CASE STUDY: Where would you have put the ? Where would you have put the dam? The history of water supply on the Central Coast.

Regional News, Dungog Chronicle Wednesday 11 July, 2007

New pipeline for Central Coast

The ‘No Tillegra Dam Group’ has welcomed the announcement … to fund the Mardi Dam to transfer pipeline on the Central Coast…

The ‘missing link’ Mardi to Mangrove transfer pipeline will secure water supply for the Central Coast well beyond 2050, according to the Gosford Wyong Authority (GWWA) in its most recent Waterplan 2050.

Chairman of the ‘No Tillegra Dam Group’ Warwick Thomas said … “We have constantly stated that there were more cost effective ways of overcoming the water shortage problems on the Central Coast, other than building the $340 million plus dam at Tillegra…”

Plate 1: Mangrove Creek Dam; Plate 2: Mangrove Creek Dam; dam Plate 3: Mangrove Creek Dam; water below the wall. (Wyong Council) storage. (Wyong Council) tower. (Wyong Council)

NOT HERE, PLEASE

Dam construction is almost always a controversial and emotive issue.

As a means of ensuring urban water supplies, the building of a dam to capture and store surface runoff from a catchment is nearly always cheaper than other options such as desalination of sea water or recycling treated wastewater. On the other hand, building a dam locks up the catchment, preventing many other forms of land use for the indefinite future. Furthermore, a dam has a wide range of environmental impacts (some good, some bad) on the catchment, both above and below the wall. Unless, as rarely happens, the dam is intended to occupy an uninhabited locality, the decision to build is often at the expense of existing land holders and their ways of life.

These issues apply not only to dam-building but to the provision of the whole gamut of infrastructure – water treatment plants, , pipelines etc concerned with providing clean water supplies for human populations.

CASE STUDY In this Case Study we will explore the decision-making processes involved in the provision of water supply. We will use the history of the development of the water supply on the Central Coast, particularly the construction of the Mangrove Creek dam, as an example of the research, planning, and political debate required to decide between competing priorities in the supply of this most precious of our resources – clean, fresh, H2O.

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CASE STUDY: The History of Water Supply on the Central Coast

1. The current Central Coast Water Supply System

What is the structure of the current Central Coast water supply system? Gosford City and Councils share a joint water supply scheme administered by the Gosford/Wyong Council’s Water Authority. This is the third largest water supply system in NSW.

Water is drawn from four streams (Mangrove and Mooney Creeks in Gosford and and in Wyong). The building of water storage infrastructure was begun 75 years ago, but most infrastructure used today was completed during the past thirty years.

Currently, the system incorporates three , three weirs, two treatment plants, 40 reservoirs, and 1900 km of pipelines. It has a total catchment area of about 10,000 hectares or 100 square kilometres. Water is drawn from Mooney Dam and weir pools on Wyong River, Mangrove Creek and Ourimbah Creek. Wyong River and Ourimbah Creek extractions are stored in Mardi Dam. During dry periods, when the Coastal Mooney and Mardi Dams cannot meet the demand for water, supply can be released from Mangrove Creek Dam to provide adequate inflows at the weirs on Mangrove Creek and Wyong River.

Before being delivered to the community the “raw” water is treated to produce a water quality that complies with the high standards of the NHMRC/ARMCANZ Australian Drinking Water Guidelines – 1996. The JWSS has two water treatment plants, one located at Somersby in Gosford City and the other at Mardi, in Wyong Shire.

(Gosford Wyong Councils’ Water Authority)

Figure 1: The Current Central Coast Water Supply System (Gosford Wyong Councils’ Water Authority)

QUESTION: Think about the water that flows so freely from our tap and that so often we take for granted. What do you think are the most important general issues that Water Authorities over the years have had to consider in providing our houses with piped water? List four of these.

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CASE STUDY: The History of Water Supply on the Central Coast 2. Historical development of the Water Supply System

Below is a brief history of the development of Water Supply on the Central Coast. This, together with the tabulated summary in Appendix 1 can be used to construct the Timeline on Page 3.

Outline of the development of the Central Coast Water Supply System.

Plate 4: Aboriginal grinding grooves in a tributary of Bucketty Gully. Attenbrow (2004) in ‘Terra Australis’ 21.

For thousands of years, Aboriginal people on the Central Coast relied on the fresh water resources of natural rivers, creeks and water holes within the Gosford Wyong region. Europeans moving into the area two centuries ago tended to build their settlements close to those same natural water supply points. As settlement expanded out from these surface water sources, they were supplemented with water from dug wells and household tanks. It wasn’t until 1929/1930 that the first centralised water supply system was implemented for the town of Wyong. A concrete-lined was constructed on Chapman Hill and water was pumped to it from the Wyong River for distribution to the residents. In 1938, town water came to Gosford, when the Mayor turned on the new water supply direct from a dam on the lower reaches of . Piping water to the northern areas of the Wyong Shire began in the 1950s. In 1960, the first stage of the Entrance Water Supply Scheme commenced. Officially opened in 1965, the expanded scheme eventually provided reticulated water throughout much of the Shire. A new dam on Mooney Mooney Creek (4600 ML) was built in 1961 to replace the old one further down the creek. A year later Mardi Dam (7400 ML) and Wyong River Weir were completed. A weir across lower Mangrove Creek was built in 1975. As dependence on these centralised facilities increased, it became more and more important that the raw water from them be treated to guarantee standards of public health. In line with this, Somersby Water Treatment Plant was constructed, the first stage in 1971 and a subsequent stage in 1986, resulting in a maximum production rate of 140 megalitres per day. In Wyong Shire, the first stage of the Mardi Water Treatment Works was opened for use in 1984 with subsequent augmentation in 1992 providing a maximum production rate of 160 ML per day. These developments in infrastructure were matched by improvements in management of the system. In 1977 Gosford and Wyong Councils entered into an agreement (the Gosford and Wyong Council Joint Water Supply Agreement) to construct, operate, maintain, and share costs of the water supply headworks. This agreement was administered by the Gosford/Wyong Joint Water Supply Committee. Under this agreement Councils and NSW Department of Public Works completed construction of a major storage dam on Mangrove Creek in 1982. This dam was an eighty feet high, rock-filled wall with a storage capacity of 190,000 ML. Provision was made to increase the height by 25 meters to a total capacity of 420,000 ML if the need arose. In 1989 an 11km tunnel linking Mangrove Creek Dam and Wyong River was completed. This tunnel enables transfers of water from the dam to Wyong River for later extraction at the Wyong River pumping station and weir (for pumping to Mardi Dam storage). Over the next two decades, this Joint Committee evolved into the Gosford/Wyong Councils’ Water Authority with an independent Chairman overseeing the management of the Joint Water Supply Scheme (JWSS). Since 1992 a severe has impacted the Central Coast. This has required implementation of a comprehensive drought management strategy by Councils. One outcome has been WaterPlan 2050 - a detailed program to expand supply and reduce per capita demand to ensure future needs are met.

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CASE STUDY: The History of Water Supply on the Central Coast 3. Timeline of development of the Central Coast Water Supply

ACTIVITY: Construct a timeline of the events outlined on the previous page using the Table below. The table below carries a list of dates in the left hand column. The right hand column contains a set of images with their matching descriptions, but the order of the events has been scrambled. Try to match the events to the listed dates. (You may like to use the template in Appendix 2, and paste photocopies of the events in the appropriate blank cells of the Table.)

Date Scrambled historical events in the development of the water supply

First stage of the Mardi Water Treatment Plant constructed. 1930 (The second stage was completed in 1994.)

Construction of the large Mangrove Creek storage dam completed. This dam stores 190,000 megalitres and is the main Central Coast water storage. Seven years later an 11km tunnel linked Mangrove 1961 Creek Dam to Wyong River .The tunnel enables transfers of water from the dam to Wyong River for later extraction at the Wyong River pumping station and weir (for pumping to Mardi Dam storage).

1962 The Entrance Water Supply System completed.

Wyong and Gosford Councils adopted the WaterPlan 2050 strategy designed to ensure adequate water supplies on the Central Coast for 1965 the next 50 years. A key part of this strategy is the Mardi to Mangrove Dam Pipeline which will be completed by 2010. Other parts of this strategy will be constructed progressively over the next 50 years.

Water pumped from Wyong River to a small reservoir on Chapman Hill 1971 for delivery to Wyong residents through a network of pipelines.

Upper Mooney Mooney dam was completed. This dam replaced the 1982 Lower Mooney Mooney Dam which had been constructed in 1937.

1982 & First stage of the Somersby Water Treatment Plant constructed. 1989

Completion of Mardi Dam and Wyong River Pumping Station and 2007 associated weir.

(Images: Wyong Council) OPEN-ENDED QUESTION: Over the years, Central Coast residents have often heard opinions expressed that Mangrove Creek Dam was an unnecessary expense or that it was built in the wrong place. Examine the information in Appendix 1 and see if you can identify the contribution that Mangrove Creek dam makes to the provision of a safe clean water supply on the Central Coast.

