Lake Rotorua

Lake Level and Volume Summary of the Rotorua Lakes

Prepared by Glenn Ellery, Manager Environmental Data Services

Environment Bay of Plenty Internal Report 2004/08 November 2004

5 Quay Street P O Box 364 Whakatane NEW ZEALAND

Working with our communities for a better environment Environment Bay of Plenty

Contents

Chapter 1: Introduction...... 1

1.1 Overview...... 1

1.2 Lake Monitoring Sites...... 2

1.3 Lake Volumes...... 2

1.4 Lake Volume and Rainfall...... 3

Chapter 2: Lake Rotorua...... 5

2.1 Introduction...... 5

2.2 Lake Control Structures ...... 5

2.3 Lake Level Hydrograph...... 6

2.4 Lake Level Distribution...... 7

2.5 Lake Level/Lake Volume Relationship ...... 8

2.6 Lake Volume Hydrograph...... 9

2.7 Lake Volume Distribution...... 10

2.8 Lake Volume and Rainfall...... 11

Chapter 3: Lake Rotoiti...... 13

3.1 Introduction...... 13

3.2 Lake Control Structures ...... 13

3.3 Lake Level Hydrograph...... 14

3.4 Lake Level Distribution...... 14

3.5 Lake Level / Lake Volume Relationship ...... 16

3.6 Lake Volume Hydrograph...... 17

3.7 Lake Volume Distribution...... 17

3.8 Lake Volume and Rainfall...... 19

Internal Report 2004/08 Lake Level and Volume Summary of the Rotorua Lakes Environment Bay of Plenty

Chapter 4: Lake Rotoehu ...... 21

4.1 Introduction...... 21

4.2 Lake Control Structures...... 21

4.3 Lake Level Hydrograph...... 22

4.4 Lake Level Distribution...... 22

4.5 Lake Level / Lake Volume Relationship ...... 23

4.6 Lake Volume Hydrograph...... 24

4.7 Lake Volume Distribution...... 25

4.8 Lake Volume and Rainfall ...... 26

Chapter 5: Lake Rotoma...... 27

5.1 Introduction...... 27

5.2 Lake Control Structures...... 27

5.3 Lake Level Hydrograph...... 28

5.4 Lake Level Distribution...... 28

5.5 Lake Level / Lake Volume Relationship ...... 29

5.6 Lake Volume Hydrograph...... 30

5.7 Lake Volume Distribution...... 31

5.8 Lake Volume and Rainfall ...... 32

Chapter 6: Lake Okataina...... 33

6.1 Introduction...... 33

6.2 Lake Control Structures...... 33

6.3 Lake Level Hydrograph...... 34

6.4 Lake Level Distribution...... 34

6.5 Lake Level / Lake Volume Relationship ...... 35

6.6 Lake Volume Hydrograph...... 36

6.7 Lake Volume Distribution...... 37

6.8 Lake Volume and Rainfall ...... 38

Lake Level and Volume Summary of the Rotorua Lakes Internal Report 2004/08 Environment Bay of Plenty

Chapter 7: Lake Okareka...... 39

7.1 Introduction...... 39

7.2 Lake Control Structures ...... 39

7.3 Lake Level Hydrograph...... 40

7.4 Lake Level Distribution...... 41

7.5 Lake Level / Lake Volume Relationship ...... 42

7.6 Lake Volume Hydrograph...... 43

7.7 Lake Volume Distribution...... 44

7.8 Lake Volume and Rainfall...... 45

Chapter 8: Lake Tikitapu...... 47

8.1 Introduction...... 47

8.2 Lake Control Structures ...... 47

8.3 Lake Level Hydrograph...... 47

8.4 Lake Level Distribution...... 48

8.5 Lake Level / Lake Volume Relationship ...... 49

8.6 Lake Volume Hydrograph...... 50

8.7 Lake Volume Distribution...... 50

8.8 Lake Volume and Rainfall...... 51

Chapter 9: Lake Tarawera...... 53

9.1 Introduction...... 53

9.2 Lake Control Structures ...... 53

9.3 Lake Level Hydrograph...... 54

9.4 Lake Level Distribution...... 54

9.5 Lake Level / Lake Volume Relationship ...... 55

9.6 Lake Volume Hydrograph...... 56

9.7 Lake Volume Distribution...... 57

9.8 Lake Volume and Rainfall...... 58

Internal Report 2004/08 Lake Level and Volume Summary of the Rotorua Lakes Environment Bay of Plenty

Chapter 10: Lake Rotokakahi...... 59

10.1 Introduction...... 59

10.2 Lake Control Structures...... 59

10.3 Lake Level Hydrograph...... 60

10.4 Lake Level Distribution...... 60

10.5 Lake Level / Lake Volume Relationship ...... 61

10.6 Lake Volume Hydrograph...... 62

10.7 Lake Volume Distribution...... 63

10.8 Lake Volume and Rainfall ...... 64

Chapter 11: Lake Rotomahana...... 65

11.1 Introduction...... 65

11.2 Lake Control Structures...... 65

11.3 Lake Level Hydrograph...... 66

11.4 Lake Level Distribution...... 66

11.5 Lake Level / Lake Volume Relationship ...... 67

11.6 Lake Volume Hydrograph...... 68

11.7 Lake Volume Distribution...... 69

11.8 Lake Volume and Rainfall ...... 70

Chapter 12: Lake Okaro...... 71

12.1 Introduction...... 71

12.2 Lake Control Structures...... 71

12.3 Lake Level Hydrograph...... 71

12.4 Lake Level Distribution...... 72

12.5 Lake Level / Lake Volume Relationship ...... 73

12.6 Lake Volume Hydrograph...... 74

12.7 Lake Volume Distribution...... 74

12.8 Lake Volume and Rainfall ...... 76

Lake Level and Volume Summary of the Rotorua Lakes Internal Report 2004/08 Environment Bay of Plenty

Chapter 13: Lake Rerewhakaaitu ...... 77

13.1 Introduction...... 77

13.2 Lake Control Structures ...... 77

13.3 Lake Level Hydrograph...... 78

13.4 Lake Level Distribution...... 78

13.5 Lake Level / Lake Volume Relationship ...... 79

13.6 Lake Volume Hydrograph...... 80

13.7 Lake Volume Distribution...... 81

13.8 Lake Volume and Rainfall...... 82

List of Figures

Figure 1 Lake Rotorua Level Hydrograph...... 6

Figure 2 Lake Rotorua Level Distribution...... 7

Figure 3 Lake Rotorua Level / Volume Relationship...... 9

Figure 4 Lake Rotorua Volume Hydrograph...... 9

Figure 5 Lake Rotorua Volume Distribution...... 10

Figure 6 Lake Volume and Seasonal Rainfall Totals ...... 11

Figure 7 Lake Volume and Monthly Rainfall Totals...... 12

Figure 8 Lake Rotoiti Level Hydrograph...... 14

Figure 9 Lake Rotoiti Level Distribution...... 14

Figure 10 Lake Rotoiti Level / Volume Relationship...... 16

Figure 11 Lake Rotoiti Volume Hydrograph...... 17

Figure 12 Lake Rotoiti Volume Distribution...... 17

Figure 13 Lake Volume and Seasonal Rainfall Totals ...... 19

Figure 14 Lake Volume and Monthly Rainfall Totals...... 19

Figure 15 Lake Rotoehu Level Hydrograph...... 22

Figure 16 Lake Rotoehu Level Distribution...... 22

Internal Report 2004/08 Lake Level and Volume Summary of the Rotorua Lakes Environment Bay of Plenty

Figure 17 Lake Rotoehu Level / Volume Relationship...... 24

Figure 18 Lake Rotoehu Volume Hydrograph...... 24

Figure 19 Lake Rotoehu Volume Distribution...... 25

Figure 20 Lake Volume and Seasonal Rainfall Totals ...... 26

Figure 21 Lake Volume and Monthly Rainfall Totals ...... 26

Figure 22 Lake Rotoma Level Hydrograph...... 28

Figure 23 Lake Rotoma Level Distribution...... 28

Figure 24 Lake Rotoma Level / Volume Relationship...... 30

Figure 25 Lake Rotoma Volume Hydrograph...... 30

Figure 26 Lake Rotoma Volume Distribution...... 31

Figure 27 Lake Volume and Seasonal Rainfall Totals ...... 32

Figure 28 Lake Volume and Monthly Rainfall Totals ...... 32

Figure 29 Lake Okataina Level Hydrograph...... 34

Figure 30 Lake Okataina Level Distribution...... 34

Figure 31 Lake Okataina Level / Volume Relationship...... 36

Figure 32 Lake Okataina Volume Hydrograph...... 36

Figure 33 Lake Okataina Volume Distribution...... 37

Figure 34 Lake Volume and Seasonal Rainfall Totals ...... 38

Figure 35 Lake Volume and Monthly Rainfall Totals ...... 38

Figure 36 Lake Okareka Level Hydrograph...... 40

Figure 37 Lake Okareka Level Distribution...... 41

Figure 38 Lake Okareka Level / Volume Relationship...... 43

Figure 39 Lake Okareka Volume Hydrograph...... 43

Figure 40 Lake Okareka Volume Distribution...... 44

Figure 41 Lake Volume and Seasonal Rainfall Totals ...... 45

Figure 42 Lake Volume and Monthly Rainfall Totals ...... 46

Figure 43 Lake Tikitapu Level Hydrograph...... 47

Figure 44 Lake Tikitapu Lake Level Distribution...... 48

Lake Level and Volume Summary of the Rotorua Lakes Internal Report 2004/08 Environment Bay of Plenty

Figure 45 Lake Tikitapu Level/Volume Relationship...... 49

Figure 46 Lake Tikitapu Volume Hydrograph...... 50

Figure 47 Lake Tikitapu Volume Distribution...... 50

Figure 48 Lake Volume and Seasonal Rainfall Totals ...... 51

Figure 49 Lake Volume and Monthly Rainfall Totals...... 52

Figure 50 Lake Tarawera Level Hydrograph...... 54

Figure 51 Lake Tarawera Level Distribution...... 54

Figure 52 Lake Tarawera Level / Volume Relationship...... 56

Figure 53 Lake Tarawera Volume Hydrograph...... 56

Figure 54 Lake Tarawera Volume Distribution...... 57

Figure 55 Lake Volume and Seasonal Rainfall Totals ...... 58

Figure 56 Lake Volume and Monthly Rainfall Totals...... 58

Figure 57 Lake Rotokakahi Level Hydrograph...... 60

Figure 58 Lake Rotokakahi Level Distribution...... 60

Figure 59 Lake Rotokakahi Level / Volume Relationship...... 62

Figure 60 Lake Rotokakahi Volume Hydrograph...... 62

Figure 61 Lake Rotokakahi Volume Distribution...... 63

Figure 62 Lake Volume and Seasonal Rainfall Totals ...... 64

Figure 63 Lake Volume and Monthly Rainfall Totals...... 64

Figure 64 Lake Rotomahana Level Hydrograph...... 66

Figure 65 Lake Rotomahana Level Distribution...... 66

Figure 66 Lake Rotomahana Level / Volume Relationship...... 68

Figure 67 Lake Rotomahana Volume Hydrograph...... 68

Figure 68 Lake Rotomahana Volume Distribution...... 69

Figure 69 Lake Volume and Seasonal Rainfall Totals ...... 70

Figure 70 Lake Volume and Monthly Rainfall Totals...... 70

Figure 71 Lake Okaro Level Hydrograph...... 71

Figure 72 Lake Okaro Level Distribution...... 72

Internal Report 2004/08 Lake Level and Volume Summary of the Rotorua Lakes Environment Bay of Plenty

Figure 73 Lake Okaro Level / Volume Relationship ...... 73

Figure 74 Lake Okaro Volume Hydrograph...... 74

Figure 75 Lake Okaro Volume Distribution...... 74

Figure 76 Lake Volume and Seasonal Rainfall Totals ...... 76

Figure 77 Lake Volume and Monthly Rainfall Totals ...... 76

Figure 78 Lake Rerewhakaaitu Level Hydrograph...... 78

Figure 79 Lake Rerewhakaaitu Level Distribution ...... 78

Figure 80 Lake Rerewhakaaitu Level / Volume Relationship ...... 80

Figure 81 Lake Rerewhakaaitu Volume Hydrograph...... 80

Figure 82 Lake Rerewhakaaitu Volume Distribution ...... 81

Figure 83 Lake Volume and Seasonal Rainfall Totals ...... 82

List of Tables

Table 1 Lake Rotorua Level Exceedance Percentiles- Pre Control...... 7

Table 2 Lake Rotorua Level Exceedance Percentiles – Controlled ...... 8

Table 3 Lake Rotorua Level / Volume Relationship...... 8

Table 4 Lake Rotorua Volume Exceedance Percentiles-Pre Control ...... 10

Table 5 Lake Rotorua Volume Exceedance Percentiles- Controlled ...... 11

Table 6 Lake Rotoiti Level Exceedance Percentiles –Pre control...... 15

Table 7 Lake Rotoiti Level Exceedance Percentiles –Controlled ...... 15

Table 8 Lake Rotoiti Volume Exceedance Percentiles – Pre Control...... 18

Table 9 Lake Rotoiti Volume Exceedance Percentiles – Controlled ...... 18

Table 10 Lake Rotoehu Level Exceedance Percentiles...... 23

Table 11 Lake Rotoehu Level / Volume Relationship...... 23

Table 12 Lake Rotoehu Volume Exceedance Percentiles...... 25

Table 13 Lake Rotoma Level Exceedance Percentiles ...... 29

Table 14 Lake Rotoma Level / Volume Relationship...... 29

Table 15 Lake Rotoma Volume Exceedance Percentiles ...... 31

Lake Level and Volume Summary of the Rotorua Lakes Internal Report 2004/08 Environment Bay of Plenty

Table 16 Lake Okataina Level Exceedance Percentiles...... 35

Table 17 Lake Okataina Level / Volume Relationship...... 35

Table 18 Lake Okataina Volume Exceedance Percentiles...... 37

Table 19 Lake Okareka Level Exceedance Percentiles – Pre Control...... 41

Table 20 Lake Okareka Level Exceedance Percentiles – Controlled...... 42

Table 21 Lake Okareka Level / Volume Relationship...... 42

Table 22 Lake Okareka Volume Exceedance Percentiles – Pre Control...... 44

Table 23 Lake Okareka Volume Exceedance Percentiles – Controlled...... 45

Table 24 Lake Tikitapu Exceedance Percentiles...... 48

Table 25 Lake Tikitapu Level / Volume Relationship...... 49

Table 26 Lake Tikitapu Volume Exceedance Percentiles...... 51

Table 27 Lake Tarawera Level Exceedance Percentiles...... 55

Table 28 Lake Tarawera Level / Volume Relationship...... 55

Table 29 Lake Tarawera Volume Exceedance Percentiles...... 57

Table 30 Lake Rotokakahi Level Exceedance Percentiles...... 61

Table 31 Lake Rotokakahi Level / Volume Relationship...... 61

Table 32 Lake Rotokakahi Volume Exceedance Percentiles...... 63

Table 33 Lake Rotomahana Level Exceedance Percentiles...... 67

Table 34 Lake Rotomahana Level / Volume Relationship...... 67

Table 35 Lake Rotomahana Volume Exceedance Percentiles...... 69

Table 36 Lake Okaro Level Exceedance Percentiles...... 72

Table 37 Lake Okaro Level / Volume Relationship...... 73

Table 38 Lake Okaro Volume Exceedance Percentiles...... 75

Table 39 Lake Rerewhakaaitu Level Exceedance Percentiles ...... 79

Table 40 Lake Rerewhakaaitu Level / Volume Relationship ...... 79

Table 41 Lake Rerewhakaaitu Volume Exceedance Percentiles ...... 81

Internal Report 2004/08 Lake Level and Volume Summary of the Rotorua Lakes

Chapter 1: Introduction

1.1 Overview

There are approximately 25 lakes within the Environment Bay of Plenty region, excluding large ponds and lagoons. Environment Bay of Plenty monitors lake levels on 12 of these lakes as at January 2004. 9 of the 12 lakes monitored have automatic sensor equipment that record lake levels every 30 minutes, the other three lakes have their levels visually recorded on a 4-6 weekly basis.

