Water in a river drainage system To accompany Lesson 3.1 of the Water resources teacher guide and lesson plans: Balancing priorities: agriculture and the environment – The Murray-Darling Basin © Commonwealth of Australia, 2011

How does water flow in this system? US Department of Agriculture © Commonwealth of Australia, 2011

Water in a river drainage system: input, transfer, storage and outputs inputs transfer storage outputs © Commonwealth of Australia, 2011

Precipitation (rain, hail or snow) enters the river drainage basin. Inputs Precipitation (rain, hail or snow) enters the river drainage basin. This precipitation is the input of water into the system (inflows). Precipitation (rain, hail or snow) enters the river drainage basin. This precipitation is the input of water into the system (inflows). US Department of Agriculture © Commonwealth of Australia, 2011

Transfer: water movement through the basin Some of the precipitation flows across the ground (surface run-off) into rivers and adds to streamflow. Surface run-off also flows into lakes, dams and reservoirs. Some of the water soaks into the ground, entering gaps between soil particles (infiltration). Some of the water that has soaked underground travels close to the land surface and soon emerges into streambeds. Some of the precipitation flows across the ground (surface run-off) into rivers and adds to streamflow. Surface run-off also flows into lakes, dams and reservoirs. Some of the water soaks into the ground, entering gaps between soil particles (infiltration). Some of the water that has soaked underground travels close to the land surface and soon emerges into streambeds. Gravity causes the remaining water to seep deep underground through soil and rock via the process of percolation. US Department of Agriculture © Commonwealth of Australia, 2011 Gravity causes the remaining water to seep deep underground through soil and rock via the process of percolation.

Transfer and storage: below ground flows The water that infiltrates the soil and seeps deeper below the surface eventually meets the water table, which is the layer where the soil is saturated. In this saturated layer, the small cracks and spaces between the rock particles are filled with water. This is what we call groundwater. Groundwater that seeps deep underground forms huge natural underground water storage areas called aquifers, where the water saturates porous rock. Typically, water moves very slowly in an aquifer and can take thousands or even millions of years to move back into the river drainage system. The water that infiltrates the soil and seeps deeper below the surface eventually meets the water table, which is the layer where the soil is saturated. In this saturated layer, the small cracks and spaces between the rock particles are filled with water. This is what we call groundwater. Groundwater that seeps deep underground forms huge natural underground water storage areas called aquifers, where the water saturates porous rock. Typically, water moves very slowly in an aquifer and can take thousands or even millions of years to move back into the river drainage system. US Department of Agriculture © Commonwealth of Australia, 2011

Storage: benefits of groundwater The slow trickle of groundwater into streams and wetlands provides essential water during periods of low rainfall. Groundwater stores provide an alternative source of water to water captured from surface water run-off. Groundwater is brought to the surface by drilling underground into the saturated zone. © Department of Sustainability, Environment, Water, Population and Communities, 2011

Often water flows through a river drainage system and out to sea. Output Large amounts of water will also re-enter the atmosphere as water vapour. The final release of water out of the river drainage system is the output (outflows). The final release of water out of the river drainage system is the output (outflows). Often water flows through a river drainage system and out to sea. Large amounts of water will also re-enter the atmosphere as water vapour. Often water flows through a river drainage system and out to sea. US Department of Agriculture © Department of Sustainability, Environment, Water, Population and Communities, 2011

Output: evaporation and evapotranspiration Evaporation of liquid water into a gas (water vapour) occurs from water stored in oceans, lakes, dams, wetlands and river channels. Water also evaporates from the soil surface. Plants draws up water from soils through their roots. The water vapour exits the plants via their leaves (transpiration). The combined loss of water to the atmosphere through evaporation and transpiration is called evapotranspiration. © Commonwealth of Australia, 2011