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CASE STUDY: The History of Water Supply on the Central Coast 4. Choosing a dam site – criteria for selection

General Considerations in the Selection of a Dam Site Choosing an optimal location for a dam, involves complex physical, environmental, financial and social considerations. The most obvious physical considerations include:

• proximity of the site to the place where the water will be used i.e. to population centres; • sufficient land area available for a large dam to be built; • a pristine, clean catchment where the land is preferably undeveloped and uninhabited • a sufficient water supply (i.e. enough rain within a large collecting area) under both normal and drought conditions; • preferably, a rock foundation – alluvial areas with a sandy base (such as coastal areas) are not desirable for dam construction because of the huge weight of the water it has to hold; • fresh water quality - building a dam too close to the coast could risk a salty supply; • a deep, natural V-shaped valley - flat areas would require major excavation and hold only a relatively small amount of water; • access to suitable land for supporting infrastructure to treat and transfer the collected and stored water to where it is needed.

ACTIVITY: 1. Examine the six locations portrayed in the following photographs. Using your own judgement, rank the six locations from most suitable to least suitable as potential sites for a dam.

Plate 5: Site 1 Plate 6: Site 2 Plate 7: Site 3 (www.greendiary.com) (Graham Eagleton) (R. Fensom)

Plate 8: Site 4 Plate 9: Site 5 Plate 10: Site 6 (www.devilcatboats.com.au) (www.adunk.ozehosting.com) (Graham Eagleton)

2. Now write a brief paragraph explaining the reasons for the ranking that you have chosen - i.e. outline the criteria you used in arriving at this ranking.

In the next few pages we will consider how these and other criteria were assessed during the decision making processes that led thirty years ago to the construction of a major storage dam on the Upper Mangrove Creek Catchment.

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CASE STUDY: The History of Water Supply on the Central Coast

5. History of the Mangrove Creek Dam – an opinion!!

A Weblog contribution posted by Rog 14 November 2005

“On the Central Coast, Wyong Shire has the Mangrove Creek Dam which is situated in a well known rain shadow area; Mardi or Ourimbah would have been much better. No doubt local politics came into play, Nimbys are everywhere. Mangrove dam has never ever been full, not even 50%. As a consequence the shortage of water is limiting growth so they are going to pipe some down from the Hunter (which fortuitously put its dams where it rains and has excess capacity). Development in the Hunter is going gangbusters. That’s democracy for you. “ (http://www.jennifermarohasy.com/blog/archives/001000.html)

ACTIVITY: Comprehension exercise - analysis of a media contribution. Carefully examine the above Blog contribution and then answer the questions below.

1. Which of the following alternatives do you think is closest to the overall intention of what the author is saying in this Weblog contribution? a. democracy is a good thing b. the Hunter region is going from strength to strength c. if political considerations had not been paramount, a dam would have been built at Mardi or Ourimbah rather than Mangrove Creek d. water is limiting growth

2. Which of the following alternatives is closest to the meaning of “rain shadow”? a. a shadow cast on the ground because of clouds blocking the sun b. a relatively dry region usually caused by it’s being sheltered behind a mountain with respect to the prevailing wind direction. c. a shadow cause by rain fall blocking the light of the sun d. a low light intensity area cause by a relatively wet environment

3. Which of the following alternatives is closest to the intended meaning of “Nimbys are everywhere”? a. wherever people are located, they are protective of their own interests b. the people of Nimby are popular and welcome all over the country c. No one Is welcome In My Backyard d. wherever people are located the health of the environment is the most important consideration

4. Which of the following alternatives is closest to the meaning of “fortuitously”? a. wisely b. with strength c. luckily d. with courage

5. Which of the following alternatives best describes the general purpose of the style of writing used in this Blog? a. to present an objective factual account b. to present an opinion aimed at persuading c. to present a balanced evaluation d. to present a poetic description.

6. What is your overall impression of what the author has said in this Blog?

Note: The issues raised in this opinion-piece will now be the subject of a detailed analysis in the rest of this case study.

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CASE STUDY: The History of Water Supply on the Central Coast 6. Geographical context of the Upper Mangrove Creek Catchment

ACTIVITY: On the map below, place the approximate positions of the following structures: Mooney Mooney Creek weir, Ourimbah Creek weir, Lower Wyong Creek weir, , . Appendix 3 has a larger version of the map.

Location of Upper Mangrove Creek Catchment

Figure 2: Location of Upper Mangrove Creek Catchment (Derived from Figure 1.1, Attenbrow, V., 2004. “What’s changing: population size or land-use patterns? The archaeology of Upper Mangrove Creek, Basin.” Terra Australis, No. 21, page 3.)

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CASE STUDY: The History of Water Supply on the Central Coast 7. Hydrological context of Upper Mangrove Creek Catchment

Thirty year ago, in the mid 1970s, after a detailed study of possible alternative schemes for ensuring the future water supply of an expanding Central Coast population, a decision was taken to build a large storage dam on the upper reaches of Mangrove Creek about 25 kilometres west of the town of Wyong. In the lead up to this decision, a thorough survey of the existing data regarding catchment areas, rainfall patterns and stream flow data was undertaken. In order to obtain a comprehensive picture of alternative water supply sources, streamflow data of varying quality and duration were considered from as many as 71 gauging stations ranging from beyond the Hunter in the north to as far south as the .

ACTIVITY: Examine the Table of data below together with the information in Appendix 4, both taken from “Hydrology” Volume 2 of Report 1 of “Report on Investigations for Water Supply to the Gosford-Wyong Region”, January 1975, Department of Public Works N.S.W., pp. 3-8. After reading this material, answer the questions following the table.

Table1: Physical and hydrological characteristics of streams in the Central Coast region of NSW, based on data available in 1975.

Stream Location of Catchment Approximate Estimated Start gauging area at average annual average annual of station gauge rainfall streamflow record ( km2) (mm) (106 cubic metres) Ourimbah Tuggerah 150 1270 35.6 1965 Creek Wyong Wyong 246 1156 48.2 1959 River Creek Mangrove Mangrove 202 1194 36.3 1970 Creek Mountain Mooney Mooney Mooney 39 1270 14.2 1965 Creek Dam MacDonald St. Albans 1735 890 150.1 1954 River Warkworth 1735 890 239.3 1908 Brook Colo Upper 4338 850 520.4 1909 River Colo

QUESTIONS: 1. Which of the streams listed receives the lowest average rainfall based on this data presented in 1975?

2. Based on this data presented in 1975, do you think it is reasonable to describe Mangrove Creek as being located in a “rainshadow”? Explain your answer?

3. Based on this data available in 1975, Ourimbah Creek has a higher yearly rainfall than , yet the estimated average annual streamflow at the gauging station is considerably greater than at the Ourimbah Creek gauging station. Can you give an explanation for this?

4. Quickly look through the information in Appendix 4 and then list three factors which you consider might have reduced the reliability of the data for “Estimated Average Annual Streamflow” listed in the above Table.

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CASE STUDY: The History of Water Supply on the Central Coast 8. Alternative scenarios for the Central Coast Water Supply 1975

Based on stream flow data, population growth predictions, and estimated water supply needs to meet this growth up until 2010, ten alternative long term water supply schemes were assessed in the 1975 investigations. The ten schemes were:

Table 2: Ten alternative Schemes evaluated in 1975 for their potential to meet the future water supply needs of the Central Coast

Scheme Principal infrastructure proposed 1. Mangrove Creek Dam Stge1, MacDonald River Weir, Mangrove Creek Dam Stge2 2 Mangrove Creek Dam Stge1, MacDonald River Weir, MacDonald River Dam (1200 ha) 3. MacDonald River Dam B (2920 ha) 4. Lower Mangrove Creek Dam, Jilliby Creek Dam, MacDonald River Dam A (780ha) 5. Mangrove Creek Dam Stge 1, MacDonald River Weir, Colo River and Webb’s Ck Weirs 6. Mangrove Creek Dam Stge 1, Wollombi Brook Weir, Mangrove Creek Dam Stge2 7. Extension from Supply with Transfer System developed in three stages 8. Extension from Newcastle Water Supply with Transfer System developed in four stages 9. Water Renovation - Mangrove Creek Dam Stge 2, Wastewater Reclamation 1& 2 10. Desalination – Desalination Stage 1 & 2

With the exception of schemes 7, 8 and 10, the different schemes called for construction of one or more dams in the region. Other infrastructural needs included extensions to the network of weirs, pipelines, pump stations and treatment plants.

ACTIVITY: Examine the Table of data taken from “Formulation and Evaluation of Alternative Schemes” Volume 1 of Report 1 of “Report on Investigations for Water Supply to the Gosford-Wyong Region”, January 1975, Department of Public Works N.S.W., p. 31.

