VubbLcation, n° 11? de. I'A&iocUvUon ïnteAnatlonaZe du Science* HydtologlqueA Sympoilum de Tokyo (Vicembie Î975)

ENVIRONMENTAL IMPLICATIONS OF DAMS AND MAN-MADE LAKES

H. BANDLER M.I.E. Aust., Turramura, N.S.W.,

Preface Much of the investigation work mentioned has been and is being carried out by the Metropolitan Water, Sewerage and Drainage Board (M.W.S. & D.B.). The opinions expressed are not necessarily those of the Board but are obser­ vations of the author.

Synopis The implications of the damming of a river and with it the creation of a man-made lake, extend over a very wide field. The technological considerations are usually given high precendence at the time of design and construction. Topography, geology and structural aspects will be the subject of investigations. The aspects of relocation of communities, the loss of valuable farming land, areas and monuments of tradition deserve serious consideration. The housing of the work force and the consequences of a construction village are hard to predict at the time of establishment. The newly created lake, once the dam is closed, will bring about a new environmental situation which at no time is static; changes occur in the chemical and biological make-up within the water body.

The surrounding area from which the water enters the lake will respond to a variety of management techniques which will have an effect on flora and fauna as well as quality and quantity of water in the lake. The length of time of existence of the lake will be subject to the control of erosion to pre­ vent siltation. Making use of the lake for recreational purposes brings ad­ vantages as well as problems with it. Water operation policy has significant effects on the population downstream.

Préface

La majorité des travaux mentionnés ici sont actuellement entrepris -ou sur le point de l'être- par le Comité Métropolitain des Eaux, Egouts et Drainage (M.W.S. & D.B.). Les points de vue exprimés ne reflètent pas nécessairement les opinions de ce Comité ; il s'agit de remarques personnelles de l'auteur.

579 60.2 Résumé Les conséquences impliquées par le barrage d'un cours d'eau et, partant, la création d'un lac artificiel, ont une portée très vaste. Les considérations d'ordre technique sont en général prioritaires au moment de la conception et de la construction ; topographie, géologie et aspects structurels feront l'objet de diverses recherches mais le relogement des communautés, la perte de terre arable, la disparition de zones et monuments traditionnels méritent d'être pris en considération. Au moment de la construction, il est difficile de prévoir le logement de la main d'oeuvre et les conséquences éventuelles de la création d'un village car, une fois le barrage terminé, le nouveau lac donnera lieu à un nouvel environnement en constante évolution tant dans la composition chimique que dans la vie biologique de l'étendue d eau.

La zone environnante dont les eaux pénétreront dans le lac va réagir à tout un éventail de nouvelles techniques qui affecteront la flore et la faune ainsi que la qualité et la quantité des eaux du lac. Quant à la durée de vie du lac, elle sera sujette à la lutte contre l'érosion qui évitera l'envasement. En outre, l'utilisation du lac à des fins de loisirs comporte avantages et inconvénients. Enfin, la politique appliquée en matière d'utilisation des eaux a une grande influence sur la population qui vit en aval du lac.

Introduction

Examination of Desirable Studies To supply drinking water to the community by the provision of water storage as a means of overcoming seasonal insufficiency dates back to antiquity. Such water impoundments have always had environmental impacts, but the implications have only more recently become recognised as significant with our present popula­ tion pressures and environmental awareness.

The initial stage is the period of feasibility studies. During this period the decision whether to build the dam is established subject to political approval. Its location is determined, purpose, use, type and basic economics are generally fixed. The next stage is the period of planning, design and construction which continues up to and until the closing of the dam. As soon as the dam is closed reservoir filling commences and ecological instability begins. This instability still continues even after the dam is filled and is operative, but adjustments are more gradual and constant variations take place throughout the remainder of the life of the reservoir. Depending on the type of structure and the method of construction some of these stages will be overlapping. Feasibility studies of certain features can extend into the design and planning stage and some dams are being filled during construction. Minor changes in climatic condition, lack of rainfall, flood flows and excessive drawdown will have destabilising effects on the environment of the man-made lake which will be established by the dam.