This report presents an overview of collected lake level and derived water volume data for the 12 monitored lakes within the Environment Bay of Plenty region.

Chapters 2-13 present the following data for each lake:

(i) Introduction

Details about lake including catchment area, data recorded, significant inflows/outflows etc.

(ii) Lake Control Structures

Details about any significant lake level inlet or outlet control structures or man- made diversions that effect lake levels and volumes.

(iii) Lake Level Hydrograph

(iv) Lake Level Distribution and Exceedance Percentiles

(v) Lake Level / Lake Volume Relationship

Derived relationship based upon bathymetry between lake levels and volume of water in lake, refer section 1.3.

(vi) Lake Volume Hydrograph

(vii) Lake Volume Distribution and Exceedance Percentiles

(viii) Lake Volume and Rainfall Hydrograph

Comparison of change in lake volume and indicative seasonal and monthly rainfall inputs, refer section 1.4

Internal Report 2004/08 Lake Level and Volume Summary of the Rotorua Lakes 2 Environment Bay of Plenty

1.2 Lake Monitoring Sites

Sites discussed in this report are given in Table 1. The ‘ID No.’ given in that table refers to the reference location displayed in Figure 1. Some lakes have historically had more than one recorder location and where this occurs the period of data used from each location is displayed in the ‘Period of Audit’ column.

Map Period of ID No. Lake Site Reference Summary

1 Rotorua Note 1. Mission Bay U15:016 455 1953-2004

2 Rotorua Note 1. Town Wharf U16:953 363 1934-

3 Kaituna Note 2. Lake Rotoiti Outlet U15:038 484 1906-2003

4 Rotoiti Note 2. Okawa Bay V15:030 447 2003-2004

5 Kaituna Taaheke U15:035 499 -

6 Rotoehu Te Pohue Bay V15:185 462 1954-2004

7 Rotoma Otangiwai Point V15:238 434 1954-2004

8 Okataina Tauranganui Bay V16:110 385 1953-2004

9 Okareka Acacia Bay U16:035 308 1952-2004

10 Tikitapu Tarawera Road U16:022 292 1973-2004

11 Tarawera Te Wairoa U16:057 274 1926-2004

12 Tarawera Lake Outlet V16:174 303 -

13 Rotokakahi Te Wairoa U16:030 272 1972-2004

14 Rotomahana Crater Bay V16:140 224 1925-2004

15 Okaro Reserve U16:067 173 1990-2004

16 Rerewhakaaitu Note 3. Awaatua Bay V16:154 182 1952-1983

17 Rerewhakaaitu Note 3. Homestead Arm V16:145 165 1983-2004 Note 1 Lake Rotorua datasets combined to create continuous dataset. Originally site was located at Town Wharf but was replaced by Mission Bay site. Town Wharf site was reinstated in 2003. Note 2 Lake Rotoiti datasets combined to create continuous dataset. Okawa Bay site installed as it is isolated from drawdown effects of Rotoiti control structure on water levels near the lake outlet. Note 3 Lake Rerewhakaaitu datasets combined to create continuous dataset.

1.3 Lake Volumes

Surveyed lake bathymetry was used to derive a relationship between recorded lake height and lake water volume. This relationship was then applied to the continuous lake height dataset to derive a lake volume dataset.

Lake Level and Volume Summary of the Rotorua Lakes Internal Report 2004/08 Environment Bay of Plenty 3

The bathymetry utilised was surveyed in the 1960-70’s and as such the accuracy in both vertical and horizontal planes is not a good as could be achieved today.

Lake bathymetry lines were digitised from a rectified paper map and coupled with 20 metre contour data for the relevant lake area so that a 3 dimensional model of the lake could be produced using GIS software. Due to some inaccuracies in the alignment of the bathymetry lines, the two data sets did not agree in some areas. Some judgement was applied to alter the data to allow the three dimensional model to be made.

Lake volume data was derived from the three dimensional model at a 0.5 metre contour step to cover the full recorded range of levels within the lake.

1.4 Lake Volume and Rainfall

In an attempt to display the effect of rainfall upon each lake, volume hydrographs are presented with associated monthly and seasonal rainfall totals.

Rainfall data is from the Environment Bay of Plenty rainfall station Kaituna at Whakarewarewa - B86124 which has an altitude of 300 metres. For the purposes of this report it is assumed that rainfall rates at this site are indicative of localised rainfall conditions at each of the lakes.

Internal Report 2004/08 Lake Level and Volume Summary of the Rotorua Lakes

Chapter 2: Lake Rotorua

2.1 Introduction

Lake Rotorua has a surface water catchment area of 521.9km2 and drains into Lake Rotoiti via the Ohau Channel.

Records on lake level in Lake Rotorua begin in February 1934 when manual staff gauge readings began near the current Town Wharf site (NZMS260 Grid Reference U16:953 363) were recorded by Hamilton Hydrological Survey. External staff gauge readings were taken until November 1966 at which time readings ceased. A 6 month period of record was undertaken at the Town Wharf site in 1977 for a seiche investigation.

External staff gauge reading were taken at the opposite end of the lake at Mission Bay (NZMS260 Grid Reference U15:017 455) from 1950 onwards. The staff gauge was situated near the Ohau Channel entrance and levels from this site could have a stage/discharge relationship applied to derive flow down the Ohau Channel. A lake level recorder was installed in March 1966 and is currently operated by NIWA.

An automatic recorder was installed at the Town Wharf site by Environment Bay of Plenty in July 2003 in response to continuing concerns regarding differing lake levels between the Town Wharf and Mission Bay ends of the lake.

Data used for this summary is a combined dataset from records at both end of the lake and covers the period1934-2003 inclusive. Data up until 7 March 1966 is from the Town Wharf site and subsequent data is from the Mission Bay site.

2.2 Lake Control Structures

The levels in Lake Rotorua are controlled by utilisation of the Ohau channel control structure (at NZMS 260 Grid Reference U15: 018 454).

Prior to 1972 lake level was controlled via natural drainage through the Ohau channel.

Due to long periods of high lake levels in the 1960’s and early 1970’s, enlargement works were undertaken in the Ohau Channel in 1972-1973. These works produced a large drop in lake levels, however levels then dropped too low during dry periods. Subsequently gabion baskets were placed at the channel entrance to maintain lake levels during periods of low flow/rainfall. Examination of lake level hydrographs suggest that Ohau Channel works had a significant effect on lake levels from September 1972 onwards.

Internal Report 2004/08 Lake Level and Volume Summary of the Rotorua Lakes 6 Environment Bay of Plenty

A consent for the installation and operation of the Ohau channel control structure for lake level management was granted to the Bay of Plenty Catchment Commission in June 1973. Levels are managed by installation and removal of stop logs at the control structure. The maximum and minimum levels specified are:

· Maximum level RL 280.11m (Moturiki datum)

· Minimum level RL 279.50m (Moturiki datum)

2.3 Lake Level Hydrograph

Levels are in terms of mean sea level Moturiki datum.

281 281

280.5 280.5

A B

280 280 B

279.5A 279.5

279 279 19340101 4401 5401 6401 7401 8401 9401 YYMM B A site 14615 Lake Rotorua at Wharf Stage metres B site 14624 Lake Rotorua at Mission Bay Stage m Figure 1 Lake Rotorua Level Hydrograph

Lake Level and Volume Summary of the Rotorua Lakes Internal Report 2004/08 Environment Bay of Plenty 7

2.4 Lake Level Distribution

Levels are in terms of mean sea level Moturiki datum.

281

280.5

280

279.5

279 1 10 20 30 40 50 60 70 80 90 100 Percentage of time stage is equalled or exceeded site 14624 Lake Rotorua at Mission Bay Stage m 19340206 120000 to 19720831 240000 – Pre Control site 14624 Lake Rotorua at Mission Bay Stage m 19720901 000000 to 20031231 234500 - Controlled

Figure 2 Lake Rotorua Level Distribution

Table 1 Lake Rotorua Level Exceedance Percentiles- Pre Control

Exceedance percentiles From 19340206 120000 to 19720831 240000 - Pre Control Level - Moturiki Datum (metres) 0 1 2 3 4 5 6 7 8 9 0 280.79 280.46 280.40 280.36 280.34 280.31 280.30 280.28 280.26 280.24 10 280.22 280.21 280.20 280.19 280.18 280.17 280.16 280.15 280.14 280.13 20 280.12 280.11 280.11 280.10 280.09 280.08 280.08 280.07 280.07 280.06 30 280.05 280.05 280.04 280.04 280.03 280.03 280.02 280.01 280.01 280.00 40 279.99 279.99 279.98 279.98 279.97 279.96 279.96 279.95 279.94 279.94 50 279.93 279.92 279.92 279.91 279.91 279.90 279.90 279.89 279.89 279.88 60 279.88 279.87 279.87 279.86 279.86 279.85 279.85 279.84 279.84 279.83 70 279.83 279.82 279.81 279.81 279.80 279.80 279.79 279.78 279.77 279.77 80 279.76 279.75 279.75 279.74 279.73 279.72 279.71 279.70 279.69 279.68 90 279.67 279.66 279.65 279.63 279.61 279.60 279.58 279.56 279.55 279.52 100 279.43 Values in the exceedance table are not exact. They are good approximations based on linear interpolation of 2000 classes.

Internal Report 2004/08 Lake Level and Volume Summary of the Rotorua Lakes 8 Environment Bay of Plenty

Table 2 Lake Rotorua Level Exceedance Percentiles – Controlled

Exceedance percentiles From 19720901 000000 to 20031231 234500 - Controlled Level - Moturiki Datum (metres) 0 1 2 3 4 5 6 7 8 9 0 280.45 280.15 280.10 280.06 280.04 280.03 280.01 280.00 279.99 279.98 10 279.97 279.96 279.96 279.95 279.94 279.93 279.93 279.92 279.91 279.91 20 279.90 279.90 279.89 279.89 279.88 279.88 279.87 279.87 279.87 279.86 30 279.86 279.85 279.85 279.85 279.84 279.84 279.84 279.83 279.83 279.83 40 279.83 279.82 279.82 279.82 279.81 279.81 279.81 279.80 279.80 279.80 50 279.80 279.79 279.79 279.79 279.78 279.78 279.78 279.78 279.77 279.77 60 279.77 279.77 279.76 279.76 279.76 279.75 279.75 279.75 279.74 279.74 70 279.74 279.73 279.73 279.73 279.72 279.72 279.72 279.71 279.71 279.71 80 279.70 279.70 279.70 279.69 279.69 279.68 279.68 279.67 279.67 279.66 90 279.66 279.65 279.65 279.64 279.63 279.62 279.61 279.59 279.57 279.55 100 279.36 Values in the exceedance table are not exact. They are good approximations based on linear interpolation of 2000 classes.

2.5 Lake Level/Lake Volume Relationship

Lake volume data was derived from the three dimensional GIS bathymetry model at a 0.5 metre contour step to cover the full recorded range of levels within the lake.

Table 3 Lake Rotorua Level / Volume Relationship

Level Volume (m) (m3 x 106) 271.3 261.43 271.8 284.72 272.3 308.59 272.8 333.06 273.3 358.14 273.8 383.84 274.3 410.17 274.8 437.13 275.3 464.74 275.8 494.12 276.3 524.25 276.8 555.13 277.3 586.77 277.8 619.16 278.3 653.29 278.8 688.59 279.3 725.09 279.8 762.79 280.3 801.69 280.8 842.31 281.3 883.27

Lake Level and Volume Summary of the Rotorua Lakes Internal Report 2004/08 Environment Bay of Plenty 9

282 281 280 279 278 277 276 275

Lake Level (m) 274 273 272 271 270 250 300 350 400 450 500 550 600 650 700 750 800 850 900 Lake Volume (m3x106)

Figure 3 Lake Rotorua Level / Volume Relationship

2.6 Lake Volume Hydrograph

849 849

840 840

820 820

800 800 A B

780 780

760 760

740 740 A

725 725 19340101 4401 5401 6401 7401 8401 9401 YYMM B A site 14615 Lake Rotorua at Wharf Volume m3 x 10^6 B site 14624 Lake Rotorua at Mission Bay Volume m3 x 10^6

Figure 4 Lake Rotorua Volume Hydrograph

Internal Report 2004/08 Lake Level and Volume Summary of the Rotorua Lakes 10 Environment Bay of Plenty

2.7 Lake Volume Distribution

854

840

820

800

780

760

740

730 1 10 20 30 40 50 60 70 80 90 100 Percentage of time volume is equalled or exceeded site 14624 Lake Rotorua at Mission Bay Volume m3 x 10^6 19340206 120000 to 19720831 240000 – Pre Control site 14624 Lake Rotorua at Mission Bay Volume m3 x 10^6 19720901 000000 to 20031231 234500 - Controlled Figure 5 Lake Rotorua Volume Distribution

Table 4 Lake Rotorua Volume Exceedance Percentiles-Pre Control

Exceedance percentiles From 19340206 120000 to 19720831 240000 - Pre Control Volume m3 x 10^6 0 1 2 3 4 5 6 7 8 9 0 841.37 814.25 809.56 806.65 804.98 802.84 801.53 800.12 798.40 796.98 10 795.71 794.70 793.69 792.84 792.06 791.21 790.57 789.75 788.86 788.23 20 787.54 786.94 786.38 785.89 785.37 784.75 784.21 783.70 783.26 782.89 30 782.41 781.97 781.49 781.14 780.74 780.27 779.86 779.30 778.77 778.34 40 777.80 777.43 776.86 776.42 775.98 775.29 774.78 774.04 773.65 773.25 50 772.87 772.33 771.83 771.60 771.18 770.76 770.47 770.02 769.57 769.32 60 768.89 768.45 768.06 767.60 767.20 766.90 766.46 766.06 765.68 765.21 70 764.73 764.33 763.84 763.37 762.87 762.35 761.89 761.31 760.76 760.09 80 759.70 759.17 758.65 757.98 757.62 756.88 756.10 755.40 754.65 753.75 90 753.01 752.25 751.11 749.84 748.42 747.24 746.16 744.70 743.84 741.36 100 734.85 Values in the exceedance table are not exact. They are good approximations based on linear interpolation of 2000 classes.