Table 3: Comparison of alternative dam sites for the alternative schemes assessed in 1975

Potential Dam Catchment Average Annual Storage Cost Site Area Streamflow Capacity in 1975 $ (km2) (106 cubic metres/year) (106 ($M) Nov 1934 to 1904 to cubic metres) Feb 1942 1973 Jilliby Creek 32 0.8 6.6 Stge 1 127.3 9.4 Stge 1& 2 155.0 25.3 Lower Mangrove 231 10.9 40.3 Stge 1 14.5 3.8 Creek Stge 1&2 164.0 20.9 Mangrove Creek 101 4.8 17.7 Stge1 181.0 18.2 Stge1&2 455.0 28.6 MacDonald 1,248 6.7 103.5 Dam A 227.0 20.7 River 455.0 25.9 Dam B 886.0 33.7 Wollombi Brook 1,030 5.5 154.7 740.0 47.0 Colo River 4,560 79.3 588.5 455.0 65.0

QUESTIONS: 1. Considering the ten schemes listed above and the data in this Table, can you suggest reasons why the recommendation was given to proceed with the construction of Stage 1 of the Mangrove Creek Dam?

2. See if you can discover what is significant about the period Nov 1934 to Feb 1942. Why were the estimated average annual streamflows so low in those years? (Suggestion: The Bureau of Meteorology website might be of assistance.)

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CASE STUDY: The History of Water Supply on the Central Coast 9. The Mangrove Creek Dam – weighing up the alternatives

In considering how the decision was arrived at to build a dam on the Upper Mangrove Creek catchment, it is important to realise the following:

Some factors in the Mangrove Creek Dam decision.

1. The construction of a dam on upper Mangrove Creek was common to Schemes 1,2,5,6, 9 and10 but not Schemes 3, 4, 7 and 8 listed in Table 2. 2. Mangrove Creek Dam was proposed as a large storage dam not primarily a collection dam. Its catchment area (101 square kilometres) was relatively small but the shape of the valley and its geology enabled the construction of an 80 metre high wall that would store 181 million cubic metres of water (Stage 1). At a later date, the height could be increased, if required, by another 25 metres, increasing its total capacity to 455 million cubic metres (Stage 2). 3. The main source of water to fill the dam would come from the Wyong River catchment. Additional water would also be required from at least one external source i.e. outside these Gosford and Wyong catchments. To quote from the report (p 29 Volume 1): “In order to meet the assessed annual demand for the region…. of 111.2x 106 cubic metres per annum and considering the average streamflows from 1904-1973, it can be seen that it would be necessary to tap at least one of the major streams outside the Shires [or from renovation of wastewater (Scheme 9) or desalination (Scheme 10]…” 4. All potential schemes required additional preliminary works such as a low weir on Ourimbah Creek with a pipeline to Mardi Dam, interconnection of Wamberal and Bateau Bay reservoirs, and increased pumping capacity at Wyong River and between lower Mangrove Creek Weir and the Somersby Water Treatment Plant. With the exception of Schemes 4, 7 and 8, there would be need of a transfer system (pressure tunnel and other infrastructure) on the Upper Wyong River in order to deliver water into storage in the Mangrove Creek Dam whenever flows exceeded demand. There would also need to be a Wyong-Gosford transfer system. 5. At the time of the report, Schemes 9 (renovation of wastewater) and 10 (desalination) were evaluated as too costly. According to the report (p. 83 Volume 1): “The present costs associated with desalination are much greater than the costs of further development of surface water resources in the Gosford-Wyong region. The costs of water renovation to potable standards are also somewhat higher than utilizing further surface water sources and renovation also carries a considerable public health risk….However it is possible that technological progress over the next twenty years could make either process more practicable and as both possess considerable environmental advantages over surface water development it would be advantageous if the chosen scheme had sufficient flexibility to conveniently incorporate either desalination or renovation if required at a later date.” It is to be noted that construction of a Mangrove Creek dam was considered to be an integral part of each of these two Schemes.

QUESTION: Apart from the obvious criteria of streamflow, catchment area, construction feasibility and cost for a potential dam site, what other factors do you think need to be considered in deciding whether or not to go ahead with the construction of a dam in an identified location? List at least three distinct considerations not referred to in the above discussion.

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CASE STUDY: The History of Water Supply on the Central Coast

10. Geophysical aspects in planning for the Mangrove Creek Dam

When the ten alternative water supply Schemes were being evaluated in 1975, 23 possible dam sites were located in upper Mangrove Creek. The “Report on Mangrove Creek Damsites”, Department of Public Works, January 1974, noted “Boomerang Creek was set as the upper limit of a suitable damsite location. The Worley’s Creek damsite was set as the lower limit of investigation due to the difficulties of construction involved with the deep compressible alluvium associated with this site and expected to be encountered to an even greater extent down stream from this”. Of these 23 sites, five of were examined in detail from a geological, geotechnical and financial point of view and one was selected as the preferred site (see map below).

Upper Mangrove Creek catchment - geological map of the site proposed for the dam in 1974.

Figure 3: Upper Mangrove Creek catchment - geological map of the site proposed for the dam in 1974 (“Mangrove Creek Dam Investigations”, Volume 4, Report 1 of “Report on Investigations for Water Supply to the Gosford-Wyong Region”, January 1975, Department of Public Works N.S.W., Figure 3 (modified))

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CASE STUDY: The History of Water Supply on the Central Coast 11. Geology of the Mangrove Creek Dam site proposed in 1974

The principle of superposition in geology is a proposition based on observation of sedimentary rocks throughout the world: The principle states that Sedimentary layers are deposited in a time sequence, with the oldest on the bottom and the youngest on the top. The principle was first proposed by the Danish scientist Nicolas Steno in the 17th century.

ACTIVITY: Examine the geological map of the catchment on the previous page (i.e. page 11), together with the diagram in Appendix 5 and the information in the Table below. Then answer the questions that follow the Table.

Findings of the 1974 investigation into 23 potential dam sites on upper Mangrove Creek.

“Present worth analysis shows that the Mangrove Creek dam could be constructed at any one of several dam sites with little economic effect on the cost of the overall scheme. However Site 7 is slightly more economic at all discount rates and is the site preferred at this level of investigation for the construction of a high embankment dam by the Department of Mines geologist and the geotechnical consultants. This site has the narrowest valley and the least amount of alluvial material and, therefore, reduced unforeseen construction difficulties. It requires less catchment control for water quality purposes as little development has occurred to date on the catchment. Additionally, it has a smaller storage basin with less inundation of the attractive Mangrove Creek valley floor. The capital cost of the Stage 1 dam at site 7 is also the lowest of all the sites compared.”

Source: “Report on Mangrove Creek Damsites, Gosford-Wyong Water Supply” Report No 1 January 1974, Department of Public Works N.S.W.

QUESTIONS:

1. Of the geological formations within the Mangrove Creek catchment, which is the oldest, the ‘Hawkesbury sandstone’ or the ‘Narrabeen Group’? Explain your answer?

2. Within the ‘Narrabeen Group’ of rock strata, which stratum is the oldest, Unit ‘P’ or Unit ‘B’ (examine the diagram in Appendix 5 to determine this)? If you happened to observe these geological formations in the field, describe what kind of differences you would expect to see between the rock layers in Unit ‘P’ and in Unit ‘B’?

3. For the purpose of constructing a dam, explain why each one of the following properties was considered an advantage in the preferred site: (a) it ‘ has the narrowest valley’ (b) it has ‘the least amount of alluvial material’ (c) it ‘requires less catchment control for water quality purposes”

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CASE STUDY: The History of Water Supply on the Central Coast

12. Social and Environmental Considerations in the decision to build Mangrove Creek Dam

Just as important as the geophysical criteria, were the potential environmental and social impacts of the proposed dam. Examine the summary of the Environmental Assessment below together with the data in Appendices 6 and 7.

Extracts from the preliminary Environmental Assessment for the Mangrove Creek Dam catchment reported in 1975

Existing Environment “Only 22.4% of the total area is suitable for agricultural clearing (i.e. area with slopes less than 20%) although much less than this has been cleared due to the relative inaccessibility of the terrain and the presence of infertile soils. Agricultural and grazing land use in the full … catchment area is restricted to the plateau regions …. and along the limited Mangrove Creek alluvial flats …. The dam site itself is in heavily timbered steep sandstone country.” Environmental Impact a. “Uncontrolled spill from the dam would be infrequent …After construction … only minimum riparian releases would be made downstream of the dam….As a result of the reduction in streamflow, there could be some marginal affect on the salinity of the tidal section of Mangrove Creek above its junction with the …” b. “Approximately 980 hectares of freehold land would be affected by water storage. This land is of minor importance for use in agriculture or grazing. 830 hectares of MacPherson State Forest would be affected…. 22x 106 tonnes of coal could not be mined, if mining were prohibited under stored water. This … represents about 3% of the total coal reserves in the … catchment” c. “The major effect [on flora] would be the area of vegetation to be cleared and flooded by the dam. As far as is known, there are no rare or endangered species in the area…. It is considered that there would only be minor effects on terrestrial vegetation down stream… The filling of the storage area would reduce the area available for terrestrial [fauna] but in its place would create additional aquatic environments and an assured supply of water for the wildlife…a detailed terrestrial fauna survey has not yet been undertaken …[this was subsequently carried out and reported in 1977, see Appendix 7]” d. “It might be considered that the replacement of the generally undeveloped valley by such a lake with deep clear water would add to the scenic qualities of the area. However, any aesthetic appeal would be diminished at times when the top water line receded …. The catchment controls [for water quality purposes] would place restrictions on use of the catchment area … water based recreation would not be permitted on the water stored ... The National Parks and Wildlife expects that a number of aboriginal sites would be found in the catchment area.”

