COLD WATER DISCHARGES FROM IMPOUNDMENTS AND IMPACTS ON AQUATIC BIOTA

Publication SR3 February 2004

1. INTRODUCTION like nature of hydroelectric power generation releases. This publication provides an overview of factors influencing thermal stratification in dams, 2. THERMAL STRATIFICATION temperature depression effects below large impoundments and the impacts on downstream When the surface water in an impoundment absorbs aquatic biota. solar energy for extended periods, the water may The construction of large dams on the majority of become thermally stratified. This stratification Australia’s large rivers has resulted in extensive commonly occurs in summer and results in the changes to natural flow regimes and temperature formation of distinct temperature bands. These patterns downstream of dam releases. Many of bands are known as the epilimnion (surface layer), these large dams have been constructed to deliver thermocline (middle transition layer) and water for irrigation farmers and hydroelectric power hypolimnion (bottom layer) (Figure 1). The stations, and for flood mitigation. epilimnion is the upper band of water that receives the full impact of solar radiation. As a result of There have been a number of published studies on thermal dynamics and density, warm water has a the effects of dams on fish migration, in particular, tendency to rise and remains at the top of the water the impacts of changed flow regimes and the column, being further warmed by continual physical barriers that large impoundments create. exposure to solar radiation. The narrow transition To date however, little research has been conducted layer between the epilimnion to the hypolimnion on the ecological implications of cold-water (thermocline) is characterised by rapid changes in discharges in flow regulated systems. Temperature temperature with depth. The bottom layer of water pollution impacts have predominantly been studied (hypolimnion) is isolated from the warming effects in the northern hemisphere, on warm water of the sun by reflection, refraction, natural turbidity, discharges to river systems associated with industry and the presence of algae in the epilimnion which and power station cooling waters. reduces the depth that light and radiant heat can Numerous researchers have suggested that cold- penetrate (Abel, 1996). water pollution may be having effects on species During summer, the temperature of the surface layer distribution and abundances in Australia. in an impoundment can be several degrees warmer Conclusions have been speculative, due to than would normally be expected in the natural river confounding factors such as changes in flow system. This is due to continued solar absorption regimes, increased water velocities and the pulse-

COLD WATER DISCHARGES FROM IMPOUNDMENTS AND IMPACTS ON AQUATIC BIOTA

and heat cycling (Cazaubon and Giudicelli, 1999). At this time, the release of water from any depth in Conversely, due to insulating effects and heat the impoundment can be warmer than expected to cycling, water temperature in the hypolimnion can occur naturally. Hence, thermal extremes tend to be be substantially cooler than in the natural river retarded by the impoundment, and a ‘winter warm, system (Gaillard, 1984). summer cool’ scenario is the product (Figure 2) (Gore, 1977; Ward and Stanford, 1979; Walker, 1980; In winter, different heat cycling processes are Cowx et al. 1987; Webb and Walling, 1988; Saltveit observed. During the preceeding autumn months, et al., 1994). air temperatures and levels of solar energy begin to decrease. The result is a cooling of the epilimnion, Thermal stratification, although more common and usually to a point where the surface layer becomes dramatic in large impoundments, may also occur in substantially cooler and denser than the insulated weir pools. Gundigera Weir on the Namoi River in hypolimnion below. A process known as “overturn” New South Wales (NSW) showed a 5OC change in then results. The warmer less dense waters that are water temperature from the surface to a depth of 7m now in the bottom layer of the impoundment rise, during the summer period of 1999. Temperature and the cooler denser waters of the top layer sink. differences of 15OC between the surface and a depth The three water layers are consequently mixed of 10m have been also recorded in Pindari Weir on which eliminates the thermal gradient created in the Severne River (DLWC, 2000). summer. The impoundment is now termed isothermal, meaning that the temperature at all water levels is approximately the same.

Solar Energy

Refraction, reflection and absorption by alga and sediment particles 0 Epilimnion 10 ) 20 m Thermocline ( h

pt 30 e r

e u t a D r e 40 p m Hypolimnion e T

r e 50 t a W Temperature oC 5101520 Figure 1: Thermal stratification occurring in impoundments during summer periods (Adapted from Abel, 1996).

