Snow Storms in Canterbury and Recharge to Groundwater

Wairakei Research Centre 114 Karetoto Road Wairakei Private Bag 2000, Taupo New Zealand T +64-7-374 8211 F +64-7-374 8199 www.gns.cri.nz

Snow storms in Canterbury and recharge to groundwater

P. A. White

GNS Science Consultancy Report 2007/87 April 2007

Environment Canterbury Report U07/27 ISBN: 978-1-86937-652-9

Institute of Geological and Nuclear Sciences Limited

CONFIDENTIAL

This report has been prepared by the Institute of Geological and Nuclear Sciences Limited (GNS Science) exclusively for and under contract to Environment Canterbury. Unless otherwise agreed in writing, all liability of GNS Science to any other party other than Environment Canterbury in respect of the report is expressly excluded.

The data presented in this Report are available to GNS Science for other use

Project Number: 520W2134 Confidential 2007

CONTENTS

EXECUTIVE SUMMARY ...... III 1.0 INTRODUCTION ...... 1 2.0 SNOW STORM OF 19 SEPTEMBER 2005 ...... 1 2.1 Description of the storm...... 1 2.2 Precipitation during the storm ...... 2 2.3 Recharge to groundwater prior to the storm ...... 2 2.4 Recharge to groundwater associated with the storm...... 3 3.0 SNOW STORM OF 12 JUNE 2006...... 3 3.1 Description of the storm of 12 June 2006 ...... 3 3.2 Description of snowfall of 22 June 2006 ...... 5 3.3 Precipitation during the storm of 12 June 2006 ...... 5 3.3.1 Precipitation during the storm ...... 5 3.3.2 Snow melt ...... 6 3.4 Recharge to groundwater prior to 12 June 2006 storm ...... 8 3.5 Recharge to groundwater after commencement of the 12 June 2006 storm....8 3.6 Under reporting of precipitation at Winchmore ...... 9 4.0 SUMMARY ...... 12 5.0 RECOMMENDATIONS ...... 13 6.0 ACKNOWLEDGEMENTS ...... 14 7.0 REFERENCES ...... 14

FIGURES

Figure 1 Location of rainfall recharge sites in Canterbury...... 16 Figure 2 Groundwater recharge, Airport lysimeter #2 in 2005 (daily mm)...... 17 Figure 3 Groundwater recharge, Hororata lysimeter #2 in 2005 (daily mm)...... 17 Figure 4 Groundwater recharge, Winchmore lysimeter #3 in 2005 (daily mm)...... 18 Figure 5 Snowfall in the South Island from 12 June 2006 storm (NASA 2006). MODIS image taken on 13 June (NASA, 2006). This date is presumed as GMT...... 19 Figure 6 Canterbury Plains looking towards Hororata and Banks Peninsula, taken from Mt Hutt on 20 June 2006 by Tim Davie...... 20 Figure 7 Canterbury Plains looking towards Rakaia River mouth, taken from Mt Hutt on 20 June 2006 by Tim Davie...... 20 Figure 8 Canterbury Plains looking towards Ashburton, taken from Mt Hutt on 20 June 2006 by Tim Davie...... 21 Figure 9 Groundwater recharge, Airport lysimeter #2 in 2005/06 (daily mm)...... 21 Figure 10 Groundwater recharge, Lincoln lysimeter #2 in 2005/06 (daily mm)...... 22 Figure 11 Groundwater recharge, Hororata lysimeter #2 in 2005/06 (daily mm)...... 22 Figure 12 Groundwater recharge, Winchmore lysimeter #3 in 2005/06 (daily mm)...... 23 Figure 13 Christchurch Airport – groundwater recharge, Lysimeter 2, 10 June 2006 to 13 June 2006 (mm/15 minutes)...... 23

TABLES

Table 1 Ground-level precipitation (rainfall/snow melt) on 18, 19, or 20 September 2005...... 2 Table 2 Groundwater recharge on, or after, 19 September 2005...... 3 Table 3 Observed maximum snow depths on the Canterbury Plains from 12 June storm...... 4 Table 4 Snow density measurements from 12 June storm...... 5 Table 5 Summary statistics for precipitation at rainfall recharge sites for 12 June 2006 storm for 15- minute data records...... 5

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Table 6 Estimated date of snow melt...... 6 Table 7 Observed precipitation in the snowfall period or early snow melt period...... 7 Table 8 Estimated snow thickness and precipitation...... 7 Table 9 Onset of precipitation of the 12 June 2006 storm and onset of groundwater recharge...... 8 Table 10 Ground-level precipitation (including snowfall) and groundwater recharge between 11 June and 30 June 2006...... 9 Table 11 Groundwater recharge between 11 June and 30 June 2006 compared with total groundwater recharge in the 2005 calendar year...... 9 Table 12 Measured precipitation at Winchmore, Dunsandel and Hororata...... 11 Table 13 Estimated precipitation at Winchmore and Dunsandel...... 11

APPENDICES

Appendix 1 Measured ground-level precipitation and measured groundwater recharge for the period 18 September 2005 to 30 September 2005...... 25 Appendix 2 Summary of measured groundwater recharge and measured ground-level rainfall for the 2000 to 2005 calendar years...... 29 Appendix 3 Measured ground-level precipitation and measured groundwater recharge for the snowfall period 10 June 2006 to 13 June 2006...... 34 Appendix 4 Measured ground-level precipitation and measured groundwater recharge for the snowfall period and the snow melt period from 11 June 2006 ...... 39 Appendix 5 Daily rainfall 11 June 2006 to 30 June 2006 ...... 44

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EXECUTIVE SUMMARY

Snow and rainfall from a snow storm on and around 19 September 2005 produced up to 77.5 mm of ground-level precipitation at rainfall recharge sites in Canterbury. Recharge to groundwater at three of the five monitoring sites is associated with the snow storm. The largest measured recharge was 24 mm at Winchmore; no recharge was measured at Lincoln and Hororata. This snowfall occurred after a period of relatively dry conditions on the Canterbury Plains.

Snowfall was widespread in Canterbury on 11 and 12 June 2006 after a period of relatively wet conditions in Canterbury. Up to 65 cm of snow was recorded on the Canterbury Plains with the largest snowfall at Winchmore. Precipitation (including rainfall, presumably, and snow melt) during the storm event in five monitoring sites was at most 59.1 mm.

Groundwater recharge began soon after (3 to 4 hours) the onset of precipitation in the storm. Precipitation and groundwater recharge for the period 11 June to 30 June 2006 (including snow and rainfall) is large:

• Christchurch Airport 100.5 mm precipitation and 65.5 mm groundwater recharge; • Lincoln 119 mm precipitation and 39.7 mm groundwater recharge; • Dunsandel 172 mm precipitation and 148 mm groundwater recharge; • Hororata 136 mm precipitation and 136.2 mm groundwater recharge; • Winchmore 102.5 mm precipitation and 58 mm groundwater recharge.

