Source
https://www.gw.govt.nz/assets/MinimumflowrecommendationsfortheWellingtonregion-TechnicalreporttosupporttheProposedNaturalResourcesPlan.PDF — original source (opens in a new tab; the file is not redistributed)
GWRC — minimum flow recommendations for the Wellington region (Thompson 2015)
A third region's minimum-flow convention for the D26 environmental-flow gate (RT_335, resolves)
Greater Wellington Regional Council technical report supporting the Proposed Natural Resources Plan (pNRP), Publication No. GW/ESCI-T-15/85, July 2015 (Mike Thompson, Senior Environmental Scientist – Hydrology; 60 pp). A council-facing technical report, not the plan itself (the disclaimer states it “does not constitute Council policy”). Filed alongside OT_099 (Hawke’s Bay observed drought flows), OT_100 (Otago default limits) and OT_101 (national NPS-FM framework) as the third region’s take on the same convention.
Summary
GWRC’s technical basis for the minimum-flow provisions in its second-generation regional plan (the pNRP, notified 2015). It sets a default minimum flow of 90% of the seven-day naturalised mean annual low flow (7d MALF-N) at the point of abstraction for every river and stream not covered by a site-specific numerical limit — adopting the Ministry for the Environment’s 2008 proposed National Environmental Standard rule (90% of MALF for mean flow ≤5 m³/s, 80% above). It explains why GWRC benchmarks on MALF rather than the 1-in-5-year low flow (Q5), catalogues the range of minimum-flow conventions used by other NZ regional councils, and proposes a de-minimis rule under which minimum-flow restrictions only “become operable” once catchment allocation reaches ~20% of 7d MALF-N.
For Neobiome it does three jobs. (1) It corroborates the 90%-of-MALF environmental-flow rule from a third region (after Otago in OT_100 and the national MBIE report OT_075) — the convention behind the engine’s D26 gate is now triangulated across councils. (2) It supplies two genuinely new parameters the sibling sources lacked: the ~1.8-year return period of MALF (how often a MALF-level low flow recurs), and a 20%-of-MALF allocation threshold below which minimum-flow restrictions may not even apply. (3) It provides the menu of alternative NZ conventions (Q5-based, 60%-of-1-in-20-year) that shows the engine’s 90%-of-MALF is squarely mainstream, not an outlier. Like OT_100, it addresses only consumptive abstraction — it neither exempts nor bans a run-of-river micro-hydro diversion, so RT_333 is untouched.
Key claims
- claim: "Default minimum flow rule for all un-scheduled rivers and streams (verbatim, primary recommendation): 'For all rivers and streams outside of catchments covered by numerical thresholds ... to apply a default minimum flow limit equating to 90% of the seven day naturalised mean annual low flow at the point of abstraction.' Stated compactly in §4.2 as 'Minimum flow = 90% of 7d MALF-N at the point of abstraction', and in the summary: 'To use the 7d MALF-N in all applications of the default minimum flow.'"
source_location: "Executive summary (p.i); §4.2 'Default minimum flows for other rivers and streams', p.21; §7 Summary, p.27"
- claim: "The MfE 2008 proposed NES defaults GWRC adopts (verbatim): 'For rivers and streams with mean flows less than or equal to 5 m3/s, a minimum flow of 90% of the mean annual low flow (MALF) as calculated by the regional council. For rivers and streams with mean flows greater than 5 m3/s, a minimum flow of 80% of MALF as calculated by the regional council.' Footnote 5: 'their definition of MALF is presumed to be the natural 7 day MALF.' Companion core-allocation limits (footnote 10): 30% of MALF for mean flow <5 m3/s and 50% of MALF for mean flow >5 m3/s, 'consistent with those recommended by Ministry for the Environment (2008) and Beca (2008)'."
