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Chapter 4Groundwater Hydrology

Prof. Dr. Ali El-NaqaHashemite UniversityJune 2013

Groundwater HydrologyWhat is Groundwater?What is Groundwater Hydrology?The Geology of GroundwaterGroundwater RechargeAquifersGroundwater MovementAge of GroundwaterLocating and Mapping GroundwaterDrilling a Groundwater Well

From Chapter 2

Groundwater HydrologyWhat is Groundwater?What is Groundwater Hydrology?The Geology of GroundwaterGroundwater RechargeAquifersGroundwater MovementAge of GroundwaterLocating and Mapping GroundwaterDrilling a Groundwater Well

What is Groundwater?Found in the subsurface, inside pores within soil and rockSpelled either as two words, Ground Water, or as one, GroundwaterGroundwater is the largest source of freshwater on earth, and was little used until recently.With electricity and the modern pump, groundwater has become very important to agriculture, cities, and industries.It is usually much cleaner than surface water.

Figure 4.2 This map of major aquifers in the United States shows an interesting distribution of groundwater formations.

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Groundwater HydrologyWhat is Groundwater?What is Groundwater Hydrology?The Geology of GroundwaterGroundwater RechargeAquifersGroundwater MovementAge of GroundwaterLocating and Mapping GroundwaterDrilling a Groundwater Well

What is Groundwater Hydrology?It is the study of the characteristics, movement, and occurrence of water found below the surface.Groundwater and aquifers are like surface water and watershedsAn aquifer is a geologic unit that transmits water.Piezometric surfaces are used to map water levels, similar to topographic lines on maps.Each aquifer has its own piezometric surface.The water level elevation in wells are used to create the piezometric surface.

Groundwater HydrologyWhat is Groundwater?What is Groundwater Hydrology?The Geology of GroundwaterGroundwater RechargeAquifersGroundwater MovementAge of GroundwaterLocating and Mapping GroundwaterDrilling a Groundwater Well

The Geology of GroundwaterSedimentary Rockssandstone, shale, limestone, conglomerateGlaciated Terrainlarge valleys and basins were carved outsediments (sands, clays) were left behindAlluvial Valleys and Fansalong rivers and streamsTectonic Formationssolid rock is fractured by pressures due to earths movement

Figure 4.3 Continental glaciers of the most recent Ice Age in North America (approximately 20,000 years ago) reached as far south as the Ohio and Missouri River Valleys.

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Aletsch Glacier, Switzerland, Wikipedia

Wikipedia

Alluvial valley complex in Death Valley, CAspace shuttle image, USGS

Alluvial fan, Idaho, http://www.gly.uga.edu/railsback/FieldImages.html

Figure 4.5 Ms. Cech inspects rock fractures along the Big Thompson River near Estes Park, Colorado.

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Groundwater HydrologyWhat is Groundwater?What is Groundwater Hydrology?The Geology of GroundwaterGroundwater RechargeAquifersGroundwater MovementAge of GroundwaterLocating and Mapping GroundwaterDrilling a Groundwater Well

Groundwater RechargeWater that replenishes aquifersUsually from surface water or precipitation that infiltrates, and then percolates through the vadose zoneRecharge happens when percolating water finally reaches the water table, which is the top of the saturated zone.Above the water table is the unsaturated zone where water is held by capillary forcesThe root zone may capture some water that infiltrates and lift it back to the atmosphere.

Figure 4.6 Lakes and wetland complexes often exist in areas with shallow groundwater elevations that intercept the land surface..

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Groundwater Recharge

Fetter, Applied Hydrology

Infiltration

PercolationSaturated zone

Evapotranspiration

Overland flow

Groundwater HydrologyWhat is Groundwater?What is Groundwater Hydrology?The Geology of GroundwaterGroundwater RechargeAquifersGroundwater MovementAge of GroundwaterLocating and Mapping GroundwaterDrilling a Groundwater Well

AquifersWater-bearing geologic formation that can store and yield usable amounts of waterAquifer types:unconsolidated, consolidated, fracturedperched, unconfined, confined, artesianthermal springsAquifer propertiesporosity = volume of pores (voids) per total volume of aquifern = Vv / Tt

Unconfined Aquifer

Figure 4.10 The Ogallala Aquifer provides water to irrigators, cities, and other groundwater users in parts of South Dakota, Nebraska, Wyoming, Colorado, Kansas, Oklahoma, Texas, and New Mexico.

Land surface elevationin meters

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Figure 4.7 Two conditions are necessary to create an artesian groundwater system: a confined aquifer and sufficient pressure in the aquifer to force water in a well or other opening to rise above the static water level of the aquifer.

Confined Aquifer

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Thermal Springs and Geysers

Aquifer Porosity

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Example Porosity CalculationTake a 1000-mL beaker (1 liter)Fill it with sand to the topMeasure how much water it takes to fill the beaker to the top (say 300 mL)The porosity = (300 mL) / (1000 mL) = 30%

Groundwater HydrologyWhat is Groundwater?What is Groundwater Hydrology?The Geology of GroundwaterGroundwater RechargeAquifersGroundwater MovementAge of GroundwaterLocating and Mapping GroundwaterDrilling a Groundwater Well

Groundwater MovementWater moves because of two factorsThe force pushing through the subsurfaceThe permeability of the geologic mediaDarcys Law says that the flux of water (flow per unit area) is calculated using these two factors:q = K iq = flux of water, ft / sK = hydraulic conductivity, ft / si = hydraulic gradient, ft / ft

Note they both have the same units

The hydraulic conductivity, K, is a measure of the permeability of the aquifergravels have large hydraulic conductivitiesclays and solid rock have small valuesThe hydraulic gradient is a measure of the force acting on the waterit is like the slope of the land surface, water flows faster where it is steepi = dh / dl = slope of the water surfaceh is the hydraulic head, or water level in a welldh is the change in water level between two wellsdl is the distance between the wellsdetermines the direction of flow.