EPA Victoria 2 COLD WATER DISCHARGES FROM IMPOUNDMENTS AND IMPACTS ON AQUATIC BIOTA

25 O 20 C re u

15 t

10 ra pe 5 m

0 Te Jan March MayJulySeptNov

Regulated stream Unregulated stream Figure 2: ‘Winter warm – Summer cool’ effect of impoundments on release waters compared to unregulated rivers.

Studies conducted by Gaillard (1984) indicated • size of the impoundment differences of 20oC between normal river • location of the dam in the river continuum temperatures and temperatures of hypolimnion • river size (bottom) waters. • influence of downstream tributaries and their characteristics (flow and temperature) 3. TEMPERATURE RECOVERY • atmospheric conditions The release of water from an impoundment at a temperature different to that of the river into which it • air temperature is released will alter the temperature in the river. • degree of shading by riparian (stream bank) The recovery distance is the length of river vegetation downstream of an impoundment that is required for • bed substrate the return to temperatures that would normally be found in an unregulated river. This distance may • stream morphology vary, between different impoundments and between • ground water influences different seasons for an individual impoundment. (Ward, 1985; Palmer and O’Keeffe, 1989; Storey and The recovery distance below an impoundment is Cowley, 1997). dependent on a number of factors. These include: During periods of high flow, water velocities and • discharge volume distance travelled per unit time is greater, therefore

• temperature of the release waters greater river distances are affected during periods of

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higher discharge. Higher flow rates also typically have dramatic effects on aquatic macroinvertebrate involve greater river depths, resulting in a reduction communities. of surface area to channel volume ratios. A The body temperature of invertebrates varies with reduction in this ratio reduces the proportion of environmental temperature. With certain water exposed to ambient warming or cooling temperature ranges necessary for successful growth temperatures, depending on the seasonal timing of and reproduction, heat consequently drives the releases. As a result, a longer period of time and growth rates and reproduction of when food distance is required to stabilise the thermal is not limiting (Gullan and Cranston, 1994). dynamics of the flow (Figure 3). The release of cold water from storages can Recent investigations of water temperatures dramatically affect aquatic invertebrates, as the downstream of storages in NSW and Victoria optimum temperature range for their developmental indicate that temperature depression is a common stages lies above that of the hypolimnion release occurrence. It has been reported that up to 400km water (Gailliard, 1984). downstream of some NSW impoundments may be Limited invertebrate research has been conducted in affected by the release of cold water. Australia on the effects of thermal pollution, with It is also believed that 14 of NSW’s largest dams are only certain taxanomic groups receiving attention. contributing to a total of 2795 river-kilometres Groups such as mayflies (Ephemeroptera) and affected by temperature depression (Lugg, 2000). stoneflies (), have been the subject of The effect on Victorian river systems to date has not research studies to investigate temperature been determined, through lack of suitable requirements for egg development and growth monitoring of many large impoundments. (Corkum and Hanes, 1991; Brittain, 1991; Brittain and Campbell, 1991; Brittain, 1995; Brittain, 1997). 4. EFFECTS OF TEMPERATURE In laboratory studies, both egg development and CHANGE ON BIOTA hatching were found to vary with temperature. Development time was longer at lower temperatures and hatching success was reduced at upper and 4.1 Aquatic invertebrates lower temperature extremes. For example, Brittain Temperature plays an important role in determining and Campbell (1991) found that at 10OC, a period of invertebrate abundance and distribution (Camargo 55 days was required for mayfly eggs and Voelz, 1999). Many Australian stream (Coloburiscidae) to hatch, while at 25OC they only communities have evolved under high summer required 15 days. Further investigations by Brittain temperatures and large variability in thermal (1991) demonstrated similar hatching responses in conditions (Lake, 1982). Consequently, it has been stonefly eggs (Eusthenidae alpina), hypothesised that changes to natural thermal with hatching taking 327 days at 5OC and 87 days at regimes induced by impoundment releases can 15OC.