source_location: "§3.6.2 'Proposed default minimum flows', p.15 (+ footnote 5); allocation limits footnote 10, p.27"
- claim: "Return period of MALF ~1.8 years (verbatim): 'the return period of MALF, which is usually about 1.8 years on average for most rivers in the Wellington region, is indicative of the low flows likely to be experienced by trout - and therefore sets a lower limit to physical space likely to be available to them - before they begin making a reproductive contribution to the population (Hay 2010a).' GWRC uses MALF (not the 1-in-5-year low flow Q5) as its primary benchmarking statistic because it is ecologically relevant (Jowett 1990, 1992 linked trout habitat at MALF to trout abundance)."
source_location: "§3.3.2 'Choice of reference flow statistics', p.11"
- claim: "Minimum-flow exclusion below a 20%-of-MALF allocation threshold (verbatim): in catchments with only minor abstractive pressure 'it may be appropriate that these minimum flows only become operable once a certain abstraction threshold has been exceeded. For example, a total catchment allocation equivalent to >= 20% of 7d MALF-N may be a suitable threshold as it represents a degree of flow alteration that is both discernible (using conventional flow measurement techniques that are typically accurate to +/- 8%) and potentially having an impact.'"
source_location: "§5.2 'Minimum flow exclusions based on allocation pressure', p.23"
- claim: "Small streams get NO extra protection in Wellington, unlike some regions (verbatim): 'there are no established criteria in the Wellington region for setting minimum flows on the basis of flow rate and no clear evidence that small streams warrant special attention. In practice there is little material difference between thresholds of 90%, 95% and 100% of MALF-N as they all describe a proportion of total flow that is typically less than the error in most flow measurements ... it is recommended that no alternative default provision be assigned to small streams.' (By contrast 'Horizons Regional Council adopts a default minimum flow value of 95% of 1d MALF-N for their smallest waterways.')"
source_location: "§3.6.3 'River and stream size / flow rate', p.15"
- claim: "The 90%-of-MALF hydrological rule maps to ~90% trout-habitat retention (ecological basis, verbatim): 'a minimum flow set at 87% of MALF-N is likely to be very similar to one set by habitat modelling to retain 90% of the adult brown trout habitat available at MALF-N' (Hay 2010a). Table 3.2 (Jowett & Hayes 2004) sets habitat-retention targets by value: 90% for large adult trout / diadromous galaxiid (highest significance), down to 60% for bullies."
source_location: "§3.5 'A regionalised approach to flow setting', p.13-14 (Hay 2010a); Table 3.2, p.14"
- claim: "Menu of alternative NZ minimum-flow conventions (Appendix 2 + Table 1.2). Q5-based: Environment Waikato sets minimum flow at '90% of the one in five year 7d low flow (Q5) for streams with a mean flow greater than 5 cumecs and 95% of the Q5 for streams with a mean flow less than 5 cumecs'; Bay of Plenty's default is '90% of the Q5 seven-day low flow'; Northland sets it at MALF for MALF <300 L/s, otherwise Q5. GWRC's own historical methods (Table 1.2) included the 1-in-5-year low flow (Tauherenikau, Waiohine, Waingawa) and '60% of the 1-in-20 year low flow' (Waitohu, Mangaone, Orongorongo). Taranaki's default 'will provide two-thirds of the habitat at MALF'."
source_location: "Appendix 2 Table A2.1 'Other regional approaches to minimum flow setting', p.35-36; GWRC historical methods Table 1.2, p.1-2"Neobiome Intelligence relevance
Triangulates the D26 environmental-flow rule across a third region. micro_hydro applies an environmental-flow cap of 10% of MALF usable flow (the 90%-of-MALF residual, taken at its cautious reading). That rule previously rested on OT_075 (national MBIE) and OT_100 (Otago). GWRC now confirms the same 90%-of-7d-MALF default for the Wellington region, adopted verbatim from the MfE 2008 proposed NES — the identical band OT_100 uses. Three independent regional/national instruments now state the same convention, so the D26 gate’s binding constraint is well-corroborated. No model change — corroboration.
