Interactions between upland catchment and lowland rivers: an applied Australian case study

Geomorphology9 (1994) 189-201

ELSEVIER

Interactions between upland catchment and lowland rivers: an applied Australian case study S.O. Brizga a, B.L. Finlayson b "School of Environmental Planning, University of Melbourne, Parkville, Vic. 3052, Australia bDepartment of Geography, University of Melbourne, Parkville, Vic. 3052, Australia

(Received October 10, 1992;accepted after revision July 27, 1993)

Abstract

Persistent allegations have been made, mainly by Victorian farmers, that channel and floodplain aggradation are occurring on the floodplain of the Snowy River in Victoria as a consequence of accelerated erosion of degraded agricultural land in parts of the New South Wales upland catchment. These claims prompted the Victorian Department of Water Resources to initiate geomorphological investigations involving reviews of historical evidence, including sequential aerial photographs, and a study of sediment sources based on environmental tracers. A qualitative approach set within a sediment budget framework was adopted for data integration, a detailed quantitative analysis being precluded by financial, temporal and practical constraints. No compelling evidence was found to support claims of recent channel aggradation in the downstream Snowy River. Transfer of sediment eroded from catchment slopes in NSW to the lowland floodplain in Victoria is indirect, with some sediments stored temporarily in fans and floodplains within tributary catchments and in the Snowy valley for long delay times. Storage and interbasin transfer of water as part of the Snowy Mountains Scheme have affected sediment delivery. The catchment upstream of Lake Jindabyne is effectively isolated by this large impoundment, and sediment transport rates as far downstream as the Delegate River junction appear to have significantly decreased as the result of the considerable reduction in discharge.

1. Introduction

The Snowy River drains a large upland catchment (more than 13,000 km 2) situated in two states, New South Wales ( N S W ) and Victoria, then flows through a short lowland alluvial reach downstream of Jarrahmond before discharging into Bass Strait (Fig. 1 ). Persistent allegations have been made, mainly by local farmers, that channel and floodplain aggradation are taking place in the lowland tract of the river due to accelerated erosion on degraded agricultural land in parts of the upland catchment in NSW. The concern is focussed on sand sized sediment which constitutes the channel bed sediments in the lowlands. Overbank deposition of sand is regarded as detrimental to agricultural 0169-555x/94/$07.00 © 1994Elsevier Science B.V. All rights reserved SSDIO 169-555X (93)E0059-L

productivity while fine sediment deposition is considered to be beneficial. The eroding upland agricultural areas are separated from the lowland tract by extensive remote forested uplands. The Victorian Department of Water Resources responded to the farmers' complaints by commissioning a geomorphological investigation to assist them in evaluating management options, including advice on the likely benefit to Victoria of implementing further erosion control measures in the eroding agricultural parts of the NSW upland catchment (Finlayson and Bird, 1989; Brizga and Finlayson, 1992; Caitcheon et al., 1992). This issue exemplifies, in a practical context, the necessity for understanding linkages between catchment erosion and downstream sediment yield. Atten-

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S.O. Brizga, B.L. Finlayson / Geomorphology 9 (1994) 189-201

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S. O. Brizga, B.L. Finlayson / Geomorphology 9 (1994) 189-201

tion has previously been drawn to the importance of this general theme (Wolman, 1977; Walling, 1983). Sediment budgeting has been used to explore such linkages, both to enhance scientific understanding (Dietrich and Dunne, 1978; Dietrich et al., 1982; Trimble, 1981, 1983; Phillips, 1987, 1991; Caine and Swanson, 1989; Sutherland and Bryan, 1991), and also to examine specific management issues such as the impact of logging roads on sediment yield (Reid et al., 1981), downstream sediment management problems resulting from the eruption of Mt. St. Helens (Lehre et al., 1983) and links between soil conservation and sediment pollution of downstream waterways (Phillips, 1986). The potential for management applications has been used to justify academic research on sediment budgets (e.g., Sutherland and Bryan, 1991). A qualitative assessment of sand delivery from the eroding upland agricultural areas in NSW to the lowland floodplain of the Snowy River in Victoria, set within a sediment budget framework, is outlined in the present paper. Guidance on this question was required for management purposes, but a detailed quantitative analysis was precluded by financial and temporal constraints, catchment size, the remoteness and inaccessibility of many parts of the catchment, and the scarcity of appropriate baseline data for much of the river channel upstream of Jarrahmond.