Lake Level and Volume Summary of the Rotorua Lakes Internal Report 2004/08 Environment Bay of Plenty 11

Table 5 Lake Rotorua Volume Exceedance Percentiles- Controlled

Exceedance percentiles From 19720901 000000 to 20031231 234500 - Controlled Volume m3 x 10^6 0 1 2 3 4 5 6 7 8 9 0 813.61 789.74 785.73 783.21 781.55 780.36 779.31 778.38 777.54 776.73 10 776.07 775.39 774.74 774.19 773.64 773.05 772.56 772.07 771.57 771.14 20 770.71 770.31 769.95 769.58 769.21 768.84 768.49 768.15 767.80 767.49 30 767.18 766.90 766.64 766.39 766.15 765.92 765.69 765.46 765.22 764.97 40 764.75 764.51 764.28 764.03 763.79 763.57 763.34 763.10 762.88 762.65 50 762.42 762.21 762.01 761.79 761.58 761.38 761.18 760.98 760.78 760.58 60 760.38 760.18 759.97 759.73 759.48 759.24 758.98 758.71 758.45 758.21 70 757.97 757.73 757.50 757.24 756.99 756.74 756.47 756.22 755.97 755.73 80 755.50 755.24 754.94 754.63 754.28 753.91 753.56 753.21 752.86 752.48 90 752.09 751.71 751.19 750.57 749.98 749.24 748.15 746.94 745.54 743.57 100 729.47 Values in the exceedance table are not exact. They are good approximations based on linear interpolation of 2000 classes.

2.8 Lake Volume and Rainfall

860 3200

840 2800

820 2400

800 2000

780 1600 A

760 1200

740 800 A B

720 400

700B 0 19331201 4301 5301 6301 7301 8301 9301 YYMM B A site 14624 Lake Rotorua at Mission Bay Volume m3 x 10^6 B site 861204 Kaituna at Whakarewarewa Rainfall mm/3mths (Total=102121) Figure 6 Lake Volume and Seasonal Rainfall Totals

Internal Report 2004/08 Lake Level and Volume Summary of the Rotorua Lakes 12 Environment Bay of Plenty

860 1600

840 1400

820 1200

800 1000

780 800 A

760 600

740 400 A

B 720 200

700B 0 19340101 4401 5401 6401 7401 8401 9401 YYMM B A site 14624 Lake Rotorua at Mission Bay Volume m3 x 10^6 B site 861204 Kaituna at Whakarewarewa Rainfall mm/mth (Total=101719) Figure 7 Lake Volume and Monthly Rainfall Totals

Lake Level and Volume Summary of the Rotorua Lakes Internal Report 2004/08 13

Chapter 3: Lake Rotoiti

3.1 Introduction

Lake Rotoiti has a surface water catchment area of 124.6km2 and additionally receives water from the Lake Rotorua catchment (521.9km2) via the Ohau channel. The outlet of Lake Rotoiti forms the source of the Kaituna River.

Initial records of regular staff gauge readings begin in November 1906 and continued until an automatic recorder was installed at the Okere Falls recorder site in January 1942. The site is operated by the National Institute of Water and Atmosphere (NIWA).

Stage discharge ratings were applied to the stage record to derive flows from the lake. Lake levels recorded at the Okere Falls site are subject to drawdown effects from the operation of the Okere Gate Control structure.

Environment Bay of Plenty installed an automatic recorder at Okawa Bay in June 2001 to be used for the management of the level within Lake Rotoiti. The Okawa Bay recorder is not subject to draw down effects from the Okere Gate Control structure.

Data used for this summary is for the period 1906-2003 inclusive. Data used is a combined dataset of Okere Falls and Okawa Bay data.

3.2 Lake Control Structures

The Okere Control Gate structure is utilised for the purposes of managing the level of Lake Rotoiti.

Prior to 9 January 1982 drainage from the lake was controlled by a natural rock bar at the outlet to the Kaituna River.

The Okere Control Gate structure was commissioned on 9 January 1982 and consists of three radial gates that are operated with the objective of maintaining lake levels within the following limits:

· Maximum level RL 279.44m (Moturiki datum)

· Minimum level RL 278.89m (Moturiki datum)

Internal Report 2004/08 Lake Level and Volume Summary of the Rotorua Lakes 14 Environment Bay of Plenty

3.3 Lake Level Hydrograph

Levels are in terms of mean sea level Moturiki datum.

280 280

279.5 279.5

A B B A

279 279

278.5 278.5

278 278 19060101 1601 2601 3601 4601 5601 6601 7601 8601 9601 YYMMB A site 14601 Kaituna at Lake Rotoiti Outlet Stage m B site 1114675 Lake Rotoiti at Okawa Bay Stage metres Figure 8 Lake Rotoiti Level Hydrograph

3.4 Lake Level Distribution

Levels are in terms of mean sea level Moturiki datum.

280

279.5

279

278.5

278 1 10 20 30 40 50 60 70 80 90 100 Percentage of time stage is equalled or exceeded site 14601 Kaituna at Lake Rotoiti Outlet Stage m 19060101 000000 to 19820108 240000 – Pre Control site 14601 Kaituna at Lake Rotoiti Outlet Stage m 19820109 000000 to 20031231 240000 - Controlled

Figure 9 Lake Rotoiti Level Distribution

Lake Level and Volume Summary of the Rotorua Lakes Internal Report 2004/08 Environment Bay of Plenty 15

Table 6 Lake Rotoiti Level Exceedance Percentiles –Pre control

Exceedance percentiles From 19060101 000000 to 19820108 240000 - Pre Control Level - Moturiki Datum (metres) 0 1 2 3 4 5 6 7 8 9 0 279.80 279.51 279.47 279.45 279.43 279.42 279.41 279.40 279.39 279.37 10 279.36 279.36 279.35 279.34 279.34 279.33 279.32 279.32 279.31 279.31 20 279.31 279.30 279.30 279.29 279.29 279.28 279.28 279.27 279.27 279.26 30 279.26 279.26 279.25 279.25 279.24 279.24 279.24 279.23 279.23 279.23 40 279.23 279.22 279.22 279.22 279.21 279.21 279.21 279.20 279.20 279.20 50 279.19 279.19 279.19 279.18 279.18 279.18 279.17 279.17 279.17 279.16 60 279.16 279.16 279.15 279.15 279.15 279.14 279.14 279.14 279.13 279.13 70 279.13 279.12 279.12 279.12 279.11 279.11 279.11 279.10 279.10 279.09 80 279.09 279.09 279.08 279.08 279.07 279.07 279.06 279.06 279.05 279.05 90 279.04 279.04 279.03 279.02 279.02 279.01 279.00 278.99 278.97 278.93 100 278.86 Values in the exceedance table are not exact. They are good approximations based on linear interpolation of 2000 classes.

Table 7 Lake Rotoiti Level Exceedance Percentiles –Controlled

Exceedance percentiles From 19820109 000000 to 20031231 240000 - Controlled Level - Moturiki Datum (metres) 0 1 2 3 4 5 6 7 8 9 0 279.59 279.37 279.35 279.33 279.32 279.31 279.30 279.30 279.29 279.29 10 279.28 279.27 279.27 279.26 279.26 279.25 279.25 279.24 279.24 279.23 20 279.23 279.23 279.22 279.22 279.21 279.21 279.21 279.20 279.20 279.20 30 279.20 279.19 279.19 279.19 279.19 279.18 279.18 279.18 279.18 279.18 40 279.18 279.17 279.17 279.17 279.17 279.17 279.17 279.17 279.17 279.16 50 279.16 279.16 279.16 279.16 279.16 279.16 279.16 279.15 279.15 279.15 60 279.15 279.15 279.15 279.15 279.15 279.15 279.14 279.14 279.14 279.14 70 279.14 279.14 279.14 279.14 279.13 279.13 279.13 279.13 279.13 279.13 80 279.13 279.12 279.12 279.12 279.12 279.12 279.12 279.11 279.11 279.11 90 279.11 279.11 279.10 279.10 279.10 279.09 279.09 279.08 279.08 279.07 100 279.02 Values in the exceedance table are not exact. They are good approximations based on linear int erpolation of 2000 classes.

Internal Report 2004/08 Lake Level and Volume Summary of the Rotorua Lakes 16 Environment Bay of Plenty

3.5 Lake Level / Lake Volume Relationship

Lake volume data was derived from the three dimensional GIS bathymetry model at a 0.5 metre contour step to cover the full recorded range of levels within the lake.

Table 3.5.1. Lake Rotoiti Level / Volume Relationship

Level Volume (m) (m3 x 106) 276.3 966.62 276.8 982.45 277.3 998.42 277.8 1014.55 278.3 1030.82 278.8 1047.25 279.3 1063.83 279.8 1082.13 280.3 1101.37 280.8 1120.97 281.3 1140.67 278.3 653.29 278.8 688.59 279.3 725.09 279.8 762.79 280.3 801.69 280.8 842.31 281.3 883.27

282

281

280

279 Lake Level (m) 278

277

276 960 980 1000 1020 1040 1060 1080 1100 1120 1140 Lake Volume (m3x106)

Figure 10 Lake Rotoiti Level / Volume Relationship

Lake Level and Volume Summary of the Rotorua Lakes Internal Report 2004/08 Environment Bay of Plenty 17

3.6 Lake Volume Hydrograph

1084 1084

1080 1080

1075 1075

1070 1070

1065 1065

A 1060 B 1060 B A

1055 1055

1050 1050 1048 1048 19060101 1601 2601 3601 4601 5601 6601 7601 8601 9601 YYMMB A site 14601 Kaituna at Lake Rotoiti Outlet Volume m3 x 10^6 B site 1114675 Lake Rotoiti at Okawa Bay Volume m3 x 10^6 Figure 11 Lake Rotoiti Volume Hydrograph

3.7 Lake Volume Distribution

1086

1080

1075

1070

1065

1060

1055

1050 1048 1 10 20 30 40 50 60 70 80 90 100 Percentage of time volume is equalled or exceeded site 14601 Kaituna at Lake Rotoiti Outlet Volume m3 x 10^6 19060101 000000 to 19820108 240000 – Pre Cpntrol site 14601 Kaituna at Lake Rotoiti Outlet Volume m3 x 10^6 19820109 000000 to 20031231 240000 - Controlled Figure 12 Lake Rotoiti Volume Distribution

Internal Report 2004/08 Lake Level and Volume Summary of the Rotorua Lakes 18 Environment Bay of Plenty

Table 8 Lake Rotoiti Volume Exceedance Percentiles – Pre Control

Exceedance percentiles From 19060101 000000 to 19820108 240000 - Pre Control Volume m3 x 10^6 0 1 2 3 4 5 6 7 8 9 0 1082.32 1071.21 1069.99 1069.14 1068.58 1068.04 1067.66 1067.23 1066.82 1066.44 10 1066.08 1065.80 1065.58 1065.33 1065.13 1064.87 1064.69 1064.56 1064.35 1064.14 20 1064.02 1063.82 1063.67 1063.53 1063.37 1063.20 1063.03 1062.90 1062.73 1062.63 30 1062.50 1062.39 1062.24 1062.09 1062.00 1061.87 1061.73 1061.66 1061.54 1061.45 40 1061.33 1061.22 1061.10 1061.00 1060.90 1060.78 1060.68 1060.58 1060.47 1060.39 50 1060.27 1060.17 1060.04 1059.96 1059.85 1059.73 1059.64 1059.53 1059.47 1059.34 60 1059.23 1059.08 1058.97 1058.88 1058.76 1058.65 1058.55 1058.44 1058.33 1058.23 70 1058.08 1057.95 1057.87 1057.74 1057.62 1057.47 1057.44 1057.29 1057.14 1056.98 80 1056.90 1056.74 1056.62 1056.46 1056.34 1056.18 1056.00 1055.86 1055.65 1055.49 90 1055.33 1055.09 1054.90 1054.63 1054.42 1054.20 1053.89 1053.48 1052.81 1051.59 100 1049.17 Values in the exceedance table are not exact. They are good approximations based on linear interpolation of 2000 classes.

Table 9 Lake Rotoiti Volume Exceedance Percentiles – Controlled

Exceedance percentiles From 19820109 000000 to 20031231 240000 - Controlled Volume m3 x 10^6 0 1 2 3 4 5 6 7 8 9 0 1074.27 1066.34 1065.54 1064.98 1064.53 1064.23 1064.00 1063.77 1063.56 1063.36 10 1063.15 1062.90 1062.72 1062.52 1062.37 1062.18 1062.03 1061.89 1061.73 1061.60 20 1061.47 1061.34 1061.21 1061.09 1060.95 1060.83 1060.71 1060.61 1060.51 1060.43 30 1060.34 1060.25 1060.17 1060.10 1060.03 1059.97 1059.91 1059.85 1059.80 1059.75 40 1059.70 1059.65 1059.61 1059.56 1059.52 1059.47 1059.43 1059.38 1059.34 1059.30 50 1059.26 1059.22 1059.18 1059.14 1059.10 1059.06 1059.03 1058.99 1058.95 1058.91 60 1058.88 1058.84 1058.81 1058.77 1058.73 1058.69 1058.65 1058.61 1058.57 1058.54 70 1058.51 1058.47 1058.42 1058.38 1058.33 1058.28 1058.24 1058.19 1058.15 1058.11 80 1058.06 1058.01 1057.95 1057.90 1057.84 1057.78 1057.72 1057.67 1057.60 1057.53 90 1057.45 1057.37 1057.29 1057.20 1057.09 1056.97 1056.82 1056.66 1056.38 1056.02 100 1054.69 Values in the exceedance table are not exact. They are good approximations based on linear interpolation of 2000 classes.

Lake Level and Volume Summary of the Rotorua Lakes Internal Report 2004/08 Environment Bay of Plenty 19

3.8 Lake Volume and Rainfall

1085 1000

1080 900

1070 700

A 1060 A 500

1050 300

1040 100

1035B 0 19060101 1601 2601 3601 4601 5601 6601 7601 8601 9601 YYMMB A site 14601 Kaituna at Lake Rotoiti Outlet Volume m3 x 10^6 B site 861204 Kaituna at Whakarewarewa Rainfall mm/mth (Total=140149) Figure 13 Lake Volume and Seasonal Rainfall Totals

1085 2000

1080 1800

1070 1400

A 1060 A 1000

B 1050 600

1040 200

1035B 0 19051201 1501 2501 3501 4501 5501 6501 7501 8501 9501 YYMM B A site 14601 Kaituna at Lake Rotoiti Outlet Volume m3 x 10^6 B site 861204 Kaituna at Whakarewarewa Rainfall mm/3mths (Total=140614) Figure 14 Lake Volume and Monthly Rainfall Totals

Internal Report 2004/08 Lake Level and Volume Summary of the Rotorua Lakes

Chapter 4: Lake Rotoehu

4.1 Introduction

Lake Rotoehu has a surface water catchment area of 49.16km2. Initial readings lake level readings began on Lake Rotoehu in February 1925 when a staff gauge was installed by the Department of Lands and Survey, however irregular staff gauge readings were only taken for a year until records effectively stopped until 1954.