Significant groundwater recharge is associated with snowfall, particularly for the June 2006 storm. Snowfall, and rainfall in large storm events, probably play a significant role in total groundwater recharge to Canterbury aquifers and therefore this report recommends:

• precipitation associated with large storm events on the Canterbury Plains is characterised at short time intervals (e.g. 15 minute) in future assessments; • groundwater recharge associated with large storm events is assessed using observations from the rainfall recharge sites during, and after, storm events; • groundwater recharge associated with large storm events is modelled using standard approaches including consideration of water flow in preferential pathways.

Other recommendations following this work are:

• groundwater recharge associated with large storms on the Canterbury Plains is reported annually; • observe snow melt at groundwater recharge sites after snow storms to identify the snow melt period; • install a ground-level rain gauge at the Winchmore rainfall recharge site because precipitation in the standard rain gauge at Winchmore probably significantly underestimates precipitation in snow storms and underestimates ground-level rainfall; • continue recording rainfall and groundwater recharge on the Canterbury Plains.

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1.0 INTRODUCTION

Recharge to groundwater systems from rainfall is essential for maintaining aquifer storage volumes in Canterbury (White et al. 2003). Snowfall on the Canterbury Plains may make a significant contribution to groundwater recharge. Snowfall on the Canterbury Plains is not uncommon; snow is recorded in Ashburton in 37 of the 80 years between 1927 and 2006 (Hendrikx, 2006) and maximum snow thickness at Ashburton was greater than 10 cm in 9 of these years.

Previously groundwater recharge in Canterbury has been assessed without distinguishing between sources of precipitation (e.g. rainfall and snowfall), White et al. (2003). Therefore, Environment Canterbury (ECAN) contracted GNS Science to assess groundwater recharge associated with snowfalls on 19 September 2005 and 12 June 2006 based on observations at ECAN/GNS Science rainfall recharge sites. ECAN and GNS Science maintain five rainfall recharge sites (Figure 1) on the Canterbury Plains (White et al. 2003) at Christchurch Airport, Dunsandel, Lincoln, Hororata and Winchmore.

This report summarises the snow storms of 19 September 2005 and 12 June 2006, summarises precipitation measured by ground-level rain gauges associated with the storms, summarises rainfall recharge to groundwater before the storms and summarises groundwater recharge associated with the storms, including groundwater recharge associated with snow melt.

2.0 SNOW STORM OF 19 SEPTEMBER 2005

Wintry conditions on 19 and 20 September 2005 included snowfall, sleet and rain causing significant disruption in Canterbury. Precipitation associated with these weather conditions came after a period of below average rainfall recharge at five Canterbury rainfall recharge sites. Recharge to groundwater occurred at three of the five sites after the storm on 19 September 2005.

2.1 Description of the storm

A fierce snow storm (Christchurch Press 2005a) on Monday 19 September 2005 resulted in businesses and schools closing. Snowfall on Banks Peninsula continued to Tuesday 20 September and resulted in some households being without power for 26 hours (Christchurch Press 2005b).

Hagley Park was closed at 10 am on Monday 19 September as many large trees snapped and smaller trees collapsed under the weight of snow (Christchurch Press 2005c). Parts of inland Canterbury had about 25 cm of snow (Christchurch Press 2005d); snow lay 7 cm deep in Cathedral Square before beginning to thaw around lunchtime on 19 September. The storm dumped up to 10 cm of snow in the central city and suburbs (Christchurch Press 2005e) and 30 cm of snow fell on Mount Hutt. Christchurch Airport was closed for about three hours and reopened by 2 pm (Christchurch Press 2005e). Hendrikx (2006) reports a maximum annual snow depth of about 6 cm in 2005 at climate station H31971 in Ashburton and it is assumed that this snow fell during the storm of 19 September. Approximately 12 cm

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of snow was recorded at the Winchmore rainfall recharge site on 19 September (Carson, pers. comm.).

The weather sequence in Christchurch City is summarised as (Christchurch Press 2005d):

• 0600 - low pressure area bringing snow forms over Christchurch; • 0900 - depression dumps heavy snow on Christchurch; • 1200 - depression moves away from Christchurch, snow eases to sleet and weather begins to clear; • 1800 - southerly change arrives in Christchurch bringing hail and thunder; • 2100 - wintry showers continue.

2.2 Precipitation during the storm

Ground-level precipitation in the ground-level recorders associated with the 19 September storm was a maximum of 77.5 mm (Table 1):

Table 1 Ground-level precipitation (rainfall/snow melt) on 18, 19, or 20 September 2005

Location Precipitation (rainfall/snow melt) (mm) Christchurch Airport 8.5 Dunsandel 77.5 Lincoln 46 Hororata 21.5 Winchmore (standard rain gauge) 39

All precipitation (rainfall and snow melt) associated with the storm appears to have occurred on 18, 19 or 20 September (Appendix 1). Most precipitation occurred on 19 September. For example 69.5 mm of precipitation at the Dunsandel site (or 90% of the three-day total of 77.5 mm) occurred on 19 September.

2.3 Recharge to groundwater prior to the storm

Recharge to groundwater was below average for the 2005 calendar year (i.e. the period including the storm) (Appendix 2) for four rainfall recharge monitoring sites in Canterbury and zero groundwater recharge for 2005 was recorded for the Lincoln site. Groundwater recharge had been below average for the 2004 and 2005 calendar years at two rainfall recharge sites.

In summary:

• rainfall recharge was less than average for two consecutive calendar years at rainfall recharge sites located near Hororata and Winchmore; • rainfall recharge was less than average for the 2005 calendar year at rainfall recharge sites located at Christchurch Airport and Lincoln; • zero rainfall recharge was measured at Lincoln in 2005.

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The Dunsandel site is excluded from the summary because this site is potentially impacted by irrigation. Note that the period of record for measurements that include full-calendar years is 2000 to 2005. This is not a long period for establishing statistically-robust estimates of mean ground-level rainfall and mean rainfall recharge.

Christchurch Airport (Figure 2), Hororata (Figure 3) and Winchmore (Figure 4) sites measured rainfall recharge through May and June before the storm so it is assumed that soil at these sites was at, or near, full saturation immediately prior to the storm.

Soil at Lincoln is assumed as less than full saturation at the time of the storm because zero rainfall recharge was measured in 2005 at the Lincoln site.

2.4 Recharge to groundwater associated with the storm

Groundwater recharge associated with the storm event occurs at Christchurch Airport, Dunsandel and Winchmore. Recharge continues after 19 September (Table 2).

Table 2 Groundwater recharge on, or after, 19 September 2005.

Location Period of recharge on, or Sum of recharge Recharge after, 19 September in period sum/precipitation (days) (mm) (%) Christchurch Airport 6 4 47

Dunsandel 7 12.5 16

Lincoln - 0 0

Hororata - 0 0

Winchmore 6 24 62

3.0 SNOW STORM OF 12 JUNE 2006

Snowfall was widespread in Canterbury, Otago and Marlborough on 12 June 2006. Significant damage to electricity distribution systems in Canterbury resulted from the snowfall. Snowfalls of up to 65 cm were recorded on the Canterbury Plains and much of the precipitation associated with the snowfall, and rainfall in June 2006, became groundwater recharge.

