Planet Earth Exam 4 Groundwater Hydrological Cycle o Powered by the sun o Precipitation Evaporation Runoff Distribution of H2O o 96 Oceans 3 Glaciers 1 Groundwater 1 Surface Water Atmosphere 001 Biosphere 0001 Groundwater is a valuable resource o Abundant 70 times more fresh water below ground than above o Constant available even in droughts o Widespread can flow from humid to dry environments Porosity of material that is empty allows liquid to flow through Permeability measure of how easily a solid allows fluids to pass through it o High porosity does not necessarily mean high permeability Clay high porosity low permeability o of pore space is high but the pores are too small for water to go through Water molecules slowly descend through the unsaturated zone due to gravity some held up by surface tension o Eventually reaches zone underground where all pore space is filled with water a k a saturated zone Water table boundary between saturated and unsaturated zone o Outcrops at the surface of streams and lakes o Changes in rainfall affect elevation of water table o Mimics surface topography hence doesn t need to be level Doesn t assume a level surface because of Capilary action and surface tension Water flows downhill faster than uphill o Hydraulic gradient slope of the water table Speed of flow of groundwater depends on slope of water table and permeability Rates of groundwater movement goes from slow to very slow 10 100 cm day 40 400 m yr Recharge where groundwater is replenished Discharge where groundwater flows from the surface Recharge area where precipitation reaches the saturated zone Discharge area where subsurface water is discharged to streams or to lakes ponds or swamps Aquifers sediment rock through which water flows easily Aquitard sediment rock that restricts the flow of water Confining bed blocks flow entirely o Unconfined interext the surface o Confined bracketed by aquitard Order Surface Unconfined aquifer Aquitard Confined aquifer Causes of Springs standard discharge perched discharge impermeable base permeable layer connected fractures aquaclude at surface artensian flow up a joint Confined Aquifer creates Artesian well o artesian means hydraulic gradient is large enough to cause groundwater to flow upwards and out of the ground Municipal Water System o Well water pumped to holding tank o Gravity maintains pressure from there to the faucet o Most drinking water comes from wells Wells o Dug or drilled through saturated zone and below water table o Water is then lifted out or pumped out o Water removed faster than recharge lowers the water table o Water table can drop below useable depth through excessive use Overpumping leads to pore collapse and ground subsidence o Groundwater being removed so fast causes ground beneath to sink Saltwater Intrusion salt groundwater intrudes fresh groundwater Chemistry of Groundwater o Contains dissolved minerals o Carries ions as function of temp and pressure o Until max possible ions are reached water is unsaturated o When it is its saturated o If temp or pressure decrease saturated becomes oversaturated Groundwater passing through o Salt too salty for use o Limestone becomes hard water o Iron rocks will have orange stain Pipe scale precipitated calcite from hard water Caves form in carbonate material limestone of dolomite Karst topography landscape in which caves and sinkholes are so numerous that they form a peculiar topography o Small closed basins o Disrupted drainage pattern o Steams disappearing into ground o Streams reappearing as large springs Karst develops on limestone dolomite or evaporites Mostly on limestone Karst Landforms o Blind valley valley that ends abruptly where stream vanishes underground o Sinking stream stream that vanishes underground o Resurgence point where waters from sinking stream reemerge o Dry valley no longer exhibits channelized flow o Cave natural underground room or rooms that s large enough to hold people Running Water Landscapes will never change without water Sheetwash thin covers surface Downcuts sheetwash becomes concentrated erodes and scours out a channel Hearward erosion fastest downcutting at channel head channel moves upslope tributaries form to feed new stream drainage network develops Downcutting vs Wall stability o Solid rock narrow canyon o Unstable walls broad valley o Hard soft rock stairstep valley spokes angles gaps cut incise sediment Streams are either permanent or nonpermanent depending on the water table Types of drainage patterns controlled by what water flows over o Dendritic veins of a leaf flow over uniform surface o Radial flow from center point mountain or volcano resembles wheel o Rectangular controlled by grid of fractures as joints or faults right o Trellis form in long valleys trunk stream cuts resistant ridges water Stream profile features are steepest near the source of the stream Longitudinal profile equilibrium Base level0 lowest elevation a stream bed can reach at a given locality Base Level Changes o Lower base level steeper profile increase in stream erosion down o Raise base level shallower profile infill shallow areas deposit o Base level decrease leads to sea level drop uplift at mouth uplift at stream head drainage of lakes o Base level increase leads to sea level rise subsidence at stream mouth subsidence at head creation of lakes Graded stream achieved its natural longitudinal profile and is in equilibrium is able to carry to the ocean all the sediment supplied by its tributaries neither erodes its bed nor fills up with sediment Superposed stream original stream course stream down cuts through unconformity and new course ignores new rock structure Antecedent drainage erosion is greater than uplift Diverted drainage erosion is less than uplift Running water causes erosion in 4 ways o Scouring removing loose fragments o Breaking lifting snapping off fragments lifting off bed o Abrasion grinding action of sand in the water column o Dissolution dissolving more soluble minerals Severity of erosion depends on water velocity water volume sediment content When flow velocity decreases o Sediment grain sizes are sorted by water o Sands are removed from gravel muds from both o Gravels settle in channels o Sands drop out in near channel environments o Silts and clays drape floodplains away from channels Parts of meandering streams curvy rivers o Cut bank outside point bar beachy area floodplain area around curvy areas Floodplain flat topography covered by