OUPUC~)E o1 ~&M3 2005 1----:-:--:-----... -.... --....; Ministry of Justice Wai 1200 #1 35 WELLINGTON Lake Taupo Hydrology Review A Report Prepared for the Waitangi Tribunal July 2005 Drawn on 25-Jul-2005 10: 357.6 La e Taupo Lake Lev I Full Record 357.4 357.2 357.0 356.8 356.6 356.4 r­ III '"~ 356.2 III c: 15 356.0 r­ III ~ 355.8 r- ~ 1906 1926 1946 1966 1986 ~ 3 -- 82795 from 13-Jul-1905 00:00:00 to 09-Jun-2005 06:00:00 David Hamilton David Hamilton & Associates Ltd Consulting Engineers POBox 1420 Dunedin Phone: 64 3 454 3380 Fax: 64 3 454 3292 Mobile: 021 338555 Email: [email protected] David Hamilton & Associates Ltd Page 1 of61 1 August 2005 Lake Taupo Review Preface This report has been prepared by David John Hamilton. My academic qualifications are Bachelor of Engineering (Hons) (Agricultural) from the University of Canterbury and a post-graduate certificate in Engineering Hydrology from the University of New South Wales. I am the Principal of David Hamilton & Associates Ltd, a consulting engineering company based in Dunedin. I am a Fellow of the Institution of Professional Engineers New Zealand. I am a member of the International Water Resources Association, New Zealand Society on Large Dams, the New Zealand Hydrological Society and the NZ Institute of Agricultural and Horticultural Science. c I have worked in river and flood control, irrigation, engineering hydrology and water resources for 34 years. This work has included irrigation investigation, design and construction on the Lower Waitaki Irrigation Scheme (1969-1977) with the Ministry of Works & Development, 2 years as a water supply engineer in Apia Western Samoa (1977-1979), 4 years as Deputy Chief and then Chief Engineer at the Hawkes Bay Catchment Board (1979-1983), 6 years as Chief Engineer of the Otago Catchment Board (1983-1989), and 8 years as Director of Operations/Director Technical Services with the Otago Regional Council (1989-1997). I now operate my own consulting firm and act as a specialist consultant, in the natural C resource engineering area, based on my experience, to a range of public and private clients. Acknowledgements Data from NIW A and Opus was sourced with approvals from Genesis Power, Mighty River Power, Contact Energy and M-Co who are part funders for the hydrological information. David Hamilton & Associates Ltd Page 2 of 61 1 August 2005 Lake Taupo Review 1. Introduction The review of hydrology relating to Lake Taupo has been prepared at the request of the Waitangi Tribunal. This review does show that the average lake level since the control gates were commissioned in 1941 has been just under 50mm higher than the pre-control recorded mean. The maximum level since 1941 has not reached the natural recorded leveL The current mode of operation is now relatively close to the natural lake level fluctuation without reaching the very high levels. There was however a period during the 1940s and 1950s when the lake was operated at significantly higher levels for extended periods. Lake Taupo is a large lake in a basin that was formed by volcanic eruption. The area is still active tectonically. The catchment area has been subject to changes in land cover through the action of nature and the actions of people. Hydroelectric power development saw the construction of outlet control gates in 1941 and the diversion of headwaters of the Whanganui and Rangitikei Rivers through the Tongariro Power Development in the 1970s. This report aims to provide an audit of the evidence provided to the Tribunal concerning the impacts, if any, of the control of the level of Lake Taupo from the time of establishment of the control gates to the present. Impacts on adjacent lands and waterways are included. In order to do this source material and data relied on have been reviewed. In order to assess the changes that have occurred through the introduction of hydro­ electric facilities at the lake outlet and affecting the catchment, it is important to also understand the nature of other factors that may have impacted over the same time. 2. Catchment 2.1 Area The Lake Taupo natural catchment is 3289 km2 in area. This is the upper part of the Waikato River catchment that has a total area of 14,258 km2 and is the largest in the David Hamilton & Associates Ltd Page 3 of 61 1 August 2005 Lake Taupo Review North Island. The Lake Taupo catchment drains parts of the Volcanic Plateau from Ruapehu (2797m asl), Tongariro (1967m asl) and Ngaruhoe (2287m asl) as well as the Kaimanawa Ranges (generally 1500-1600m asl), and the eastern slopes of the Hauhungaroa Ranges (generally 800-900m asl) (Purerora Forest Park). The average lake level is RL 356.7m above mean sea level (Moturiki datum). 