191

The climate of the Snowy catchment is predominantly Koppen Cfb, with limited areas of Cfc in the alpine zone (Linacre and Hobbs, 1977). Snowfalls regularly occur at high elevations in winter. Precipitation varies considerably throughout the catchment. The highest values are found in the Snowy Mountains where annual precipitation of more than 2000 mm has been recorded. In contrast, average annual precipitation is less than 500 mm in the rainshadow area near Dalgety (James, 1989). European settlement began in the Monaro district in the 1820s and 1830s (Wakefield, 1969). Substantial parts of the NSW catchment are used for agricultural purposes, chiefly grazing. Relatively small parts of the upland catchment in Victoria have been cleared (Fig. 1). Some parts of the catchment are naturally devoid of forest cover (Costin, 1954), but much was formerly forested. Parts of the upland catchment in both states have been reserved as National Parks, but timber harvesting is carried out in other places, and gold mining has also occurred. The floodplain downstream from Jarrahmond has been substantially modified. Historic maps indicate that much of the floodplain was forest, "jungle" or morass at time of European settlement. Subsequent clearing and drainage has taken place, and the land is now grazed and cultivated.

2.1. The Snowy Mountains Scheme and its hydrologic impact 2. The Snowy catchment The Snowy River rises on the north-eastern slopes of Mt. Kosciusko, flows in a circuitous course via Jindabyne and Dalgety to the Victorian border and from there in a generally southerly direction to the sea at Marlo (Fig. 1). For most of its length, the river flows in a relatively narrow valley, in some places gorge-like, carved into Palaeozoic granitic, sedimentary and volcanic bedrock. Small deposits of Cainozoic sediments exist in some parts of this valley. Only downstream of Jarrahmond, where it leaves the highlands, does the Snowy have a substantial floodplain. Here the river is perched between natural levees, and during large floods water in excess of bankfull discharge flows away from the channel to low parts of the floodplain, escaping at crevasses in the levees. The downstream end of the Snowy River is estuarine, with tidal influence persisting as far upstream as Orbost.

The Snowy Mountains Scheme (SMS) is a major water resources development involving the damming and westward diversion of water from the Snowy River and its tributaries upstream of Jindabyne through tunnels to the Murray and Murrumbidgee catchments where it is used for irrigation. The westward flow of the water involves a fall of more than 900 m, which is exploited for hydro-electric power generation (Neal, 1982). The major developments relevant to downstream hydrology have been summarized by the Snowy Mountains Hydro-electric Authority (SMHA) (1970). The SMS began to have an impact on the Snowy River on 10 January 1955, when the storage of water in the Guthega Pondage commenced. The Guthega project led to diurnal fluctuations in streamflows, but is considered to have had no significant effect on large floods or monthly discharge (SMHA, 1970). Later stages of the scheme have led to progressive

S.O. Brizga, B.L. Finlayson / Geomorphology 9 (1994) 189-201

192

Table 1 Mean annual discharge of the Snowy River at Dalgety, Basin Creek and Jarrahmond Site

Time period

No. of water years

Mean annual flow (GI)

Dalgety

1950/51-1966/67 1968/69-1988/89

17 21

1187 68

Basin Creek

1936/37-1954/55 1955/56-1966/67 1968/69-1977/78

19 12 10

2056 2121 1137

1923/24-1949/50 1968/69-1987/88

25 20

2020 1212

Jarrahmond

prior to the SMS (Table 1). Annual series flood frequency analysis using the Log Pearson Type III distribution reveals a dramatic reduction in the magnitude of flood flows at all recurrence intervals at Dalgety

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reductions in streamflow in the Snowy River. Water storage in Lake Eucumbene commenced in June 1957. The closure of the Jindabyne dam in April 1967 enabled the complete diversion of flows generated upstream of this site out of the Snowy catchment, with flow in the Snowy River immediately downstream of the dam only occurring due to small releases to satisfy riparian rights or during rare spills. Monthly records show that the Jindabyne dam has spilled only during 5 months in the period 1968-1990. The hydrologic impact of the SMS on the Snowy River was examined by comparing streamflow and flood regimes before construction commenced, during the construction phase, and after closure of the Jindabyne dam. Five gauging stations are currently operated by the Rural Water Commission of Victoria (RWC) or Water Resources Commission of NSW (WRC) on the Snowy River between Jindabyne and Jarrahmond. However, data from only three stations, including a discontinued gauging site at Basin Creek, were analysed because the length of record for the others is insufficient. The actual periods of data selected for analysis at these three gauging stations were also constrained by the availability of records. Water years beginning in March were used. Massive reductions in mean annual discharge are apparent following the completion of the SMS: at Dalgety the post-Jindabyne mean annual flow is less than one seventeenth of the pre-Jindabyne mean annual flow, and even as far downstream as Jarrahmond mean annual flow after closure of the Jindabyne dam is only slightly greater than half the mean annual discharge