Lake level data was recorded at this site by the Hamilton Hydrological Survey, then Ministry of Works Water and Soil Division before the site was transferred to the Bay of Plenty Catchment Commission on 17 September 1979. The site is currently operated by Environment Bay of Plenty.

Data used for this summary is for the period 1954-2003 inclusive.

4.2 Lake Control Structures

There are no known man-made outlet structures that affect Lake Rotoehu lake levels, however the lake may receive water from Lake Rotoma during periods of high water. The diverted water enters Lake Rotoehu at Te Wairoa Bay (NZMS 260 Grid Reference V15: 2145 4596) via an open drainage channel. The maximum discharge rate from Lake Rotoma is 0.85 m3/s.

Internal Report 2004/08 Lake Level and Volume Summary of the Rotorua Lakes 22 Environment Bay of Plenty

4.3 Lake Level Hydrograph

Levels are in terms of mean sea level Moturiki datum.

297

296

295 A A

294

293

292 19540101 6001 6601 7201 7801 8401 9001 9601 YYMM A site 14716 Lake Rotoehu at Te Pohue Bay Level m

Figure 15 Lake Rotoehu Level Hydrograph

4.4 Lake Level Distribution

Levels are in terms of mean sea level Moturiki datum.

297

296

295

294

293

292 1 10 20 30 40 50 60 70 80 90 100 Percentage of time level is equalled or exceeded site 14716 Lake Rotoehu at Te Pohue Bay Level m 19540101 000000 to 20031231 240000 Figure 16 Lake Rotoehu Level Distribution

Lake Level and Volume Summary of the Rotorua Lakes Internal Report 2004/08 Environment Bay of Plenty 23

Table 10 Lake Rotoehu Level Exceedance Percentiles

Exceedance percentiles From 19540101 000000 to 20031231 240000 Level - Moturiki Datum (metres) % 0 1 2 3 4 5 6 7 8 9 0 296.97 296.79 296.66 296.54 296.46 296.30 296.23 296.20 296.17 296.13 10 296.11 296.06 296.03 295.98 295.94 295.90 295.88 295.86 295.83 295.80 20 295.75 295.71 295.66 295.59 295.56 295.52 295.49 295.46 295.43 295.39 30 295.36 295.33 295.31 295.29 295.27 295.25 295.22 295.20 295.18 295.16 40 295.14 295.13 295.10 295.09 295.07 295.04 295.02 295.01 294.98 294.97 50 294.95 294.93 294.92 294.91 294.89 294.88 294.86 294.85 294.84 294.83 60 294.81 294.80 294.78 294.76 294.74 294.72 294.70 294.69 294.67 294.66 70 294.64 294.62 294.60 294.58 294.55 294.53 294.51 294.49 294.46 294.43 80 294.39 294.35 294.31 294.25 294.19 294.13 294.07 294.01 293.97 293.93 90 293.89 293.85 293.80 293.74 293.67 293.60 293.31 293.00 292.85 292.55 100 292.35 Values in the exceedance table are not exact. They are good approximations based on linear interpolation of 2000 classes.

4.5 Lake Level / Lake Volume Relationship

Lake volume data was derived from the three dimensional GIS bathymetry model at a 0.5 metre contour step to cover the full recorded range of levels within the lake.

Table 11 Lake Rotoehu Level / Volume Relationship

Level Volume (m) (m3 x 106) 291.9 36.94 292.9 43.34 293.4 46.67 293.9 50.10 294.4 53.63 294.9 57.26 295.4 61.00 295.9 65.03 296.4 69.09 296.9 73.18 297.4 77.32 297.9 81.49 298.4 85.69

Internal Report 2004/08 Lake Level and Volume Summary of the Rotorua Lakes 24 Environment Bay of Plenty

299

298

297

296

295

Lake Level (m) 294

293

292

291 36 41 46 51 56 61 66 71 76 81 86 Lake Volume (m3x106)

Figure 17 Lake Rotoehu Level / Volume Relationship

4.6 Lake Volume Hydrograph

A A 55

39 19540101 6001 6601 7201 7801 8401 9001 9601 YYMM A site 14716 Lake Rotoehu at Te Pohue Bay Volume m3 x 10^6

Figure 18 Lake Rotoehu Volume Hydrograph

Lake Level and Volume Summary of the Rotorua Lakes Internal Report 2004/08 Environment Bay of Plenty 25

4.7 Lake Volume Distribution

39 1 10 20 30 40 50 60 70 80 90 100 Percentage of time volume is equalled or exceeded site 14716 Lake Rotoehu at Te Pohue Bay Volume m3 x 10^6 19540101 000000 to 20031231 240000 Figure 19 Lake Rotoehu Volume Distribution

Table 12 Lake Rotoehu Volume Exceedance Percentiles

Internal Report 2004/08 Lake Level and Volume Summary of the Rotorua Lakes 26 Environment Bay of Plenty

4.8 Lake Volume and Rainfall

75 1000

70 900

60 700

A A

50 500

40 300

30 100

25B 0 19540101 6001 6601 7201 7801 8401 9001 9601 YYMM B A site 14716 Lake Rotoehu at Te Pohue Bay Volume m3 x B 10^6site 861204 Kaituna at Whakarewarewa Rainfall mm/mth (Total=72504) Figure 20 Lake Volume and Seasonal Rainfall Totals

75 1000

70 900

60 700

A A

50 500

40 300

30 100

25B 0 19540101 6001 6601 7201 7801 8401 9001 9601 YYMM B A site 14716 Lake Rotoehu at Te Pohue Bay Volume m3 x 10^6 B site 861204 Kaituna at Whakarewarewa Rainfall mm/mth (Total=72504)

Figure 21 Lake Volume and Monthly Rainfall Totals

Lake Level and Volume Summary of the Rotorua Lakes Internal Report 2004/08 27

Chapter 5: Lake Rotoma

5.1 Introduction

Lake Rotoma has a surface water catchment area of 21.9km2.

Lake level data was recorded at this site from by the Ministry of Works Water and Soil Division before the site was transferred to the Bay of Plenty Catchment Commission in September 1979. The site is now operated by Environment Bay of Plenty.

Data used for this summary is for the period 1954-2003 inclusive.

5.2 Lake Control Structures

A diversion of water from the lake occurs on the southwestern shore (NZMS260 Grid Reference V15: 221 448) by the means of a control weir and pipeline. The water is diverted to Lake Rotoehu by means of an open channel for the purposes of controlling high lake levels. The maximum rate of diversion is set at 0.85m3/s

Internal Report 2004/08 Lake Level and Volume Summary of the Rotorua Lakes 28 Environment Bay of Plenty

5.3 Lake Level Hydrograph

Levels are in terms of mean sea level Moturiki datum.

318

317

316 A

315

A 314

313

312 19540101 6001 6601 7201 7801 8401 9001 9601 YYMM A site 14717 Lake Rotoma at Otangiwai Point Level m Figure 22 Lake Rotoma Level Hydrograph

5.4 Lake Level Distribution

Levels are in terms of mean sea level Moturiki datum.

318

317

316

315

314

313

312 1 10 20 30 40 50 60 70 80 90 100 Percentage of time level is equalled or exceeded site 14717 Lake Rotoma at Otangiwai Point Level m 19540101 000000 to 20031231 240000 Figure 23 Lake Rotoma Level Distribution

Lake Level and Volume Summary of the Rotorua Lakes Internal Report 2004/08 Environment Bay of Plenty 29

Table 13 Lake Rotoma Level Exceedance Percentiles

Exceedance percentiles From 19540101 000000 to 20031231 240000 Level - Moturiki Datum (metres) % 0 1 2 3 4 5 6 7 8 9 0 317.73 317.49 317.30 317.20 317.05 316.92 316.82 316.74 316.68 316.64 10 316.57 316.50 316.44 316.38 316.29 316.25 316.22 316.18 316.14 316.10 20 316.07 316.02 315.97 315.92 315.85 315.81 315.76 315.72 315.69 315.65 30 315.62 315.59 315.57 315.55 315.52 315.50 315.47 315.45 315.44 315.42 40 315.39 315.37 315.35 315.33 315.30 315.29 315.27 315.24 315.21 315.19 50 315.17 315.14 315.12 315.10 315.08 315.06 315.04 315.01 314.99 314.97 60 314.95 314.93 314.90 314.88 314.86 314.84 314.81 314.78 314.75 314.70 70 314.65 314.61 314.58 314.55 314.51 314.47 314.44 314.42 314.39 314.34 80 314.28 314.23 314.19 314.14 314.10 314.05 314.01 313.98 313.95 313.91 90 313.86 313.80 313.72 313.67 313.60 313.44 313.26 312.88 312.57 312.40 100 312.17 Values in the exceedance table are not exact. They are good approximations based on linear interpolation of 2000 classes.

5.5 Lake Level / Lake Volume Relationship

Lake volume data was derived from the three dimensional GIS bathymetry model at a 0.5 metre contour step to cover the full recorded range of levels within the lake.

Table 14 Lake Rotoma Level / Volume Relationship

Level Volume (m) (m3 x 106) 311.680 386.56 312.180 391.58 312.680 396.7 313.180 401.85 313.680 407.07 314.180 412.35 314.680 417.68 315.180 423.08 315.680 428.54 316.180 434.11 316.680 439.75 317.180 445.46 317.680 451.24 318.180 457.09 318.680 463.03 319.180 469.04 319.680 475.13

Internal Report 2004/08 Lake Level and Volume Summary of the Rotorua Lakes 30 Environment Bay of Plenty

320

319

318

317

316

315

314 Lake Level (m) 313

312

311

310 386 391 396 401 406 411 416 421 426 431 436 441 446 451 456 461 466 471 476 Lake Volume (m3x106)

Figure 24 Lake Rotoma Level / Volume Relationship

5.6 Lake Volume Hydrograph

455

450

440

430 A

420

A 410

400

391 19540101 6001 6601 7201 7801 8401 9001 9601 YYMM A site 14717 Lake Rotoma at Otangiwai Point Volume m3 x 10^6 Figure 25 Lake Rotoma Volume Hydrograph

Lake Level and Volume Summary of the Rotorua Lakes Internal Report 2004/08 Environment Bay of Plenty 31

5.7 Lake Volume Distribution

456

450

440

430

420

410

400

391 1 10 20 30 40 50 60 70 80 90 100 Percentage of time volume is equalled or exceeded site 14717 Lake Rotoma at Otangiwai Point Volume m3 x 10^6 19540101 000000 to 20031231 240000

Figure 26 Lake Rotoma Volume Distribution

Table 15 Lake Rotoma Volume Exceedance Percentiles

Exceedance percentiles From 19540101 000000 to 20031231 240000 Volume (m3x106) % 0 1 2 3 4 5 6 7 8 9 0 451.87 448.99 446.83 445.64 443.98 442.42 441.32 440.40 439.75 439.27 10 438.54 437.70 437.03 436.35 435.38 434.91 434.52 434.15 433.70 433.26 20 432.84 432.32 431.78 431.16 430.45 429.95 429.47 429.03 428.63 428.22 30 427.86 427.60 427.31 427.05 426.83 426.55 426.28 426.05 425.89 425.68 40 425.40 425.19 424.95 424.70 424.42 424.22 424.02 423.77 423.45 423.21 50 422.95 422.64 422.41 422.22 422.03 421.77 421.55 421.28 421.05 420.81 60 420.57 420.34 420.09 419.88 419.63 419.38 419.07 418.76 418.40 417.94 70 417.39 416.97 416.63 416.24 415.81 415.45 415.13 414.88 414.53 414.06 80 413.43 412.86 412.43 411.94 411.49 410.98 410.53 410.19 409.87 409.50 90 408.96 408.35 407.51 406.92 406.25 404.59 402.68 398.76 395.54 393.81 100 391.49 Values in the exceedance table are not exact. They are good approximations based on linear interpolation of 2000 classes.

Internal Report 2004/08 Lake Level and Volume Summary of the Rotorua Lakes 32 Environment Bay of Plenty

5.8 Lake Volume and Rainfall

455 2000

440 1700

420 1300

400 900

380 500

360 100 355B B 0 19531201 5901 6501 7101 7701 8301 8901 9501 0101 YYMMB A site 14717 Lake Rotoma at Otangiwai Point Volume m3 x 10^6 B site 861204 Kaituna at Whakarewarewa Rainfall mm/3mths (Total=72985) Figure 27 Lake Volume and Seasonal Rainfall Totals

455 1000

440 850

420 650

400 450

380 250 B

360 50 355B 0 19540101 6001 6601 7201 7801 8401 9001 9601 YYMM B A site 14717 Lake Rotoma at Otangiwai Point Volume m3 x 10^6 B site 861204 Kaituna at Whakarewarewa Rainfall mm/mth (Total=72504)

Figure 28 Lake Volume and Monthly Rainfall Totals

Lake Level and Volume Summary of the Rotorua Lakes Internal Report 2004/08 33

Chapter 6: Lake Okataina

6.1 Introduction

Lake Okataina has a surface water catchment area of 56.8km2.

Lake level data was recorded at this site from October 1952 by the Ministry of Works Water and Soil Division before the site was transferred to the Bay of Plenty Catchment Commission in September 1979. The site is now operated by Environment Bay of Plenty.

Data used for this summary is for the period 1953-2003 inclusive.

6.2 Lake Control Structures

There are no known man-made inlet/outlet structures that effect Lake Okataina lake levels.

Internal Report 2004/08 Lake Level and Volume Summary of the Rotorua Lakes 34 Environment Bay of Plenty

6.3 Lake Level Hydrograph

Levels are in terms of mean sea level Moturiki datum.

314

313

312

311

310

309

A 308A

307

306 19530101 5901 6501 7101 7701 8301 8901 9501 0101 YYMM A site 15309 Lake Okataina at Tauranganui Bay Level metres Figure 29 Lake Okataina Level Hydrograph

6.4 Lake Level Distribution

Levels are in terms of mean sea level Moturiki datum.

