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(Filesize: 1.15 MB) | Environmental Scan of the Namoi River Valley. Report for the Department of Land and Water Conservation and the Namoi River Management Committee.
Thoms, M., Norris, R., Harris, J., Williams, D. & Cottingham, P. |
Table of Contents
EXECUTIVE SUMMARY
The Department of Land and Water Conservation (DLWC) and the Namoi River Management Committee (NRMC) are currently developing a river management plan for the Namoi River and its tributaries. An assessment of the current biophysical condition of the Namoi River (environmental scan) is essential to develop a common understanding of the processes and management activities that affect the health of the river. This work, along with other socio-economic information, forms the basis for the development and implementation of the river management plan for the Namoi River.
This report of the environmental scan draws on previous investigations of the Namoi River system to identify the key ecological issues to be addressed in the river management plan, and important scientific knowledge gaps to be addressed in order to overcome barriers to, or improve the implementation of, management actions aimed at improving the ecological health of the river. The specific issues addressed are:
· The importance of maintaining riverine health;
· The nature of the catchment;
· The level of knowledge of the biophysical condition of the Namoi;
· Threats to riverine health along the Namoi;
· A program to address scientific knowledge gaps.
A watershed or catchment focus is required for managing river health so that the interaction of landscapes, rivers and humans may be considered. Humans may alter the biological systems in a river by altering physical habitat, modifying seasonal water flow, changing the system’s food base, changing interactions among stream organisms, and contaminating the water with pollutants.
The connection of the riparian (stream bank) zone and floodplain with a river system is also important, as riparian vegetation and the floodplain provides organic matter (energy) and nutrients that drive primary production, and shade and refuge for biota such as fish. The linkage of rivers with their floodplains also helps maintain wetlands that are often important sources of local and regional biodiversity (e.g. populations of birds, fish and invertebrates).
The flow regime of a river plays a major role in river processes, as flow helps shape the river (affects geomorphology), provides cues for key biological processes (e.g. breeding cycles) and links the river with its floodplain. Flow regulation through dam and weir construction and water abstraction has led to severe stress being placed on many river ecosystems in the Murray Darling Basin, including the Namoi. Changes to flow and sediment regimes following catchment modification can markedly alter the physical nature of the channel and consequently the habitats that support organisms. We now recognise the need to allocate water to fulfil the needs of riverine environments and to protect these systems.
The health of a river may be assessed by comparing a site or area of interest with another thought to be in good condition (the reference condition). The reason for establishing reference conditions is to compare like with like. The approach most commonly used has been to select reference sites that are ‘minimally disturbed’. Often, pre-European disturbance conditions are set as restoration goals, but those conditions may not be attainable as this denies the place of humans in the landscape. In such circumstances, management targets should initially be set so they are achievable. A key aim should be to maintain the biological integrity of a system, that is “the ability of a system to support a balanced, integrated, adaptive community of organisms with a species composition, diversity and function comparable to that of natural habitat in the area”.
An assessment of the current condition of the Namoi identified the following as major contributors to the generally moderate to poor riverine condition that prevails:
· Degradation of the riparian zone, or complete lack of riparian zone;
· Channel morphology impacts such as bank instability, riverbed instability, and aggradation of sediments. This is primarily due to two factors: 1) excessive sand and gravel extraction, and 2) fluctuating water levels;
· Morphological and biological effects of dams and river regulation;
· Poor land management practices;
· Poor water quality, mainly because of high total phosphorus, turbidity and salinity levels, and localised incidence of pesticide contamination;
· Poor native fisheries, with low species diversity and abundance, especially in upland areas due to the presence of barriers to fish migration.
Seven river zones have been identified for the Namoi River system: pool, constrained, armoured, mobile, meander and distributary. A total of 23 major threats to river condition have been identified, with the anabranch, distributary and meander zones most at risk to environmental degradation. The alteration of river flows, clearing or absence of riparian vegetation, and threats resulting from land management activities (e.g. nutrient and pesticide transport to waterways) are threats common to each of the river zones. Addressing these threats is consistent with the aims and objectives of the Integrated Monitoring or Environmental Flows (IMEF) program, which is part of the NSW Water Reforms, and the recommendation of numerous reports on the state of natural resources in the Namoi River catchment. The NRMC has identified the following key issues to be addressed in their river management plan:
· Fish passage;
· Thermal pollution;
· Floodplain management;
· Off-allocation access;
· Wetland status and other riparian vegetation;
· Operation of dams and weirs;
· Cultural and spiritual issues;
· Carp reduction.