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Fig. 2. Hood frequency distributions of the Snowy River. (a) At Dalgety prior to the closure of the Jindabyne dam ( 1951/52-1966/ 67) and after the closure of the Jindabyne dam ( 1968/69-1988/ 89), (b) at Basin Creek prior to the construction phase ( 1936/371954/55), during the construction phase ( 1955/56-1966/67) and after the closure of the Jindabyne dam (1968/69-1977/78), and (c) at Jarrahmond prior to the construction phase ( 1923/24--1949/ 50) and after the closure of the Jindabyne Dam ( 1968/69-1988/ 89). Based on discharge data from the RWC and WRC.

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following the closure of the Jindabyne dam (Fig. 2). Less dramatic changes are apparent at the Basin Creek and Jarrahmond gauging sites, where the magnitude of small floods has decreased since the closure of the Jindabyne dam, but the size of large, infrequent floods appears to have marginally increased.

SLOPEEROSION

SLOPEANDFAN DEPOSITS

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TRIBUTARIES

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3. M e t h o d s and data sources

A sediment budget has been defined as "a quantitative statement of the rates of production, transport, and discharge of detritus" (Dietrich et al., 1982, p. 6). A qualitative rather than quantitative approach was adopted for the Snowy catchment for a number of reasons. Firstly, the Snowy catchment is large by comparison with catchments for which sediment budgets have previously been reported. For example, the Coon Creek catchment studied by Trimble (1981, 1983) is only 360 km 2 and the Upper Tar catchment examined by Phillips (1986) is 1121 krn2. The most detailed quantitative sediment budgets have been prepared for catchments many orders of magnitude smaller than the Snowy (Dietrich and Dunne, 1978; Caine and Swanson, 1989; Sutherland and Bryan, 1991). Phillips (1987), who examined the Tar River catchment which is of comparable size to the Snowy (11,140 kin2), adopted a qualitative approach. Secondly, many parts of the Snowy catchment upstream of Jarrahmond are remote and inaccessible. This is a serious obstacle to a detailed field study, and has probably contributed to the relative scarcity of historic data for the river between Jindabyne and Jarrahmond. No sediment transport records exist for the area of interest: the only sediment transport data available for the Snowy River are suspended sediment records collected at and upstream of Jindabyne in conjunction with the SMS, and the collection of these data ceased in 1967 when the dam was closed (SMHA, 1972). Scarcity of sediment load data is a problem on most Australian rivers (Hean and Nanson, 1987). Detailed baseline data such as used by Trimble (1983) do not exist for the Snowy catchment. Thirdly, budgetary limitations imposed another constraint because the tax base is small. Land use adjoining the Snowy River in Victoria is predominantly National Park and forest (upstream of Jarrahmond) and agricultural land and the small township of Orbost (downstream of Jarrahmond) Fourthly, tern-

TRIBUTARY FLOODPLAINS

t ~

TRIBUTAFIYSTREAM~ CHANNELS

; "-LOODPLAIN& CHANNELMARGIN DEPOSITS

SNOWY RIVER

t

t RIVER CHANNEL

JARRAHMOND

Fig. 3. Conceptualmodelof sediment storage and transportin the Snowy Rivercatchmentupstreamof Jarrahmond. Arrowsindicate directionsof sedimenttransfer. poral constraints precluded any approach that would involve long term monitoring- an answer was required relatively quickly for management purposes. This situation is common worldwide; management decisions cannot be delayed for the length of time necessary to collect data by monitoring and there are few long term data sets already in existence. Sediment storage and transport were assessed by inference from sequential aerial photographs and other historical material, including maps, photographs, written descriptions, and records relating to the construction and maintenance of bridges; as well as field inspection. Similar historical data sources as well as newspapers, Land Selection Files, and repeated cross sections compiled by the RWC (1988) were used in evaluating channel changes downstream of Jarrahmond (Finlayson and Bird, 1989). Our assessment of sediment storage and transport upstream of Jarrahmond was complemented by a concurrent study of sediment sources using mineral magnetics and radionuclides (Caitcheon et al., 1992). A conceptual model of sediment storage and transport in the Snowy catchment (Fig. 3) summarizes in a

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generalized fashion the paths which sediment eroded from the catchment slopes may follow as it travels through the system to Jarrahmond. The following dis-

cussion begins with an assessment of the validity of the claims regarding sedimentation downstream of Jarrahmond which prompted the Department of Water

Photo 1. Aerial photographs of the Snowy River at Jarrahmond in (a) 1940 and (b) 1973 showing changes in bar morphology. Source: Australian Survey and Land Information Group & VICIMAGE.