2.2 Lake Lake Taupo was formed by a major eruption about 22,000 years ago, the Oranui Eruption [Hancox, #H31, paras 4.4-4.8]. The Taupo Eruption of 181 AD emptied Lake Taupo and deposited Taupo Pumice Ignimbrite radially around the vent. After this eruption Lake Taupo refilled to about 34m above present lake level (~390m). This developed a high alluvial terrace. The Waikato River scoured the barrier outlet ( about 30 years after the eruption and released a large flood down the Waikato River. Lake Taupo's surface area is 611 km2 or 18.6% of the overall Lake Taupo natural catchment area. This is a high proportion of lake area to catchment area. As a result the lake has large balancing influence through: • Reduction of flood peak flows through the lake storage slowing down the rate of outflow • Maintaining higher outflows when inflows are low. These characteristics are common to most large lakes but the high proportion of the catchment as lake means that these characteristics are amplified or more significant for Lake Taupo, and can occur over a relatively small range of water levels. ( The minimum lake level on record (1905-200S) is 35S.772m and the maximum lake level on the continuous record is 357.723m, giving an overall range of 1.951m or just under 2.0 metres. Based on average flows the lake has a volume equal to 13.S years of flow under natural conditions. This same volume now equates to about 10.S years including the additional Tongariro Power Development diverted water. The active volume over 2 the last 100 years is the surface area times the operating range or 611 km x 1.951 = David Hamilton & Associates Ltd Page 4 of 61 1 August 2005 Lake Taupo Review 3 1192 Mm . The normal operating range in terms of the Mighty River Power consents is now 357.25-355.85=1.4m, although flood storage up to 357.387m or greater can be utilised. 2.3 Geology Hancox [#H31, sections 2 & 3] describes the active Taupo Volcanic Zone that includes volcanism, high crustal heat flow (geothermal and volcanic activity), active normal (extensional or pull apart) faulting and ongoing tectonic deformation, and numerous shallow earthquakes. The ranges of older greywacke rocks border the taupo Volcanic Zone, with the Hauhungaroa Range located to the west, and the Kaimanawa Mountains to the east. There are many volcanic deposits in the catchment that are soft and unconsolidated. These deposits include pumice gravels and breccias derived from the 181 AD Taupo eruption. Brown ash and pumice \ gravels have also been derived from Mt Ruapehu and Mt Ngaruhoe in the upper catchment area. ·2.4 Soils As there is very little clay in the soil parent materials to provide cohesiveness, the pumice and ash soils are extremely fragile and prone to severe gully, sheet, rill, . streambank and wind erosion. 2.5 Land Cover Figure 2.1 shows the land use within the total catchment area of lake Taupo including the lake area. This data is sourced from Environment Waikato. Indigenous forest at 21 % is larger than the lake area (18%), pasture (17%) or plantation forest (17%). The changes in land use since 1840 are presented in the next section. David Hamilton & Associates Ltd Page 5 of 61 1 August 2005 Lake Taupo Review Bare ground/lava/quarry 4% Tussock Urban Settlement 5% 5% Wetland 1% Indigenous forest 21% Scrub/shrubland 12% ( 18% Planted forest 17% Figure 2.1: Laud Use Taupo Catchmeut (2000) 2.6 Rainfall The seasonal pattern of rainfall is shown as Figure 2.2. This is copied from Figure 4.2, "Waikato Catchment Hydrological Overview" prepared for Mighty River Power Ltd by NIWA and Opus, May 1999. These show average rainfall as generally higher in the winter. High monthly totals can however occur at any time of year. ( David Hamilton & Associates Ltd Page 6 of 61 1 August 2005 Lake Taupo Review 60.0 s.oo e ~oo ! ':iiio · : : f: . : . :': : :{::.' : : :: : :. ': : : t' : : :1:" : . :t: .: : :: ::f: . 'if I'~" , "1',0, :~:: , .' . ·c or.; 200 ...... ••·.·.C •••••••••.•.•• ·: •••••• ' .•• , .................. ~ · .....•.••.• : •.~ .... , .••.••.•.••.•...• ,••••...• "! ••. '. 100 . ,.. ',10 10 () Jan feb Mar Apr May Joo Jtil. Aug Scp Oct Nov Dec (i) Mt.Ruapehu, Chateau.(C9.5152); p'eriod: 3/9/Si to 3'111/98 900 800 · ......• '" • - - , . - , - - •. , .. " •.. , - , • , ,. , , •. , 'r"' , - .. - - - , , 70.0 .......... " ............. ", ................... ; .... - ...... , ....................................... .. E 600 ............................' ...................... ".... -" ...................... " .................. .. ! 500 ·3 40.0 '. r' , •.•.•• - ..• , • , , ....••• 't. ' ., ... i<' , , ' .• , .. , , •• , , , , . , .::<: 300 ~ ~ 'f .- .. ... .,. '" I- ,... ,- 'f' ..... 200 , .... ". .. -I ', 10.0 ~ ::: :::;:::::::: : : : : ; : : : ~:: ::::::::::::: : : : : 0 • • .' , .., 1 , , • • Jan Feb Mar Apr May lun Jul Aug Sop Oct Nov Dec (ii) Tongariro Hatchery (C9S0B1), Period:. 3/4129 to 3111/98 250 2.00 , . • . .. .r, . , . , . , . .... r' • . , • • . • . r', • • • .. , .. E 3 150 :§ 10.0 'r" 'r' ...... ,.. '1' . e: ...... I····'· .I' .............. or; ~ 50 ••.••••• :::::1:1::·::: ::::: :::I::. 0 • 10 • .•••• Jan Feb Mar Al'f May Joo lui Aug Scp Oct 'Nov Dec (iii) RlIinbowPoirit (BB6703), Period: 3/9/78 to 3111/98 Figure 4;2 Waikato Catchment ~ Minimum, Mean and Maximum Monthly Rainfall Figure 2.2: Monthly Rainfalls at Chateau, Tongariro Hatchery ) and Rainbow Point 2.7 Wind Data is available for the daily wind run at Taupo Airport.