EPA Victoria 4 COLD WATER DISCHARGES FROM IMPOUNDMENTS AND IMPACTS ON AQUATIC BIOTA

Low Release High Release

9Co 200ML/Day Inflow 100ML/Day Dam or o Impoundment Dam or 9C Inflow Impoundment

15oC

o 150ML/Day Tributary 1 15 C Tributary 1 2000ML/Day Dam Release 70 ML/Day Tributary 2 30ML/Day o Dam Release 50 ML/Day 15 C 10oC 15oC 13oC Tributary 2 o 10oC 30ML/Day 10 C o

er 10 C o t 14 C 10oC 14oC Win 12oC 12oC

10oC 10oC

o 270ML/Day 10 C 2060ML/Day

Winter high inflow, low volume Winter low inflow, high volume release, short recovery distance release, long recovery distance

18oC 200ML/Day Dam or Inflow 100ML/Day Impoundment Dam or 18oC Inflow Impoundment

12oC Tributary 1 o 150ML/Day 70ML/Day 12 C Dam Release 2000ML/Day Tributary 1 Tributary 2 12oC Dam Release 30ML/Day 50ML/Day o Tributary 2 14 C 30ML/Day o o o 19oC 19 C 12 C 19 C mer 19oC

o o 14 C 19 C Sum o 15 C 13oC 18oC

20oC 17oC

270ML/Day 2060ML/Day

Summer high inflow, low volume Summer low inflow, high volume release, short recovery distance release, long recovery distance

Figure 3: Hypothetical stream recovery distances, influenced by system inflows and discharge volumes for summer and winter seasons.

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It has also been hypothesised that aquatic thermal regimes downstream of impoundments may invertebrates require a ‘peaking’ (sharp and eliminate temperature cues required for Australian sustained increase) temperature to undergo native fish (Lugg, 2000). Following comparison with moulting from juvenile to adult, and to promote current knowledge of temperature and flow successful egg hatching. While depressed water deviations, it appears that there are several temperatures downstream of impoundments may be regulated systems that may be having serious within the optimum temperature range required for negative impacts on native fishes. larval growth, a ‘peaking’ water temperature would Competition and predation by exotic species further not occur. This would prevent invertebrates from exacerbate problems with native fish recruitment. receiving the hypothesised developmental cue Introduced salmanoids such as (Gore, 1977). (Oncorhynchus mykiss) and brown trout (Salmo Changes in downstream invertebrate communities trutta) prefer temperatures between 12 and 14OC, and species richness were observed following with fatality occurring at temperatures above 24 to releases of cold hypolymnetic waters after 25OC. These two species, along with redfin perch construction of the Thompson Dam (Marchant, (Perca fluviatilis), have been associated with 1989). These changes in species richness were dramatic declines in native fish populations and partly attributed to cold water releases and also due local extinctions, especially of native Galaxid to disruption of invertebrate drift patterns. When species. Competition for food, habitat and summer water temperatures were raised to pre- predation on juveniles of native species has placed release temperatures, a return of invertebrate additional pressures on declining native fish species richness followed. It follows then, that populations. Altered temperature regimes below hypolimnial flows may completely prevent species impoundments and active trout restocking programs from living in a stretch of river where they are have led to the dominance of exotic species normally found or cause a reduction in their relative populations in numerous waterways, both above abundance. and below impoundments. Recent research by NSW Fisheries has demonstrated that increasing 4.2 Native Fish temperatures below Burrendong Dam by 6-10OC has greatly improved survival and growth of native silver Egg hatching of fish has also been hypothesised to perch (Bidyanus bidyanus) (Astles et al. 2000). be affected by reduction in water temperatures. Studies conducted by Lugg (2000), suggest that 4.3 Microbial processes increased egg mortality may be occurring in native fishes due to reduced temperatures below In addition to effects on macroinvertebrates and impoundments in the Murray Darling Basin river fish, reductions in temperature may also reduce or systems. Native fishes have certain reproductive stop microbial activity in streams. Microbial activity habitats and temperature requirements (Table 1). It is important in the breakdown of organic matter to a has also been hypothesised that alterations in

EPA Victoria 6 COLD WATER DISCHARGES FROM IMPOUNDMENTS AND IMPACTS ON AQUATIC BIOTA

soluble form, which is then made available to plants and other organisms.

Changes in temperature may reduce the normal or natural metabolic rate of microbes, or replace these microbes with cold water strains transported from cooler sections of the river above, or from within, the impoundment. Recovery from cold water releases, that is the return back to a warm water system, may then remove the cool water specialised microbes. This would leave sections of a river without substantial populations of microbes to breakdown organic matter, until the warm water microbes are reintroduced by motile fish and other organisms re- populating these reaches, which may take some time.

