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WASH Cluster – Emergency Training GWD Groundwater Development and Drilling Session 2 Characteristics of Groundwater Systems GWD2 1 WASH Cluster – Emergency Training GWD Debunking Groundwater Myths • You can’t drill anywhere and get groundwater • Groundwater is not static – it flows through pores in rocks • Aquifers are not underground rivers – only really in caves • Not all groundwater obtained will be drinkable GWD2 2 WASH Cluster – Emergency Training GWD Interconnection and Flow Interconnection of the pores in rock or soil allows water to: •enter the groundwater, •be stored in an aquifer below ground, •flow through the subsurface, •discharge naturally to a river, swamp, spring or the sea, •be recovered in a well or bore This all relates to the geology of the area and the different types of soil and rock. GWD2 3 WASH Cluster – Emergency Training GWD Groundwater Recharge Recharge is the process by which water gets into an aquifer. Recharge quiz GWD2 4 WASH Cluster – Emergency Training GWD Rainfall to Groundwater RAINFALL Some rainfall runs off across ground surface, Water entering the soil is used by plants (Evapotranspiration) Some evaporates at the surface Remainder enters soil Storage of water in the soil (unsaturated zone) Becoming wetter closer to water table Water that isn’t used or stored in the soil seeps down below water table – becomes Groundwater - known as recharge GWD2 Aquifer 5 WASH Cluster – Emergency Training GWD Groundwater Flow • Groundwater flows through an aquifer under an hydraulic gradient • effectively the difference in potential energy of the water – (hydrogeologists and groundwater engineers refer to the potential as the “head”). • Groundwater flows from areas of higher to lower head GWD2 6 WASH Cluster – Emergency Training GWD EXERCISE 1 GWD2 7 WASH Cluster – Emergency Training GWD EXERCISE 1 Cross section GWD2 8 WASH Cluster – Emergency Training GWD Rate of groundwater flow Rate of groundwater flow is a function of the hydraulic gradient Flow through the soil and within aquifers occurs by different pathways through different types of rocks GWD2 9 WASH Cluster – Emergency Training GWD Permeability Rock permeability governs the ease at which groundwater flows K (cm/s) 10² 10 Permeability 0 10 =1 10 −1 10 −2 Pervious Aquifer potential Unconsolidated sediments / Soils 1 10 −4 10 −5 10 −6 Clean Sand or Sand & Gravel 10 −7 10 −8 10 −9 10 −10 Impervious Poor None Very Fine Sand, Silt, Loess, Loam Peat Consolidated Rocks* 10 Semi-Pervious Good Clean Gravel −3 Stratified clay Oil Reservoir Rocks Sandstone Unweathered Clay Limestone, Dolomite Granite after Bear and Verruijt, 1987 GWD2 10 WASH Cluster – Emergency Training Impact on well supply GWD After: Don Armstrong, Australian Groundwater School, AMF course notes 1987 (unpublished) GWD2 11 WASH Cluster – Emergency Training GWD Aquifers and Aquitards Aquifer: A layer of soil or rock that has relatively higher porosity and permeability than the surrounding layers, enabling usable quantities of water to be extracted. Aquitard: GWD2 A layer of soil or rock that has relatively lower porosity and/or permeability than the surrounding layers, limiting the movement of groundwater through it and the capacity to extract useable quantities of water. 12 WASH Cluster – Emergency Training GWD Activity • • • • • GWD2 Fill the kettle Plug spout with cork Keep filling Use different things to plug spout Time how long it takes for water to come out 13 WASH Cluster – Emergency Training GWD Confined and Unconfined aquifers GWD2 14 WASH Cluster – Emergency Training GWD Groundwater Discharge • Water flows preferentially through higher permeability zones • Water will move to areas that have least restriction to flow • Groundwater will discharge at a point where constraints are released DISCHARGE QUIZ GWD2 15 WASH Cluster – Emergency Training GWD Discharge sites after Bear and Verruijt, 1987 GWD2 16 WASH Cluster – Emergency Training GWD EXERCISE 2 cross section Seepage - springs or soaks Seepage - springs or soaks GWD2 17 WASH Cluster – Emergency Training Climatic influence on Groundwater occurrence GWD2 GWD 18 WASH Cluster – Emergency Training GWD Springs GWD2 19 WASH Cluster – Emergency Training GWD Interaction with Rivers • Water table above river • Groundwater discharge to river GWD2 20 WASH Cluster – Emergency Training GWD Interaction with Rivers High flow in the river can lead to seepage into the groundwater GWD2 21 WASH Cluster – Emergency Training GWD • River above the water table • Downward seepage into groundwater GWD2 22 WASH Cluster – Emergency Training GWD Coastal Zones GWD2 23 WASH Cluster – Emergency Training GWD Variability of Water Quality Groundwater salinity can vary within the same aquifer From Elrail et al 2009 GWD2 24