Environmental literature scan of the Barron River Catchment

[Extract] Executive Summary. Queensland Department of Natural Resources is formulating a Water Allocation and Management Planning (WAMP) framework to achieve the sustainable use and management of water resources. This review provides a background for the WAMP process in the Barron River Catchment Basin. There was no provision for field work so the report relies on available reports and on the knowledge of the writers. More intensive and primary work will be required as part of the WAMP process. The Barron River rises at about 1000 m, east of Herberton, then flows north through Atherton and Mareeba, east through Kuranda and the Barron Gorge, then across a narrow floodplain to its mouth 15 km north of Cairns. Its length is about 165 km and its catchment is about 2100 km2. It is dammed at Tinaroo, in its upper reaches, providing water for irrigation and domestic supply, and there is a weir at Kuranda in its lower reaches for power generation. The climate varies from humid to subhumid, with well defined wet and dry seasons. Stream flow is high but highly variable in the wet season, and moderate and less variable in the dry season. There are four major parental rock materials in the region (Barron River metamorphics, Atherton basalts, Granites, and Carboniferous rhyolites) together with alluvium derived from them. Vegetation includes rainforest (27% of the area), Eucalyptus Woodland (31%), Tussock Grassland (17%), Dense Sown Pasture (15%) and sugar cane (5%). Six management zones are recognised on the basis of physiographic and demographic and ecological information. The lack of information on river morphology and ecological processes necessitated adopting these zones in this review. Some of the zones overlap with the Wet Tropics World Heritage Area (WTWHA) which includes rare rainforest species and vegetation types, endangered and vulnerable faunal species, and areas of special evolutionary significance. The zones are: 1. Upper Barron and 2. Tinaroo, including the headwaters of the river and overlapping with the WTWHA; the landscape comprises rainforest, woodlands, improved pastures, and agricultural and horticultural crops; 3. Central which includes a large tract of irrigated agricultural land, rainforest on the mountains and eucalypt and paperbark woodland elsewhere; 4. Northern, characterised by extensive grazing and intensive agriculture, and rainforest, much of which is in the WTWHA; 5. Kuranda, which includes the Barron Gorge and immediately upstream and a large area of the WTWHA; 6. Lower Barron, which includes the lowland floodplain which is used for extensive urban development and sugarcane growing. This zone is sub-divided into estuarine and non-estuarine sections; the lower end of the estuary is surrounded by extensive mangrove forest. No comprehensive geomorphological and ecological description of the Barron River appears to exist, and there is a paucity of detailed research on the flora and fauna of the river. Because of this, and the variability in morphology, geology and vegetation along the river, it is difficult to evaluate major ecological processes. A targeted study on the river’s habitats and other features relevant to ecological processes is warranted. Major issues, their ecological effects and possible remedial actions are detailed in the report. They include: 1. Flow, which is the single most important physical characteristic that influences the ecology of streams and rivers. Habitats are structured by the flow regime in combination with geological and geomorphological factors. The biota is generally well adapted to the flow regime that has selected it, so its character is directly related to the flow regime. The Barron’s flow has predictable strong seasonality, but the timing and size of spates are not predictable. Substantial changes to the flow are expected to result in changes to the biota through reduction in habitat extent, habitat diversity, biodiversity, riparian zone viability, water quality, dilution of contaminants, reproductive cues, and so on. 2. Riparian Vegetation, which plays a key role in influencing the structure and function of stream ecosystems. A wide natural riparian zone has strong positive influences on water quality, stream morphology and habitat availability, instream primary production, litter accession and wildlife habitat. Alteration of the flow regime can seriously affect the riparian zone. 3. Water quality which encompasses the physical and chemical constituents of water, such as temperature, and dissolved and suspended material, including contaminants All of these variables are affected by flow, and can be differently affected by flows from different sources. 4. Sedimentation and Bank Erosion are natural processes which are the basis for habitat construction, determining distribution of different substrata and plants, and the animals that associate with them. Change in the flow regime is capable of causing major changes to the character of stream habitats, either on the bed or by increasing bank erosion. 5. Weeds and introduced animal species which can have devastating effects on native vegetation and animals. Changed flow regimes can aid dispersal and establishment of these exotic species. 6. Significant species and habitats occur in much of the Barron catchment, in all of the zones, but the data available on important species are fragmentary and do not relate to the Barron specifically. For species with direct relationships with the river (e.g. platypus), any change to the flow regime of the river has the potential for serious impact. Loss of native species has been identified as a major issue in the catchment. 7. Major impacts accrue from extensive land clearing in the catchment, causing sedimentation and poor water quality, 8. Continuation of required water supply for domestic and agricultural use is a major issue in the catchment. Addressing this problem has direct impact on stream flows, and requires careful management. The Barron catchment is quite remarkable in its diversity of climate, landscape, agricultural output and conservation values. Its diversity of habitats contributes to high species richness of plants and animal. It is situated in one of the most rapidly developing regions of the country, with urban, agricultural and tourist developments moving ahead rapidly. Increasing water supplies are required to provide domestic and irrigation water. The Barron is an obvious source of water, and already is heavily regulated via the Tinaroo Dam and Kuranda weir. There appears to be little published information on the effects of these impoundments on the ecology of the river. This review found a large body of information, yet it is fragmentary, because most of the information has little to do with the river itself. While it was possible to describe the general catchment, it was not possible to describe the aquatic environments and their biota in detail. Therefore, assessment of the impacts of changes in flow regime require extensive field work. Even a moderate survey of the river’s morphology and habitats would greatly improve the ability to predict the effects of change in flow regime. Targeted seasonal sampling of flows, water quality, and the biota will be required in assessing impacts of change. Such studies are not difficult, but given the size of the river would be quite time consuming. We therefore recommend that as a preliminary to impact assessment and new developments, a basic ecological survey of the river be undertaken. This should include: •description of major habitat types and their extent; •assessment of the integrity of the riparian zone along the whole river; •modelling of seasonal patterns of flow; •measurement of stream channel parameters to investigate the relationship between absolute flow and the extent of each habitat; and •sampling of fish and invertebrates to investigate habitat requirements of the biota and probable life cycle strategies. This survey would provide a baseline for all future impact assessment. It could also contribute in a major way to State of the Environment Reporting, allowing long-term assessments of change in the environment to be made