3.1 Description of the storm of 12 June 2006

The snow storm of 12 June dropped snow over widespread areas of the South Island, Figure 5 (NASA, 2006). The author attempted to identify the exact date and time that this image was recorded but was unable to obtain that information through the MODIS web site or the Geoscience Australia web site. A 13 June date is identified in the original caption to this figure. The image may have been taken on 13 June (GMT) i.e. on 13 June (NZST) or 14 June (NZST).

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This storm started as a “mid-Tasman depression which deepened on 11 June” (Hendrikx, 2006) and the “centre of this depression tracked over the north of the South Island on 12 June” (Hendrikx, 2006). The depth of snowfall is summarised by Hendrikx (2006) at climate stations, including locations on the Canterbury Plains (Table 3).

Table 3 Observed maximum snow depths on the Canterbury Plains from 12 June storm.

Location Maximum snow depth Source of observations (cm) Christchurch 5 – 15 Hendrikx (2006)

Darfield 40 Hendrikx (2006)

Sheffield 50 Hendrikx (2006)

Amberly 10 – 15 Hendrikx (2006)

Oxford 15 Hendrikx (2006)

Lincoln 10 - 15 Hendrikx (2006)

Rakaia 30 Hendrikx (2006)

Ashburton 38 Hendrikx (2006)

Methven 55 Hendrikx (2006)

Geraldine 40 – 50 Hendrikx (2006)

Mt Peel 45 Hendrikx (2006)

Temuka 30 Hendrikx (2006)

Timaru 30 Hendrikx (2006)

Christchurch Airport* 5 (Tony Hawkins pers. comm.)

Hororata* 50 (approximately) (Hororata Hotel pers. comm.)

Winchmore* 60 – 65 (Carson pers. comm.)

* snow thickness information was solicited, on 13 June, from local people by the author for locations near rainfall recharge sites.

The storm caused widespread damage to the electricity distribution systems in Canterbury (Hendrikx, 2006) with large areas of South Canterbury, inland Canterbury and inland Otago without power for many days.

Hendrikx (2007) estimates an average snow thickness on the Canterbury Plains of 25 – 30 cm. Hendrikx (2006 and 2007) reports snow density measurements as in Table 4.

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Table 4 Snow density measurements from 12 June storm. Location Snow density Source (kg/m3) Hororata 190 Hendrikx (2006) Lyndhurst Station 170 Hendrikx (2006) Methven 160 Hendrikx (2006) Te Kapo 180 Hendrikx (2006) Geraldine 300 Hendrikx (2007)

3.2 Description of snowfall of 22 June 2006

Light snow fell in Canterbury on Thursday 22 June 2006:

• at Christchurch Airport less than 1 cm fell and briefly lay on the ground at day break before melting by 10 am (Met. Service, 2006 ); • at Hororata a little bit less than 2.5 cm fell (Hororata Hotel, 2006); • at Winchmore less than 3 mm of snow fell that didn’t settle (Carson, 2006).

3.3 Precipitation during the storm of 12 June 2006

3.3.1 Precipitation during the storm

A relatively rapid increase in precipitation over time identifies the storm at the rainfall recharge sites (Appendix 3). Precipitation began first at Hororata (Table 5), followed by Dunsandel, followed by Lincoln, and lastly Christchurch Airport. Precipitation is continuous for up to 10 hours 15 minutes (at Lincoln) after commencement of precipitation. The cessation of recorded precipitation probably coincides with solid snow in the ground-level recorders and freezing conditions.

The Winchmore data provided by NIWA (Walter, 2007) is the sum of daily rainfall from a standard rain gauge. Therefore the start of precipitation and the end of precipitation is not defined to 15-minute intervals as with the other sites. A total of 59.1 mm precipitation is observed at Winchmore on 11, 12 and 13 June.

Table 5 Summary statistics for precipitation at rainfall recharge sites for 12 June 2006 storm for 15-minute data records.

Location Start of Maximum ‘Cessation’ of Precipitation during event precipitation precipitation continuous precipitation between start and ‘cessation’ (mm/15 mins) (mm) Airport 0 hrs, 20 mins, 12 June 2.5 06 hrs, 50 mins, 12 June 35.5 Dunsandel 23 hrs, 15 mins, 11 June 3.0 03 hrs, 40 mins, 12 June 33 Lincoln 0 hrs, 15 mins, 12 June 1.5 10 hrs, 30 mins, 12 June 37.5 Hororata 22 hrs, 50 mins, 11 June 3.0 02 hrs, 10 mins, 12 June 24 Winchmore daily data, 11 June daily data daily data, 13 June 59.1

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3.3.2 Snow melt

Groundwater recharge may be summed in the snow melt period. However no records of snow thickness after 12 June are available from the network of rain gauges in Canterbury (Hendrikx, 2007) and so the history of snow melt (Table 6) is assembled from miscellaneous observations.

Table 6 Estimated date of snow melt.

Location Estimated end of Evidence for assumed date of snow melt end snow melt Airport 14 June No snow observed in the general area of Christchurch City on 20 June (Figure 5). No snow cover apparent in Figure 4. Dunsandel 30 June John Carson (2006) report of snow cover only in sheltered places at Winchmore on 30 June. Lincoln 14 June No snow observed in the general area of Lincoln on 20 June (Figure 5). No snow cover apparent in Figure 4. Hororata 30 June Approximately 30 cm of snow from 12 June storm remained on the ground at 22 June (Hororata Hotel, 2006). Winchmore 30 June John Carson (2006) report of snow cover only in sheltered places at Winchmore on 30 June.

Snow melt occurred relatively quickly in and around Christchurch, for example:

• no snow cover is apparent in and around Christchurch in the 13 June satellite image (Figure 5, presumed as a GMT date) taken on 13 or 14 June (NZST); • no snow cover is observed in the general locality of Christchurch City and Lincoln on 20 June (Figure 6).

Snow melt was relatively slow on the inland regions of the Canterbury Plains, for example:

• snow is possibly observed near Dunsandel on 20 June (Figure 6); • snow is observed around Hororata on 20 June (Figure 6); • by 22 June approximately 30 cm of snow remained on the ground at Hororata (Hororata Hotel, 2006); • by 30 June 2006 at Winchmore farm approximately 10% to 20% of the ground was covered by snow in sheltered places (John Carson 2006); • snow is observed on the upper Canterbury Plains (Figure 7) and extensive areas of mid Canterbury and South Canterbury (Figure 8) on 20 June.

A “snow melt period” of 11 to 30 June is defined as the time interval when snow from the 12 June storm melted. Identification of the snow melt period allows estimation of groundwater recharge associated with snowfall.

Precipitation in the snow melt period (Appendix 4 and Appendix 5) includes the 12 June storm and rainfall events. For example a presumed rainfall event is observed at all sites on 16 June (Appendix 5).

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Identification of snow melt in the ground-level rain gauges is complicated by rainfall in the snow melt period. Therefore unique identification of groundwater recharge associated with snowfall on 12 June is impossible with the observed data for the period 16 June to 30 June i.e. for the Dunsandel, Hororata and Winchmore observation sites.