314

313

312

311

310

309

308

307

306 1 10 20 30 40 50 60 70 80 90 100 Percentage of time level is equalled or exceeded site 15309 Lake Okataina at Tauranganui Bay Level metres 19530101 000000 to 20031231 240000

Figure 30 Lake Okataina Level Distribution

Lake Level and Volume Summary of the Rotorua Lakes Internal Report 2004/08 Environment Bay of Plenty 35

Table 16 Lake Okataina Level Exceedance Percentiles

Exceedance percentiles From 19530101 000000 to 20031231 240000 Level - Moturiki Datum (metres) % 0 1 2 3 4 5 6 7 8 9 0 313.46 313.12 312.91 312.56 312.02 311.93 311.87 311.83 311.77 311.72 10 311.60 311.52 311.43 311.34 311.29 311.24 311.18 311.13 311.06 310.98 20 310.83 310.76 310.68 310.30 310.20 310.13 309.96 309.87 309.83 309.77 30 309.72 309.65 309.55 309.46 309.39 309.34 309.30 309.25 309.22 309.18 40 309.14 309.10 309.07 309.05 309.02 308.98 308.96 308.94 308.91 308.87 50 308.85 308.82 308.80 308.78 308.76 308.74 308.73 308.71 308.70 308.68 60 308.67 308.65 308.63 308.62 308.60 308.58 308.56 308.54 308.52 308.50 70 308.48 308.45 308.41 308.37 308.34 308.31 308.28 308.26 308.23 308.17 80 308.12 308.08 308.04 308.01 307.97 307.94 307.90 307.86 307.77 307.69 90 307.64 307.56 307.44 307.35 307.26 307.13 307.02 306.92 306.78 306.62 100 306.31 Values in the exceedance table are not exact. They are good approximations based on linear interpolation of 2000 classes.

6.5 Lake Level / Lake Volume Relationship

Lake volume data was derived from the three dimensional GIS bathymetry model at a 0.5 metre contour step to cover the full recorded range of levels within the lake.

Table 17 Lake Okataina Level / Volume Relationship

Level Volume (m) (m3 x 106) 306.50 419.18 307.00 424.27 307.50 429.38 308.00 434.53 308.50 439.71 309.00 444.91 309.50 450.14 310.00 455.41 310.50 460.70 311.00 466.02 311.50 471.41 312.00 476.82 312.50 482.25 313.00 487.70

Internal Report 2004/08 Lake Level and Volume Summary of the Rotorua Lakes 36 Environment Bay of Plenty

500.0

490.0

) 480.0 6 470.0 x 10 3 460.0

450.0

440.0

Lake Volume (m 430.0

420.0

410.0 306.0 307.0 308.0 309.0 310.0 311.0 312.0 313.0 314.0 Lake Level (m)

Figure 31 Lake Okataina Level / Volume Relationship

6.6 Lake Volume Hydrograph

498

490

480

470

460

450

440 A A 430

417 19530101 5901 6501 7101 7701 8301 8901 9501 0101 YYMM A site 15309 Lake Okataina at Tauranganui Bay Volume m3 x 10^6 Figure 32 Lake Okataina Volume Hydrograph

Lake Level and Volume Summary of the Rotorua Lakes Internal Report 2004/08 Environment Bay of Plenty 37

6.7 Lake Volume Distribution

498

490

480

470

460

450

440

430

417 1 10 20 30 40 50 60 70 80 90 100 Percentage of time volume is equalled or exceeded site 15309 Lake Okataina at Tauranganui Bay Volume m3 x 10^6 19530101 000000 to 20031231 240000 Figure 33 Lake Okataina Volume Distribution

Table 18 Lake Okataina Volume Exceedance Percentiles

Exceedance percentiles From 19530101 000000 to 20031231 240000 Volume (m3x106) % 0 1 2 3 4 5 6 7 8 9 0 492.70 489.04 486.68 482.90 477.08 476.03 475.44 474.96 474.32 473.75 10 472.48 471.59 470.69 469.69 469.11 468.59 467.96 467.41 466.70 465.76 20 464.25 463.44 462.65 458.53 457.53 456.82 454.98 454.02 453.57 452.96 30 452.43 451.66 450.62 449.68 448.95 448.47 448.04 447.54 447.19 446.84 40 446.33 445.97 445.67 445.42 445.07 444.75 444.52 444.24 443.99 443.60 50 443.30 443.06 442.85 442.62 442.41 442.23 442.06 441.87 441.77 441.60 60 441.48 441.29 441.10 440.92 440.74 440.56 440.32 440.08 439.88 439.68 70 439.46 439.19 438.80 438.39 438.06 437.74 437.43 437.18 436.86 436.33 80 435.74 435.34 434.99 434.61 434.24 433.91 433.50 433.10 432.17 431.33 90 430.81 429.98 428.80 427.83 426.92 425.57 424.45 423.45 422.04 420.43 100 417.25 Values in the exceedance table are not exact. They are good approximations based on linear interpolation of 2000 classes.

Internal Report 2004/08 Lake Level and Volume Summary of the Rotorua Lakes 38 Environment Bay of Plenty

6.8 Lake Volume and Rainfall

500 2000

480 1600

460 1200

440 800 A A B

420 400

400B 0 19521201 5801 6401 7001 7601 8201 8801 9401 0001 YYMMB A site 15309 Lake Okataina at Tauranganui Bay Volume m3 x 10^6 B site 861204 Kaituna at Whakarewarewa Rainfall mm/3mths (Total=74637)

Figure 34 Lake Volume and Seasonal Rainfall Totals

500 1000

480 800

460 600

440 400 A A

B 420 200

400B 0 19530101 5901 6501 7101 7701 8301 8901 9501 0101 YYMMB A site 15309 Lake Okataina at Tauranganui Bay Volume m3 x 10^6 B site 861204 Kaituna at Whakarewarewa Rainfall mm/mth (Total=74044)

Figure 35 Lake Volume and Monthly Rainfall Totals

Lake Level and Volume Summary of the Rotorua Lakes Internal Report 2004/08 39

Chapter 7: Lake Okareka

7.1 Introduction

Lake Okareka has a surface water catchment area of 19.58 km2.

Data used for this summary is for the period 1952-2003 inclusive.

7.2 Lake Control Structures

An intake structure and pipeline is utilised for the purposes of managing the level of Lake Okareka.

Prior to March 1963 all drainage from the lake was natural.

A pump and pipeline were installed in March 1963 and operated until March 1964 in an attempt to control rising lake levels.

A controlled gravity pipeline was installed in May 1965 and is currently operated by Rotorua District Council. The intake takes water from the western end of Lake Okareka (at grid reference NZMS 260 U16: 061 305) and diverts water by pipeline into the Waitangi Stream (at grid reference NZMS 260 U16: 064 305) which subsequently runs into Lake Tarawera. The rate of discharge through the pipeline is to be kept between 100–239 litres per second and the maximum and minimum lake levels specified are:

· Maximum level RL 353.90m (Moturiki datum)

· Minimum level RL 353.50m (Moturiki datum)

Internal Report 2004/08 Lake Level and Volume Summary of the Rotorua Lakes 40 Environment Bay of Plenty

7.3 Lake Level Hydrograph

Levels are in terms of mean sea level Moturiki datum.

357

356.5

356

355.5

355

A 354.5

354 A

353.5

353 19520101 5801 6401 7001 7601 8201 8801 9401 0001 YYMM A site 15307 Lake Okareka at Acacia Rd. Level m Figure 36 Lake Okareka Level Hydrograph

Lake Level and Volume Summary of the Rotorua Lakes Internal Report 2004/08 Environment Bay of Plenty 41

7.4 Lake Level Distribution

Levels are in terms of mean sea level Moturiki datum.

357

356.5

356

355.5

355

354.5

354

353.5

353 1 10 20 30 40 50 60 70 80 90 100 Percentage of time level is equalled or exceeded site 15307 Lake Okareka at Acacia Rd. Level m 19520101 000000 to 19630228 240000 – Pre Control site 15307 Lake Okareka at Acacia Rd. Level m 19630301 000000 to 20031231 240000 – Controlled

Figure 37 Lake Okareka Level Distribution

Table 19 Lake Okareka Level Exceedance Percentiles – Pre Control

Exceedance percentiles From 19520101 000000 to 19630228 240000 - Pre Control Level - Moturiki Datum (metres) 0 1 2 3 4 5 6 7 8 9 0 356.34 356.24 356.09 355.99 355.72 355.64 355.58 355.46 355.41 355.36 10 355.32 355.29 355.26 355.2 355.18 355.15 355.13 355.12 355.10 355.08 20 355.06 355.04 355.02 355.00 355.00 354.98 354.97 354.97 354.97 354.95 30 354.95 354.94 354.94 354.93 354.92 354.91 354.9 354.89 354.88 354.88 40 354.88 354.87 354.86 354.85 354.85 354.85 354.85 354.84 354.83 354.82 50 354.82 354.81 354.8 354.8 354.79 354.78 354.77 354.77 354.76 354.75 60 354.75 354.74 354.73 354.72 354.72 354.71 354.69 354.68 354.66 354.65 70 354.64 354.63 354.62 354.60 354.60 354.59 354.57 354.57 354.56 354.56 80 354.55 354.53 354.51 354.50 354.49 354.48 354.48 354.46 354.45 354.43 90 354.42 354.41 354.39 354.37 354.36 354.33 354.28 354.25 354.19 354.09 100 354.04 Values in the exceedance table are not exact. They are good approximations based on linear interpolation of 2000 classes.

Internal Report 2004/08 Lake Level and Volume Summary of the Rotorua Lakes 42 Environment Bay of Plenty

Table 20 Lake Okareka Level Exceedance Percentiles – Controlled

Exceedance percentiles From 19630301 000000 to 20031231 240000 - Controlled Level - Moturiki Datum (metres) 0 1 2 3 4 5 6 7 8 9 0 355.94 355.41 355.03 354.88 354.83 354.77 354.63 354.57 354.35 354.27 10 354.23 354.19 354.16 354.11 354.06 354.04 354.02 353.99 353.96 353.94 20 353.92 353.91 353.90 353.89 353.88 353.87 353.86 353.86 353.85 353.84 30 353.84 353.83 353.83 353.82 353.82 353.81 353.81 353.80 353.80 353.79 40 353.79 353.78 353.78 353.78 353.77 353.76 353.76 353.76 353.75 353.74 50 353.74 353.73 353.72 353.72 353.71 353.71 353.70 353.70 353.69 353.69 60 353.68 353.68 353.67 353.67 353.66 353.66 353.65 353.65 353.64 353.64 70 353.63 353.63 353.62 353.62 353.61 353.61 353.60 353.60 353.59 353.58 80 353.58 353.57 353.56 353.55 353.55 353.54 353.53 353.52 353.51 353.49 90 353.48 353.47 353.45 353.44 353.42 353.40 353.38 353.35 353.32 353.30 100 353.20 Values in the exceedance table are not exact. They are good approximations based on linear interpolation of 2000 classes.

7.5 Lake Level / Lake Volume Relationship

Lake volume data was derived from the three dimensional GIS bathymetry model at a 0.5 metre contour step to cover the full recorded range of levels within the lake.

Table 21 Lake Okareka Level / Volume Relationship

Level Volume (m) (m3 x 106) 352.02 55.04 352.52 56.59 353.02 58.17 353.52 59.78 354.02 61.42 354.52 63.10 355.02 64.84 355.52 66.61 356.02 68.69 356.52 70.20

Lake Level and Volume Summary of the Rotorua Lakes Internal Report 2004/08 Environment Bay of Plenty 43

358

357

356

355

Lake Level (m) 354

353

352 54 56 58 60 62 64 66 68 70 Lake Volume (m3x106)

Figure 38 Lake Okareka Level / Volume Relationship

7.6 Lake Volume Hydrograph

498

490

480

470

460

450

440 A A 430

417 19530101 5901 6501 7101 7701 8301 8901 9501 0101 YYMM A site 15309 Lake Okataina at Tauranganui Bay Volume m3 x 10^6 Figure 39 Lake Okareka Volume Hydrograph

Internal Report 2004/08 Lake Level and Volume Summary of the Rotorua Lakes 44 Environment Bay of Plenty

7.7 Lake Volume Distribution

56 1 10 20 30 40 50 60 70 80 90 100 Percentage of time volume is equalled or exceeded site 15307 Lake Okareka at Acacia Rd. Volume m3x10^6 19520101 000000 to 19630228 240000 – Pre Contol site 15307 Lake Okareka at Acacia Rd. Volume m3x10^6 19630301 000000 to 20031231 240000 - Controlled

Figure 40 Lake Okareka Volume Distribution

Table 22 Lake Okareka Volume Exceedance Percentiles – Pre Control

Exceedance percentiles From 19520101 000000 to 19630228 240000 - Pre Control Volume m3x10^6 0 1 2 3 4 5 6 7 8 9 0 67.91 67.51 66.91 66.55 65.54 65.27 65.07 64.62 64.47 64.30 10 64.13 64.03 63.92 63.73 63.65 63.55 63.50 63.45 63.37 63.29 20 63.24 63.18 63.12 63.03 63.03 62.98 62.94 62.93 62.92 62.88 30 62.87 62.83 62.82 62.81 62.76 62.72 62.71 62.67 62.65 62.62 40 62.61 62.58 62.56 62.55 62.52 62.52 62.52 62.48 62.46 62.44 50 62.41 62.40 62.36 62.35 62.32 62.31 62.27 62.25 62.21 62.21 60 62.19 62.16 62.13 62.11 62.08 62.05 62.00 61.95 61.90 61.86 70 61.83 61.80 61.76 61.70 61.69 61.65 61.60 61.59 61.56 61.55 80 61.52 61.47 61.40 61.36 61.32 61.30 61.28 61.24 61.19 61.14 90 61.09 61.05 61.00 60.93 60.89 60.81 60.65 60.53 60.33 60.00 100 59.84 Values in the exceedance table are not exact. They are good approximations based on linear interpolation of 2000 classes.

Lake Level and Volume Summary of the Rotorua Lakes Internal Report 2004/08 Environment Bay of Plenty 45

Table 23 Lake Okareka Volume Exceedance Percentiles – Controlled

Exceedance percentiles From 19630301 000000 to 20031231 240000 - Controlled Volume m3x10^6 0 1 2 3 4 5 6 7 8 9 0 66.34 64.46 63.15 62.62 62.47 62.27 61.80 61.60 60.87 60.62 10 60.48 60.35 60.25 60.07 59.93 59.85 59.78 59.67 59.60 59.52 20 59.47 59.43 59.39 59.35 59.33 59.30 59.27 59.25 59.23 59.21 30 59.20 59.18 59.16 59.14 59.13 59.11 59.09 59.08 59.06 59.05 40 59.03 59.02 59.00 58.99 58.98 58.96 58.95 58.93 58.91 58.89 50 58.87 58.85 58.83 58.81 58.79 58.77 58.76 58.74 58.73 58.71 60 58.69 58.67 58.66 58.64 58.63 58.62 58.60 58.58 58.57 58.55 70 58.54 58.52 58.51 58.49 58.48 58.46 58.44 58.42 58.40 58.38 80 58.36 58.33 58.31 58.28 58.25 58.23 58.20 58.17 58.13 58.09 90 58.05 58.00 57.95 57.91 57.86 57.80 57.72 57.63 57.55 57.48 100 57.15 Values in the exceedance table are not exact. They are good approximations based on linear interpolation of 2000 classes.

