exceedance rainfall event (AEP) event. The
maximum discharge rate from the pond during large rainfall events is 1,060 L/s as this is dictated by the size
of the outfall pipe (750 mm). However, there is also provision for the pond to overflow via a spillway
structure to a discharge swale (i.e. bypassing the 750 mm discharge pipe).
At the time of the application it was indicated that, as a result of stormwater inputs to the pond, the
discharge rate from the pond to the Mangorei Stream would be
Executive Audit and Risk agenda February 2024 v2
generally very good. It is noted that the protocol for sampling has changed in the last couple of
years so that samples are collected irrespective of weather or tide, unlike previously where samples were
collected around high tide in fine weather only. Prolonged and/or heavy rainfall will often result in high
levels of enterococci in the samples as these are washed down flooded streams and rivers from farmland.
This can be exacerbated by a low tide where a sea sample collected from a site near a
excess of water may enter the
system during heavy or sustained rainfall, or if rainfall occurs when the plant is not operating. This excess is
discharged via a sand filter prior to entering the NPDC stormwater system, which discharges to the
Mangaone Stream immediately upstream of State Highway 3.
Allied Concrete holds water discharge permit 4539-2 to cover the discharge of stormwater and treated
wastewater from truck washing at a concrete batching plant into the Mangaone Stream in the
Mangorei Hydroelectric Power Scheme - Hydrology ReportHydrology Report
Trustpower Ltd
November 2020 (Final)
Job No: 1008726.200
Table of contents
1 Introduction 1
1.1 Context 1
1.2 Scope of assessment 1
1.3 Scheme description and key locations 1
2 Catchment characteristics and water resources 5
2.1 Waiwhakaiho catchment 5
2.1.1 Drainage and geology 5
2.1.2 Catchment area and cover 5
2.1.3 Rainfall 6
2.2 Hydrometric data 6
2.3 Water use in the catchment 7
2.4 Waiwhakaiho River flows
performance for consent 10247-1.1 17
Table 10 Evaluation of environmental performance over time 18
List of figures
Figure 1 Sampling site locations, Everett Road Quarry 10
Figure 2 Discharge rates from Civil Quarries stormwater system, plotted against rainfall in 10 minute
interval totals. The red line is the consented discharge rate limit 12
Figure 3 Abstraction rates from Civil Quarries Emergency pump. The red line is the consented
abstraction rate limit 13
List of
................................................................................................ 43
3.1.6 Hot days ................................................................................................... 46
3.1.7 Growing degree days ............................................................................... 49
3.2 Rainfall .................................................................................................................... 52
3.2.1 Rainfall totals ........................................................................................... 52
3.2.2 Dry
and coastal receiving
environments including rivers, lakes and estuaries.
Climate change is expected to exacerbate soil loss and present challenges to the future
management of erosion-prone land. It is estimated that extreme storm events resulting in
flooding and slips are likely to occur somewhere in Taranaki about once every five to six
years. In coming years, the region is expected to experience more frequent and intense
heavy rainfall events, increasing both the frequency and
during the 2021-2022 monitoring year, with south Taranaki
commencing irrigation in November and the rest of the region beginning in January. Irrigation concluded
late April through to early May across the region. Rainfall recorded at the Council’s monitoring locations
over the summer irrigation period ranged between 82% and 203% of historical mean values. Even though
rainfall volumes were higher than previous years, the irrigation season was longer with total irrigation water
usage of 6,960 ML