Two parameters here are genuinely new to the corpus (neither is in OT_099/OT_100/OT_101):
| Parameter | Value | Why it matters to NI |
|---|---|---|
| Return period of MALF | ~1.8 years | A MALF-level low flow is roughly a once-every-two-years event, not a rare extreme — so the environmental-flow cap binds in most years, and the D34 drought derate (a worse-than-MALF year) sits below an already-frequent floor. |
| Minimum-flow “operable” threshold | catchment allocation ≥ 20% of 7d MALF-N | Below ~20%-of-MALF total allocation, GWRC suggests the minimum-flow restriction need not even apply (the take is below detectable flow alteration, ±8% gauging error). A community take/diversion sized well under this may sit below where restrictions bite — a de-minimis angle for the currently-inert stream_abstraction lever (RT_310). ⚠ It is a policy suggestion (“may be a suitable threshold”), not an operative rule, and it is about consumptive allocation, not run-of-river diversion. |
The engine’s 10%-of-MALF usable flow is confirmed conservative from a third direction. GWRC’s small-stream finding is that the difference between 90%, 95% and 100% of MALF is within flow-measurement error — i.e. the residual floor sits so close to MALF that only ~10% headroom exists at MALF, exactly the fraction the engine allows. Note a divergence from OT_100’s caution: where the Cawthron/ORC memo argued ecological risk rises as streams shrink (a reason to protect small streams harder), GWRC explicitly declines to give small streams any extra provision, finding “no clear evidence that small streams warrant special attention.” The two regions genuinely differ on small-stream policy — worth surfacing rather than smoothing over.
Does NOT resolve RT_333 (run-of-river control) — same limitation as OT_100
The report is entirely about consumptive abstraction (takes, allocation, restriction, suspension). It contains no run-of-river, non-consumptive, or hydro-generation language, so it neither exempts nor bans a micro-hydro diversion. RT_333 (what control a regional plan imposes on a diversion at low flow — residual-flow condition vs cessation) stays open; OT_101 remains the source that confirms diversions are regulated at all.
Research targets
Documents to retrieve
- None new. The companion allocation report referenced throughout (Thompson & Mzila 2015, water-allocation recommendations for the pNRP) would give the region’s allocation limits (this report is minimum-flow only), but the allocation convention (30%/50% of MALF) is already sourced via OT_100 and footnote 10 here, so it is not worth a new RT unless a Wellington-specific allocation figure is later needed.
Research gaps
- None new. RT_335 resolved (third region’s convention captured, incl. Q5 and 60%-of-1-in-20-year alternatives). RT_333 unchanged (consumptive-only source). RT_334 unchanged — this report gives annual-minimum-flow variability (CoV mostly 0.2–0.5 across 29 records, smaller streams toward the top end) but that is between-year variability, not how far a small stream falls in a drought, and its dataset is “biased towards larger river systems”, so it does not advance the small-stream drought question.
Notes
Authoritative GWRC technical report (not AI-prepared) — data_quality: high (one strong source; the 90%-of-MALF headline is independently corroborated by OT_075/OT_100, which is what strengthens the model cell rather than this page’s rating). All figures read verbatim via pdftotext -layout at ingest. Citation: Thompson M. 2015. Minimum flow recommendations for the Wellington region: Technical report to support the Proposed Natural Resources Plan. Greater Wellington Regional Council, Publication No. GW/ESCI-T-15/85, Wellington. ISBN 978-1-927217-80-1 (online).
Source-internal count inconsistency (non-material)
The Executive summary states 17 numerical waterways, “14 … the same … remaining three are new” (14+3=17, and Table 4.1 shows exactly three yellow-shaded new limits: Parkvale 100 L/s, Papawai 180 L/s, Otukura 95 L/s). The §7 Summary instead says “remaining five are new” (14+5=19, which does not reconcile with 17). The Executive-summary figure is the internally consistent one; the count is not used in any NI claim.
Connections
Links to
Sources (4): OT_075 · OT_099 · OT_100 · OT_101
Technologies (1): Micro-hydro (run-of-river, community-scale)
Referenced by
EDT domains (1): D03: Water, Waste & Circular Systems
Technologies (1): Micro-hydro (run-of-river, community-scale)