These issues are a mixture of ecological, water management and social-economic issues. In terms of managing environmental conditions, the above issues may be considered as part of two key questions:
1. How do we maintain or improve native fish populations?
2. How do we manage our river system to maintain or improve biodiversity and important functions such as riverine and wetland productivity?
Native fish populations are often used as an indicator of river health, as their presence is dependent on a number of factors such as energy (food) availability, water quality, flow regime and habitat availability. Maintaining biodiversity, and riverine functions such as production and respiration, are also important because they help maintain the resilience of ecosystems upon which we all ultimately depend; the connection of a river with its floodplain and floodplain wetlands is a key component in maintaining riverine health. Maintaining or improving the condition of Namoi River system is therefore dependent on the management of both in-stream and floodplain processes, and factors that threaten them.
Establishing a reference condition that serves as a target for future management in catchments that have been extensively modified (e.g. for agriculture) can be a difficult task, and will largely depend on the values attached to the riverine system by local communities. This can be achieved for in-stream conditions by the use of tools such as the Index of Biotic Integrity (based on fish populations) and AUSRIVAS modelling (based on macroinvertebrates). Both models use regional data sets to identify ‘reference’ sites where human impacts are considered minimal and conditions are indicative of healthy ecosystems. Comparison of the fish and invertebrate populations at test sites in the Namoi system with that expected to occur at reference sites can be used to establish the relative in-stream health of the Namoi. The reference sites may also serve as targets against which the effects of future management in the Namoi may be assessed.
While the IBI and AUSRIVAS are valuable tools for identifying in-stream reference conditions, no such formal tools are currently available for assessing riparian and floodplain conditions. Given that the riparian zone and the floodplain have been extensively modified and will often not be economically returned to their pre-development state, it is unrealistic to develop reference conditions based solely on pre-development (pre-European) conditions and use them as a target for future management. In this case, measures of intactness and functionality (e.g. length of stream with riparian vegetation that performs key ecosystem functions), or biodiversity and connectivity in key floodplain wetlands are likely to provide a guide to targets that may realistically be achieved or the result of best management practices.
In-stream priorities
The following recommendations are drawn from assessments of riverine condition and consideration of other factors:
· The MacDonald River above Lowry is considered to be in excellent condition and may be considered as a reference site for upland streams in the Namoi. The maintenance of its condition should receive the highest priority in future management and restoration efforts.
· Given its impact on biological and ecological function (e.g. breeding and growth of fish and macrophytes), a review of the extent and persistence of cold-water releases from major dams should be undertaken as soon as possible. This is especially important to ensure that future environmental flows are effective and that cold-water pollution does not prevent migratory fish from using fishways when installed.
· The Peel and Cockburn Rivers are in relatively good condition, as is the Manilla River above Split Rock Dam, and should be given the next highest priority in management and restoration efforts. Important issues to be addressed include improving riparian zone condition, reducing the transport of nutrients from the catchments above Chaffey and Split Rock Dams that help sustain algal blooms, managing the salinity threat and managing the effects of stream instability resulting from sand and gravel extraction. The effectiveness of the fishway at Split Rock Dam should be evaluated and research undertaken to develop fishways for high dams such as Chaffey.
· The priority given to the remaining rivers or river zones requires further consideration by the NRMC. Opportunities may exist to significantly improve the relative condition of rivers by addressing one or two factors (e.g. improved riparian condition along the Namoi River between the Manilla River confluence and Narrabri; effective fishways at Weeta, Gunindera and Mollee weirs). The effect of environmental flows should also be reviewed as recommended by the IMEF process, especially in terms of their effects on creeks, flood runners and wetlands in the lower Namoi distributary zone.
Floodplain priorities
Increased salinity is expected to continue as a major land and water management issue. The ecological effects of increased salinity have the potential to negate improvements achieved through management efforts such as the delivery of environmental flows and installation of fishways. Salinity management should continue to have a high priority in floodplain areas. While high stream salinity is already evident in the streams of the Liverpool Plains and areas of the Peel catchment, a review of trends in groundwater levels will be useful for identifying other areas at risk to salinity.
Surveys of the riparian condition should be undertaken to identify the remnant stands of intact vegetation in each of the major river zones. Existing high quality riparian vegetation should be protected as an example of realistically achievable conditions (future targets for improvement) and as natural seedbanks that will assist efforts for improving degraded riparian habitat.
The condition and biodiversity of key wetlands should be reviewed to provide a baseline to measure the effectiveness of future management, including environmental flows delivered through the NSW water reforms. Given their history in supporting a diversity or abundance of bird and fish populations, or habitat complexity, the following wetlands may be considered as part of this review: Lake Goran, and Gunnible, Gulligal, Barbers and Wirebrush Lagoons. Other wetlands may be added, depending on community priorities.
