The National Institute of Water and Atmospheric Research Ltd (NIWA) has been commissioned by the Ministry for the Environment to estimate 11 components of the national and regional water balance of New Zealand for each of the 20 years from 1 July 1994 to 30 June 2014. This information is for use by Statistics New Zealand in a set of annual national water accounts they are developing, as part of a set of environmental accounts for New Zealand. Specifically, this work is a contribution to the Water Physical Stock Accounts. The data were analysed to summarise the water stock accounts of New Zealand and the 16 regions administered by regional councils or unitary authorities,using a combination of direct measurement and modelled data. The average annual precipitation across the country was 550,000 m3/year (equal to over nine times the volume of Lake Taupo), a reduction from previous years’ calculations. Roughly 20% of this evaporates before reaching the coast, leaving an average of 440,000 million m3/year. There is substantial variation in this water flux from year to year due to a range of climatic factors. Changes in storage – lakes, soil moisture, snow, and ice – represent very small components of the annual water balance. Use of water for hydroelectric power generation represents a significant portion of the nation’s freshwater resource, equating to 36% of the total freshwater flows, but this figure includes multiple use of water within the same catchment. Water fluxes at the regional scale vary depending on the region’s size as well as the spatial variability in the delivery and movement of water. The West Coast receives the largest portion of precipitation – 26% of the national total – and possesses 30% of the nation’s freshwater flow. Nelson City, due to its small size, accounts for the smallest portion in both cases. Canterbury accounts for the greatest portion of hydro-generation water use (mainly for the Waitaki scheme), followed by Waikato. Data are for 11 water balance components: 1. Precipitation 2. Inflows from rivers (regional scale only) 3. Evapotranspiration 4. Abstraction by hydro-generation companies 5. Discharges by hydro-generation companies 6. Outflows to sea from surface water 7. Outflows to other regions (regional scale only) 8. Net change in lakes and reservoirs 9. Net change in soil moisture 10. Net change in snow 11. Net change in ice

The TopNet hydrological model was calibrated based on a combination of Virtual Climate Network stations and existing sub-daily precipitation information located within Lake Waahi surface water catchment. The hydrological models were calibrated at one continuous monitoring streamflow station in each of the surface water catchments discharging to the lakes. Due to the large potential impact of water consented activities above Awaroa at Sansons Br (within Lake Waahi surface water catchment), calibration for the Lake Waahi model was carried out taking into account only winter flows. Analysis of the calibration indicates that the models are able to better represent low flow conditions than high flow conditions when compared with streamflow observations. This result is expected due to the low density of observed precipitation gauges across the catchments and the area of the surface water catchments. Validation of the models over the whole period of record indicates that the hydrological models reproduce the range of hydrological characteristics observed at the gauging stations. Over the period 1973-2013 Lake Whangape inflows are estimated to average 5.81 cumecs (ranging from 3.80-8.8 cumecs) while Lake Waahi inflows are estimated to average 1.88 cumecs (ranging from 1.00-2.57 cumecs). Inter-comparison of the calibrated Topnet parameters used for both catchments indicates that most of the parameter multipliers are similar across both models. This indicates a consistency of the hydrological process representation across the large watershed. The TopNet hydrological model is routinely used for hydrological modelling applications in New Zealand. It is a spatially distributed, time-stepping model of water balance. It is driven by time series of precipitation and temperature data, and of additional weather elements where available. TopNet simulates water storage in the snowpack, plant canopy, rooting zone, shallow subsurface, lakes and rivers. It produces time series of modelled river flow (under natural conditions) throughout the modelled river network, as well as evaporation. TopNet has two major components, namely a basin module and a flow routing module. Climate information was obtained from Virtual Climate Station Network. Annual average precipitation and evaporation were estimated by NIWA. Spatial information in TopNet is provided by national datasets on catchment topography (i.e. 30m digital elevation model), physical (Land Cover Database, Land Resource Inventory, and hydrological properties (River Environment Classification). The method for deriving TopNet initial parameter estimates from GIS data sources in New Zealand is given in Table 1 of Calrk et al. (2008). [Clark, M.P.;Rupp,D.E.;Woods,R.A.;Zheng,X.;Ibbitt,R.P.;Slater,A.G.;Schmidt,J.;Uddstrom,M.J.(2008). Hydrological data assimilation with the ensemble Kalman filter: Use of streamflow observations to update states in a distributed hydrological model. Advances in Water Resources 31(10):1309-1324.]