Certain major impacts will require study and consideration. The impounded lake, the dam, the catchment area and the river downstream have to be considered as eccosystems which are being subjected to change. Independent of whether the project is a large or a small one, many aspects of the system are subjected to rather sudden changes. During the early stagesof the feasibility study for the dam across the river channel, it will become apparent that the submergence of

580 60.3 the valley upstream will necessitate displacement of those people living and/or working in the area. Another socio-cultural impact will be the introduction of a group of persons who will be working on the construction of the dam. This com­ munity may, if the project is large, take up residence for long periods and estab­ lish local associations which will have considerable impact on the area. Finally, there is the population who will be resident or transient to maintain the struc­ ture and the lake for the remainder of the term of its existence and others who may choose to reside in the area.

The creation of a new water body which had not been there before will be al­ most sudden in its evolvement when the dam is being closed and water fills the valley. The change from a terrestial environment to an extensive flat water sur­ face brings with it changes in micro climate, flora and fauna within the lake area. There will also be variations within the water body due to stratification at various dep ths.

The dam will also change the regimen of the river flow downstream due to interception of run-off as well as human manipulation of draw-off or release of water. This will have more or less predictable hydrologie implications.

The disturbance of the earth's crust, the additional loading imposed by the dam structure and the weight of water in the lake, can bring about seismic activity which needs to be monitored.

None of the changes caused by the establishment of the lake can be reversed. Minor changes are constantly taking place in and around the water body due to in­ flow and outflow conditions. Maintenance of the lake to ensure its permanency, control of water quality and conditions of the catchment area as well as safety of the dam structure and the population in the vicinity and downstream will be envi­ ronmentally meaningful.

Selection of for Examination It is proposed to examine some of the environmental implications, in retro­ spect, with regard to Warragamba Dam and Lake Burragorang in N.S.W., Australia. The dam was built for water supply to the city of . The construction exten­ ded from 1942 to 1960 if the time of early investigation is included. The physical details give an indication of the magnitude of the structure. (1)

TABLE 1 Storage Capacity 2 057 000 Mega litres 452,500 Million Gallons Length of wall 350 m 1,150 feet Length of Spillway over Crest 95 m 310 feet Concrete in Wall 1.2 Million m3 1.6 million yard3 Maximum Height of Concrete 137 m 450 feet Greatest Depth of Water 104 m 340 feet Width of Wall at Base 104 m 340 feet Catchment Area 8,762 km2 3,833 miles2 Annual Average Rainfall 825 mm 32.5 inches Annual Average Evaporation 1,270 mm 50 inches Lake Area at Full Supply Level 75 km2 29 miles2 Maximum Length of Lake 52 km 32% miles Length of Foreshores 353 km 220 miles Hydro Electric Station 50,000 KiloWatts Estimated Cost (up to completion £35% Million in 1960)

Water famines and serious shortages were a frequent occurrence since the establishment of the first white settlement on the Australian Continent at Sydney Cove in 1788.

581 60.4 The concept of using the as a source of drinking water for the population of Sydney was apparent at an early stage of colonial develop­ ment. (2) But only in August 1943 was it possible for construction of Warragamba Dam to proceed.

The Dam, approximately 75 km (40 miles) from Sydney, was built in a steep sided gorge which was cut by the river in Triassic rocks of the Narrabeen group and the Hawkesbury sandstones.

The Warragamba River flows have been recorded since 1880. These records show the irregular rate of flow which continues as inflow to the lake.

By statistical analysis of river flow records and comparison with other methods, including that for maximum possible precipitation, a peak intensity of flood flow of 14,0003m /sec (500,000 cusec) was arrived at.

The minimum flow for a period of 96 months is the basis for con­ siderations .

Drowning Burragorang Valley The valley upstream of the dam, was extensively farmed and possessed a natural charm and beauty all its own. The towering rock cliffs which formed the valley walls enhanced a thriving tourist activity. In 1930 collieries were opened in the area. Several collieries are still in operation on the escarpment of Burragorang Valley.