Plate 11: Aerial view of catchment (Wyong Council) Plate 12: Dam wall (Wyong Council)

Source: “Potential Scheme Components” Volume 3 of Report 1 of “Report on Investigations for Water Supply to the Gosford-Wyong Region”, January 1975, Department of Public Works N.S.W. pp. 9-11.

QUESTION: Considering the statements in this general Environmental Assessment, what additional detailed investigations do you think might have been required to give confidence that the construction of a dam in this locality would not cause unreasonable bad social or environmental impacts?

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CASE STUDY: The History of Water Supply on the Central Coast 13. The Heritage Value of the Mangrove Creek Catchment

Before deciding to construct any major item of water supply infrastructure, we must weigh up the physical, environmental, social and economic benefits and costs. These considerations focus on the perceived needs of current and future generations. Just as important however, is the impact these decisions have on the heritage value of the region in which the infrastructure is to be built.

Plate 13: Abu Simbel, Egypt (Wikipedia)

Perhaps the best known example of this is the building of the Aswan dam in Egypt which inundated much of lower Nubia, displaced over 90,000 people, and would have drowned the famous Abu Simbel Temples had action not been taken to excavate and entirely relocate the temples during the construction of the dam.

When a dam was first proposed for upper Mangrove Creek, steps were taken to buy existing properties that might affect the closed catchment status needed to ensure water quality in the dam. One farm, “Fairview”, was resumed by Gosford Council in 1973. In recent years, the history of Fairview has been recorded in an effort to preserve the heritage of the area.

Brief history of “Fairview Farm” on upper Mangrove Creek. “Richard Woodbury was one of the earliest settlers in the upper valleys of the catchment in the area of Fairview … The Fairview property (then known as ‘Parks’) was purchased by John Martin Andrews (1834-1902) in 1872. It was previously occupied by Ester Park and her family who lived in a small hut on the property... Andrews married Sarah Craft (1838-1924) ... They built the first house and outbuildings ... Later they moved … and Alfred John Andrews (1860-1943) then took over the farm. Alfred and his wife Amanda … built the “Fairview” homestead to replace the original house…. Their son Stanley Andrews and his wife Hannah (nee Thompson) took over the property …. The property was expanded through purchase of additional land in 1899, 1909 and 1920. The property was sold to Donald and Annieles Crone in 1964 and was resumed by Gosford Council in 1973.” Based on the source: “Fairview Heritage Assessment” by Elizabeth Evans, 2006.

Plate 14: “Fairview” farmhouse located between Mangrove Creek dam and the Mangrove weir. ( “Fairview Heritage Assessment” by Elizabeth Evans, 2006)

ACTIVITY: Evaluation of arguments for and against a Controversial Issue Consult the following Website where arguments are presented (beginning on page 5) both for and against the long term preservation of the Fairview homestead http://www.gosford.nsw.gov.au/council/council_meetings/agenda_reports/2007/04/03/environ ment-and-planning.pdf Construct a table with columns “For” and “Against” the long term preservation of the farm buildings. List three arguments under each column. Now write a brief paragraph with your own judgement as to what should be done at the Fairview site.

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CASE STUDY: The History of Water Supply on the Central Coast 14. Prehistory of the upper Mangrove Creek Catchment

It is a little over two hundred years since the first European settlements were established on the Hawkesbury River catchment of which Mangrove Creek is part. When the Mangrove Creek Dam was first being considered in the mid 1970s, there was already awareness that the history of human habitation in the area was much older than that represented by sites like Fairview Farm. A team of archaeologists was brought in to uncover as much of the evidence of this prehistory as possible before it would be drowned by the rising waters of the dam.

Val Attenbrow was one of the team. Her report of the work carried out in the valley bottoms and then later in the entire catchment of the dam, revealed a fascinating pattern of human land use stretching over more than 10,000 years.

Archaeological sites from randomly sampled units within Upper Mangrove Creek catchment

Plate 15: Loggers shelter with archaeological deposit dating back to ca 11,000 BP. (Attenbrow (2004))

Plate 16: Grinding grooves at Sharp Gully: Scale has 1/5/10cm divisions. (Attenbrow (2004)) Figure 4: Archaeological sites from randomly sampled units within Upper Mangrove Creek catchment (Attenbrow, V., 2004. “What’s changing: population size or land-use patterns? The archaeology of Upper Mangrove Creek, .” Terra Australis, No. 21, page 79.)

15

CASE STUDY: The History of Water Supply on the Central Coast 15. More on the prehistory of Upper Mangrove Creek

ACTIVITY: Archaeologists used a carefully designed sampling procedure to obtain valid estimates of the intensity of land use over the past 12,000 years based on radioactive carbon dating. Examine the following diagram together with Appendix 8, which summarise some of the results of the investigation. Then answer the questions below:

The distribution of human habitations used in the upper Mangrove Creek catchment in each millennium (1000 year period) for the past 12 000 years, based on evidence from random sampling units of the archaeological investigation (Note: 12th Mill BP means between 12,000 and 11,000 years ago and 1st Mill BP from 1000 years ago until present.) Attenbrow (2004).

Figure 5: Prehistory of catchment (Attenbrow, V., 2004, Terra Australis, No. 21, page 133.)

QUESTIONS: 1. According to Appendix 8, what kind of climate existed in 4,000 years ago compared with today? How important would the water resources of Mangrove Creek have been to the aboriginal peoples of the area at that time?

2. By the time European settlers began to move into the area 200 years ago, do you think that these water resources would have been of greater or lesser importance to the aboriginal inhabitants than they had been 4,000 years ago? Explain your opinion in terms of the information presented.

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CASE STUDY: The History of Water Supply on the Central Coast 16. The Political Processes in the Mangrove Creek Dam decision

In Australia, there are three levels of Government responsible for decisions about water supply: Federal, State and Local government. In the case of the Mangrove Creek Dam decision in the mid seventies, Federal Government played only a minor role; it was mainly a matter for the NSW State parliament and the councils of Gosford and Wyong. Much of the debate occurred in the Chambers of the two Councils and amongst the public at large. Not everyone was happy about the decisions taken:

“Sir, Because of pressure from minority groups with a loud voice and a strong lobby, the proposal to dam the Colo River was abandoned…. The price for retaining this wilderness is now being paid by the people of the Central Coast who are desperately short of water….

(Letters to Editor, Sydney Morning Herald, 4 Oct 1980.) “Sir, There is no doubt that the Central Coast is desperately short of water, but I doubt the reason given …. is the cause….Planning for the Central Coast, urged on by local councils has stepped on the treadmill of development… Despite the deliberately encouraged expansion of industry and urbanisation, the Mangrove Creek dam is unfinished and still to demonstrate its capacity to satisfy the imaginations of developers…. so why blame the Colo wilderness enthusiasts?...

(Letters to Editor, Sydney Morning Herald, 14 Oct 1980.)

ACTIVITY: The Role of State Government Read the following account, along with Appendix 9. Then complete the activity below.

NSW State Parliament and the Mangrove Creek Dam decision • During the 1970s, investigations by the NSW Department of Public Works into the need for new water supply infrastructure and the planning for the possibility of a dam on the upper Mangrove Creek began during the period of the Liberal-Country Party governments of Askin (1965-1975) and Lewis (1975-1976) and continued in the period of the Wran Labour government (1976-1986). • Within State Parliament, one or two concerns were raised by individual members during the planning stages (see Appendix 9) but there was little substantial parliamentary debate concerning the various alternatives put forward by the Department Of Public Works. • Support for the decision by the Wran government to provide for construction of the Mangrove Creek dam appears to have been bipartisan - i.e. neither major parties nor minor parties were opposed to its construction according to the record of the parliamentary debates of the time. • On 14th August 1979, in his address to parliament, His Excellency the Governor, Sir Arthur Roden Cutler announced the appropriation of $25 million for a ‘dam on Mangrove Creek, near Gosford, for domestic water supply purposes’. The decision was met with approval by the opposition in parliament; the member for Young, The Hon. George Fraudenstein, representing the opposition, in his reply to the Governor’s address, noted: ‘the $25 million water storage at Mangrove Creek near Gosford is one of the really desirable developments mentioned in the Governor’s Speech.’ • By mid 1982, the dam had been completed and the Member for Tuggerah, Mr Harry Moore, representing the government benches, noted in parliament on 26 August: ‘At the foot of the ranges, we have the new Mangrove Creek dam … This dam has one-third the capacity of Sydney Harbour and it should ensure that in future we are not confronted by the dramatic situation of having to inform residents of drastic water restrictions. This was a joint venture of the Gosford City Council, the Wyong Shire Council and the State Government, at a cost of $56 million, $ 28 million of which was funded by the State Government for which I thank it.” (“NSW Parliamentary Debates”)

QUESTION - The Debate Assume that you were member of the NSW State Parliament in the late 1970s. Your task is to draft two “Questions Without Notice” to put to the Minister of Public Works concerning the planned Mangrove Creek Dam. One question should be written attacking the proposed dam. The other question should support the dam.