Precipitation in the snowfall period is measured for the Airport and Lincoln sites from 11 June to 13 June (Table 7). Precipitation for the Dunsandel, Hororata and Winchmore sites in the interval between 11 June and rainfall on 16 June (Table 7) is at most 68 mm and is a probable minimum for the storm because much of the potential snow melt period is outside this time interval.

Table 7 Observed precipitation in the snowfall period or early snow melt period.

Location Period Observed precipitation Notes (mm) Airport 11 June @ 0 hrs to 13 June @ 2400 hrs 54

Dunsandel 11 June @ 0 hrs to rainfall on 16 June 65.5 To 16 June @ 0700 rainfall event Lincoln 11 June @ 0 hrs to 13 June @ 2400 hrs 58

Hororata 11 June @ 0 hrs to rainfall on 16 June 68 To 16 June @ 0700 rainfall event Winchmore 11 June to 16 June 59.1 Daily data

Table 8 Estimated snow thickness and precipitation.

Location Snow thickness Estimated Observed Notes (mm) precipitation precipitation (mm)* (Table 7) Airport 50 10 54

Dunsandel 300 60 65.5 Rakaia, snow thickness estimates (Table 3) Lincoln 100 20 58

Hororata 500 100 68

Winchmore 600 120 59.1

* estimated from snow thickness assuming a snow density of 200 kg/m3.

Possible implications of comparisons between estimated precipitation (Table 8) and observed precipitation (Table 7) include:

• rainfall at the Airport and Lincoln was much more significant to total precipitation than snowfall; • snow at Hororata and Winchmore was melting after 16 June at the rainfall recharge sites (note observations of snow melt in Section 3.1).

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3.4 Recharge to groundwater prior to 12 June 2006 storm

Rainfall recharge was not observed or was minor at four rainfall recharge sites in summer 2005/2006 (Figures 9 to 12).

Major groundwater recharge (defined at 1 mm/day, or greater) began in winter 2006 at the following dates:

• Airport 12 May, Figure 9; • Lincoln 4 June, Figure 10; • Hororata 25 April, Figure 11; • Winchmore 30 May, Figure 12.

Therefore, it is assumed that soil was close to saturation at the onset of the 12 June storm.

3.5 Recharge to groundwater after commencement of the 12 June 2006 storm

All groundwater recharge sites record recharge soon after the commencement of the 12 June storm (Appendix 3). For example groundwater recharge at the Airport (Figure 13) began on 12 June at 0435 hrs. The onset of the storm event and the onset of groundwater recharge are listed in (Table 9).

Table 9 Onset of precipitation of the 12 June 2006 storm and onset of groundwater recharge. Location Onset of precipitation Onset of groundwater recharge

Airport 0 hrs, 20 mins, 12 June 04 hrs, 35 mins, 12 June

Dunsandel 23 hrs, 15 mins, 11 June 02 hrs, 25 mins, 12 June

Lincoln 0 hrs, 15 mins, 12 June 04 hrs, 15 mins, 12 June

Hororata 22 hrs, 50 mins, 11 June 01 hrs, 30 mins, 12 June

Winchmore not identifiable in daily data 00 hrs, 40 mins, 12 June (lysimeter 1*)

* lysimeter 1 begins to respond to recharge approximately 5.5 hours before lysimeter 3 responds to recharge.

Groundwater recharge from snow is not uniquely identifiable because rainfall probably occurs during the period of snow melt (Section 3.3). Therefore groundwater recharge is compared with total precipitation in the period 11 June to 30 June (Table 10).

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Table 10 Ground-level precipitation (including snowfall) and groundwater recharge between 11 June and 30 June 2006. Location Ground-level Groundwater Recharge/precipitation precipitation recharge (%) (mm) (mm) Airport 100.5 65.5 65 Dunsandel 172 148 86 Lincoln 119 39.7 33 Hororata 136 136.2 100 Winchmore 102.5* 58 (lysimeter 3) 57

* Winchmore is a standard rain gauge.

The month of June 2006 produced significant rainfall recharge in all lysimeters. For example the approximately 136 mm of groundwater recharge at the Hororata site in June 2006 is about 1.7 times greater than the total groundwater recharge for the 2005 calendar year (Appendix 2) of 79 mm for lysimeter #2. The large groundwater recharge in June 2006 presumably reflects the large precipitation and the cold conditions leading to low evaporation.

Groundwater recharge in the period associated with the snow event (Table 10) is significant compared with the historic record of groundwater recharge (Appendix 2). For example groundwater recharge in the period 11 June 2006 to 30 June 2006 is greater than groundwater recharge in the whole of the 2005 calendar year at the Lincoln and Hororata sites (Table 11).

Table 11 Groundwater recharge between 11 June and 30 June 2006 compared with total groundwater recharge in the 2005 calendar year.

Location* Groundwater recharge 11 June Groundwater recharge in the Notes to 30 June 2006 2005 calendar year (mm) (mm) Airport 65.5 78 Lysimeter 2 Lincoln 39.7 0 Lysimeter 2 Hororata 136.2 79 Lysimeter 2 Winchmore 58 81 Lysimeter 3

* The Dunsandel site is not included in this table as groundwater recharge measurements at this site are impacted by irrigation.

3.6 Under reporting of precipitation at Winchmore

Measurements of precipitation at Winchmore are made with a standard rain gauge and this probably under reports precipitation associated with the 12 June 2006 storm.

Precipitation at Winchmore is compared with ground-level precipitation at Dunsandel and Hororata, the nearest rainfall recharge sites to Winchmore (Table 12).

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The Winchmore standard recorder collects precipitation that is significantly less than measured precipitation at Dunsandel and Hororata (Table 12):

• in the period 11 June to 16 June; and • in the period 11 June to 30 June.

Estimated precipitation in snowfall in the 12 June storm at Winchmore is 120 mm which is significantly greater than the other two sites (Table 12) yet the Winchmore recorder collects significantly less precipitation than the other two sites.

The under reporting of precipitation at the Winchmore standard rain gauge is estimated by comparing Winchmore with Dunsandel as Dunsandel occupies a similar elevation on Canterbury Plains. Total precipitation at Winchmore and Dunsandel in the period 11 June to 30 June includes snow and rainfall. Precipitation in the period 11 June to 30 June is estimated (Table 13) as the sum of:

• rainfall on 11 June immediately before the snow storm (Table 7); • precipitation in snow (Table 8); • precipitation in the period 17 June to 30 June; • precipitation in the period 17 June to 30 June at the Winchmore and Dunsandel sites probably includes rainfall and snow melt. Precipitation at Dunsandel is probably representative of rainfall at Winchmore in the period 17 June to 30 June; snow was more likely to have melted at Dunsandel by 17 June.

Observed precipitation at Winchmore is only 48% of estimated precipitation at Winchmore. However observed precipitation at Dunsandel is 99% of estimated precipitation at Dunsandel. Therefore the standard rain gauge at Winchmore probably under reports precipitation associated with the 12 June storm. Hence results from standard rain gauges are not recommended for assessing relationships between precipitation in snow and groundwater recharge on the Canterbury Plains.

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Table 12 Measured precipitation at Winchmore, Dunsandel and Hororata.