«hen it became known that the construction of the Dam would cause the flood­ ing of the valley, the local inhabitants formed a Defence League which asked for a Royal Commission on the need for Warragamba Dam. A Royal Commission was never granted. An area of 140 km2 (37,700 acres) which included all properties to be submerged and those lying within 3 km (2 miles) of the ultimate stored water were acquired by the Board at the cost of £800,000 ($1,600,000). Payment to the owners was at the 1947 valuation plus 10% displacement money. Removing the residents and demolishing the buildings took quite a few years. In the process of filling the lake behind the Dam, Burragorang Valley, a fertile farming district and popular holiday resort was submerged.

While the inhabitants of the Burragorang Valley were removed, another popu­ lation was introduced to the area as work force. At an early stage it was deter­ mined that the whole area to be submerged had to be cleared of standing trees. Up to 500 men were employed in the work offelling, stacking and burning the timber.

The Aboriginal population in the Burragorang Valley is considered to have been quite numerous before white settlement. However, apart from the ethnological descriptions (3), no cultural relics have been retained. Before flooding there was an example of rock art in the Burragorang Valley which was well known as the "Hands of the Rock". The hands were both right and left with fingers invariably pointing upward and beneath them four white curved bands resembling boomerangs or ribs. Each hand imprint and the whitebands below them were carefully prepared by incising the surface to the shape leaving a slightly raised margin around each.

It is regrettable that this record of the tribe was lost with the drowning of the Burragorang Valley. Consideration might have been given to its preserva­ tion by removing the whole of the rock with the painting to a position where it would not have been inundated. The rock, about 6 m (17 ft) long by about 4 m (12 ft) high, was separate from the rock walls and could have been cut for removal and reassembled as has been done with other much larger archaeological treasures. The "Hands on the Rock" was the only such relic of the local tribe and with its disappearance no art work by the Gundungarra tribe is now in existence.

582 60.5 Construction Force and Township Construction of the Dam was started with dredging, in 1948. In 1950 ex­ cavation commenced and the first concrete was placed in 1953. At the height of construction of the Dam the Board employed a work force of 35 engineers, 220 staff and 1800 men which was accommodated in a construction township on a mountain spur above the Dam. A diversity of nationalities made up its popula­ tion.

With the completion of the Dam the workforce was encouraged to find em­ ployment elsewhere; the engineers and staff were transferred to Sydney head office and construction centres in the suburbs. The Board arranged for the sale of most of the houses in the township in 1960. In 1962 the Township came under the control of Wollondilly Shire. Contrary to expectations and usual patterns, its population did not disperse on completion of construction work. The numbers dropped to approximately 1000 with a remarkable percentage of older people who .had purchased comparatively cheap residences from the Water Board. Currently the township is again flourishing and the population has risen to approx. 1700, with younger age groups gaining prominence.

Catchment Area - Vegetation and Land Use Approximately half of the catchment is uncleared crownland, half freehold and only a small proportion of the area is leasehold. There is a great variety of topography and some variations in climate. Much of the area is timbered, mainly in the centre of the catchment while there are two distinct pastoral and agricultural areas in the north and in the south. The total and the per­ centage areas of the various land use classifications established in a survey by the Soil Conservation Service of N.S.W. (4), are shown in Table II.

Total Area Classification Acres km2 Percent area Native Pasture 614,350 2,486 27.3 (Cleared) Native Pasture 62,360 253 2.8 (semi-cleared) Improved Pasture 292,660 1,184 13.0 Timbered Area 1,231,160 4,982 54.8 Pine Forest 11,460 46 0.5 Urban Area 16,040 65 0.7 Lake Area 19,155 78 0.9

The area under improved pasture, i.e. land which has been fertilized and sown with introduced legume or grass species has increased since the building of the dam. Most of this in the Southern Highlands which is suited to high production. Topography is a major factor determining land use. With much of the area steeper than 8 percent (5 ) land is not suitable for cultivation. Land steeper than 25% is unsuitable for clearing. Remoteness and poor access has also mitigated against cultivation. Where agriculture is in operation dairy­ ing, beef production and sheep grazing for both wool and meat are the main enter­ prises . Catchment Management The M.W.S. & D.B. manages the catchment area under the M.W.S. & D. Act, By-law 16, which gives the Board extensive powers with regard to any activity within the catchment area. For convenience an outer and an inner catchment were delineated. Within the inner catchment complete control is exercised by the Board while in the outer catchment control is less rigorous. Within the inner catchment area there are a number of settlements, coalmines and many kilometers