Direction of Flow?

Geological Regions of Georgia

Georgia Piedmont Region

Soil surfaceWater table

dh

dl

dl = 1,000 mh = 50 mh = 55 mK = 5 m/day

dl = 1,000 mh = 50 mh = 55 mK = 5 m/daydh = 5 m

dl = 1,000 mh = 50 mh = 55 mK = 5 m/daydh = 5 mdh/dl = 5/1,000 = 0.005

dl = 1,000 mh = 50 mh = 55 mK = 5 m/daydh = 5 mdh/dl = 5/1,000 = 0.005q = K i = 5 x 0.005q = 0.025 m/day

Karst Aquifers

Wikipedia

Underground Rivers?

Only in Karst aquifers!!Wikipedia

Specific YieldVolume of water that can be removed per unit volume of aquiferless than the porosity - hard to get the last drop!

Specific Yield CalculationTake a 1000-mL beaker (1 liter)Fill it with sand to the topMeasure how much water it takes to fill the beaker to the top (say 300 mL)The porosity = (300 mL) / (1000 mL) = 30%We pour the water out and 250 mL is collectedWhat is the specific yield?(250 mL) / (1000 mL) = 25%Cant get the last drop!

Groundwater HydrologyWhat is Groundwater?What is Groundwater Hydrology?The Geology of GroundwaterGroundwater RechargeAquifersGroundwater MovementAge of GroundwaterLocating and Mapping GroundwaterDrilling a Groundwater Well

Age of GroundwaterTime it takes for water to move through the subsurfaceMaybe 1 to 25 years in aquifers near AthensUp to 30,000 years for water down on the coast

Groundwater HydrologyWhat is Groundwater?What is Groundwater Hydrology?The Geology of GroundwaterGroundwater RechargeAquifersGroundwater MovementAge of GroundwaterLocating and Mapping GroundwaterDrilling a Groundwater Well

Locating and Mapping GroundwaterThe first step is to generate a piezometric surface, which maps water table elevationWells are plotted on a map, and water levels in the wells are indicatedLines of constant water level elevations are plotted (called equipotentials)Flowlines (also call streamlines) are drawn so that they are perpendicular to the equipotential linesLocal rivers, lakes, and other surface water features are plotted on the map.

Groundwater HydrologyWhat is Groundwater?What is Groundwater Hydrology?The Geology of GroundwaterGroundwater RechargeAquifersGroundwater MovementAge of GroundwaterLocating and Mapping GroundwaterDrilling a Groundwater Well

Drilling a Groundwater WellVarious methods are available for drilling a wellA simple method is the auger method, which uses a screw-like bit. This works in soft materialsFor solid rock, a simple technique is the hammer or percussion method which pounds a hole in the rockRotary methods uses a harden steel bit tipped with diamonds to cut through the rock. Either water, air or mud can be used to lubricate and to lift the cuttings.

Well ComponentsA well pad is placed on the surface to hold up the well.A blank casing is used from the surface down to the aquifer. Clay or concrete fills the space outside the casing.A screened casing is used in the aquifer. Sand or gravel fills the space outside the casingA submerged turbine pump lifts the water to the surface. The motor that drives the pump is either on the surface or also submerged.

Piedmont Wells

Cone of depression in potentiometric surface near Albany GA

South Georgia Water UseFloridan aquifer important supply for drinking water and irrigation waterWater wars between Georgia and Florida over flow in the Apalachicola RiverAre irrigation wells reducing flow in the Flint and Apalachicola Rivers?

Wikipedia

Flint

ChattahoocheeApalachicola

Stream Depletion FactorsUsed to assess the effects of well pumping on stream flowDepend on the distance to the stream (less effect with greater distance)properties of the aquifer

Quiz 4Two wells are located 1 km (1,000 meters) apart. Well A has a water level of 105 m and Well B has a water level of 102 m.Which direction is the groundwater flowing? From Well ____ to Well ____What is the hydraulic gradient between the two wells?What is the flux (flow rate) if the hydraulic conductivity is K = 10 m/day?A one-liter (1,000 mL) beaker is filled with sand and filled to the top with water.What is the porosity of the material if 250 mL was required to fill the beaker?We pour the water out, and 200 mL is collected. What happened to the rest of the water?What would the porosity be if we use clay instead of sand? (more, less, the same)How much water would pour out if we use clay instead of sand? (more, less, the same)True - False Questions [T / F] An aquiclude is a geologic formation that holds a lot of water.[T / F] Perched aquifers are a kind of artesian aquifer.[T / F] The Ogallala aquifer is the major aquifer in the Southeastern U.S.[T / F] The water table is found at the top of the saturated zone.[T / F] The two factors that determine how much horsepower is needed to lift water are the amount of water that must be lifted and the height that you must lift the water.Explain what Stream Depletion Factors are used for