S.O. Brizga, B.L. Finlayson / Geomorphology 9 (1994) 189-201

8

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195

1988 1971 1960 1936 1920

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I 60 80 Distance (metres)

100

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Fig. 4. Cross sections of the Snowy Riverat a site downstreamof Jarrahmond in 1920, 1936, 1960, 1971, 1988. Surveysof this site carried out in 1939, 1964, 1965 and 1978 are not shown on this diagrambecauseof the high degree of overlap. Source:RWC (1988). Resources to initiate the study. Then sediment transport and storage within tributary basins as well as in the Snowy River are examined separately. The Snowy River is dealt with two parts: Jindabyne dam to Delegate River confluence, and Delegate River confluence to Jarrahmond. There are pronounced differences in present flood regime between these reaches, and the hydrologic regime upstream of the Delegate River has changed to a greater degree following the completion of the SMS than the reach downstream.

4. Channel and floodplain problems in the lowlands Floodplain sedimentation is clearly occurring during floods, as would be expected given the geomorphic setting, with substantial accumulations occurring as crevasse splays. Historical maps and aerial photographs indicate that apart from the location of the river mouth and one artificial cut through a meander bend, the position of the river channel downstream of Jarrahmond has not changed since the first survey in the 1860s. However, periodic changes in bar morphology are apparent from comparisons of historic and recent aerial photographs (Photos la and lb).

Repeated cross section surveys, dating from 1920, have been carried out at a large number of sites on the lower Snowy River by the RWC, some sites having been surveyed as many as nine times. Compilations of these cross sections provide no indication of any significant change in width or bed elevation, although there are fluctuations in bed elevation presumably related to sand bar movement (RWC, 1988) (Fig. 4). A review of other historical evidence yielded no compelling evidence of major aggradation (Finlayson and Bird, 1989). An illusion of increased sedimentation in the channel has been created by the hydrological changes stemming from the SMS through an increase in the duration of low flows, making the sand in the river bed visible for longer periods of time. The RWC (1988) reports that the 70 percentile flow pre-diversion was 2400 M1/day and that this reduced to 560 M1/day post-diversion. These flow volumes mean that the difference in water depth at the Jarrahmond gauge is 0.40 m, which represents 37 m of additional channel width where sand is visible (RWC, 1988). Flows at this level occur for nearly four months in total each year, giving a prolonged period of sand exposure in the river bed. This appears to have given rise to the popular conception that the channel has been partially infilled with sediment.

196

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Overall, channel changes downstream of Jarrahmond were found to be much less significant than previously thought. Local disturbances to the river channel downstream of Jarrahmond may have contributed to some of the observed problems. Clearing of the river banks and floodplain took place last century, and this may have affected crevasse development. The river channel has been deliberately interfered with in order to increase its capacity. Extensive desnagging has taken place over the past 110 years and vegetation has been removed from sand bars in the river. This could have contributed to the observed instability in sand bar morphology. The Snowy River may still be in a phase of adjustment to these disturbances (c.f., Warner and Bird, 1988).

5. Sediment storage and transport in the uplands The catchment of the Snowy upstream of Lake Jindabyne was not examined in any detail as Lake Jindabyne can be expected to be a highly efficient sediment trap. Lake Jindabyne has a capacity of 689,790 M1 (Neal, 1982) and natural average annual discharge at the dam site has been estimated to be 1,193,085 M1 (SMHA, 1970). From these figures, the capacityinflow ratio can be calculated to be 0.58, which on the basis of Brune's (1953) relationship between trap efficiency and capacity-inflow ratio means that Lake Jindabyne could be expected to have a trap efficiency of more than 90 percent. The trap efficiency might be expected to even be greater than calculated for several reasons: (1) actual inflows are less than natural inflows due to interbasin diversions at several sites upstream, and (2) outflows are much less than inflows due to interbasin diversions at the Jindabyne dam. 5.1. Catchment and tributaries