583 60.6 of public roads. Only a relatively small staff is entrusted with the work of control of this vast area. Management is concerned with municipal development, control of coal mining activities and possible infringements of the Act. As most of the catchment is timbered much attention has to be devoted to forestry matters. Although some of the areas could be developed for commercial forestry, the current policy is to permit no silvicultural development beyond natural regrowth. Management is essentially Protection Forestry which, in turn, essen­ tially means fire protection. Some trial lots have been established and have shown that introduced species such as Pinus Radiata would do well. However, present policy is to maintain the forest cover in native species. It has also been established that cedar and eucalypts, such as Sydney Blue Gum, Blackbutt and other native hardwoods could be commercially grown and exploited. At this stage, however, there is no intention to devote any part of the catchment to such activities. Forest fires are the most significant hazard in the extensive timbered areas. To combat this threat some 560 km (350 miles) of fire trails and fire roads have been built and are maintained in the catchment area. Two look-out towers have been constructed and radio connection is maintained to adjoining Forestry Commission centres and the Blue Mountains Fire Organisation. Aeroplanes are used for fire spotting. The worst fires are caused by lightning and it is not infrequent that several fires are started, almost simultaneously, by a single thunder storm. If these occur in a greater number than can be con­ trolled by the available staff they can, if adverse conditions of high tem­ peratures and wind velocities exist, spread over large areas. Usually the fires start in inaccessible places. Hazard reduction is carried out by low under story burning at the right times. In the past this was done on foot, but more recently incendiary burning by air drop was successfully practised.

Environmentally, it is essential that tight controls be enforced on ex­ cessive urban development by sub-division and on poor farm management. The exisitng forest cover is a great asset in its effect on water yield and in its natural beauty. Every effort should be made to continue and where possible extend the existing forest stands.

Erosion In such a huge catchment area some of which is only loosely administered, the control of erosion is most important. To this end the M.W.S. & D.B. call­ ed on the Soil Conservation Service of N.S.W. for assistance. The Board agreed to contibute half the cost of mechanical soil conservation works constructed by landholders, designed, carried out, supervised and certified by the Conser­ vation Service. This work, which is in operation by agreement for 20 years has resulted in considerable improvements in much of the pasture lands. In the tim­ bered areas, stabilisation work is also consistently undertaken. Annual reports are submitted by the Service to the Board with a consequent result of a much improved catchment area in which erosion is constantly monitored and improve­ ments brought about in co-operation with the agricultural land users. The work of the Soil Conservation Service has become generally accepted by landholders within the catchment and Councils and the Department of Main Roads are co­ operating in the efforts to keep erosion down to a minimum.

Recreational Use of Construction and Catchment Area Area around Dam and Township On completion of the construction work at Warragamba much of the works area was transformed into a recreation area. Work sheds, equipment stores, work­ shops, office blocks, barracks and major mechanical installations such as cable ways, mixing plant etc. were disposed of. Over two thousand trees and shrubs, mostly native, were planted, roads sealed and a picnic area, about 1.6 km long by 0.6 km, provided with a kiosk, shelter, shed, tables and benches, barbecues,

584 drinking fountains, boiling water points, toilet facilities and an information centre. Several large parking areas and parks extend to the crest of the dam and to the Valve House area. The whole layout of the surrounds of the dam was extensively landscaped and is exemplary in layout and natural beauty. The public make extensive use of these facilities, latest counts put the number of visitors to the area at approximately 700,000 per year (5). The installation of a Lion Park has provided an additional attraction as well as creating em­ ployment for the local population. This environmental anachronism was intro­ duced in 1968. With its 50 ha. (122 acres) it caters for an annual passage of 300,000 to 400,000 persons through its 5 km (3 mlles)of roads. The present pressures on the recreation areas around the Dam could be re­ duced by a change of policy with regard to accessibility to the huge lake as the public is not permitted to within 3 km (2 miles) of the waters edge. The Lake Area The breathtaking beauty of Lake Burragorang is fascinating, extremely varied and has not been described in the poetic terms it deserves because so very few people get an opportunity to visit it, see it from a boat or from one of the shores. Those who do are usually on a work mission which involves their use of the magnificent surroundings with the obligation of certain tasks and duties to be performed. The towering sandstone walls of the Burragorang Valley, the gentler slopes of the Southern Tablelands and some of the upper reaches of the rivers, are certainly worthy of opportunities for the general public to have access. The lack of use of this exquisite environment for a greater public is most regrettable. It is quite likely that some of the quiet majesty could be disturbed by the invasion of large numbers of visitors.