Site Type of rain Measured precipitation 11 June to 16 June Measured precipitation 11 June to 30 June Estimated precipitation 12 June storm from snow gauge (mm) (mm), (mm), Table 10 Table 8 Winchmore standard 59.11 102.5 120

Dunsandel ground level 912 172 60

Hororata ground level 962 136 100

1 Table 7 2 precipitation recorded in Table 7 plus rainfall on 16 June

Table 13 Estimated precipitation at Winchmore and Dunsandel.

Site Type of rain Estimated precipitation 12 June storm Estimated precipitation at Sum of estimated Observed precipitation Ratio gauge (mm) Dunsandel precipitation 11 June to 30 June observed Rainfall 11 June Snow (Table 8) 17 June to 30 June 11 June to 30 June (mm) estimated (mm) (mm) (%) rounded Winchmore Standard 14.71 120 813 215.74 102.5 48

Dunsandel ground level 332 60 813 1744 172 99

1 Total observed precipitation on 11 June (Table 7) 2 Observed precipitation to 03 hrs, 40 mins, 12 June (Table 7) 3 Observed precipitation, Dunsandel i.e. 172 mm – 91 mm (Table 12) 4 Equals: rainfall on 11 June immediately before snowfall (Table 7) plus estimated precipitation as snow in the 12 June storm (Table 8) plus estimated precipitation in the period 17 June to 30 June for the Dunsandel site.

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4.0 SUMMARY

This report aims to summarise precipitation and groundwater recharge associated with snowfalls in Canterbury on 19 September 2005 and 11/12 June 2006. The primary sources of data for this study are rainfall recharge monitoring sites located at: Christchurch Airport, Dunsandel, Lincoln, Hororata and Winchmore.

Snow and rainfall from a snow storm on and around 19 September 2005 produced up to 77.5 mm, (at Dunsandel), of ground-level precipitation at groundwater recharge sites in Canterbury. This snow storm came after a period of dry conditions in Canterbury. For example rainfall recharge to groundwater was less than average for the 2004 and 2005 calendar years at the Hororata and Winchmore sites and zero rainfall recharge to groundwater was measured at Lincoln in the 2005 calendar year indicating dry antecedent conditions.

Recharge to groundwater at three of the five monitoring sites is associated with the snow storm. The largest measured recharge was 24 mm at Winchmore; no recharge was measured at Lincoln and Hororata.

Snowfall was widespread in Canterbury on 11 and 12 June 2006. Up to 65 cm of snow is recorded on the Canterbury Plains. Soils were probably close to saturation at the commencement of snowfall because groundwater recharge is observed before the snow event.

Precipitation is continuous for up to 10 hours 15 minutes after commencement of precipitation in the ground-level records at Airport, Dunsandel, Lincoln and Hororata. The onset of freezing conditions is probably what halts the measurement of precipitation in these recorders. A range of 24 mm to 37.5 mm in precipitation is recorded at these sites before the cessation of precipitation recording. Precipitation during the storm event at Winchmore, measured with a standard rain gauge, was 59.1 mm.

Snow melted quickly in the Christchurch City area and at Lincoln as no snow is observed in these areas in a satellite image taken on 13 June (presumed as GMT).

Groundwater recharge began soon after (3 to 4 hours) the onset of precipitation and up to 68 mm (at Hororata) recharge was observed that probably relates to precipitation in the storm. The snow melt period for inland Canterbury Plains is poorly defined so the quantum of groundwater recharge uniquely associated with this snowfall event is difficult to identify. Therefore, the period of potential snow melt is defined as 11 to 30 June 2006 for three sites (Dunsandel, Hororata and Winchmore).

Precipitation and groundwater recharge for the period 11 to 30 June 2006 (including snow and rainfall) are large at recharge sites:

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• Hororata 136 mm precipitation and 136.2 mm groundwater recharge; • Winchmore 102.5 mm precipitation and 58 mm groundwater recharge.

Groundwater recharge in the period 11 June to 30 June 2006 is large compared to the historic record.

For example:

• groundwater recharge in the June 2006 period is greater than groundwater recharge in the whole of the 2004 calendar year at the Lincoln and Hororata sites; • groundwater recharge at Winchmore during the estimated snow melt period is 58 mm, compared to a total groundwater recharge of 81 mm in the 2005 calendar year.

The Winchmore precipitation record is from a standard rain gauge that probably collects less precipitation in snow conditions than the ground-level gauges at all other sites.

5.0 RECOMMENDATIONS

Groundwater recharge associated with snowfall is significant.

Therefore:

• further studies of snow, and storm events, and groundwater recharge on the Canterbury Plains could usefully be undertaken; • groundwater recharge associated with future snow storm events should be assessed using observations from the rainfall recharge sites and this recharge assessed in relation to recharge from rainfall; • the technical approach to modelling groundwater recharge associated with storm events needs to consider: standard water balance models, or “black box models” (e.g. White et al. 2003); water flow in preferential pathways; and ideally a detailed model of ground- level precipitation at a short (e.g. 15 minute) time interval; • annual reporting on large storms and groundwater recharge on the Canterbury Plains is completed by ECAN.

Other recommendations, coming from this work, are:

• observe snow melt at groundwater recharge sites after snow storms to identify the snow melt period and measure groundwater recharge associated with snow storms; • install a ground-level rain gauge at the Winchmore groundwater recharge site as the standard rain gauge (NIWA site H31883) probably under-catches precipitation in snowfall and probably under-catches rainfall (White et al. 2003); • continue recording ground-level rainfall and groundwater recharge on the Canterbury Plains. The Dunsandel site has been of questionable relevance to the assessment of groundwater recharge from rainfall because groundwater recharge at the site is significantly impacted by irrigation. However the site occupies a middle-Plain position and this report shows that records at the Dunsandel site are useful to provide data in a gap between other rainfall recharge sites. Therefore continuance of the ground-level rainfall, and groundwater recharge, measurements at Dunsandel is recommended.

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6.0 ACKNOWLEDGEMENTS

The following contributions to this report are gratefully acknowledged:

• Bryan Todd, ECAN, for supplying groundwater recharge data; • Tim Davie, Landcare Research, for providing photographs; • Kathy Walter, NIWA, for supplying Winchmore rainfall data; • Jordy Hendrikx , NIWA, for supplying snow-fall data; and to • John Carson, Agresearch, for snow thickness data.

Thanks also to David Scott and Gil Zemansky for the comments on a draft of this report.