17

CASE STUDY: The History of Water Supply on the Central Coast 17. The Construction of the Mangrove Creek Dam

The preliminary work on construction of the dam started in 1977 “In 1975, after considering the Public Works Department report, the Gosford and Wyong Shire Councils adopted in principle, a joint water supply scheme [which involved among other things] “a large dam on the upper reaches of Mangrove Creek, providing the key storage. … In November, 1977, work started on the excavation of the diversion tunnel portals by ...Public Works. …After initial tree and overburden clearing, the siltstone rock was drilled and blasted before removal. During the period in which the tunnel portal excavation was being carried out, a contract was let to Bass Civil Engineering for construction of the diversion tunnel and another contract let to Goninans of Newcastle for the manufacture and supply of mild steel…”

Figure 6: (“Gosford-Wyong Water Supply; The construction of Mangrove Creek Dam Stage 1” Volume 1, Public Works Department, 1982.)

Figure 7: Initial design outline for Mangrove Creek dam ( “Report on Mangrove Creek Damsites, Gosford-Wyong Water Supply” Report No 1 January 1974, Department of Public Works N.S.W. (Note: These initial design concepts were amended in their details during the implementation phase.))

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CASE STUDY: The History of Water Supply on the Central Coast

18. The Grand Opening of the Dam

Over the next few years, requests for tender to supply and construct a wide range of components in the scheme were advertised in the media of the day.

“Department of Public Works NSW – Tenders invited” “Tenders are invited for the clearing of approximately 750 hectares of medium to dense forest within the Mangrove Creek Dam storage area…..” (The Sydney Morning Herald, Tuesday, 5 May 1980)

Plate 17 to 20: Men at work (Gosford Library - photographs by Denis Gibbons, NSW Department of Public Works)

The public were kept informed. Appendix 10 summarise the construction features of the dam.

“$13 m for Gosford Dam” “The Department of Public works has awarded a $13 million contract for the construction of a dam on Mangrove Creek, near Gosford to Citra Constructions Ltd. . .It will be completed in 1981.The first stage of the rock-filled dam will be 81.5 metres high…The wall will be the second highest in NSW for domestic water supply. The highest is Warragamba Dam.” Source: The Sydney Morning Herald, Tuesday, 3 July 1979 Dam nearing completion in October 1981

Plate 21 & 22: Dam near completion (State Library of ; GPO 3 – 37631, GPO 3 – 37644) “A $60 m drink for Sydney’s dry fringe” “In a bold attempt to resolve the water crisis in Gosford, the Public Works Department is building a $40 million dam across Mangrove Creek … Mr Alan Griffiths, the project’s resident engineer, says the new dam will be able to meet the needs of Gosford to the year 2000. By then the district is expected to have 400,000 people compared with the 150,000 it now has….The 160 workers who have been toiling six days a week to complete the project have placed the previously peaceful Mangrove Creek …on the tourist map…” Source: The Sydney Morning Herald, 24, March, 1981?

Eventually, on 19th July 1982, the Mangrove Creek Dam was officially opened by the Premier of NSW, The Hon. Neville Wran, in the presence of the Mayor of Gosford City, Ald D.E. Leggett, Mayor of Wyong Shire Council Cr F. N. Farrell and hundreds of others who had participated in its construction.

ACTIVITY: Speech! Speech! Assume that in 1982 you were a member of a community organisation on the Central Coast called upon to give a brief (5 minute) address at the opening of the Mangrove Creek Dam. Prepare a draft of the speech you would give to represent the feelings of local residents in the region on this important occasion.

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CASE STUDY: The History of Water Supply on the Central Coast 19. Forward Twenty Five Years

It is twenty five years since Mangrove Creek Dam was built. Although many developments have taken place in the Wyong-Gosford Water Supply System since then (Appendix 1), a number of possible additions to the system considered in the 1970s (e.g. Mangrove Creek Dam Stage 2, a dam on the MacDonald River) did not come to pass. There were good reasons for this:

• a lower human population growth than was predicted; • a reduction in average annual residential and per capita water consumption; • lower peak day water demands than were predicted; • higher than average rainfall experienced in the decade after dam construction.

ACTIVITY: The nature of Predictions Predictions are hypothesised outcomes about the future, based on what we already know. Examine Table 4 which shows predictions about population growth compared with actual outcomes of population growth on the Central Coast. Then answer the questions below.

Table 4 : Central Coast Population Growth – predictions and reality *

Year 1975 1985 2005 Range (lowest- highest) 1954 38,000 38,000 38,000 1961 53,000 53,000 53,000 1971 89,000 89,000 89,000 1981 150,000 -170,000 166,000 166,000 1991 240,000 - 290,000 248,000 240,000 2001 350,000 - 430,000 326,000 295,000(3) 2011 460,000 - 530,000(1) 390,000 330,000 2021 - 450,000(2) 370,000 2031 - - 405,000 2041 - - 445,000 2051 - - 480,000(4)

* Figures in bold are actual Central Coast populations taken from census data. Figures in regular type are predicted populations, based on trends at the time. The 1975 predictions show the range in expected outcomes - from the lowest estimate to the highest estimate. Sources: (1) Volume 1 of “Report on Investigations for Water Supply to the Gosford-Wyong Region”, January 1975, Department of Public Works N.S.W. (2) Summary Volume of “Report on Investigations for Water Supply to the Gosford- Wyong Region”, July 1985, Department of Public Works N.S.W. (3) “Central Coast: Regional Profile & Social Atlas”, 2004, p 38. (4) “Review of Scheme and Formulation of Options for Further Investigation”, March 2002, Gosford-Wyong Joint Water Supply Authority.

QUESTIONS: Compare the actual population in 2001 with the prediction made in 1975 for that year. What effect do you think this would have had on actual water consumption versus predicted water consumption for the Central Coast?

OPEN-ENDED QUESTION: Appendix 11 tabulates present day predictions about Central Coast water usage up to the year 2050. Do you think it is any easier in the year 2007 to predict the Central Coast’s population and water use forty years ahead than it was in say 1975? Why?

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CASE STUDY: The History of Water Supply on the Central Coast 20. Mangrove Creek Dam storage records

ACTIVITY: Storage levels in Mangrove Creek Dam Examine this graph which shows the levels of water storage in the dam since 1982 as a percentage of total dam capacity. Then answer the questions below.

Mangrove Dam storage in relation to rainfall received since 1982

Figure 8: Mangrove Dam Storage in relation to rainfall received since 1982 (Wyong Council)

QUESTIONS: 1. Describe the trend in the amount of rainfall received during the period 1982 to1992. What impact did this have on the amount of water stored in the dam?

2. The total storage capacity of the dam (i.e. if 100 % full) is 190,000 Megalitres. How many megalitres of water were stored in the dam in January 1990?

3. Describe the trend in the amount of rainfall received during the period 1994 to 2004. What impact did this have on the amount of water stored in the dam?

4. How many megalitres of water were stored in the dam in January 2006? If the daily demand for water on the Central Coast was 95 Megalitres per day, how many days storage were in the dam in January 2006 assuming no topping up.

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CASE STUDY: The History of Water Supply on the Central Coast

21. The Worst Drought on Record

During the late 1980s and 1990 Mangrove Creek dam filled rapidly during significant wet weather events. With lower than predicted demand and higher than average rainfall there was little perceived need to proceed rapidly in the construction of new large scale water supply infrastructure. If put to the test, public opinion at that time may well have regarded such expenditure as an unnecessary extravagance.

However, like human population growth, rainfall is a fickle thing. In the years since 1993, the Central Coast and much of the rest of Australia has experienced the worst drought on record as a result of 15 years of below average rainfall and stream flows (see Appendix 12). By mid February 2007, the amount of water stored in Mangrove Creek Dam had fallen to as low as 10.3%, and in the three storage dams taken together (Mangrove Creek, Mardi and Mooney Mooney), to 12.8% of capacity. As the crisis developed particularly over the period 2004 to 2007, the Gosford/Wyong Councils’ Water Authority responded step by step with a wide range of measures aimed at conserving water and exploring previously untapped water resources.