At Lake Burragorang, fishing and sailing clubs could be established which would provide supervision over prescribed areas of activity. Even swimming could be made available in the upper reaches of the lake. Such locations would, however, be quite some distance from major population centres and thus require more travelling by the visiting public. Such clubs with toilet and other facilities could ensure a minimum of litter which is one of the objections to public access to the water. It is also important to realise the vast extent of the lake with consequent problems of ensuring the safety of boating parties, swimmers and even bush walkers. A major objection to public access is vandalism and the danger of bushfires which is a particular feature of the Australian situation. More extensive patrolling by rangers on the land and on the water would be a necessity and incur considerable extra cost. The variations of the lake level will create some difficulties in establishing suitable locations for such activities. Continuation of the current extensive water quality monitor­ ing and chlorine dosing should ensure maintenance of the present standard of water supplied.

The recreational use of drinking water storage areas has been the subject of much discussion internationally and in Australia (6)(7). The consensus of opinion is that recreational activities such as boating, sailing and fishing are acceptable and swimming is allowed in drinking water storage lakes, some much smaller than Lake Burragorang.

Effects of the Dam in the Valley Downstream Any water which passes the Dam flows 3% km (2.2 miles) downstream to the confluence with the which after some 11 km (7 miles) enters open country which is extensively used for agricultural pursuits. The rich flood plains, particularly after the junction with when the river becomes the , are suitable for fodder crops, animal husbandry, citrus

585 60.8 growing and vegetable production. Due to the spillover from Warragamba, Nepean and other tributary dams irregular flows and floods of varying severity occur in the Hawkesbury Valley. The building of the huge Warragamba Dam was looked upon as a salvation from future flooding. However, major flooding has occurred on two occasions since completion of the Dam. As Warragamba is gated some reduction in flooding could be effected by lowering the lake level. This however would interfere with the safe draft for drinking water supply. The four dams on the Nepean River and its tributaries are without control devices i.e. they have no gates which could be used to hold flood flows. The flood problem of the Valley has been the subject of investigations of an interdepartmental committee since 1966. In the near future the introduction of the will bring with it the possibility of reducing the operating level of Lake Burragorang by the provision of pumped storage from a new dam introduced into the system.

Conclusions

Of the many environmental implications of Warragamba Dam the most signi­ ficant in the long term have been the development of a township, the serious pressures of demand for recreational opportunities and the incomplete flood mitigation for the valley downstream.

REFERENCES (1) Warragamba Dam - T.B. Nicol - Institution Civil Engineers - (London) March 1964 - also - Journal Institution of Engineers Australia - Oct. - Nov. 1964.

(2) Water Supply, Sewerage and Drainage of Sydney - W.V. Aird - 1961.

(3) The Organisation, Language and Initiation Ceremonies of the Aborigines of the South East Coast of N.S.W. - R.H. Mathews & Miss M.M. Everitt - Royal Society of N.S.W. Journal and Proceedings V.34 1900 p.262-281.

(4) Report of the Detailed Erosion Survey of the Warragamba Catchment Area by J.R. Dyson - Soil Conservation Service of N.S.W. 1969.

(5) M.W.S. & D.B. Annual Report Year Ended 30th June 1974.

(6) New York Congress 1972 - Recreational Ose of Gathering Grounds and Reservoirs - Subject 12.

(7) Management of Water Resources - Water Research Foundation of Australia - Report No.41 - Sept. 1974.

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