Assessing the effectiveness of the river management plan currently being prepared by the DLWC and NRMC will require a specifically designed monitoring and evaluation strategy such as the Integrated Monitoring of Environmental Flows (IMEF) program. With the establishment of this program in the Namoi Valley, particularly if the IMEF is further integrated with the Central and North West Regions Water Quality Program, a greater understanding of the linkages between catchment management practices and processes affecting water quality and biotic response to river flows may be achieved. Both the plan and associated monitoring and evaluation programs may be modified in the future as new information and insight becomes available (i.e. within an adaptive management framework).
Other areas of research that will provide valuable information for future riverine management include:
· Biological control methods for carp as part of national efforts;
· The effects of persistence of cold-water releases on fish, invertebrate and macrophyte biology;
· Improved fishway design, especially for high dams.
TABLE OF CONTENTS
1 INTRODUCTION 1
1.1 Background 1
1.2 Project Terms of Reference 1
1.3 Project Scope 1
2 THE IMPORTANCE OF MAINTAINING RIVERINE HEALTH 3
2.1 Why do we need healthy rivers? 3
2.2 How do rivers work? 5
2.2.1 Natural flows are variable 8
2.2.2 High flows feed rivers 9
2.3 Assessing River Health 9
2.3.1 Physical and chemical indicators 9
2.3.2 Biotic indicators 10
2.4 Why is a river management plan important? 10
3 The Namoi River Catchment 12
3.1 Catchment Character 12
3.2 River Geomorphology 13
3.3 Hydrology 15
4 THE CURRENT CONDITION OF THE NAMOI RIVER SYSTEM 19
4.1 Physical Condition 19
4.2 Physico-Chemical Water Quality Conditions 22
4.3 Biological Conditions 25
4.3.1 Invertebrates 25
4.3.2 Fish 26
4.3.3 Instream and Riparian Vegetation 28
4.4 Stream Condition Assessment 30
4.5 Summary of Condition 33
5 THREATS TO RIVER HEALTH 34
5.1 Current Threats and their Scientific Basis 37
5.1.1 Physical condition of the river channel 37
5.1.2 Riparian and aquatic vegetation 38
5.1.3 Fish 38
5.2 Emerging Threats 40
5.2.1 Water Quality 40
5.2.2 Riparian and aquatic vegetation 41
5.2.3 Fish 41
5.3 Prioritisation of Threats 42
5.3.1 Recommended DLWC and NRMC Priorities 42
6 PROGRAM TO ADDRESS SCIENTIFIC KNOWLEDGE GAPS 47
6.1 River Geomorphology 47
6.2 Water quality 48
6.3 Macroinvertebrates 49
6.4 Fish 49
6.5 Riparian Inventory and Priorities 50
6.5.1 Collation of existing knowledge of riparian systems 50
6.5.2 Vegetation and geomorphic survey of riparian zones 50
7 references 52
Figures
Figure 1: Components of a river system 6
Figure 2: Processes in upland rivers 6
Figure 3: Processes in lowland constrained rivers 7
Figure 4: River – floodplain interactions 7
Figure 5: River zones in the Namoi catchment 14
Figure 6: Long-term monthly flows (observed and simulated natural) for the Namoi River system: a) Peel River; b) Gunnedah, and c) Narrabri. Source: DLWC, Integrated Quantity and Quality Model (IQQM) 18
Figure 7: Namoi River Catchment Index of Stream Condition. * - Water Quality and Aquatic Life sub-indices could not be calculated. 32
Figure 8: Summary of key issues confronting riverine management in the Namoi catchment 45
Tables
Table 1: Geomorphological zones of the Namoi Catchment. 15
Table 2: Total Annual Flow Statistics for the Namoi River (ML). 15
Table 3: Changes in average return intervals of floods for selected sites in the Namoi River system. Source: DLWC, Integrated Quantity and Quality Model (IQQM) 17
Table 4: Characteristics of sites sampled in the Namoi River Catchment. 20
Table 5: Physical habitat assessment of sites in the Namoi River Catchment. 21
Table 6: Abundance of fish species recorded at sites in the Namoi River catchment. Data from the NSW Rivers Survey (Harris and Gehrke 1997). Surveys 1 – 5 occurred from October 1994 to April 1999. 27
Table 7. Summary of dominant riparian species in various reaches of the Namoi system (Source DWR 1992). 29
Table 8: Five-point scale for indicator measurements. 31
Table 9: Major threats to environmental condition of the 7 river regions in the Namoi 34
Table 10: Interaction of effects associated with degrading influences 37
Table 11: Combined assessment scores for sites across the Namoi catchment 46
Table 12: Physical indicators of river system condition 47
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