7.8 Lake Volume and Rainfall

70 2000

68 1800

66 1600

64 1400

62 1200 A

60 A 1000

58 800

B 56 600

54 400

52 200

50B 0 19511201 5701 6301 6901 7501 8101 8701 9301 9901 YYMM B A site 15307 Lake Okareka at Acacia Rd. Volume m3x10^6 B site 861204 Kaituna at Whakarewarewa Rainfall mm/3mths (Total=76055) Figure 41 Lake Volume and Seasonal Rainfall Totals

Internal Report 2004/08 Lake Level and Volume Summary of the Rotorua Lakes 46 Environment Bay of Plenty

70 1000

68 900

66 800

64 700

62 600 A

60 500 A

58 400

56 300

B 54 200

52 100

50B 0 19520101 5801 6401 7001 7601 8201 8801 9401 0001 YYMMB A site 15307 Lake Okareka at Acacia Rd. Volume m3x10^6 B site 861204 Kaituna at Whakarewarewa Rainfall mm/mth (Total=75574) Figure 42 Lake Volume and Monthly Rainfall Totals

Lake Level and Volume Summary of the Rotorua Lakes Internal Report 2004/08 47

Chapter 8: Lake Tikitapu

8.1 Introduction

Lake has a surface water catchment area of 6.2 km2.

Records on Lake Tikitapu commence in January 1972. Lake level data is obtained from manual staff gauge readings that are taken at approximately 4-6 week intervals. The site is operated by Environment Bay of Plenty.

Data used for this summary is for the period 1972-2003 inclusive.

8.2 Lake Control Structures

There are no known man-made inlet/outlet structures that effect Lake Tikitapu lake levels.

8.3 Lake Level Hydrograph

Levels are in terms of mean sea level Moturiki datum.

498

490

480

470

460

450

440 A A 430

417 19530101 5901 6501 7101 7701 8301 8901 9501 0101 YYMM A site 15309 Lake Okataina at Tauranganui Bay Volume m3 x 10^6 Figure 43 Lake Tikitapu Level Hydrograph

Internal Report 2004/08 Lake Level and Volume Summary of the Rotorua Lakes 48 Environment Bay of Plenty

8.4 Lake Level Distribution

Levels are in terms of mean sea level Moturiki datum.

498

490

480

470

460

450

440

430

Table 24 Lake Tikitapu Exceedance Percentiles

Exceedance percentiles From 19730101 000000 to 20031231 240000 Level - Moturiki Datum (metres) % 0 1 2 3 4 5 6 7 8 9 0 418.15 418.11 418.07 418.03 418.02 418.01 417.99 417.97 417.95 417.93 10 417.92 417.9 417.89 417.88 417.85 417.83 417.82 417.81 417.8 417.79 20 417.77 417.76 417.75 417.74 417.73 417.72 417.71 417.7 417.69 417.67 30 417.66 417.65 417.63 417.62 417.61 417.6 417.59 417.58 417.57 417.56 40 417.55 417.54 417.53 417.52 417.51 417.5 417.48 417.46 417.44 417.42 50 417.4 417.38 417.37 417.35 417.33 417.31 417.29 417.28 417.26 417.24 60 417.23 417.22 417.21 417.19 417.18 417.16 417.15 417.14 417.12 417.11 70 417.09 417.08 417.06 417.05 417.03 417.02 417.01 416.99 416.97 416.95 80 416.94 416.92 416.9 416.88 416.87 416.86 416.85 416.83 416.81 416.79 90 416.75 416.72 416.7 416.67 416.66 416.64 416.62 416.59 416.49 416.39 100 416.27 Values in the exceedance table are not exact. They are good approximations based on linear interpolation of 2000 classes.

Lake Level and Volume Summary of the Rotorua Lakes Internal Report 2004/08 Environment Bay of Plenty 49

8.5 Lake Level / Lake Volume Relationship

Lake volume data was derived from the three dimensional GIS bathymetry model at a 0.5 metre contour step to cover the full recorded range of levels within the lake.

Table 25 Lake Tikitapu Level / Volume Relationship

Level Volume (m) (m3 x 106) 415.800 23.52 416.300 24.21 416.800 24.91 417.300 25.61 417.800 26.32 418.300 27.04 418.800 27.76 419.300 28.49 419.800 29.22

420.0

419.5

419.0

418.5

418.0

417.5

417.0 Lake Level (m) 416.5

416.0

415.5

415.0 23 24 25 26 27 28 29 30 Lake Volume (m3x106)

Figure 45 Lake Tikitapu Level/Volume Relationship

Internal Report 2004/08 Lake Level and Volume Summary of the Rotorua Lakes 50 Environment Bay of Plenty

8.6 Lake Volume Hydrograph

24 19720101 7501 7801 8101 8401 8701 9001 9301 9601 9901 0201 YYMM site 15347 Lake Tikitapu Volume m3*10^6 Figure 46 Lake Tikitapu Volume Hydrograph

8.7 Lake Volume Distribution

24 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 Fraction of time volume is equalled or exceeded site 15347 Lake Tikitapu Volume m3*10^6 19720127 130500 to 20031231 240000 Figure 47 Lake Tikitapu Volume Distribution

Lake Level and Volume Summary of the Rotorua Lakes Internal Report 2004/08 Environment Bay of Plenty 51

Table 26 Lake Tikitapu Volume Exceedance Percentiles

Exceedance percentiles From 19730101 000000 to 20031231 240000 Volume (m3x106) % 0 1 2 3 4 5 6 7 8 9 0 26.83 26.76 26.71 26.65 26.63 26.61 26.59 26.57 26.54 26.51 10 26.49 26.47 26.44 26.43 26.40 26.36 26.34 26.33 26.32 26.30 20 26.28 26.27 26.25 26.24 26.22 26.20 26.19 26.18 26.16 26.14 30 26.12 26.10 26.08 26.06 26.05 26.03 26.02 26.00 25.99 25.98 40 25.96 25.95 25.93 25.92 25.90 25.89 25.87 25.84 25.81 25.78 50 25.75 25.73 25.70 25.68 25.66 25.62 25.60 25.58 25.55 25.53 60 25.51 25.50 25.48 25.45 25.44 25.42 25.39 25.38 25.36 25.34 70 25.32 25.29 25.28 25.25 25.23 25.22 25.19 25.17 25.15 25.12 80 25.10 25.07 25.04 25.02 25.00 24.99 24.97 24.95 24.92 24.89 90 24.83 24.79 24.76 24.73 24.71 24.68 24.65 24.61 24.48 24.33 100 24.16 Values in the exceedance table are not exact. They are good approximations based on linear interpolation of 2000 classes.

8.8 Lake Volume and Rainfall

28 2000

27 1600

26 1200 A

25 800

24 400

23B 0 19711201 7701 8001 8301 8601 8901 9201 9501 9801 0101 YYMM B A site 15347 Lake Tikitapu Volume m3*10^6 B site 861204 Kaituna at Whakarewarewa Rainfall mm/3mths (Total=45002)

Figure 48 Lake Volume and Seasonal Rainfall Totals

Internal Report 2004/08 Lake Level and Volume Summary of the Rotorua Lakes 52 Environment Bay of Plenty

28 1000

27 800

26 600

25 400

B 24 200

23B 0 19720101 7501 7801 8101 8401 8701 9001 9301 9601 9901 0201 YYMMB A site 15347 Lake Tikitapu Volume m3*10^6 B site 861204 Kaituna at Whakarewarewa Rainfall mm/mth (Total=44410) Figure 49 Lake Volume and Monthly Rainfall Totals

Lake Level and Volume Summary of the Rotorua Lakes Internal Report 2004/08 53

Chapter 9: Lake Tarawera

9.1 Introduction

Lake Tarawera has a surface water catchment area of 143.1 km2, however 5 other lakes within the area drain into Lake Tarawera and when included increase the catchment area to 412 km2.

Intermittent lake level data were recorded at this site up until October 1944 when lake level recording ceased. Intermittent lake level recordings recommenced in January 1948 until 12 March 1951 when an automatic chart recorder was installed by the Ministry of Works Water and Soil Division. Site ownership and operation was transferred to Environment Bay of Plenty on 17 February 1994.

Data for the lake is also recorded at the Lake Tarawera at Lake Outlet recorder which is operated by the National Institute of Water and Atmosphere.

Data used for this summary is for the period 1926-2003 inclusive.

9.2 Lake Control Structures

There are no known man-made outlet structures that effect Lake Tarawera lake levels, however there are a number of inlet structures that effect lake levels.

A controlled gravity pipeline was installed in Lake Okareka in May 1965 and is currently operated by Rotorua District Council. The intake takes water from the western end of Lake Okareka (grid reference NZMS 260 U16: 061 305) and diverts water by pipeline into the Waitangi Stream (grid reference NZMS 260 U16: 064 305) which subsequently runs into Lake Tarawera. The rate of discharge through the pipeline is to be kept between 100–239 litres per second.

There is a control structure in place for the purpose of discharging excess water from Lake Rotomahana into Lake Tarawera. The intake structure is situated at grid reference NZMS 260 V16: 107 218 and discharges to the west of the Rapatu Bay jetty at grid reference NZMS 260 V16:118 231 . The maximum flow through the structure is limited to 62200m3/day with a maximum rate is 0.72m3/second.

Internal Report 2004/08 Lake Level and Volume Summary of the Rotorua Lakes 54 Environment Bay of Plenty

9.3 Lake Level Hydrograph

Levels are in terms of mean s ea level Moturiki datum.

299

298.8

298.6

298.4 A 298.2

298 A

297.8

297.6

297.4

297.2

297 19260101 3601 4601 5601 6601 7601 8601 9601 YYMM A site 15301 Tarawera at Te Wairoa Level m

Figure 50 Lake Tarawera Level Hydrograph

9.4 Lake Level Distribution

Levels are in terms of mean sea level Moturiki datum.

299

298.8

298.6

298.4

298.2

298

297.8

297.6

297.4

297.2

297 1 10 20 30 40 50 60 70 80 90 100 Percentage of time level is equalled or exceeded site 15301 Tarawera at Te Wairoa Level m 19260101 000000 to 20031231 240000 Figure 51 Lake Tarawera Level Distribution

Lake Level and Volume Summary of the Rotorua Lakes Internal Report 2004/08 Environment Bay of Plenty 55

Table 27 Lake Tarawera Level Exceedance Percentiles

Exceedance percentiles From 19260101 000000 to 20031231 240000 Level - Moturiki Datum (metres) % 0 1 2 3 4 5 6 7 8 9 0 298.55 298.42 298.38 298.35 298.33 298.31 298.30 298.29 298.27 298.27 10 298.26 298.25 298.24 298.23 298.22 298.22 298.21 298.20 298.20 298.19 20 298.19 298.19 298.18 298.17 298.16 298.16 298.15 298.14 298.13 298.13 30 298.12 298.11 298.10 298.10 298.09 298.09 298.08 298.08 298.07 298.07 40 298.06 298.06 298.06 298.05 298.04 298.03 298.03 298.03 298.03 298.03 50 298.02 298.02 298.01 298.00 298.00 298.00 298.00 297.99 297.98 297.98 60 297.97 297.97 297.97 297.96 297.96 297.95 297.95 297.94 297.94 297.93 70 297.93 297.92 297.92 297.91 297.91 297.91 297.90 297.90 297.89 297.89 80 297.88 297.88 297.87 297.87 297.86 297.86 297.85 297.85 297.84 297.84 90 297.83 297.83 297.82 297.81 297.80 297.80 297.79 297.78 297.77 297.75 100 297.68 Values in the exceedance table are not exact. They are good approximations based on linear int erpolation of 2000 classes.

9.5 Lake Level / Lake Volume Relationship

Lake volume data was derived from the three dimensional GIS bathymetry model at a 0.5 metre contour step to cover the full recorded range of levels within the lake.

Table 28 Lake Tarawera Level / Volume Relationship

Level Volume (m) (m3 x 106) 294.940 2147.86 295.440 2167.87 295.940 2187.98 296.440 2208.16 296.940 2228.43 297.440 2248.79 297.940 2269.23 298.440 2289.90 298.940 2310.64 299.440 2331.46 299.940 2352.39 300.440 2373.35

Internal Report 2004/08 Lake Level and Volume Summary of the Rotorua Lakes 56 Environment Bay of Plenty

301

300

299

298

297 Lake Level (m)

296

295

294 2100 2150 2200 2250 2300 2350 2400 Lake Volume (m3x106)

Figure 52 Lake Tarawera Level / Volume Relationship

9.6 Lake Volume Hydrograph

2298

2295

2290

2285 A

2280

2275

2270 A

2265

2260 2258 19260101 3601 4601 5601 6601 7601 8601 9601 YYMM A site 15301 Tarawera at Te Wairoa Volume m3 x 10^6 10^6

Figure 53 Lake Tarawera Volume Hydrograph

Lake Level and Volume Summary of the Rotorua Lakes Internal Report 2004/08 Environment Bay of Plenty 57

9.7 Lake Volume Distribution

2299

2295

2290

2285

2280

2275

2270

2265

2260 2258 1 10 20 30 40 50 60 70 80 90 100 Percentage of time item 1 is equalled or site 15301 Tarawera at Te Wairoa Volume m3 x 10^6 19260101 exceeded 120000 to 20031231 240000 Figure 54 Lake Tarawera Volume Distribution

Table 29 Lake Tarawera Volume Exceedance Percentiles

Exceedance percentiles From 19260101 120000 to 20031231 240000 Volume (m3x106) % 0 1 2 3 4 5 6 7 8 9 0 2294 2289 2287 2286 2285 2285 2284 2284 2283 2283 10 2283 2282 2282 2282 2281 2281 2281 2281 2280 2280 20 2280 2280 2279 2279 2279 2278 2278 2278 2278 2277 30 2277 2277 2277 2276 2276 2276 2275 2275 2275 2275 40 2274 2274 2274 2274 2274 2274 2274 2273 2273 2273 50 2273 2273 2273 2272 2272 2272 2272 2272 2272 2271 60 2271 2271 2271 2271 2270 2270 2270 2270 2269 2269 70 2269 2269 2269 2269 2268 2268 2268 2268 2268 2267 80 2267 2267 2267 2267 2266 2266 2266 2266 2266 2265 90 2265 2265 2265 2264 2264 2264 2263 2263 2263 2262 100 2258 Values in the exceedance table are not exact. They are good approximations based on linear interpolation of 2000 classes.