5 DIRECTIONS IN MANAGEMENT AND MONITORING

Currently, the Department of Sustainability and Environment (DSE, formerly NRE) is conducting an assessment of downstream temperature regimes for 22 of Victoria’s 411 large impoundments (wall height greater than five metres). The selection of these impoundments as investigation priorities has been based on the perception of an associated higher level thermal pollution risk than others (Ryan et al. 2001).

It is expected that the results from these investigations will be used to facilitate the management of thermal impacts from impoundments, particularly in abating risks to threatened native biota.

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Table 1: Biological requirements of native Murray-Darling Basin Fishes. Summarised from Lake (1967), Llewellyn(1971), Koehn and O’Connor (1990), McDowall (1996).

Species Spawning Season Required Water Spawning site and conditions Temperature Bony Herring Start Oct – end Dec 20oC Eggs laid in shallow waters during floods Australian Smelt Start Sept – end Nov 15-18 oC Over aquatic vegetation Freshwater Catfish Start Oct – end Mar >24 oC Eggs laid in gravel nests in shallows, guarded by adults Golden Perch Start Nov – end Mar >23.5 oC Eggs laid near surface in flooded backwaters following long distance upstream migration Silver Perch Start Oct – end Dec >23 oC Eggs laid near surface in flooded backwaters Spangled Perch ? >26.5 oC surface Scattered over substrate >22 oC bottom Chanda Perch Nov – Dec 23 oC Eggs probably attached to plants Macquarie Perch mid Oct – mid Dec 16 oC In shallow gravel beds with running water Southern Pygmy Perch mid Jul – mid Nov 16 – 21 oC Over aquatic plants or bare substrates in fairly still waters Murray Cod Start Oct – end Dec 16 – 21 oC Adhesive eggs laid on hard (silt free) substrates, especially in association with increasing day length and rising water levels following upstream migration Trout Cod Start Sept – end Nov >17 oC Probably similar to Murray Cod Crimson-spotted Rainbowfish Start Oct – end Dec 20 – 25 oC Among aquatic plants Purple-spotted Gudgeon Start Dec – end Feb 19 – 30 oC Eggs deposited in clusters on solid objects (rocks, wood, broad-leaved plants) Flat-headed Gudgeon Start Oct – end Feb 21 – 27 oC Adhesive eggs laid on hard substrates and protected by male Western Carp Gudgeon Start Dec – end Feb >21 oC Eggs dispersed over vegetation in shallow flooded backwaters Freshwater Hardihead Oct – Nov 24.5 oC surface Eggs dispersed over vegetation or the substrate 23.5 oC bottom Murray Galaxias ? 9 – 14 oC Scattered over substrate Freshwater Blackfish Start Nov – mid Jan >16 oC In hollow logs

