/day).
Darcy · CCC Rain Garden Manual Eq. 1Manning normal depth, velocity and freeboard for trapezoidal channels, V-drains and GD01 swales, with NZ lining velocity limits.
GD01 §C6 · TR2013/018 · CCC WWDGHeadwater by HDS-5 inlet/outlet control (the E1/VM1 nomograph basis) with Auckland's headwater, freeboard, velocity and blockage acceptance checks.
FHWA HDS-5 · E1/VM1 · Auckland SWCoP 4.3.9.8What a catchpit actually captures — published capacities with the mandatory blockage factors — plus pits required, bypass and spacing rules.
AT TDM §6 · CCC WWDG 22.10Scour trigger by receiving ground, then rock size, apron dimensions and energy-dissipation guidance to Auckland TR2013/018 with the CCC Isbash check.
TR2013/018 · CCC WWDG 22.7Depth × velocity classified to the H1–H6 vulnerability curves used in NZ flood mapping, with the road-flow and Auckland depth limits — and a live chart.
Smith et al. 2014 · ARR 2019 Book 6 · AT TDM · AUP E36Gravity pipe capacity, velocity and normal-depth checks for NZ concrete, PVC and PE pipes. Self-cleansing and maximum velocity checks built in.
Manning's equation · NZS 4404 · council CoP limitsCouncil minimum-cover checks, then the engineering for reduced cover — concrete class selection to AS/NZS 3725 and PVC/PP deflection & buckling to AS/NZS 2566.1 under HN-HO-72 highway traffic loading — plus trench dimensions.
NZS 4404 · AS/NZS 3725 · AS/NZS 2566.1 · NZTA Bridge ManualMinimum riser diameter for depth and the precast penetration check (Concrete Pipe Association of Australasia rules) — cored-hole size and clear distance between any number of pipes, from each pipe's plan angle and invert.
NZS 4404 · councils · CPAA / Hynds precast rulesAverage dry-weather, peak dry-weather and peak wet-weather flows (ADWF / PDWF / PWWF) to the local council's own rates and peaking method (six rule sets), with a gravity main capacity and self-cleansing check.
Watercare · Wellington Water · CCC · RITS · TCC · NZS 4404Wet well sizing (900·Q/N), emergency storage hours and rising main velocity/septicity checks — including Watercare's current ESF-500 standard.
Watercare ESF-500 v2 · CCC SPSDS · RITS · TCC · WW RSWSPeak demand to the local council's method, then Hazen-Williams or Darcy-Weisbach headloss in the main with verified NZ coefficients and gradient limits.
Watercare · WW RSWS · CCC · RITS · NZS 4404SNZ PAS 4509 classification (FW1–FW7) from building type and firecell, with the required flows, hydrant distances and storage alternatives checked against supply.
SNZ PAS 4509:2008 (verified tables)Convert Scala dynamic cone penetrometer (DCP) rates to inferred CBR (California Bearing Ratio) per test layer, and pick a design subgrade CBR from multiple tests.
NZS 4402 Test 6.5.2 · NZTA correlationThin-surfaced unbound granular pavement thickness from design CBR (California Bearing Ratio) and traffic in equivalent standard axles (ESA), with NZ basecourse/subbase layering suggestions.
Austroads AGPT02 empirical · NZTA M/4Driveways, crossings, carparks and forklift hardstands — NZ catalogue thicknesses with mesh, subbase and joint layout (carriageways flagged for AGPT02 specific design).
CCANZ IB 80 · AT TDM Table 23 · TM38Sediment retention pond, decanting earth bund, silt fence and stabilised entrance sizing to GD05 — the design basis most NZ regions follow.
Auckland GD05 · GWRC ESC Guide 2021