This core-funded research project aimed to map river reaches that gain and lose water to, and from, the groundwater system from two regions of New Zealand (Southland and Otago). A survey of river reaches that lose and gain flow in these regions of New Zealand was conducted at Environment Southland (ES), and Otago Regional Council (ORC) with key hydrologists, groundwater scientists and ecologists to record their knowledge of the locations of flow losing and gaining reaches on rivers and streams in their region. Following these interviews, the information was then transferred to a GIS layer to enable mapping of losing and gaining reaches in Southland and Otago. This work could serve as a platform for groundwater related research or engineering by NIWA in New Zealand.

NIWA has published a lake chart for every lake in New Zealand that can be surveyed, except for Lake Dunstan. The charts are of various scales that are determined to be the most appropriate for the size of the lake. The compilation of bathymetry from echo-sounding surveys with publication dates ranging from 1966 to 1989. This dataset also contains newly surveyed bathymetry using multibeam information. New data as and when available shall be added to this dataset. Some of the lakes may have more than one set of bathymetry files. The earlier one could be from the period 1966 to 1989 and the new information from recent surveys undertaken for comparison purposes.

The Waipori Power Scheme uses the outflow from Lake Mahinerangi, passing this flow through four dams and power stations in the upper Waipori gorge. The data and associated report provide flow information in the lower Waipori Gorge below the last (No. 4) Power Station, and below the last Weir (No. 4). The flow recording site (74395) was located three kilometres below the No. 4 Power Station at grid reference H44:802714. The site was shifted upstream on 15 August 2003 to a location 200m downstream of the power station (H44:789715) to enable TrustPower to monitor the flow information by linking the station Program Logic Controller to the site. The flow recording station at H44:777721, site (74398) below the No. 4 Weir was installed on 19 November 2003 for monitoring of minimum flows and ramping rates downstream of the Weir. The following outputs are available from the quarterly data Oct to Dec 2014. Tabulation of daily mean flows at site 74395 for the Waipori at Below No. 4 Power Station from 1 January to 31 December 2014. Full range plot of flows at site 74395 for the Waipori at Below No. 4 Power Station for the reporting period from 1 October to 31 December 2014. A partial range plot (<1000 l/s) to better show the detail of the low flows at site 74395 for the Waipori at Below No. 4 Power Station from 1 October to 31 December 2014. A tabulation of daily mean flows at site 74398 for the Waipori at Downstream No. 4 Weir from 1 January to 31 December 2014. A full range plot of flows at site 74398 for the Waipori at Downstream No. 4 Weir from 1 October to 31 December 2014. A partial range plot (<500 l/s) to better show the detail of the low flows at site 74398, for the Waipori at Downstream No.4 Weir from 1 October to 31 December 2014.

Te Waikoropupu Springs emerge from a complex of aquifers (for convenience here called the Te Waikoropupu Springs aquifer complex (WaiSAC) and, because of the extremely high natural, ecological, biodiversity, spiritual, cultural and economic values associated with this remarkable feature, work towards ensuring that their values are sustained has commenced. This initiative seeks a Water Conservation Order to sustainably manage the springs themselves, plus the surface and ground waters that supply and sustain them. NIWA was requested to recommend tentative numerical water quality limits for these waters, based on a desk-top evaluation of available information on groundwater ecosystem responses to key water quality variables. Limited available information on stygofauna tolerances to a few key water quality variables (nitrates, ammonia) was reviewed and compared this toxicity information with the relevant concentrations in New Zealand’s surface water quality guidelines (i.e., the ANZECC guidelines ((ANZECC & ARMCANZ 2000)). Two key variables, organic carbon and dissolved oxygen, however are not covered by the ANZECC guidelines, but there importance to the conservation of groundwaters was reviewed. The guideline concentrations discussed here must be regarded as tentative because they are based on a review of a very small body of empirical information. A more rigorous and comprehensive approach is highly desirable, but the scant information on toxicities, tolerances and sublethal effects for groundwater ecosystems, including biofilms, and specifically for New Zealand or WaiSAC stygofauna will require significant time and other resources. (a) A literature review on stygofauna tolerances to a key water quality aquifer variables: organic carbon, dissolved oxygen, nitrate and ammonia, (b) Comparison this toxicity information with the relevant concentrations in New Zealand’s surface water quality guidelines (i.e., the ANZECC guidelines) and (c) Tentative water quality limits suggested.

