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Groundwater Terms and Definitions

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Groundwater Terms and Definitions Groundwater Terms and definitions November 2015 Document Number: 2977263 Version: 8 Table of Contents 1 Groundwater occurrence .................................................................................................................... 4 1.1 Water cycle ................................................................................................................................. 4 1.2 Groundwater............................................................................................................................... 5 2 Aquifer types ...................................................................................................................................... 6 2.1 Aquifer ........................................................................................................................................ 6 2.2 Aquitard ...................................................................................................................................... 6 2.3 Unconfined aquifer ..................................................................................................................... 6 2.4 Confined aquifer ......................................................................................................................... 7 2.4.1 Deep lead .............................................................................................................................. 7 2.5 Perched aquifer .......................................................................................................................... 8 3 Aquifer properties ............................................................................................................................... 9 3.1 Hydraulic head ........................................................................................................................... 9 3.2 Hydraulic gradient .................................................................................................................... 10 3.3 Transmissivity (T) ..................................................................................................................... 11 3.4 Hydraulic conductivity (K) ......................................................................................................... 12 3.5 Storage coefficient (S) .............................................................................................................. 13 3.5.1 Unconfined aquifer .............................................................................................................. 13 3.5.2 Confined aquifer .................................................................................................................. 13 4 Groundwater flow ............................................................................................................................. 14 4.1 Groundwater flow ..................................................................................................................... 14 4.2 Recharge .................................................................................................................................. 15 4.3 Discharge ................................................................................................................................. 16 4.4 Spring ....................................................................................................................................... 17 4.5 Groundwater interaction with surface water ............................................................................. 18 4.6 Groundwater dependent ecosystem ........................................................................................ 19 5 Groundwater pumping ...................................................................................................................... 20 5.1 Pumping test ............................................................................................................................ 20 5.2 Cone of depression .................................................................................................................. 21 5.3 Bore construction ..................................................................................................................... 22 5.4 Pumping interference ............................................................................................................... 23 5.5 Entitlement ............................................................................................................................... 24 5.6 Allocation .................................................................................................................................. 24 6 Groundwater monitoring ................................................................................................................... 25 6.1 Groundwater monitoring ........................................................................................................... 25 6.2 Water measurement information system (WMIS) .................................................................... 25 6.3 Hydrograph ............................................................................................................................... 26 6.4 Recovery level .......................................................................................................................... 27 Document Number: 2977263 Version: 8 Page 2 of 34 6.5 Drawdown level ........................................................................................................................ 27 6.6 Nested monitoring bores .......................................................................................................... 28 6.7 Water table ............................................................................................................................... 30 6.8 Potentiometric surface ............................................................................................................. 31 6.9 Groundwater quality ................................................................................................................. 32 7 References ....................................................................................................................................... 33 Document Number: 2977263 Version: 8 Page 3 of 34 1 Groundwater occurrence 1.1 Water cycle The water cycle is the perpetual movement of water on earth (Figure 1). The suns heat evaporates water from open water bodies and land. Water vapour rises into the atmosphere and condenses to form clouds with lower air temperature. Precipitation falls back down to earth under gravity as rain, hail or snow. Precipitation may: • return to the atmosphere through evaporation; • contribute directly to surface water bodies, glaciers or snow; • fall on the landscape and run-off into streams and rivers that feed into the ocean; • infiltrate the soil and be taken up by plants and returned to the atmosphere through transpiration; and • enter the ground to recharge groundwater systems. Figure 1 Water Cycle (DSE 2009) Document Number: 2977263 Version: 8 Page 4 of 34 1.2 Groundwater Groundwater is water beneath the earth’s surface in pores and fractures of soil and rocks (Figure 2). Groundwater is also water that drains through the unsaturated soil to a saturated zone where pores and fractures can store water. Groundwater supports a significant amount of agricultural activity, provides urban supplies to a number of towns across Victoria, and is an essential source of water for domestic and stock supply. Groundwater is also an important environmental asset that provides base flow to streams and supports wetlands and other groundwater dependent ecosystems (definition provided in section 4.6). Figure 2 Groundwater occurrence (Ghost Watershed Alliance Society 2015) Document Number: 2977263 Version: 8 Page 5 of 34 2 Aquifer types 2.1 Aquifer An aquifer may be broadly described as saturated fractured rock or sand from which usable volumes of groundwater can be pumped. 2.2 Aquitard An aquitard restricts the flow of water from one aquifer to another, for example a clay layer or solid rock. 2.3 Unconfined aquifer An unconfined aquifer is a section of rock or sand that does not have a confining layer (e.g. clay aquitard) on top of it (Figure 3). An unconfined aquifer is often shallow. The top of an unconfined aquifer is the watertable. An unconfined aquifer acts similar to a sponge, in that the watertable surface can fluctuate up and down depending on the recharge and discharge rate. Figure 3 Aquifer types (National Groundwater Association 2007) Document Number: 2977263 Version: 8 Page 6 of 34 2.4 Confined aquifer A confined aquifer is a section of rock or sand that is overlain by a confining layer (e.g. clay aquitard on top) that restricts movement of water into another aquifer (Figure 3) Groundwater in confined aquifers can be under high pressure because of the confining layer on top of the aquifer and the recharge zone is higher in the catchment. In a confined aquifer the water level in a bore will rise to a level higher than the top of the aquifer because of the high pressure. This is referred to as the potentiometric surface and is similar to squeezing a juice box with a straw in it, casuing the juice to rise up the straw. In some bores the water level may be above the ground surface in which case it is called artesian. 2.4.1 Deep lead A deep lead is an ancient river bed (paleochannel) that has been buried by sediment or basalt resulting from volcanic
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