Severe sheet and gully erosion is unquestionably occurring on much of the agricultural land in the NSW catchment, and many of the tributaries of the Snowy in this area have become incised. This erosion has been previously documented (Costin, 1954; Taylor, 1957/ 58). Historical research by Hancock (1972) suggests that accelerated erosion began when the area was settled by Europeans in the nineteenth century, probably initiated by pastoral and agricultural development, or

rabbits. Channel incision on the nearby Southern Tablelands has also been ascribed to post-settlement environmental change (Eyles, 1977; Prosser, 1991 ). Some erosion control measures have been attempted in the Snowy catchment, but erosion remains widespread and further remedial works have been proposed. Tributary streams draining the eroded agricultural land are clearly delivering sand to the Snowy River (Caitcheon et al., 1992), but not all of the sediment eroded from the catchment slopes has been delivered to the Snowy River. Sediment deposition is apparent downslope of many sites of erosion, with the sediments stored there only finding their way into tributary streams or the Snowy River when they are remobilized by further erosion. Incision of tributary systems is in many places discontinuous, with incised reaches terminating in fan deposits or alternating with swampy overgrown reaches. There is some evidence to suggest that temporal alternation between transporting phases and storage phases occurs (an example is shown in Photo 2). Costin (1971) reported wood aged 7010 + 110 and 6250 + 90 years in peat deposits overlying gravel along Wullwye Creek, which implies relatively long periods of sediment storage. Previous research elsewhere in NSW supports the contention that sediment delivery from tributary catchments may be quite slow. Melville and Erskine (1986) reported that most of the sediment eroded by postEuropean discontinuous gullying in the catchment of Fernances Creek has been transported only a short distance downstream. Prosser ( 1991 ) observed that along Wangrah Creek in the nearby Southern Tablelands, valley fill deposits were generally hundreds to thousands of years old. 5.2. Snowy River: Jindabyne dam to Delegate River

There is little unvegetated sand in or adjacent to the channel of the Snowy River between the Jindabyne dam and Dalgety, and the channel margins are in many places overgrown with reeds, scrub and willows. This is a response to the alteration of the flood regime resulting from the closure of the Jindabyne dam. Sediments in the riverbed appear dominated by inputs from nearby tributaries. For example, Caitcheon et al. (1992) found that approximately 87 percent of the sand in the Snowy River a short distance downstream from Wullwye Creek had been supplied to the river by Wullwye Creek.

S.O. Brizga, B.L. Finlayson / Geomorphology 9 (1994) 189-201

197

Photo 2. Aerial photographs of Wullwye Creek near Dalgety showing (a) the incised, sandy channel upstream of "A" in 1959 which had changed to an apparently stable, overgrown channel by 1988 (h). Source: Lands Department, New South Wales. This suggests low rates o f sediment transport in this part of the Snowy River. Downstream from Dalgety, unvegetated sand and gravel bars become more common, but the channel margins are still overgrown in many places.

Sequential aerial photographs and historical maps of the Snowy River between the Jindabyne dam and the Delegate River confluence suggest that the size of the active channel and the extent of unvegetated sediment deposits have decreased since the closure of Lake Jin-

198

S.O. Brizga, B.L. Finlayson / Geomorphology 9 (1994) 189-201

Photo 3. The SnowyRiverat Dalgety:(a) ca. 1906and (b) in 1991.The 1906photographis reproducedcourtesyof the MitchellLibrary,State Libraryof New South Wales. dabyne. This is supported by field evidence and historical photographs (an example is shown in Photo 3). The contraction of the channel is perhaps more pronounced in the upstream parts of this reach than at the downstream end. A reduction in channel size could be expected in response to the large reduction in discharge

resulting from the SMS described earlier in this paper. A downstream decrease in the degree of channel contraction could also be expected as the hydrologic impact of the SMS is mitigated by tributary inflows. The changes in channel morphology imply a reduction in bedload transport, particularly at the upstream

s.o. Brizga, B.L. Finlayson/ Geomorphology 9 (1994) 189-201

end of this reach. Bedload transport rates could also be expected to have decreased on the basis of the reduction in discharge. Sediment retention times in vegetated deposits have probably increased as a result of the altered flood regime, because floods capable of liberating sediment would occur less often than prior to the closure of Lake Jindabyne. Many of the tributaries entering the Snowy River between the Jindabyne dam and the Delegate River drain eroding agricultural land. The retention time of this sediment in the Snowy upstream of the Delegate River could be expected to have increased as the result of the hydrologic changes brought about by the SMS, and thus the rates of delivery of sediment from this part of the catchment to the floodplain downstream of Jarrahmond could be expected to have considerably decreased. 5.3. Snowy River: Delegate River to Jarrahmond