Actions taken to manage the drought 1. System Upgrades • increase in the capacity of Wyong River pump station • construction of a new transfer system from Mardi Dam to Mardi water Treatment Plant • construction of a new high lift pumping station to Mardi dam • raising the Mardi dam wall to increase its storage capacity • construction of a connection from the lower Mangrove Creek Weir to Mooney Mooney Dam 2. Reduction in Demand • stringent mandatory water restrictions • extensive community education (including a schools program) • provision of rebates for rainwater tanks, efficient washing machines and greywater systems • provision of subsidised REFIT kit (shower heads, tap aerators and toilet cistern weights) • increased use of stormwater, treated wastewater etc for sports fields and public facilities • active leak detection and water pressure management program • significantly reduced water use by Gosford City and Wyong Shire Councils 3. Accessing more Water • construction of the $37 million Hunter Connection able to deliver 30 ML drinking water /day • development of seven Central Coast groundwater bore fields - up to 9 ML drinking water /day • investigations into use of temporary mobile desalination units (“WaterPlan 2050 – A long term water supply strategy for the central Coast” Adopted Plan, August 2007, Gosford-Wyong Councils’ Water Authority. p 3.)

ACTIVITY: Responding to drought Visit the Gosford/Wyong Councils’ Water Authority website http://gwcwater.nsw.gov.au/ and click on Restrictions in the Menu, examine its content and then click on Rebates in the same Menu.

QUESTIONS: 1. What level of Water Restrictions affect householders in the Central Coast at the present time? List three specific restrictive measures that apply to your own household at the present time.

2. From the list of possible rebates that Central Coast households may qualify for, to reduce their water usage write down any that your household has actually taken advantage of. Then for each of the other potential rebates, write down the reason why your household may/may not wish to carry out the particular water-conserving practice that the rebate addresses.

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CASE STUDY: The History of Water Supply on the Central Coast

22. Waterplan 2050 – Lessons for the Future

What the twenty five years since the construction of the Mangrove Creek Dam have taught us, and especially the last fifteen years of drought, is that:

• an effective planning process is essential if adequate supplies of freshwater are to be made available for the needs of future generations; • this planning need to be flexible and be able to respond in a practical and cost- effective way to unpredictable changes in the trends of both water supply and water demand; • a renewed emphasis on self-help and the user-pay principle - with the return of household water tanks and of more carefully managed household water economies - promotes a more effective response to changing circumstances and fosters a sense of shared ownership of and responsibility for the plan; • local planning must be integrated with wider regional planning (in the case of Gosford and Wyong, this has taken the form of closer cooperation between the Central Coast and the Hunter River catchment authorities); • protecting the health of our catchments and of the wider environment is an integral component of a secure future for us all; • public education across all ages and sectors of society in ways of water wise living is essential to keeping per capita the demand for water within reasonable limits.

In response to these lessons, Gosford City and Wyong Shire Councils recognised the need for a more diverse water management strategy recognising both the supply and demand side of the water equation. There has also been a more genuine, formal process of community consultation in planning for the future. Community education campaigns have brought about a significant reduction in per capita water use within the region.

The fruits of these developments are to be seen in the recent production of “Water Plan 2050” - Gosford/Wyong Councils’ Water Authority’s “Long-term water supply strategy for the Central Coast”.

ACTIVITY: Mardi-Mangrove Link Visit the Gosford/Wyong Councils’ Water Authority website http://gwcwater.nsw.gov.au/ and click on WaterPlan 2050 in the Menu. (Note: you may then download and printout a pdf-file of the “Adopted WaterPlan 2050 Strategy (Oct 2007)” clicking on the relevant icon on this page.)

Once on the this page click on the Mardi-Mangrove Link icon in order to obtain the latest information about the importance of this Mardi to Mangrove pipeline in fulfilling part of the agenda of the WaterPlan 2050. Research the information on these pages and the Map reproduced in Appendix 13 and then answer the questions below:

QUESTIONS: 1. What is the purpose of the pipeline that is to be built from Mardi Dam to Mangrove Creek Dam?

2. How much is the pipeline and two new pumping stations expected to cost? When is it expected to be completed?

3. Give reasons why “Community Consultation” is an important part of the planning and implementation of the pipeline construction?

4. What demand management strategies will the Councils provide under WaterPlan 2050?

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CASE STUDY: The History of Water Supply on the Central Coast

23. PostScript Is Mangrove Creek Dam located in a “rain shadow”?

ACTIVITY: Analysing the Distribution of Rainfall Examine Table 5 showing rainfall data extracted from the Bureau of Meteorology records.

Table 5. Long Term Rainfall Records Location Years of Record Mean Latitude Longitude No. annual No. Name Period of rainfall 0 0 S E years total (mm) CD Chichester Dam 32.24 151.68 1942-2007 65 1309.7 OF Olney State Forest 33.10 151.25 1938-1967 28 1582.5 GD Glen Davis 33.12 150.25 1940-1969 29 633.6 NH Norah Head (Lt. Hs.) 33.28 151.58 1969-2004 35 1229.6 MM Mangrove Mountain 33.29 151.21 1994-2007 13 1014.7 OA Orange Airport 33.38 149.12 1968-2007 39 886.0 NA Narara 33.39 151.33 1916-2007 90 1311.6 RI Richmond (U.W.S.) 33.62 150.75 1881-2007 126 800.0 KA Katoomba 33.71 150.31 1885-2007 121 1397.3 (Bureau of Meteorology)

For each of the locations listed in the Table identify each location on the Map below. Use the code for each location to label its position on the map.

Figure 9: Locations of some rainfall record sites (Modified from Bureau of Meteorology)

Now, using a good atlas or an online mapping program such as Google maps, try to identify the geographical features of each location.

OPEN-ENDED QUESTIONS:

1. Is there any evidence that Mangrove Creek dam is located in a ”rain shadow” ?

2. In your opinion is this issue relevant to its current value as a storage dam? Explain your answer.

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CASE STUDY: The History of Water Supply on the Central Coast

APPENDIX 1: Table 6: Important Components of the Joint Water Supply Scheme up to the Year 2000 (see page 3).

Locality Asset Catchment area Capacity/size Year and % of total and % of total Mangrove Mangrove Creek dam 101 sq km (14%) 190,000 ML (93.7%) 1982 Creek Mangrove Creek weir 140 sq km (20%) 300 ML (0.15%) 1975 Pumping station 73 ML/d 1975 RM to Somersby WTP 18 km x 900 mm pipe 1975 Balance Tank 13.5 ML 1975 PS Amplification 142 ML/d 1986 Boomerang Creek tunnel 11 km x 3000 mm tunnel 1989 Wyong Lower Wyong River weir 355 sq km (49%) 300 ML (0.15%) River Pumping station 53/72 ML/d Mardi dam (off-stream) 7,400 ML (3.65%) 1962 Mardi dam upgrade 0 ML 1989 Mardi Water Treatment Plant 80 ML/d 1982 Water Treatment Plant Stage 2 80 ML/d 1994 Transfer system to Mardi WTP 100 ML/d 1982 Ourimbah Upper Ourimbah Creek weir 88 sq km (12%) 45 ML (0.05%) 1982 Creek Pumping station 39/56 ML/d 1988 RM to Mardi dam 5km x 600 mm & .6km x 1600 mm 1982 Lower Ourimbah Creek weir Salt water barrier – no storage Mooney Mooney Creek dam 39 sq km (5%) 4,600 ML (2.27%) 1960 Mooney Somersby Water Treatment Plant 73 ML/d 1971 Creek Water Treatment Plant Stage 2 67 ML/d 1986 Main from WTP to Kariong Res. 73 ML/d 1975 Kariong Reservoir No. 1 9.1 ML 1973 Reservoir No. 2 50 ML 1986 Tuggerah Link Main from Mardi WTP 1986 Reservoir No. 2 40 ML 1986 Link Main from Kariong Res. 17 km x 1050/900/750 mm 1986 Bateau Forrester Beach Pumping Station 20 ML/d 1987 Bay Bateau/Wamberal Transfer Main 10 km x 450 mm with flow meter 1984

(Source: “Technical Overview of Gosford-Wyong’s Joint Water Supply Scheme.“ (Technical Overview of the twelve volumes of the NSW Department of Commerce’s review Of the JWSS and Future Options Report) 2003, page 5.)

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CASE STUDY: The History of Water Supply on the Central Coast

APPENDIX 2: Table 7: Blank template for the Time Line of the Central Coast Water Supply (see page 4).

Date Historical events in the development of the water supply 1930

1961

1962

1965

1971

1982

1982 & 1989

2007

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CASE STUDY: The History of Water Supply on the Central Coast

APPENDIX 3: Larger version for the map locating the Upper Mangrove Creek Catchment in context. (see page 7).

Figure 10: Upper Mangrove Creek Catchment (Derived from Figure 1.1, Attenbrow, V., 2004. “What’s changing: population size or land-use patterns? The archaeology of Upper Mangrove Creek, Sydney Basin.” Terra Australis, No. 21, page 3.)

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CASE STUDY: The History of Water Supply on the Central Coast

APPENDIX 4: Extracts from pages 3 to 8 of “Hydrology” Volume 2 of Report No 1 of the Gosford-Wyong Water Supply Project Section entitled “Report on Investigations for Water Supply to the Gosford-Wyong Region”, January 1975, Department of Public Works N.S.W. (see page 8)

2. REVIEW OF HYDROLOGICAL DATA 2.1. INTRODUCTION The principle streams in Gosford and Wyong Shire comprising Wyong River, Ourimbah Creek, Mooney Mooney Creek as well as major rivers in neighbouring catchments comprising the MacDonald River, Colo River and Wollombi Brook have been considered as potential sources for supplying water to Gosford and Wyong Region....