7.0 REFERENCES

Carson, J. 2006. Manager, Winchmore Agresearch farm, pers. comm. Christchurch Press 2005a. Region reopens after big storm. Article of 21/9/2005. Christchurch press 2005b. Storm effects linger on Peninsula. Article of 21/9/2005. Christchurch Press 2005c. Heavy toll on spring growth. Article of 21/9/2005. Christchurch Press 2005d. September shocker: wintry blast smothers garden city. Article of 20/9/2005. Christchurch Press 2005e. Storm batters city and farms. Article of 20/9/2005. Hendrikx, J. 2006. Preliminary analysis of the 12 June 2006 Canterbury snow storm. National Institute of Water and Atmospheric Research Limited report CHC2006-088. Hendrikx, J. 2007. NIWA, Christchurch, pers. comm. Hororata Hotel 2006. Hororata, pers. comm Met. Service 2006. Christchurch, pers. comm. NASA 2006. Moderate Resolution Imaging Spectro-radiometer (MODIS). Image from the Aqua satellite captured on 13th June (modis.gsfc.nasa.gov). Reference to image is: http://earthobservatory.nasa.gov/Newsroom/NewImages/ images.php3?img_id=17307 Walter, K. 2077. NIWA, Christchurch, pers. comm White, P.A., Hong, Y-S., Murray, D., Scott, D.M., Thorpe, H.R. 2003. Evaluation of regional models of rainfall recharge to groundwater by comparison with lysimeter measurements, Canterbury, New Zealand. Journal of Hydrology (NZ) 42(1), 39-64.

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FIGURES

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Figure 1 Location of rainfall recharge sites in Canterbury.

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(Item 2 )/1000/day 6

0 Jan-2005 Feb-05 Mar-05 Apr-05 May-05 Jun-05 Jul-05 Aug-05 Sep-05 Oct-05 Nov-05 Dec-05 site 324510(2) < Untitled > (Item 2 )/1000/day (Total=78.32) Figure 2 Groundwater recharge, Airport lysimeter #2 in 2005 (daily mm).

(Item 2 )/1000/day 6

0 Jan-2005 Feb-05 Mar-05 Apr-05 May-05 Jun-05 Jul-05 Aug-05 Sep-05 Oct-05 Nov-05 Dec-05 site 315911(2) < Untitled > (Item 2 )/1000/day (Total=79.44) Figure 3 Groundwater recharge, Hororata lysimeter #2 in 2005 (daily mm).

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(Item 3 )/1000/day 6

0 Jan-2005 Feb-05 Mar-05 Apr-05 May-05 Jun-05 Jul-05 Aug-05 Sep-05 Oct-05 Nov-05 Dec-05 site 317710(3) < Untitled > (Item 3 )/1000/day (Total=80.73) Figure 4 Groundwater recharge, Winchmore lysimeter #3 in 2005 (daily mm).

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Figure 5 Snowfall in the South Island from 12 June 2006 storm (NASA 2006). MODIS image taken on 13 June (NASA, 2006). This date is presumed as GMT.

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Figure 6 Canterbury Plains looking towards Hororata and Banks Peninsula, taken from Mt Hutt on 20 June 2006 by Tim Davie.

Figure 7 Canterbury Plains looking towards Rakaia River mouth, taken from Mt Hutt on 20 June 2006 by Tim Davie.

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Figure 8 Canterbury Plains looking towards Ashburton, taken from Mt Hutt on 20 June 2006 by Tim Davie.

0 Jul-2005 Aug-05 Sep-05 Oct-05 Nov-05 Dec-05 Jan-06 Feb-06 Mar-06 Apr-06 May-06 Jun-06 site 324510(2) (Total=154.2) Figure 9 Groundwater recharge, Airport lysimeter #2 in 2005/06 (daily mm).

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15 (Item 2 )/1000/day

0 Jul-2005 Aug-05 Sep-05 Oct-05 Nov-05 Dec-05 Jan-06 Feb-06 Mar-06 Apr-06 May-06 Jun-06 site 326411(2) < Untitled > (Item 2 )/1000/day (Total=49.36) Figure 10 Groundwater recharge, Lincoln lysimeter #2 in 2005/06 (daily mm).

15 (Item 1 )/1000/day 10

0 Jul-2005 Aug-05 Sep-05 Oct-05 Nov-05 Dec-05 Jan-06 Feb-06 Mar-06 Apr-06 May-06 Jun-06 site 315911 < Untitled > (Item 1 )/1000/day (Total=187.4) Figure 11 Groundwater recharge, Hororata lysimeter #2 in 2005/06 (daily mm).

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13 12

6 (Item 3 )/1000/day

0 Jul-2005 Aug-05 Sep-05 Oct-05 Nov-05 Dec-05 Jan-06 Feb-06 Mar-06 Apr-06 May-06 Jun-06 site 317710(3) < Untitled > (Item 3 )/1000/day (Total=143) Figure 12 Groundwater recharge, Winchmore lysimeter #3 in 2005/06 (daily mm).

0.8

0.6

(Item 2 )/1000/15mins 0.4

0.2

0 10-Jun-2006 10 12: 11 00: 11 12: 12 00: 12 12: 13 00: 13 12: site 324510(2) < Untitled > (Item 2 )/1000/15mins (Total=27.36) Figure 13 Christchurch Airport – groundwater recharge, Lysimeter 2, 10 June 2006 to 13 June 2006 (mm/15 minutes).

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APPENDICES

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APPENDIX 1 MEASURED GROUND-LEVEL PRECIPITATION AND MEASURED GROUNDWATER RECHARGE FOR THE PERIOD 18 SEPTEMBER 2005 TO 30 SEPTEMBER 2005

20 (Item 3 )/1000/day (Item

0 18-Sep-2005 20-Sep 21-Sep 22-Sep 23-Sep 24-Sep 25-Sep 26-Sep 27-Sep 28-Sep 29-Sep 30-Sep site 324510(3) < Untitled > (Item 3 )/1000/day (Total=38.5) Christchurch Airport – ground-level precipitation 18 September 2005 to 30 September 2005.

1.5

1 (Item 2 )/1000/day (Item

0.5

0 18-Sep-2005 20-Sep 21-Sep 22-Sep 23-Sep 24-Sep 25-Sep 26-Sep 27-Sep 28-Sep 29-Sep 30-Sep site 324510(2) < Untitled > (Item 2 )/1000/day (Total=3.92) Christchurch Airport – Lysimeter #2, groundwater recharge 18 September 2005 to 30 September 2005.

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0 18-Sep-2005 1.25 hrs/mm 21-Sep 22-Sep 23-Sep 24-Sep 25-Sep 26-Sep 27-Sep 28-Sep 29-Sep 30-Sep site 327110(3) < Untitled > (Item 3 )/1000/day 0.64(units/day)/mm (Total=77.5) Dunsandel – ground-level precipitation 18 September 2005 to 30 September 2005.

0 18-Sep-2005 1.25 hrs/mm 21-Sep 22-Sep 23-Sep 24-Sep 25-Sep 26-Sep 27-Sep 28-Sep 29-Sep 30-Sep site 327110(2) < Untitled > (Item 2 )/1000/day 0.08(units/day)/mm (Total=12.48) Dunsandel – Lysimeter #2, groundwater recharge 18 September 2005 to 30 September 2005.

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0 18-Sep-2005 20-Sep 21-Sep 22-Sep 23-Sep 24-Sep 25-Sep 26-Sep 27-Sep 28-Sep 29-Sep 30-Sep site 326411(3) < Untitled > (Item 3 )/1000/day (Total=46) Lincoln – ground-level precipitation 18 September 2005 to 30 September 2005.

Lincoln – rainfall recharge 18 September 2005 to 30 September 2005 is zero.