The character of the Snowy River changes dramatically at the Delegate River confluence. The active channel is much larger and has the appearance of being cleared out by floods more often than the channel upstream of the Delegate River, which is not surprising since it is subject to larger floods because of a major input of discharge from the Delegate River. Sand and other sediments are stored where conditions are conducive; within the channel where its gradient is relatively low, and in bars and small "floodplains" adjacent to the channel where the valley is relatively wide. Many of the bars and "floodplains" are vegetated: from the sequential aerial photographs, some appear to have been stripped by floods of their vegetation, and presumably some sediment, whereas others have remained intact. Sediment transport is likely to occur at higher rates than upstream. The work of Caitcheon et al. (1992) suggests that Wullwye Creek and the Delegate and Maclaughlin Rivers contribute more sand to the Snowy River than the Jacobs, Deddick and Buchan Rivers, which enter the Snowy further downstream. Their work was based on mineral magnetics of sediments sampled in the Snowy River downstream of the tributary confluences and the apparent differences in sand contribution may well be a reflection of greater mixing and more rapid transport rates in the Snowy River further downstream due to higher discharges.

199

Comparisons of recent and historic aerial photographs provide no evidence of any significant change in the extent of unvegetated sediment deposits, the major sediment accumulations tending to occur in the same general areas on the earliest aerial photographs (1940s) as they do on more recent photographs. More detailed comparisons are made difficult by differences in flow levels between photograph dates. The SMS does not appear to have had a major impact on sediment storage and (by inference) transport within this reach. The hydrological data presented earlier indicate that while low flows have been reduced considerably, the magnitude of larger, less frequent events has not significantly changed since the closure of Lake Jindabyne, due to discharge contributions by the Delegate River as well as other major tributaries further downstream. Some of the NSW tributaries entering the Snowy River downstream of the Delegate River (including Matong Creek, Currowang Creek, and the Delegate itself) drain eroding agricultural land. Sediment delivered to the Snowy River by these tributaries can be expected to be transported downstream relatively efficiently compared with the tributaries entering upstream of the Delegate. However, the distance from tributaries draining the Monaro Tableland to Jarrahmond is considerable. Also, some tributaries with forested catchments are contributing significant quantities of sand: for example, Caitcheon et al. (1992) reported that the contribution of the Jacobs River was 17% ( _ 8%). These contributions, together with the sand stored in the Snowy valley, mean that even if all sand delivery from NSW agricultural areas were halted, sand would continue to be delivered by the Snowy River at Jarrahmond.

6. Conclusions

The research reported in this paper has shed light on two issues central to the management of the Snowy River downstream of Jarrahmond. Firstly, it has revealed that channel aggradation downstream of Jarrahmond is not the serious problem it was previously assumed to be. Secondly, it has shown that the relationship between erosion rates in the agricultural parts of the NSW catchment and sediment delivery to the channel and floodplain downstream of Jarrahmond is indirect. Natural delays resulting from the incorpora-

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tion of sediment into slope, fan and floodplain deposits within tributary catchments, and into "floodplains" in the Snowy River valley are apparent This conclusion is consistent with Phillips' (1992) finding that upperand lower-basin sediment systems in the Neuse River, North Carolina are not linked in any simple way. The SMS appears to have had a major impact on sediment delivery in the Snowy River. The catchment upstream of Lake Jindabyne has become virtually isolated from the lower Snowy River by this major impoundment. Rates of sediment delivery from those parts of the catchment draining into the Snowy River between the Jindabyne dam and Delegate River could also be expected to have decreased because of a massive reduction in discharge. These findings suggest that it would be more profitable to direct management attention to issues other than the perceived sedimentation problem which has been a major preoccupation. While erosion control works in the eroded upland areas of the NSW catchment may be of local benefit, they are unlikely to provide any immediate benefit to the lowland floodplain. This example illustrates how a qualitative sediment budget-based analysis can be used to provide guidance for management. Management decisions constantly need to be made, irrespective of the availability of relevant information. Even choosing to do nothing or maintain the status quo is a decision. Detailed quantitative sediment budgets are certainly more powerful. However, in situations where neither the time nor resources are available for such an approach, a less detailed qualitative analysis can contribute significant insights.

Acknowledgements Funding for this research was provided by the Department of Water Resources Victoria. We would like to thank Chandra Jayasuriya and Wendy Nicol for producing the diagrams and photos.

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