The following review of hydrological data is therefore discussed from this viewpoint: • The reliability of recorded streamflow at the potential source stream. • The duration and reliability of streamflow data utilized for extending recorded streamflow at the source of the streams. • Rainfall data which may be used to provide an index of catchment rainfall for use in estimating catchment streamflow. • Evaporation data to provide an estimate of catchment evaporation for use in estimating streamflows. 2.2. STREAMFLOW ... The following factors are common to all stations and result in inaccuracy in the recorded streamflow: • Infrequent stream gauging (average of once per two months or less). • Nil or very few gauging at high flows. • Missing records due to discontinuous reading of staff gauges and to failure of recorders (almost invariably pressure recorders). • Changing control at the gauge site. The extent to which a particular gauging station has been affected by the above factors will greatly influence the accuracy of a recorded streamflow…. 2.2.2 Stream Gauges in Gosford and Wyong Shires a) Wyong River Wyong River is the principal source in Gosford and Wyong Shires and flows have been recorded at the following locations: Wyong Creek - May 1959 to May 1966 - Staff gauge, catchment of 246 square kilometres, very few missing months. Wyong Weir - June 1966 to December 1971- float recorder, catchment of 356 square kilometres, few missing records. Collapsible gates installed on Wyong Weir in 1971 have made this gauge suitable only for recording large floods. Gracemere - December 1972 to date -.dulpex pressure recorder, catchment 236 square kilometres, no missing records. The value of the Wyong River stream gauging has been diminished by the necessity to relocate the gauging station i.e. estimation of flow from one gauge to another has introduced an .additional uncertainty. The relocation of the gauging station in the middle of the severe 1965-66 drought was particularly unfortunate and the 8 months of missing record in 1965 result in a loss of extremely valuable information. If this record were available it would be possible to be much more confident about any subsequent streamflow estimates because of the severity of this 2 year drought which was the most severe recorded in many coastal streams in N.S.W.

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CASE STUDY: The History of Water Supply on the Central Coast APPENDIX 4 continued:

b) Ourimbah Creek The Ourimbah Creek gauge is a float recorder with a catchment of 150 square kilometres, and has been operating continuously since October 1965. This is a relatively accurate stream gauging station and the main disadvantage is the short length of record available at the time of analysis (until 1971) and the fact that the record did not include a long, severe drought. c) Mangrove Creek October 1970 to date - pressure recorder, catchment of 202 square kilometres no missing records. The station has been gauged very extensively and although there have been substantial shifts in the alluvial control, the recorded flow is considered accurate and the main disadvantage is the extremely short duration of recorded flow. d) Mooney Dam An operational record has been kept at Mooney Dam from March 1965 to February 1968 on a weekly basis. Unfortunately, the early part of the 1965-66 drought was missed and it is considered that the operational record is only effective when water level in the dam is several millimetres below the spillway as the weekly record is inadequate for estimation of overflows. From 1968 a daily operational record has been kept and this has provided much better estimates of streamflow into the dam, although the record is still doubtful when the dam is overflowing by more than about 50 millimetres. 2.2.3 Major Rivers a) MacDonald River The MacDonald River is the nearest major source to Gosford and Wyong Shires with a catchment area of 1 735 square kilometres at St. Albans. A staff gauge has been installed since October 1954, but there are long periods of missing records especially during 1954-57 and 1960-61. A servo manometer pressure recorder was installed in 1969 but considerable records have been lost since this date due to failure of the recorder. There has been very little gauging of high flows on the MacDonald River, making high flow values questionable. b) Colo River A staff gauge was installed on the Colo River in 1909; however, it was closed during the depression years and lost the extremely severe 1935-42 drought. c) Wollombi Brook A staff gauge has been installed on the Wollombi Brook at Warkworth since 1908. The catchment area is about 1 735 square kilometres and there is a large missing period during 1950-1954. 2.2.4. Other Stream Gauging Stations The other stream gauging stations were utilized to extend the streamflow records of the potential source streams using multiple regression techniques. Where a choice was available, the more accurate stations where utilized· in the regression analysis with preference being given to stations with long continuous records. 2.3. RAINFALL The rainfall data.... was utilized for estimating a catchment rainfall index for streams in Gosford and Wyong Shires and for the MacDonald River. Very few rainfall stations with long records were found within the catchments and the Thiessen method or similar was used to estimate the catchment rainfall, usually from 2 or 3 stations close to the catchment boundary. Rainfall records in Gosford and Wyong Shires were checked using Double-Mass Analysis to determine inconsistencies in the recorded rainfall which may be caused by changes in gauge location exposure or observational procedure. All stations were found to be consistent and it was not necessary to adjust or discard any records. 2.4. EVAPORATION The evaporation stations considered are shown in Table 3. Because of the fairly limited variation in evaporation within a region, it was assumed that Prospect Dam evaporation would provide a reasonable estimate of evaporation for the catchments considered. Comparison of adjacent evaporation stations would often show discrepancies but these are not considered significant in the streamflow estimation discussed in Chapter 3.

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CASE STUDY: The History of Water Supply on the Central Coast

APPENDIX 5: Schematic diagram of the rock strata (i.e. stratigraphy) for the selected Mangrove Creek dam site (see page 11).

Figure 11: Profile of rock strata at the Mangrove Creek Dam site. (“Mangrove Creek Dam Investigations”, Volume 4, Report 1 of “Report on Investigations for Water Supply to the Gosford-Wyong Region”, January 1975, Department of Public Works N.S.W., Figure 4 (modified))

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CASE STUDY: The History of Water Supply on the Central Coast

APPENDIX 6: Summary of land use in upper Mangrove Creek catchment (see page 13).

Table 8: Existing land use in the catchment of the preferred Mangrove Creek dam site as reported in 1975.

Freehold or Leasehold McPherson Vacant Zones of impact for Stage 1 (hectares) State Unreserved of the Mangrove Creek dam Agriculture Forest Forest Crown Land (hectares) (hectares)

Stored waters 140 690 340 0 Within 0.8 km of stored waters 0 370 3310 0 Within 0.8 km to 3.2 km of waters 90 720 3210 740 Remainder of Catchment area 120 50 100 160 (“Land Use Planning for the Catchment of the Proposed Mangrove Creek Dam” “Report on Investigations for Water Supply to the Gosford-Wyong Region”, Report No 2, Sept 1975, Department of Public Works N.S.W (page 11))

Land Use Map

Figure 11: Land use of catchment. (“Environmental Impact of the Proposed Dam“Volume 2, “Mangrove Creek Dam – Environmental Impact Statement” 1977, Gosford-Wyong Water Supply, NSW Department of Public Works.)

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CASE STUDY: The History of Water Supply on the Central Coast

APPENDIX 7: Extracts from the Environmental Impact Statement (see page 13).

Impact on Land Owners “Approximately 2200 hectares of freehold land in the dam catchment under the ownership of 26 landowners will need to be acquired. Of these landowners, two live on their properties and will be required to move elsewhere. “(page vii).

Impact on Vegetation Communities “Four different vegetation communities …. were recognised by two officers of the Royal Botanic gardens. The stored water will flood the remaining stands in the dam catchment of two of these communities but this loss ii not regarded as highly significant by the Botanic Gardens since other similar stands still remain in the neighbouring and Upper MacDonald River valleys. … No rare or endangered species were recorded during the survey though no attempt was made to list every species present. The mangrove and saltmarsh vegetation along the lower reaches of Mangrove Creek will not be affected…” (page v).

Vegetation Units recognise in the Dam catchment (page 30)

Mapping Unit Vegetation Community Geology Physiography Tall open-forest Eucalyptus deanei Angophora Recent alluvium. Sheltered valleys. and open-forest floribunda Narrabeen Group. S to SW facing slopes. Tall open-forest E. tereticornis Narrabeen Group Lower slopes of hills. E. eugenoides Dryer aspects. Open-forest A. costata Hawkesbury Sheltered gullies. E. piperita Sandstone S to E facing slopes. Open-forest Woodland E. eximia, E. gummifera, Hawkesbury Ridgetops and E. punctata Sandstone exposed slopes. woodland N to W facing slopes.

Impact on Wildlife “During the fauna survey of the dam catchment, 24 mammal, 81 bird and 12 reptile species were recorded in the catchment. … Most of the mammal species were widespread and occurred outside as well as inside the storage area. The same may also be stated for the birds and reptiles and the storage therefore does not constitute a threat to the survival of any particular wildlife species. The survey did not show the presence of any rare or endangered species….

The Australian bass and possibly the freshwater mullet will ultimately be limited, in Mangrove Creek, to waters downstream of the dam. It is expected that the freshwater cat fish and forage species will populate the stored waters of the dam.” (page v). Source: “Environmental Impact of the Proposed Dam “Volume 2, “Mangrove Creek Dam – Environmental Impact Statement” 1977, Gosford-Wyong Water Supply, NSW Department of Public Works.