8 (Item 3 )/1000/day 6

0 18-Sep-2005 20-Sep 21-Sep 22-Sep 23-Sep 24-Sep 25-Sep 26-Sep 27-Sep 28-Sep 29-Sep 30-Sep site 315911(3) < Untitled > (Item 3 )/1000/day (Total=21.5) Hororata – ground-level precipitation 18 September 2005 to 30 September 2005.

Hororata – rainfall recharge 18 September 2005 to 30 September 2005 is zero.

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0 18-Sep-2005 20-Sep 21-Sep 22-Sep 23-Sep 24-Sep 25-Sep 26-Sep 27-Sep 28-Sep 29-Sep 30-Sep site 318803 (Total=39) Winchmore – precipitation 18 September 2005 to 30 September 2005, NIWA site H31883 (Walter pers. comm.).

6 (Item 3 )/1000/day (Item

0 18-Sep-2005 20-Sep 21-Sep 22-Sep 23-Sep 24-Sep 25-Sep 26-Sep 27-Sep 28-Sep 29-Sep 30-Sep site 317710(3) < Untitled > (Item 3 )/1000/day (Total=25.12) Winchmore – Lysimeter #3, groundwater recharge 18 September 2005 to 30 September 2005

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APPENDIX 2 SUMMARY OF MEASURED GROUNDWATER RECHARGE AND MEASURED GROUND-LEVEL RAINFALL FOR THE 2000 TO 2005 CALENDAR YEARS Christchurch Airport Rainfall recharge site 324510

This site consists of: 1) Groundwater recharge lysimeter No.1; 2) Groundwater recharge lysimeter No.2; 3) Ground-level rain gauge.

1) Calendar year Total groundwater recharge lysimeter #1 (mm) 2000 201 2001 76 2002 incomplete record 2003 92 2004 129 2005 54 Mean 88

2) Calendar year Total groundwater recharge lysimeter #2 (mm) 2000 224 2001 115 2002 incomplete record 2003 139 2004 168 2005 78 Mean 125

3) Calendar year Total ground-level rainfall (mm) 2000 incomplete record 2001 483 2002 incomplete record 2003 497 2004 696 2005 469 Mean 536

4) Percentage groundwater recharge (lysimeter #2) of ground-level rainfall 2000 ? % 2001 24 % 2002 ? % 2003 28 % 2004 24 % 2005 17 %

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Lincoln

Rainfall recharge site 326411

This site consists of: 1) Groundwater recharge lysimeter No.1; 2) Groundwater recharge lysimeter No.2; 3) Ground-level rain gauge.

1) Calendar year Total groundwater recharge lysimeter #1 (mm) 2000 199 2001 40 2002 34 2003 74 2004 94 2005 0 Mean 73

2) Calendar year Total groundwater recharge lysimeter #2 (mm) 2000 234 2001 38 2002 25 2003 58 2004 76 2005 0 Mean 72

3) Calendar year Total ground-level rainfall (mm) 2000 826 2001 630 2002 717 2003 540 2004 724 2005 471 Mean 651

4) Percentage groundwater recharge (lysimeter #1) of ground-level rainfall 2000 24 % 2001 6 % 2002 5 % 2003 14 % 2004 13 % 2005 0 %

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Hororata

Rainfall recharge site 315911

This site consists of: 1) Groundwater recharge lysimeter No.1; 2) Groundwater recharge lysimeter No.2; 3) Ground-level rain gauge.

1) Calendar year Total groundwater recharge lysimeter #1 (mm) 2000 370 2001 109 2002 197 2003 248 2004 125 2005 38 Mean 181

2) Calendar year Total groundwater recharge lysimeter #2 (mm) 2000 416 2001 174 2002 204 2003 249 2004 132 2005 79 Mean 209

3) Calendar year Total ground-level rainfall (mm) 2000 895 2001 614 2002 767 2003 776 2004 780 2005 478 Mean 718

4) Percentage groundwater recharge (lysimeter #2) of ground-level rainfall 2000 46% 2001 28% 2002 27% 2003 32% 2004 17% 2005 16%

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Winchmore Rainfall recharge site 317710

This site consists of: 1) Groundwater recharge lysimeter No.1; 2) Groundwater recharge lysimeter No.2; 3) Groundwater recharge lysimeter No.3; 4) Groundwater recharge lysimeter No.4;

1) Calendar year Total groundwater recharge lysimeter #1 (mm) 2000 231 2001 163 2002 incomplete record 2003 294 2004 132 2005 77 Mean 179

2) Calendar year Total groundwater recharge lysimeter #2 (mm) 2000 294 2001 85 2002 incomplete record 2003 237 2004 61 2005 0 Mean 135

3) Calendar year Total groundwater recharge lysimeter #3 (mm) 2000 457 2001 136 2002 incomplete record 2003 285 2004 128 2005 81 Mean 217

4) Calendar year Total groundwater recharge lysimeter #4 (mm) 2000 362 2001 115 2002 incomplete record 2003 261 2004 65 2005 53 Mean 171

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Rainfall site is a standard rain gauge, NIWA site H31883. Data is supplied by Kathy Walter (NIWA).

1) Calendar year Total rainfall (mm) 2000 966 (one days record missing) 2001 533 2002 686 2003 760 2004 800 2005 561

2) Percentage groundwater recharge (lysimeter #3) of standard rain gauge rainfall Calendar year Total rainfall 2000 47% 2001 25% 2002 incomplete record 2003 38% 2004 16% 2005 14%

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APPENDIX 3 MEASURED GROUND-LEVEL PRECIPITATION AND MEASURED GROUNDWATER RECHARGE FOR THE SNOWFALL PERIOD 10 JUNE 2006 TO 13 JUNE 2006

2.5

1.5

0.5

0 10-Jun-2006 10 12: 11 00: 11 12: 12 00: 12 12: 13 00: 13 12: site 324510(3) (Total=54) Christchurch Airport – ground-level precipitation 10 June 2006 to 13 June 2006 (mm/15 minutes).

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0.6

(Item 2 )/1000/15mins 0.4

0.2

0 10-Jun-2006 10 12: 11 00: 11 12: 12 00: 12 12: 13 00: 13 12: site 324510(2) < Untitled > (Item 2 )/1000/15mins (Total=27.36) Christchurch Airport – groundwater recharge, Lysimeter 2, 10 June 2006 to 13 June 2006 (mm/15 minutes).

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2 (Item 3 )/1000/15mins

0 10-Jun-2006 10 12: 11 00: 11 12: 12 00: 12 12: 13 00: 13 12: site 327110(3) < Untitled > (Item 3 )/1000/15mins (Total=45) Dunsandel – ground-level precipitation 10 June 2006 to 13 June 2006 (mm/15 minutes).