Internal Report 2004/08 Lake Level and Volume Summary of the Rotorua Lakes 58 Environment Bay of Plenty

9.8 Lake Volume and Rainfall

2295 2000

2290 1800 A

2280 1400

2270 1000

B 2260 600

2250 200

2245B 0 19251201 3501 4501 5501 6501 7501 8501 9501 YYMM B A site 15301 Tarawera at Te Wairoa Volume m3 x 10^6 B site 861204 Kaituna at Whakarewarewa Rainfall mm/3mths (Total=113107) Figure 55 Lake Volume and Seasonal Rainfall Totals

2295 1000

2290 900

2280 700

2270 500 A

2260 300

2250 100

2245B 0 19260101 3601 4601 5601 6601 7601 8601 9601 YYMM B A site 15301 Tarawera at Te Wairoa Volume m3 x 10^6 B site 861204 Kaituna at Whakarewarewa Rainfall mm/mth (Total=112669) Figure 56 Lake Volume and Monthly Rainfall Totals

Lake Level and Volume Summary of the Rotorua Lakes Internal Report 2004/08 59

Chapter 10: Lake Rotokakahi

10.1 Introduction

Lake Rotokakahi has a surface water catchment area of 19.71km2.

The lake drains naturally via the Te Wairoa Stream into Lake Tarawera.

Lake level records commenced in January 1972 by the Ministry of Works Soils and Water Division. Regular manual staff gauge readings were taken at a staff gauge installed at the outlet of the lake in the Te Wairoa Stream. Data is now collected by Environment Bay of Plenty. All data are observed staff gauge levels.

Data used for this summary is for the period 1972-2003 inclusive.

10.2 Lake Control Structures

There are no known man-made outlet structures that effect Lake Rotokakahi lake levels. Historically there has been some modification of the Te Wairoa Stream, which may have had some minor effect on the outlet from the lake.

Internal Report 2004/08 Lake Level and Volume Summary of the Rotorua Lakes 60 Environment Bay of Plenty

10.3 Lake Level Hydrograph

Levels are in terms of mean sea level Moturiki datum.

396

395.8

395.6

395.4

395.2

395

394.8

394.6

394.4

394.2

394 19720101 7501 7801 8101 8401 8701 9001 9301 9601 9901 0201 YYMM site 15344 Te Wairoa at Lake Rotokakahi Stage m

Figure 57 Lake Rotokakahi Level Hydrograph

10.4 Lake Level Distribution

Levels are in terms of mean sea level Moturiki datum.

396

395.8

395.6

395.4

395.2

395

394.8

394.6

394.4

394.2

394 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 Fraction of time stage is equalled or exceeded site 15344 Te Wairoa at Lake Rotokakahi Stage m 19720127 131000 to 20031231 240000 Figure 58 Lake Rotokakahi Level Distribution

Lake Level and Volume Summary of the Rotorua Lakes Internal Report 2004/08 Environment Bay of Plenty 61

Table 30 Lake Rotokakahi Level Exceedance Percentiles

Exceedance percentiles From 19720127 131000 to 20031231 240000 Level - Moturiki Datum (metres) % 0 1 2 3 4 5 6 7 8 9 0 395.17 395.09 395.07 395.05 395.04 395.03 395.03 395.02 395.02 395.01 10 395.01 395.01 395.00 395.00 395.00 394.99 394.99 394.99 394.99 394.98 20 394.98 394.98 394.98 394.97 394.97 394.97 394.97 394.96 394.96 394.96 30 394.95 394.95 394.95 394.94 394.94 394.94 394.94 394.93 394.93 394.93 40 394.93 394.93 394.92 394.92 394.92 394.92 394.92 394.92 394.91 394.91 50 394.91 394.91 394.91 394.91 394.91 394.90 394.90 394.90 394.90 394.90 60 394.90 394.90 394.89 394.89 394.89 394.89 394.89 394.89 394.88 394.88 70 394.88 394.88 394.88 394.88 394.87 394.87 394.87 394.87 394.87 394.86 80 394.86 394.86 394.86 394.86 394.85 394.85 394.85 394.85 394.85 394.84 90 394.84 394.84 394.83 394.83 394.82 394.82 394.82 394.81 394.80 394.78 100 394.74 Values in the exceedance table are not exact. They are good approximations based on linear interpolation of 2000 classes.

10.5 Lake Level / Lake Volume Relationship

Lake volume data was derived from the three dimensional GIS bathymetry model at a 0.5 metre contour step to cover the full recorded range of levels within the lake.

Table 31 Lake Rotokakahi Level / Volume Relationship

Level Volume (m) (m3 x 106) 391.33 59.89 391.83 61.93 392.33 64.00 392.83 66.08 393.33 68.18 393.83 70.31 394.33 72.45 394.83 74.62 395.33 76.81 395.83 79.02 396.33 81.25 396.83 83.49 397.33 85.75 397.83 88.02 398.33 90.30

Internal Report 2004/08 Lake Level and Volume Summary of the Rotorua Lakes 62 Environment Bay of Plenty

399

398

397

396

395

394 Lake Level (m)

393

392

391 58 60 62 64 66 68 70 72 74 76 78 80 82 84 86 88 90 Lake Volume (m3x106)

Figure 59 Lake Rotokakahi Level / Volume Relationship

10.6 Lake Volume Hydrograph

76.5

75.5

74.5

74 19720101 7501 7801 8101 8401 8701 9001 9301 9601 9901 0201 YYMM site 15344 Te Wairoa at Lake Rotokakahi Volume m3 x10^6 Figure 60 Lake Rotokakahi Volume Hydrograph

Lake Level and Volume Summary of the Rotorua Lakes Internal Report 2004/08 Environment Bay of Plenty 63

10.7 Lake Volume Distribution

76.5

75.5

74.5

74 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 Fraction of time volume is equalled or exceeded site 15344 Te Wairoa at Lake Rotokakahi Volume m3 x10^6 19720127 131000 to 20031231 240000 Figure 61 Lake Rotokakahi Volume Distribution

Table 32 Lake Rotokakahi Volume Exceedance Percentiles

Exceedance percentiles Source is Rotokakahi.mtd Site 15344 Te Wairoa at Lake Rotokakahi From 19720127 131000 to 20031231 240000 Volume (m3x106) % 0 1 2 3 4 5 6 7 8 9 0 76.11 75.76 75.67 75.60 75.55 75.51 75.47 75.45 75.43 75.41 10 75.40 75.38 75.37 75.36 75.35 75.34 75.32 75.31 75.30 75.29 20 75.28 75.27 75.26 75.25 75.24 75.22 75.21 75.20 75.18 75.17 30 75.16 75.14 75.13 75.12 75.11 75.09 75.08 75.07 75.07 75.06 40 75.05 75.04 75.03 75.03 75.02 75.01 75.00 74.99 74.99 74.98 50 74.97 74.97 74.96 74.96 74.95 74.94 74.93 74.93 74.92 74.92 60 74.91 74.90 74.90 74.89 74.88 74.88 74.87 74.86 74.86 74.85 70 74.84 74.84 74.83 74.82 74.81 74.80 74.80 74.79 74.78 74.77 80 74.76 74.75 74.74 74.73 74.72 74.71 74.70 74.69 74.69 74.68 90 74.66 74.65 74.63 74.61 74.59 74.57 74.56 74.54 74.48 74.41 100 74.24 Values in the exceedance table are not exact. They are good approximations based on linear interpolation of 2000 classes.

Internal Report 2004/08 Lake Level and Volume Summary of the Rotorua Lakes 64 Environment Bay of Plenty

10.8 Lake Volume and Rainfall

77 2000

76.5

76 1600

75.5

75 1200

74.5

74 800

73.5

73 400

72.5

72 0 19720101 7501 7801 8101 8401 8701 9001 9301 9601 9901 0201 YYMM site 15344 Te Wairoa at Lake Rotokakahi Volume m3 x10^6 site 861204 Kaituna at Whakarewarewa Rainfall mm/3mths (Total=44416) Figure 62 Lake Volume and Seasonal Rainfall Totals

77 1000

76.5 900

76 800

75.5 700

75 600

74.5 500

74 400

73.5 300

73 200

72.5 100

72 0 19720101 7501 7801 8101 8401 8701 9001 9301 9601 9901 0201 YYMM site 15344 Te Wairoa at Lake Rotokakahi Volume m3 x10^6 site 861204 Kaituna at Whakarewarewa Rainfall mm/mth (Total=44410)

Figure 63 Lake Volume and Monthly Rainfall Totals

Lake Level and Volume Summary of the Rotorua Lakes Internal Report 2004/08 65

Chapter 11: Lake Rotomahana

11.1 Introduction

Lake has a surface water catchment area of 83.2km2.

Lake level data was recorded intermittently at this site from November 1924 by the Ministry of Works Water and Soil Division (formerly the Hamilton Hydrological Survey) until the site was transferred to the Bay of Plenty Catchment Commission in September 1979. The site is now operated by Environment Bay of Plenty. Data used for this summary is for the period 1925-2003 inclusive.

11.2 Lake Control Structures

There is a control structure in place for the purpose of discharging excess water from Lake Rotomahana into Lake Tarawera. The intake structure is situated at grid reference NZMS 260 V16: 107 218 and discharges to the west of the Rapatu Bay jetty at grid reference NZMS 260 V16:118 231. The maximum flow through the structure is limited to 62200m3/day with a maximum rate is 0.72m3/second.

Internal Report 2004/08 Lake Level and Volume Summary of the Rotorua Lakes 66 Environment Bay of Plenty

11.3 Lake Level Hydrograph

Levels are in terms of mean sea level Moturiki datum.

343

342

340

338

336

334

333 19250101 3501 4501 5501 6501 7501 8501 9501 YYMM site 15338 Lake Rotomahana at Crater Bay Level metres Figure 64 Lake Rotomahana Level Hydrograph

11.4 Lake Level Distribution

Levels are in terms of mean sea level Moturiki datum.

344

342

340

338

336

334

333 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 Fraction of time level is equalled or exceeded site 15338 Lake Rotomahana at Crater Bay Level metres 19250101 000000 to 20031231 240000 Figure 65 Lake Rotomahana Level Distribution

Lake Level and Volume Summary of the Rotorua Lakes Internal Report 2004/08 Environment Bay of Plenty 67

Table 33 Lake Rotomahana Level Exceedance Percentiles

Exceedance percentiles From 19250101 000000 to 20031231 240000 Level - Moturiki Datum (metres) % 0 1 2 3 4 5 6 7 8 9 0 342.12 341.92 341.48 341.09 340.96 340.89 340.82 340.78 340.72 340.67 10 340.62 340.55 340.51 340.47 340.44 340.42 340.39 340.36 340.31 340.22 20 340.14 340.00 339.92 339.84 339.63 339.48 339.39 339.33 339.29 339.24 30 339.18 339.13 339.10 339.06 339.02 338.99 338.94 338.90 338.81 338.74 40 338.63 338.59 338.53 338.45 338.40 338.38 338.36 338.32 338.29 338.25 50 338.22 338.17 338.12 338.08 337.99 337.93 337.85 337.77 337.71 337.64 60 337.59 337.54 337.48 337.44 337.39 337.37 337.34 337.31 337.28 337.26 70 337.23 337.20 337.16 337.11 337.08 337.04 337.00 336.96 336.91 336.88 80 336.83 336.75 336.68 336.59 336.54 336.48 336.42 336.36 336.30 336.24 90 336.16 336.07 335.91 335.75 335.24 334.85 334.61 334.37 334.27 333.94 100 333.57 Values in the exceedance table are not exact. They are good approximations based on linear interpolation of 2000 classes.

11.5 Lake Level / Lake Volume Relationship

Lake volume data was derived from the three dimensional GIS bathymetry model at a 0.5 metre contour step to cover the full recorded range of levels within the lake.

Table 34 Lake Rotomahana Level / Volume Relationship

Level Volume (m) (m3 x 106) 332.965 425.70 333.465 429.45 333.965 433.22 334.465 437.01 334.965 440.95 335.465 444.93 335.965 448.94 336.465 452.99 336.965 457.07 337.465 461.30 337.965 465.59 338.465 469.94 338.965 474.35 339.465 478.84 339.965 484.75 340.465 490.81 340.965 496.91 341.465 503.06 341.965 509.26 342.465 515.51 342.965 521.81

Internal Report 2004/08 Lake Level and Volume Summary of the Rotorua Lakes 68 Environment Bay of Plenty

343

342

341

340

339

338

337

Lake Level (m) 336

335

334

333

332 425 430 435 440 445 450 455 460 465 470 475 480 485 490 495 500 505 510 515 520 Lake Volume (m3x106)

Figure 66 Lake Rotomahana Level / Volume Relationship

11.6 Lake Volume Hydrograph

514 510

500

490

480

470

460

450

440

430 19250101 3501 4501 5501 6501 7501 8501 9501 YYMM site 15338 Lake Rotomahana at Crater Bay Volume m3 x 10^6 Figure 67 Lake Rotomahana Volume Hydrograph

Lake Level and Volume Summary of the Rotorua Lakes Internal Report 2004/08 Environment Bay of Plenty 69

11.7 Lake Volume Distribution

515

510

500

490

480

470

460

450

440

430 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 Fraction of time volume is equalled or exceeded site 15338 Lake Rotomahana at Crater Bay Volume m3 x 10^6 19250101 000000 to 20031231 240000 Figure 68 Lake Rotomahana Volume Distribution

Table 35 Lake Rotomahana Volume Exceedance Percentiles

Exceedance percentiles From 19250101 000000 to 20031231 240000 Volume (m3x106) % 0 1 2 3 4 5 6 7 8 9 0 511.23 508.73 503.21 498.40 496.82 495.95 495.12 494.61 493.87 493.30 10 492.65 491.89 491.31 490.88 490.50 490.23 489.95 489.53 488.98 487.84 20 486.90 485.18 484.19 483.13 480.63 479.04 478.18 477.64 477.26 476.78 30 476.24 475.86 475.52 475.15 474.82 474.57 474.14 473.80 473.01 472.35 40 471.38 471.05 470.51 469.80 469.40 469.18 468.97 468.70 468.37 468.04 50 467.77 467.40 466.97 466.55 465.80 465.25 464.58 463.93 463.35 462.80 60 462.39 461.98 461.44 461.06 460.68 460.45 460.23 459.98 459.75 459.53 70 459.27 459.03 458.71 458.33 458.03 457.66 457.32 457.02 456.62 456.34 80 455.97 455.33 454.74 453.99 453.57 453.08 452.60 452.14 451.64 451.19 90 450.52 449.82 448.54 447.19 443.10 440.07 438.14 436.31 435.53 433.03 100 430.25 Values in the exceedance table are not exact. They are good approximations based on linear interpolation of 2000 classes.

Internal Report 2004/08 Lake Level and Volume Summary of the Rotorua Lakes 70 Environment Bay of Plenty

11.8 Lake Volume and Rainfall

515 2000

500 1700

480 1300

460 A 900

440A 500

420 100 415B 0 19241201 3401 4401 5401 6401 7401 8401 9401 YYMM B A site 15338 Lake Rotomahana at Crater Bay Volume m3 x 10^6 B site 861204 Kaituna at Whakarewarewa Rainfall mm/3mths (Total=114757) Figure 69 Lake Volume and Seasonal Rainfall Totals

515 1000

500 850

480 650

460 A 450

440A 250 B

420 50 415B 0 19250101 3501 4501 5501 6501 7501 8501 9501 YYMM B A site 15338 Lake Rotomahana at Crater Bay Volume m3 x 10^6 B site 861204 Kaituna at Whakarewarewa Rainfall mm/mth (Total=114210) Figure 70 Lake Volume and Monthly Rainfall Totals

Lake Level and Volume Summary of the Rotorua Lakes Internal Report 2004/08 71

Chapter 12: Lake Okaro

12.1 Introduction

Lake Okaro has a surface water catchment area of 2.9km2

Manual staff gauge reading records from the lake began in August 1980 however these were infrequent until November 1989 when regular 4-6weekly readings of lake level were taken. The site is operated by Environment Bay of Plenty.