Plate 23, 24 & 25: Dam Site ( Gosford Library - photographs by Denis Gibbons, NSW Department of Public Works)

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CASE STUDY: The History of Water Supply on the Central Coast

APPENDIX 8: Analysis of three aspects of the archaeological data from upper Mangrove Creek, in relation to the hypothesised changes in the Earth’s climate and sea levels over the last 20 millennia, i.e. 20,000 years . Note 12th millennium is between 12,000 and 11,000 years ago and 1st millennium is from 1,000 year ago until the present day (see page 16).

Figure 12: Archaeological data (Attenbrow, V., 2004. “What’s changing: population size or land-use patterns? The archaeology of Upper Mangrove Creek, Sydney Basin.” Terra Australis, No. 21, page 205)

Figure 13: Geological time chart (Attenbrow, V., 2004. “What’s changing: population size or land-use patterns? The archaeology of Upper Mangrove Creek, Sydney Basin.” Terra Australis, No. 21, page 205)

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CASE STUDY: The History of Water Supply on the Central Coast

APPENDIX 9: Text of two ‘Questions’ raised in the Parliament of NSW regarding the proposals for the ‘Gosford and Wyong Water Supply’ during the 1970s, and the answers given, based on extracts from the ‘NSW Parliamentary Debates’ (see page 17).

TEXT 1 ‘Question upon Notice’ in the Legislative Assembly, 26 October 1977’ “Mr ROZOLLI [Member for Hawkesbury] asked the deputy Premier and Minister for Public Works … Are plans envisaged for amplifying the water supply to the Gosford-Wyong area beyond year 2000? 1) Do these plans include construction of a dam and weir on the McDonald River? 2) Is it true that considerable environmental damage would result from construction of such works? 3) Is he aware that any such proposal would meet with strenuous local opposition? 4) What is the present state of investigations defining alternate water supplies for Gosford-Wyong? Answer- 1) There are no firm plans for the area beyond the year 2000. In April, 1975, the Gosford and Wyong Shire Councils adopted in principle, recommendations of the Department of Public Works for a regional water supply scheme, with the key storage being provided by a large dam on the upper reaches of Mangrove Creek. On present population projections, it is estimated that this scheme will be adequate for the water supply requirements of the two shires until the year 2006. The two councils also resolved that a decision on further augmentation of this scheme be deferred until more accurate population projections and streamflow information are available, probably in the late 1980s. 2) The McDonald River is one of several possible supplementary sources to augment the water resources of the two shires, after the present resources have been fully developed. 3) The investigations carried out so far have been purely on a feasibility basis and no detailed investigations have been undertaken, nor have any decisions been made. The environmental impact would depend very much upon the size and location of any structures decided upon. 4) Yes. The opposition relates particularly to the question of a weir on the McDonald River below the junction of the McDonald River and Mogo Creek, but as I have said, no decisions have been taken. 5) Major water supply works are being undertaken in the region, with the State Government providing a 50 per cent subsidy. The works involved in Stage 1 include a connection to link the water supply systems of the two shires concerned. This involves the Ourimbah Creek system, which transfers run of the river flows from Ourimbah Creek to Mardi Dam, the Mangrove Creek Dam, water treatment plants at Gosford and Wyong, and water distribution works to deliver water to consumers within the two shires. All of the Stage 1 works are expected to be completed by 1981. The next planned stage is the Mangrove Creek to Upper Wyong River Transfer System, proposed for construction in about 1993. No further investigations are being carried out at this time on subsequent stages.”

TEXT 2 ‘Question without Notice’ in the Legislative Assembly, 29 August 1978’ “ Mr O’CONNELL [Member for Peats]: I ask the Deputy Premier, Minister for Public Works and Minister for Ports whether he visited recently the Central Coast and inspected the Mangrove Creek dam. Will he advise me and the House of the stage of construction reached with the dam and when it might be available to fulfil its intended purpose of providing major augmentation of the Gosford and wyong water supply scheme?

Mr FERGUSON [Minister for Public Works]: Yes, recently I visited the site of the proposed Mangrove Creek Dam, which is part of an extensive $60 million water supply scheme for the Gosford and Wyong shires. The scheme has been financed 50% by the State Government and 25% each by the Gosford shire council and the Wyong shire council. I take this opportunity to pay tribute to the Gosford and Wyong shire councils and the Department of Public Works, and indeed the Government, for their cooperation in the funding of this scheme.

The first stage of the project provides for a wall height of 81.5 metres and provision has been made for a final height of 108 metres. The dam will be capable of storing 420,000 megalitres or 90,000 million gallons. Stripping and rock excavation of the site are now being carried out by the Department of public works. This work is nearing completion and tenders will soon be invited for the construction of the dam wall. Work is already well advanced on a 490-meter diversion tunnel being constructed at a cost of $1.3 million. Following completion of the dam, which is programmed for 1980, water will flow by pipeline and tunnel to a new water treatment plant at Wyong and from there it will be distributed to Wyong and Gosford shires. This will guarantee adequate water supplies for the two shires for at least the next twenty years….”

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CASE STUDY: The History of Water Supply on the Central Coast

APPENDIX 10: Construction of the Stage 1 dam (see page 19).

Statistics of the completed Mangrove Creek dam Dam Structure The completed dam has an 80 metre high wall with a crest length of 380 metres, a spillway 300 meters in length and a 50 m1tres high intake tower. Scope of the Dam The dam has a catchment area of 100,000 hectares. Its storage capacity is 170,000 million litres, or approximately 30% of the capacity of Sydney Harbour. The stored waters will have a surface area of 700 hectares. Composition of the Dam Rolled, soft rockfill, using 1.2 million cubic metres of the Narrabeen group of sandstones and siltstones. The embankment also contains 100,000 cubic metres of processed basalt. Upstream Face The upstream side of the dam has a concrete face tapering from 0.6 metres at the base to 0.3 metres thick at the crest. It contains 20,000 cubic metres of concrete and covers an area of 30,000 square metres. (Programme for the Official Opening Ceremony, Mangrove Creek Dam, 19th July 1982)

Difficulties during construction

The implementation of any major public work is a continuous problem-solving exercise in which the original design features and targets have to be continuously adjusted to meet the realities of what unfolds in the field.

Preliminary work on the dam including construction of access roads began in early 1977. Initial clearing of vegetation, construction of diversion tunnels, overburden removal and toe-slab construction proceeded more or less on schedule aiming for a completion date in mid 1981. However, in October 1979, soon after the Citra Construction contract commenced, significant problems arose in the foundation surface on which the embankment was to be constructed, due to ‘valley heave in the creek bed” and “valley bulging” :

“The siltstone layers exposed, showed an upward bulge (anticline) of some 2 metres from the edges of cliffs bounding the creek bed to the approximate centre of the creek (i.e. over a distance of some 40 metres).” (page 13-2)

This unwelcome development required a major alteration in the contract specifications in order to ensure a stable foundation for the embankment. As a result, the construction time was expanded (as was the cost) and the actual completion date for the dam was extended from may 1981 to 7th June 1982.

(“The Construction of Mangrove Creek Dam Stage1- Gosford-Wyong water Supply” Volume 1, NSW Department of Public Works, 1982)

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CASE STUDY: The History of Water Supply on the Central Coast

APPENDIX 11:

Table 9: Predicted growth in population and water demand according to Gosford and Wyong Council estimations made in 2007 (see page 20).

Year Serviced Without water-saving With water-saving population measures measures Annual Peak Annual Peak water daily water Daily demand demand demand Demand (ML/a) (ML/d) (ML/a) (ML/d)

2001 285,200 34,280 254 34,280 216 2011 318,960 38,340 284 36,150 228 2021 355,120 42,680 316 38,360 242 2031 391,340 47,040 348 41,080 259 2041 427,570 51,440 381 44,510 280 2051 463,800 55,220 409 47,630 300

(“WaterPlan 2050 – Long Term Water Supply Strategy” Preliminary Working Draft, December 2006, Gosford-Wyong Council’s Authority. pp 31-35)

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CASE STUDY: The History of Water Supply on the Central Coast

APPENDIX 12: Estimation of total annual stream flow in the Central Coast catchment for each year since rainfall records began in 1885. Also shown for comparative purposes are the average annual stream flow estimations over selected periods - i.e. the long term average for the whole period from 1885 to 2006; the average 1900-1949; the average 1950-1990; and the average 1991-2006 (see page 22).

Figure 14: Central Coast Streamflows (“WaterPlan 2050 – A long term water supply strategy for the central Coast” Plan Adopted August 2007, Gosford-Wyong Councils’ Water Authority. p 2)

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CASE STUDY: The History of Water Supply on the Central Coast

APPENDIX 13: The new Central Coast water supply system showing the location of the planned transfer Pipeline between Mardi dam and Mangrove Creek dam ( see page 23).

Figure 15: The New Central Coast Water Supply System (“WaterPlan 2050 – A long term water supply strategy for the central Coast” Plan Adopted August 2007, Gosford-Wyong Councils’ Water Authority. p 7.)

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