Gulf Water Study Roper River Region Front cover: Painting of the Rainbow Serpent by Rex Wilfred. (see Appendix A for the story of the painting) Satellite image of the Roper River. Yawurrwarda Lagoon. GULF WATER STUDY Early morning at Roper Bar, Roper River WATER RESOURCES OF THE ROPER RIVER REGION REPORT 16/2009D U. ZAAR DARWIN NT © Northern Territory of Australia, 2009 ISBN 978-1-921519-64-2 ii ACKNOWLEDGEMENTS This project was co -funded through the Australian Government Water Smart Australia Program and the Northern Territory Government Department of Natural Resources, Environment the Arts and Sport. I would like to thank my colleagues who provided help on this project: Peter Jolly (now retired) who instigated this project; Des Yin Foo for his generous support as our team manager; Anthony Knapton, my co-worker on this project who provided technical and field assistance; Steve Tickell, Danuta Karp and Jon Sumner for their technical advice; Lynton Fritz for his outstanding cartographic skills in drawing up the maps; Renee Ramsay for the production of the GIS and collation of the DVD and our experienced technical team – Rodney Metcalfe, Steve Hester, Roger Farrow and Rob Chaffer for all their efficient fieldwork. A special thanks also to Phil O’Brien who not only provided enthusiastic field assistance but wise advice. I take pleasure in also thanking members of our technical working group; Max Gorringe - the manager of Elsey Station, Frank Shadforth – the manager of Seven Emu Station and Glenn Wightman – ethnobiologist who all kindly took the time to provide advice at our meetings. All were always ready to help. I am very much indebted to the local people in the region. I thank the traditional owners for sharing their knowledge of water resources and providing excellent guidance in the field; in particular Stephen Roberts, Robert Roberts and Walter Rogers. I thank the station owners and managers who were generous with their time in providing key information on the region and were very hospitable. I would like to thank the Northern Land Council who provided liaison assistance particularly Bobby Nununmadjbarr, the Roper Gulf Shire (Ngukurr and Minyerri) and the Yugul Mangi Rangers for their assistance. Lynton Fritz Technical working group Yugul Mangi Rangers 1 SUMMARY This report provides details of the groundwater and Dry season surface water resources of the Roper River region of the Gulf as depicted on the accompanying water resource map. It is one of five regions which make up the mapping area of the Gulf Water Study (Figure 1.1). The study was co-funded by the Australian Government Water Smart Australia Program and the Northern Territory Department of Natural Resources, Environment, the Arts and Sport. The purpose of this work is to provide readily accessible and easily understandable information on water resources in the region. The project was undertaken with the dual perspective of western science and indigenous knowledge and both are represented in the products of this study. It is hoped that common understandings will develop between indigenous people and land managers about water in the region. The key aim is to provide a fundamental data set to guide sustainable development of water resources, maintaining social values, healthy groundwater systems and rivers as well as the ecosystems which depend upon them. The groundwater resource has been classified into five aquifer types: Fractured and Karstic Rocks (yields up to 10 L/s) Fractured and Weathered Rocks – carbonate rocks (yields 0.5 – 10 L/s) Fractured and Weathered Rocks – carbonate rocks (yields 0.5 – 5 L/s) Fractured and Weathered Rocks (yields 0.5 – 5 L/s) Fractured and Weathered Rocks with minor groundwater resources (yields 0 - 1 L/s) The area is generally poor in groundwater. Of the better yielding aquifers, the fractured and karstic rock aquifers are minor in extent and have not been drilled, and the fractured and weathered carbonate rock aquifers are local in scale but are an important resource as they supply the largest settlement in the area, Ngukurr. Across the area small groundwater discharges host water dependent ecosystems often marked by lush vegetation pockets. Given the generally poor and limited groundwater prospects, water supplies are often sought from surface water sources; from rivers, waterholes, springs and dams. The Roper River and its tributaries dominate the map sheet. A number of cattle stations as well as Ngukurr draw supplies from the Roper River. River flow has been classified according to the minimum recorded flow at the end of the Dry season during a dry period. There are four categories that describe river flow; River with a minimum flow greater than 100L/s at the end of the Dry season River with a minimum flow of between 10 and 100L/s at the end of the Dry season River with permanent waterholes and minimum flows up to 10 L/s at the end of the Dry season River which is dry at the end of the Dry season Only the upper reaches of the Roper River fits into the highest flow category. Most of the rivers in the area fit into the latter two categories reflecting the lack of groundwater discharge (baseflow) provided by ‘fractured and weathered rock’ aquifers which cover almost the entire map area. Dry season discharges (baseflow) of the Roper River and its tributary the Wilton River, are sourced from springs (groundwater discharges) which lie in their headwaters outside the map sheet. These rivers and ecosystems that depend on their baseflow are therefore groundwater dependent. Dry season flow in these rivers decreases with downstream distance due to evapotranspiration losses. In drier periods such as in the 1960’s these rivers can cease to flow for kilometres upstream from the Roper estuary. The amount of freshwater input into the estuary influences the location of the freshwater/saltwater interface in the estuary. In drier times the interface can move more than 70 kilometres upstream causing the usually fresh reaches of the estuary to turn salty, thus effecting Ngukurr’s water supply. This outlines the crucial role of groundwater discharge in maintaining the dynamic natural environment as well as community water supplies. To sustainably manage the Roper River requires consideration of the whole groundwater catchment supplying water to the river as well as the surface water catchment of the Roper River. Recorded rainfall, groundwater level and river baseflow were correlated on a yearly basis and strong trends emerged. From the long term rainfall and river flow record it was observed that there were dry periods and wet periods. 1952 to 1967 was a dry period in which every year the Roper River ceased to flow at Roper Bar by the end of the Dry. The last decade however has been a wet period with exceptionally high rainfall resulting in high groundwater levels and river baseflows. In fact, the flow at Roper Bar, which is situated at the head of the Roper river estuary, has hardly dropped below 1 m3/s since 1998. Such high variability needs to be taken into account in water allocation planning so the health of the river system is maintained. As part of the Gulf Water Study, an integrated surface water / groundwater computer model has been developed which analyses the surface water and groundwater elements, and their interplay, in the entire Roper River catchment. This work has been undertaken by A. Knapton and will provide vital information to water allocation planning in the region currently underway as there is high demand for water in the Mataranaka region. His reports provide a greater level of detail on the Roper River catchment and the modelling of water resources within it. (See Knapton, 2009) Indigenous knowledge on specific sites has been provided by traditional owners and is documented in this report. Many of the sites are shown on the map. To provide a background to this knowledge an overview on how indigenous people in the region view land and water is discussed. Indigenous people believe that the Spirit Ancestors created their environment as well as a charter that is the Law for existence. Through this law all land, water, plants, animals, natural phenomena, people and the Spirit Ancestors (Dreamings) are inextricably connected. It is through these intricate connections that indigenous people relate to water and everything else. Water sites not only have a physical entity and a purpose in the connected environment but also social, emotional, cultural and spiritual significance. Effective management of land and water therefore involves consideration of all these realms. Much can be learnt from their holistic view as it engenders responsible land and water management. 3 Aside from the maps and reports other products from the Gulf Water Study include a geographic information system (GIS), posters and spatial photographic and video collection which are all available on DVD data disc. 4 TABLE OF CONTENTS ACKNOWLEDGEMENTS ....................................................................................................................... 2 SUMMARY .............................................................................................................................................. 2 Table of Contents .................................................................................................................................... 5 List of Figures...................................................................................................................................... 7 List of Tables......................................................................................................................................