Data used for this summary is for the period 1990-2003 inclusive.

12.2 Lake Control Structures

There are no known man-made outlet structures that effect Lake Okaro lake levels.

12.3 Lake Level Hydrograph

Levels are in terms of mean sea level Moturiki datum.

413

412.5

412

411.5

411 19900101 9201 9301 9401 9501 9601 9701 9801 9901 0001 0101 0201 0301 YYMM site 1015325 Lake Okaro at Reserve. Stage m Figure 71 Lake Okaro Level Hydrograph

Internal Report 2004/08 Lake Level and Volume Summary of the Rotorua Lakes 72 Environment Bay of Plenty

12.4 Lake Level Distribution

Levels are in terms of mean sea level Moturiki datum.

413

412.8

412.6

412.4

412.2

412

411.8

411.6

411.4

411.2

411 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 Fraction of time stage is equalled or exceeded site 1015325 Lake Okaro at Reserve. Stage m 19900101 000000 to 20031231 240000 Figure 72 Lake Okaro Level Distribution

Table 36 Lake Okaro Level Exceedance Percentiles

Exceedance percentiles From 19900101 000000 to 20031231 240000 Level - Moturiki Datum (metres) % 0 1 2 3 4 5 6 7 8 9 0 412.02 412.00 411.98 411.97 411.96 411.96 411.95 411.95 411.94 411.93 10 411.92 411.92 411.91 411.91 411.90 411.89 411.89 411.88 411.87 411.87 20 411.86 411.86 411.85 411.84 411.83 411.83 411.82 411.82 411.82 411.81 30 411.81 411.81 411.80 411.80 411.80 411.80 411.80 411.79 411.79 411.79 40 411.79 411.79 411.78 411.78 411.78 411.78 411.77 411.77 411.77 411.76 50 411.76 411.76 411.75 411.75 411.75 411.74 411.74 411.74 411.73 411.73 60 411.72 411.72 411.72 411.72 411.71 411.71 411.71 411.71 411.71 411.70 70 411.70 411.70 411.70 411.70 411.69 411.69 411.69 411.69 411.69 411.69 80 411.68 411.68 411.68 411.68 411.68 411.67 411.67 411.67 411.67 411.66 90 411.66 411.65 411.65 411.64 411.64 411.63 411.63 411.62 411.61 411.58 100 411.54 Values in the exceedance table are not exact. They are good approximations based on linear interpolation of 2000 classes.

Lake Level and Volume Summary of the Rotorua Lakes Internal Report 2004/08 Environment Bay of Plenty 73

12.5 Lake Level / Lake Volume Relationship

Lake volume data was derived from the three dimensional GIS bathymetry model at a 0.5 metre contour step to cover the full recorded range of levels within the lake.

The Lake Okaro bathymetry was related to a historical benchmark that no longer exists and has an unknown origin and level. To enable the bathymetry to be used it an assumed level for the historical benchmark was derived by levelling in ground level at the approximate location of the benchmark and relating this to current datum.

Table 37 Lake Okaro Level / Volume Relationship

Level Volume (m) (m3 x 106) 407.97 2.32 408.47 2.45 408.97 2.59 409.47 2.73 409.97 2.87 410.47 3.01 410.97 3.15 411.47 3.30 411.97 3.46 412.47 3.62 412.97 3.78 413.47 3.95 413.97 4.13

415

414

413

412

411

410

409 Lake Level (m) 408

407

406

405 1.5 2.0 2.5 3.0 3.5 4.0 4.5 Lake Volume (m3 x 10 6)

Figure 73 Lake Okaro Level / Volume Relationship

Internal Report 2004/08 Lake Level and Volume Summary of the Rotorua Lakes 74 Environment Bay of Plenty

12.6 Lake Volume Hydrograph

3.8

3.6

3.4

3.2

3 19900101 9201 9301 9401 9501 9601 9701 9801 9901 0001 0101 0201 0301 YYMM site 1015325 Lake Okaro at Reserve. Volume m3 x10^6 Figure 74 Lake Okaro Volume Hydrograph

12.7 Lake Volume Distribution

3.8

3.6

3.4

3.2

3 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 Fraction of time volume is equalled or exceeded site 1015325 Lake Okaro at Reserve. Volume m3 x10^6 19900101 000000 to 20031231 240000 Figure 75 Lake Okaro Volume Distribution

Lake Level and Volume Summary of the Rotorua Lakes Internal Report 2004/08 Environment Bay of Plenty 75

Table 38 Lake Okaro Volume Exceedance Percentiles

Exceedance percentiles From 19900101 000000 to 20031231 240000 Volume (m3x106) % 0 1 2 3 4 5 6 7 8 9 0 3.47 3.47 3.46 3.46 3.46 3.45 3.45 3.45 3.45 3.45 10 3.44 3.44 3.44 3.44 3.44 3.43 3.43 3.43 3.43 3.43 20 3.42 3.42 3.42 3.42 3.42 3.41 3.41 3.41 3.41 3.41 30 3.41 3.41 3.41 3.41 3.41 3.40 3.40 3.40 3.40 3.40 40 3.40 3.40 3.40 3.40 3.40 3.40 3.40 3.40 3.39 3.39 50 3.39 3.39 3.39 3.39 3.39 3.39 3.39 3.39 3.38 3.38 60 3.38 3.38 3.38 3.38 3.38 3.38 3.38 3.38 3.38 3.38 70 3.37 3.37 3.37 3.37 3.37 3.37 3.37 3.37 3.37 3.37 80 3.37 3.37 3.37 3.37 3.37 3.37 3.37 3.36 3.36 3.36 90 3.36 3.36 3.36 3.36 3.36 3.35 3.35 3.35 3.35 3.34 100 3.33 Values in the exceedance table are not exact. They are good approximations based on linear interpolation of 2000 classes.

Internal Report 2004/08 Lake Level and Volume Summary of the Rotorua Lakes 76 Environment Bay of Plenty

12.8 Lake Volume and Rainfall

4 2000

3.8 1600

3.6 1200

3.4 800

3.2 400

3 0 19891201 9201 9301 9401 9501 9601 9701 9801 9901 0001 0101 0201 0301 YYMM site 861204 Kaituna at Whakarewarewa Rainfall mm/3mths (Total=19768) site 1015325 Lake Okaro at Reserve. Volume m3 x10^6

Figure 76 Lake Volume and Seasonal Rainfall Totals

4 1000

3.8 800

3.6 600

3.4 400

3.2 200

3 0 19900101 9201 9301 9401 9501 9601 9701 9801 9901 0001 0101 0201 0301 YYMM site 1015325 Lake Okaro at Reserve. Volume m3 x10^6 site 861204 Kaituna at Whakarewarewa Rainfall mm/mth (Total=19317) Figure 77 Lake Volume and Monthly Rainfall Totals

Lake Level and Volume Summary of the Rotorua Lakes Internal Report 2004/08 77

Chapter 13: Lake Rerewhakaaitu

13.1 Introduction

Lake Rerewhakaaitu has a surface water catchment area of 38.2km2.

Lake Rerewhakaaitu level data was recorded originally recorded at a site in Awaatua Bay from October 1952. The site was shifted to its current location at Homestead Arm in April 1983 due to continuing low water levels at the Awaatua Bay site. Datasets from both sites are combined for the purposes of this data summary.

The Awaatua Bay site was operated by site the Ministry of Works Water and Soil Division before the site was transferred to the Bay of Plenty Catchment Commission in September 1979. The site is now operated by Environment Bay of Plenty.

Data used for this summary is for the period 1953-2003 inclusive.

13.2 Lake Control Structures

An outlet control structure was placed on the northern tributary of the Mangaharakeke Stream to act as a lake outfall structure if the lake level exceeds 436.6 metres Moturiki datum (McIntosh et al, 2001), this outfall discharges into the Rangitaiki river catchment The exact date of this installation of this structure is unknown but is believed to be the mid 1960’s.

Internal Report 2004/08 Lake Level and Volume Summary of the Rotorua Lakes 78 Environment Bay of Plenty

13.3 Lake Level Hydrograph

Levels are in terms of mean sea level Moturiki datum.

438

437

436

435

434

433 19530101 5901 6501 7101 7701 8301 8901 9501 0101 YYMM site 1015310 Lake Rerewhakaaitu at Homestead Arm Level metres Figure 78 Lake Rerewhakaaitu Level Hydrograph

13.4 Lake Level Distribution

Levels are in terms of mean sea level Moturiki datum.

438

437

436

435

434

433 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 Fraction of time level is equalled or exceeded site 1015310 Lake Rerewhakaaitu at Homestead Arm Level metres 19530101 000000 to 20031231 240000 Figure 79 Lake Rerewhakaaitu Level Distribution

Lake Level and Volume Summary of the Rotorua Lakes Internal Report 2004/08 Environment Bay of Plenty 79

Table 39 Lake Rerewhakaaitu Level Exceedance Percentiles

Exceedance percentiles From 19530101 000000 to 20031231 240000 Level - Moturiki Datum (metres) % 0 1 2 3 4 5 6 7 8 9 0 437.39 437.27 437.19 437.13 437.08 437.03 436.99 436.96 436.92 436.89 10 436.87 436.85 436.83 436.80 436.78 436.76 436.74 436.72 436.71 436.69 20 436.69 436.67 436.65 436.63 436.61 436.59 436.57 436.54 436.52 436.49 30 436.47 436.44 436.42 436.40 436.37 436.33 436.29 436.26 436.22 436.17 40 436.12 436.08 436.04 435.99 435.93 435.89 435.85 435.83 435.80 435.80 50 435.78 435.76 435.73 435.71 435.69 435.66 435.62 435.60 435.58 435.56 60 435.54 435.52 435.50 435.48 435.45 435.43 435.41 435.38 435.35 435.33 70 435.32 435.30 435.27 435.25 435.24 435.21 435.18 435.15 435.12 435.07 80 435.05 435.03 435.01 434.99 434.96 434.93 434.91 434.89 434.87 434.84 90 434.81 434.79 434.75 434.70 434.62 434.53 434.44 434.35 434.18 433.96 100 433.78 Values in the exceedance table are not exact. They are good approximations based on linear interpolation of 2000 classes.

13.5 Lake Level / Lake Volume Relationship

Lake volume data was derived from the three dimensional GIS bathymetry model at a 0.5 metre contour step to cover the full recorded range of levels within the lake.

Table 40 Lake Rerewhakaaitu Level / Volume Relationship

Level Volume (m) (m3 x 106) 431.600 47.66 432.100 49.09 432.600 50.54 433.100 52.01 433.600 53.51 434.100 55.04 434.600 56.59 435.100 58.17 435.600 59.78 436.100 61.42 436.600 63.10 437.100 64.84 437.600 66.61 438.100 68.39 438.600 70.20

Internal Report 2004/08 Lake Level and Volume Summary of the Rotorua Lakes 80 Environment Bay of Plenty

439

438

437

436

435

434 Lake Level (m)

433

432

431 47 49 51 53 55 57 59 61 63 65 67 69 71 Lake Volume (m3x106)

Figure 80 Lake Rerewhakaaitu Level / Volume Relationship

13.6 Lake Volume Hydrograph

54 19530101 5901 6501 7101 7701 8301 8901 9501 0101 YYMM site 1015310 Lake Rerewhakaaitu at Homestead Arm Volume m3 x 10^6 Figure 81 Lake Rerewhakaaitu Volume Hydrograph

Lake Level and Volume Summary of the Rotorua Lakes Internal Report 2004/08 Environment Bay of Plenty 81

13.7 Lake Volume Distribution

54 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 Fraction of time volume is equalled or exceeded site 1015310 Lake Rerewhakaaitu at Homestead Arm Volume m3 x 10^6 19530101 000000 to 20031231 240000 Figure 82 Lake Rerewhakaaitu Volume Distribution

Table 41 Lake Rerewhakaaitu Volume Exceedance Percentiles

Exceedance percentiles From 19530101 000000 to 20031231 240000 Volume (m3x106) % 0 1 2 3 4 5 6 7 8 9 0 65.86 65.43 65.15 64.93 64.76 64.61 64.46 64.35 64.20 64.11 10 64.03 63.95 63.88 63.80 63.73 63.66 63.59 63.52 63.48 63.42 20 63.39 63.33 63.28 63.19 63.14 63.08 62.98 62.91 62.83 62.72 30 62.64 62.57 62.50 62.43 62.32 62.20 62.06 61.96 61.81 61.64 40 61.48 61.35 61.22 61.04 60.84 60.71 60.60 60.53 60.45 60.43 50 60.38 60.29 60.20 60.14 60.06 59.98 59.85 59.79 59.72 59.66 60 59.59 59.52 59.45 59.38 59.30 59.24 59.17 59.06 58.97 58.91 70 58.86 58.80 58.71 58.66 58.60 58.53 58.42 58.33 58.22 58.08 80 58.01 57.95 57.88 57.81 57.72 57.64 57.57 57.50 57.43 57.34 90 57.26 57.17 57.05 56.91 56.65 56.37 56.09 55.80 55.29 54.61 100 54.06 Values in the exceedance table are not exact. They are good approximations based on linear interpolation of 2000 classes.

Internal Report 2004/08 Lake Level and Volume Summary of the Rotorua Lakes 82 Environment Bay of Plenty

13.8 Lake Volume and Rainfall

70 2000

68 1800

66 1600

64A 1400

62 1200

60 1000

58 800 A B 56 600

54 400

52 200

50B 0 19521201 5801 6401 7001 7601 8201 8801 9401 0001 YYMM B A site 1015310 Lake Rerewhakaaitu at Homestead Arm Volume m3 x 10^6 B site 861204 Kaituna at Whakarewarewa Rainfall mm/3mths (Total=74637) Figure 83 Lake Volume and Seasonal Rainfall Totals

70 1000

68 900

66 800

A 64 700

62 600

60 500

58 400 A

56 300

B 54 200

52 100

50B 0 19530101 5901 6501 7101 7701 8301 8901 9501 0101 YYMMB A site 1015310 Lake Rerewhakaaitu at Homestead Arm Volume m3 x 10^6 B site 861204 Kaituna at Whakarewarewa Rainfall mm/mth (Total=74044)

Figure 84 Lake Volume and Monthly Rainfall Totals

Lake Level and Volume Summary of the Rotorua Lakes Internal Report 2004/08