1.5

1 (Item 2 )/1000/15mins

0.5

0 10-Jun-2006 10 12: 11 00: 11 12: 12 00: 12 12: 13 00: 13 12: site 327110(2) < Untitled > (Item 2 )/1000/15mins (Total=32.08) Dunsandel – groundwater recharge, Lysimeter 2, 10 June 2006 to 13 June 2006 (mm/15 minutes)

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1 (Item 3 )/1000/15mins

0.5

0 10-Jun-2006 10 12: 11 00: 11 12: 12 00: 12 12: 13 00: 13 12: site 326411(3) < Untitled > (Item 3 )/1000/15mins (Total=58) Lincoln– ground-level precipitation 10 June 2006 to 13 June 2006 (mm/15 minutes).

1.5

1 (Item 2 )/1000/15mins

0.5

0 10-Jun-2006 10 12: 11 00: 11 12: 12 00: 12 12: 13 00: 13 12: site 326411(2) < Untitled > (Item 2 )/1000/15mins (Total=37.76) Lincoln – groundwater recharge, Lysimeter 2, 10 June 2006 to 13 June 2006 (mm/15 minutes).

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2 (Item 3 )/1000/15mins

0 10-Jun-2006 10 12: 11 00: 11 12: 12 00: 12 12: 13 00: 13 12: site 315911(3) < Untitled > (Item 3 )/1000/15mins (Total=28.5) Hororata– ground-level precipitation 10 June 2006 to 13 June 2006 (mm/15 minutes).

1.5

1 (Item 2 )/1000/15mins

0.5

0 10-Jun-2006 10 12: 11 00: 11 12: 12 00: 12 12: 13 00: 13 12: site 315911(2) < Untitled > (Item 2 )/1000/15mins (Total=28.16) Hororata – groundwater recharge, Lysimeter 2, 10 June 2006 to 13 June 2006 (mm/15 minutes).

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0 10-Jun-2006 10 12: 11 00: 11 12: 12 00: 12 12: 13 00: 13 12: site 318803 (Total=59.1) Winchmore– precipitation measured at H31883 10 June 2006 to 13 June 2006 (mm/day), Walter pers. comm.

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0.6

(Item 3 )/1000/15mins 0.4

0.2

0 10-Jun-2006 10 12: 11 00: 11 12: 12 00: 12 12: 13 00: 13 12: site 317710(3) < Untitled > (Item 3 )/1000/15mins (Total=12.22) Winchmore – groundwater recharge, Lysimeter 3, 10 June 2006 to 13 June 2006 (mm/15 minutes).

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APPENDIX 4 MEASURED GROUND-LEVEL PRECIPITATION AND MEASURED GROUNDWATER RECHARGE FOR THE SNOWFALL PERIOD AND THE SNOW MELT PERIOD FROM 11 JUNE 2006

2.5

1.5 (Item 3 )/1000/15mins 1

0.5

0 11-Jun-2006 11 12: 11 18: 12 00: 12 06: 12 12: 12 18: 13 00: 13 06: 13 12: 13 18: site 324510(3) < Untitled > (Item 3 )/1000/15mins (Total=54) Christchurch Airport – ground-level precipitation 11 June 2006 to 13 June 2006 (mm/15 minutes).

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0.6

(Item 2 )/1000/15mins 0.4

0.2

0 11-Jun-2006 11 12: 11 18: 12 00: 12 06: 12 12: 12 18: 13 00: 13 06: 13 12: 13 18: site 324510(2) (Total=27.28) Christchurch Airport – Lysimeter #2, groundwater recharge 11 June 2006 to 13 June 2006 (mm/15 mins).

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2 (Item 3 )/1000/15mins

0 11-Jun-2006 14-Jun 17-Jun 20-Jun 23-Jun 26-Jun 29-Jun site 327110(3) < Untitled > (Item 3 )/1000/15mins (Total=172) Dunsandel – ground-level precipitation 11 June 2006 to 30 June 2006 (mm/15 minutes).

1.5

1 (Item 2 )/1000/15mins

0.5

0 11-Jun-2006 14-Jun 17-Jun 20-Jun 23-Jun 26-Jun 29-Jun site 327110(2) (Total=147.8) Dunsandel – Lysimeter #2, groundwater recharge 11 June 2006 to 30 June 2006 (mm/15 mins).

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1 (Item 3 )/1000/15mins

0.5

0 11-Jun-2006 11 12: 11 18: 12 00: 12 06: 12 12: 12 18: 13 00: 13 06: 13 12: 13 18: site 326411(3) < Untitled > (Item 3 )/1000/15mins (Total=58) Lincoln – ground-level precipitation 11 June 2006 to 13 June 2006 (mm/15 minutes).

1.5

1 (Item 2 )/1000/15mins

0.5

0 11-Jun-2006 11 12: 11 18: 12 00: 12 06: 12 12: 12 18: 13 00: 13 06: 13 12: 13 18: site 326411(2) (Total=37.68) Lincoln – Lysimeter #2, groundwater recharge 11 June 2006 to 13 June 2006 (mm/15 mins).

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2 (Item 3 )/1000/15mins

0 11-Jun-2006 14-Jun 17-Jun 20-Jun 23-Jun 26-Jun 29-Jun site 315911(3) < Untitled > (Item 3 )/1000/15mins (Total=136) Hororata – ground-level precipitation 11 June 2006 to 30 June 2006 (mm/15 minutes).

1.5

1 (Item 2 )/1000/15mins

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0 11-Jun-2006 14-Jun 17-Jun 20-Jun 23-Jun 26-Jun 29-Jun site 315911(2) (Total=136) Hororata – Lysimeter #2, groundwater recharge 11 June 2006 to 30 June 2006 (mm/15 mins).

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0 11-Jun-2006 14-Jun 17-Jun 20-Jun 23-Jun 26-Jun 29-Jun site 318803 (Total=102.5) Winchmore – precipitation measured at H31883 11 June 2006 to 30 June 2006 (mm/day), Walter pers. comm.

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APPENDIX 5 DAILY RAINFALL 11 JUNE 2006 TO 30 JUNE 2006

40 (Item 3 )/1000/day

0 11-Jun-2006 14-Jun 17-Jun 20-Jun 23-Jun 26-Jun 29-Jun site 324510(3) (Total=100.5) Christchurch Airport – ground-level precipitation 11 June 2006 to 30 June 2006 (mm/day).

40 (Item 3 )/1000/day

0 11-Jun-2006 14-Jun 17-Jun 20-Jun 23-Jun 26-Jun 29-Jun site 327110(3) (Total=172) Dunsandel – ground-level precipitation 11 June 2006 to 30 June 2006 (mm/day).

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0 11-Jun-2006 14-Jun 17-Jun 20-Jun 23-Jun 26-Jun 29-Jun site 326411(3) (Total=119) Lincoln – ground-level precipitation 11 June 2006 to 30 June 2006 (mm/day).

40 (Item 3 )/1000/day

0 11-Jun-2006 14-Jun 17-Jun 20-Jun 23-Jun 26-Jun 29-Jun site 315911(3) (Total=136) Hororata – ground-level precipitation 11 June 2006 to 30 June 2006 (mm/day).

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0 11-Jun-2006 14-Jun 17-Jun 20-Jun 23-Jun 26-Jun 29-Jun site 318803 (Total=102.5) Winchmore – precipitation 11 June 2006 to 30 June 2006 (mm/day) at site H31883 (a standard rain gauge), Walter pers. comm.

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