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5. REFERENCES impounded rivers with different impoundment use. Environmental Monitoring and Assessment, 50 Abel, P.D. (1996) Water Pollution Biology, Second (2):143-158. Edition. Taylor and Francis, London. Cazaubon, A. and Giudicelli, J. (1999) Impact of the Astles, K.L.; Winstanley, R.K.; Harris, J.H. and residual flow on the physical characteristics and Gehrke, P.C. (2003) Regulated Rivers and Fisheries benthic community (algae, invertebrates) of a Restoration Project – Experimental study o the regulated Mediterranean river: the Durance, France. effects of cold water pollution on native fish. NSW Regulated Rivers: Research and Management, 15 Fisheries Final Report Series No. 44. NSW Fisheries (5):441-461. Cronulla. Corkum, L.D. and Hanes, E.C. (1991) Effects of Brittain, J.E. (1991) Effect of temperature on egg temperature and photoperiod on larval size and development in the Australian stonefly , survivourship of a burrowing mayfly Austrocercella Illies (Plecoptera: Notonemouridae). (Ephemeroptera, Ephemeridae). Canadian Journal Of Australian Journal of Marine and Freshwater Zoology, 70:256-263. Research, 42:107-114. Cowx, I.G.; Young, W.O. and Booth, J.P. (1987) Brittain, J.E. (1995) Egg Development in Australian Thermal characteristics of two regulated rivers in Mayflies (Ephemeroptera). In “Current Directions in Mid-Wales, U.K. Regulated Rivers, 1:85-91. Research on Ephemeroptera.” Corkum, L.D. DLWC, (2000) Status of Temperature Management Ciborowski, J.J.H. eds., Canadian Scholars’ Press Capabilities at Water Storages Operated by DLWC: Inc., Toronto. pp. 307-316. Internal report for surface water management- Brittain, J.E. (1997) Egg development in planning. Centre for Natural Resources, Parramatta. Thaumatoperla, an endangered stonefly genus, Gaillard, J. (1984) Multilevel withdrawal and water endemic to the Australian Alps (Plecoptera: quality. Journal of Environmental Engineering, 110 ). In “Ephemeroptera and Plecoptera: (1):123-130. Biology-Ecology-Systematics.” Landolt, P., Sartori, M., eds., Mauron, Tinguely and Lachat, Fribourg. pp. Gore, J.A. (1977) Reservoir manipulations and 30-33. benthic macroinvertebrates in a prairie river. Hydrobiologia, 55:113-123. Brittain, J.E. and Campbell, I.C. (1991) The effect of temperature on egg development in the Australian Gullan, P.J. and Cranston, P.S. (1994) The Insects: An Mayfly genus Coloburiscoides (Ephemeroptera: Outline of Entomology. Chapman and Hall, London. Coloburiscidae) and its relationship to disturbance pp150-179. and life history. Journal of Biogeography, 18:231- Koehn, J.D. and O’Connor, W.G. (1990) Biological 235. information for management of native freshwater Camargo, J.A. and Voelz, N.J. (1998) Biotic and fish in Victoria. Department of Conservation and abiotic changes along the recovery gradient of two

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Environment Freshwater Fish Management Branch. benthos of a Norwegian regulated river. Regulated Victorian Government Printing Office, Melbourne. Rivers: Research and Management, 9:93-102.

Lake, J.S. (1967) Rearing experiments with five Storey, R.G. and Cowley, D.R. (1997) Recovery of species of Australian freshwater fishes. I. three New Zealand rural streams as they pass Inducement to spawning. Australian Journal of through native forest remnants. Hydrobiologia, 353 Marine and Freshwater Research, 18:137-153. (1/3):63-76, September.

Lake, P.S. (1982) Ecology of the macroinvertebrates Walker, K.F. (1980) The downstream effects of Lake of Australian upland streams – a review of current Hume on the Murray. In “An Ecological Basis for knowledge. Bulletin of the Australian Society for Water Resource Management.” Williams, W.D. ed., Limnology, 8: 1-15. Australian National University Press, Canberra. pp. 182-191. Llewellyn, L.C. (1971) Breeding studies on the freshwater forage fish of the Murray-Darling River Ward, J.V. (1985) Thermal Characteristics of running System. Fisherman (NSW), 3(13): 1-12. waters. Hydrobiologia. 125:31-46.

Lugg, A. (2000) Eternal Winter in Our Rivers: Ward, J.V. and Stanford, J.A. (1979) Ecological factors Addressing the issue of cold water pollution. NSW controlling stream zoobenthos with emphasis on Fisheries, Unpublished. thermal modification of regulated streams. In “The Ecology of Regulated Streams.” Ward, J.V. and Marchant, R. (1989) Changes in the benthic Stanford, J.A. eds., Plenum Press, New York. pp. 35- invertebrate communities of the Thompson River, 56. southeastern Australia, after dam construction. Regulated Rivers:Research and Management, 4: 71- Webb, B.W. and Walling, D.E. (1988) Modification of 89. temperature behaviour through regulation of a British river system. Regulated Rivers: Research and McDowall, R. (ed) (1996) Freshwater Fishes of Management. 2:103-116. south-eastern Australia, Reed Books Sydney.

Palmer, R,W. and O’Keeffe, J.H. (1989) Temperature characteristics of an impounded river. Archives of Hydrobiologia, 1 (6):471-485.

Ryan, T.; Webb, A.; Lennie, R.; and Lyon, J. (2001) Status of cold water releases from Victorian dams: Report for Catchment and Water, Department of Natural Resources and Environment.

Saltveit, S.J., Bremnes, T. and Brittain, J.E. (1994) Effect of a changed temperature regime on the

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