Predicting the effects of clearing on groundwater discharge to the Daly River

The Daly River is a perennial stream. Dry season base flows in the Daly River are sourced from spring inflows, largely from the Oolloo Dolostone aquifer. Springs are critical to the river health and changes in the volume of water entering the river will affect water quality and impact upon water dependent ecosystems. In this study the impacts of changes due to clearing and extraction for irrigation on sprign flows have been predicted using analytical and numerical models of groundwater flow. The emphasis of this work was to understand the processes occurring and hence guide the development of land and water practices that will prevent adverse impacts on the ecosystems sustained by springs flows into the Daly River.Made available by the Northern Territory Library via the Publications (Legal Deposit) Act 2004 (NT).Executive Summary -- 1. Introduction -- 1.1. Background -- 1.2. Objectives -- 1.3. Modelling Steps -- 1.4. Location -- 1.5. Climate -- 1.6. Geomorphology -- 1.6.1. Topography -- 1.7. Clearing history -- 2. Hydrogeological setting and conceptual model -- 2.1. Hydrogeology -- 2.1.1. Cretaceous Rocks -- 2.1.2. Oolloo Dolostone -- 2.1.3. Jinduckin Formation -- 2.2. Observation date -- 2.2.1. Rainfall and potential recharge -- 2.2.2. River gauging data -- 2.2.3. Terrain elevation -- 2.3. Conceptual model -- 3. Model design -- 3.1. Model specifications -- 3.1.1. Spatial discretisation -- 3.1.2. Temporal discretisation -- 3.1.3. Error and convergence criteria -- 3.2. Boundary conditions -- 3.3. Hydraulic parameters -- 3.3.1. Recharge distribution -- 4. Results -- 4.1. Groundwater level hydrographs -- 4.2. Comparing groundwater levels to surface elevations -- 4.3. Groundwater discharge hydrographs -- 5. Discussion -- 5.1. Chloride mass balance to estimate component due to diffuse and direct recharge mechanisms -- 5.2. Comparison of modelling results with recharge estimates based on choride mass balance -- 5.3. Assessment of water logging in the Douglas/Daly agricultural area -- 6. Conclusions -- 7. Recommendations -- 8. References -- Appendix A Chloride Histories at gauging stations along Daly river