Datasets for work undertaken for the Christchurch City Council (CCC) include hydrometric network data (Climate variables, Rainfall, Water level and Ground water levels) from Oct-Dec 2014. Metadata include: 1 Introduction 2 Christchurch climate summary (October – December 2014) 3 Appendix: Maintenance / Fault log Data include: 1 Rainfall monitoring 2 Water-level monitoring 3 Groundwater monitoring 4 Miscellaneous data 5 Additional activities Data are derived from national climate databases and CCC rain gauges. Water-levels are derived from gauges owned by ECan, CCC and NIWA. Ground water levels are measured on either a weekly or fortnightly basis, depending on the site requirements and are measured relative to the CCC datum.

NIWA has published a lake chart for every lake in New Zealand that can be surveyed, except for Lake Dunstan. The charts are of various scales that are determined to be the most appropriate for the size of the lake. The compilation of bathymetry from echo-sounding surveys with publication dates ranging from 1966 to 1989. This dataset also contains newly surveyed bathymetry using multibeam information. New data as and when available shall be added to this dataset. Some of the lakes may have more than one set of bathymetry files. The earlier one could be from the period 1966 to 1989 and the new information from recent surveys undertaken for comparison purposes.

NIWA is currently carrying out a study for Auckland Council and Waikato Regional Council collating and analysing data on suspended sediment yields across the Northland, Auckland and Waikato regions. The aim of this study is to develop a predictor model of catchment suspended sediment yields based on various catchment characteristics. As an additional task in this study Auckland Council has commissioned NIWA to assess the Weiti Stream suspended sediment dataset for evidence of a trend or change in sediment loads that can be related to forestry harvesting activities. The data support analysis that looks for temporal change in the ‘rating’ relationship between suspended sediment yield (SSY) and event peak discharge (Qpeak). We are interested in whether the rating relationship between SSY and Qpeak for the period prior to forestry harvesting (2008-2012) still adequately predicts SSY for the period during (2013) and following (2014) forestry harvesting. The data analysis is summarised in plots that show: The rating relationship between event suspended sediment yield (SSY) and event peak discharge (Qpeak) for the pre-harvesting period. The during- and post-harvest data are also included on the plot, but the rating is based on the pre-Harvest data only. The during- and post-harvest period data all plot above the rating trendline, but are within the bounds of the preharvest data. A further two plots show the relationships between the residuals derived from the previous plot and time over the pre-Harvest period and time over the full data period respectively. It is the gradient of the trendlines in these two plots that we test to see if each is statistically different from zero.

Attributes associated directly with network:FieldTypeDescriptionCatareaRealWatershed area in m2CUM_Area RealArea upstream of a reach (and including this reach area) in m2.NzsegmentIntegerReach identifier to be used with REC2 (supercedes nzreach in REC1).nz_fnodeIntegerUnique number of preceding river segment's outlet node.nz_tnodeIntegerUnique number of following river segment's inlet node.LengthdownRealThe distance to coast from any reach to its outlet reach, where the river drains (m).HeadwaterIntegerNumber (0) denoting whether a stream is a “source” (headwater) stream. Non-zero for non-headwater streams.HydseqIntegerA unique number denoting the hydrological processing order of a river segment relative to others in the newtork.StreamOrderIntegerA number describing the Strahler order a reach in a network of reaches.euclid_distRealThe straight line distance of a reach from the reach “inlet” to its “outlet”.upElevRealHeight (asl) of the upstream end of a reach section in a watershed (m).downElevRealHeight (asl) of the downstream end of a reach section in a watershed (m).upcoordXRealEasting of the upstream end of a river segment in m (NZTM2000).upcoordYRealNorthing of the upstream end of a river segment in m (NZTM2000).downcoordXRealEasting of the downstream end of a river segment in m (NZTM2000).downcoordYRealNorthing of the downstream end of a river segment in m (NZTM2000).sinuosityRealActual distance divided by the straight line distancegiving the degree of curvature of the streamnzreach_rec1IntegerThe REC1 identifiying number for the corresponding\closest reach from REC1 (can be used to retrieve the REC management classes)headw_distIntegerDistance of the furthermost “source” or headwater reach from any reach (m).Shape_lengthRealThe length of the reach (vector) as calculated by ArcGIS.SegslpmaxRealMaximum segment slope along length of reach.SegslpmeanRealMean segment slope along length of reach.LIDIntegerLake Identifier number(LID) of overlapping lake.ReachtypeIntegerA value of 2 is assigned if the segment is an outlet to the lake, otherwise 0 or null.nextdownidintegersegment number of the most downstream reach