mer1e ch05 lecture.ppt · groundwater stores •spring – groundwater flowing out where the water...

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Visualizing Earth ScienceBy Z. Merali and B. F. Skinner

Chapter 5 – Water On and Under the Ground

• The Hydrologic Cycle

Chapter Overview

• Surface water flow and its effects

• Water resources underground

The Hydrologic Cycle• Movement of water through

the Earth System– Reservoirs of water in the Earth

System• Ocean• Clouds and atmospheric water C ouds a d at osp e c ate

vapor• Groundwater• Glaciers

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The Hydrologic Cycle



• Processes and pathways– Evaporation – and Transpiration– Condensation – and Deposition– Precipitation– Surface runoff– Infiltration

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Water in the Earth System

• The hydrologic cycle– Closed

• No matter (water) exchange

Consists of open– Consists of open systems

• Exchange processes link water reservoirs

Surface runoff and its effects

• Stream or river– Flowing body of liquid water

• Flows down a slope– The steepness of the slope is

the gradient

Streams and Streamflow

the gradient• Flows along channels

– A channel is a clearly defined natural passageway

• Straight• Meandering• Braided

– Stream discharge is the amount of water at any point

– Stream load is the sediment carried

Surface runoff and its effectsStreams and Streamflow

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• Stream deposits form along– Channel margins

• Meandering streams – Flow faster toward the outer bend and create a cut bank


– Flow slower toward the inner bend and create a point bar– Change shape

• Form oxbow lakes



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• Stream deposits form along– Valley floors

• Flood alluvium deposits create– Floodplains– Natural levees

– Stream mouths and gradient


transitions• Deltas• Alluvial fans


• Drainage Basin– Intake area of a stream– Divide

• The boundary of a stream’s

Stream Systems and Lakes

drainage basin

• Lake– Body of inland surface water

• Fresh water lakes have inlets and outlets

• Salt water lakes lack outlets


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• Floods are overflows of water bodies– Stream flooding

D t l i i t

Floods

• Due to large increase in stream discharge

– Excessive precipitation leads to storm runoff

– Coastal flooding• Storm surge

– Hurricane Katrina


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• Chances of floods sometimes increased by human activity– Subsidence due to groundwater depletion

• Recurrence interval of flooding

Floods prediction and prevention

g– Typical time between floods of equal magnitude


• Flood prediction– Weather upstream– Water level monitoring

• Flood prevention

Floods prediction and prevention

• Flood prevention– Channelization

• Can cause environmental degradation• Can lead to inaccuracies in accumulated water level data

Surface runoff and its effectsFloods prediction and prevention

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• Fresh water supply– Essential for

• Direct human consumption• Crop and livestock• Industry

• Major problem in many countries• Cause of socio-political conflicts

Surface water resources

– Scarcity of water resources

Surface runoff and its effectsSurface water resources


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Fresh water underground

• Groundwater and groundwater movement– Water in pore spaces in underground rock– Saturation

• All pores spaces filled with water• Top of the saturation zone called the water table

– Rock porosity• Relative amount of space in underground rock

– Rock permeability• Ease of downward flow through rock


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Groundwater Movement• Water percolation

– Process of water seepage through rocks

• Recharge– Replenishment of groundwater

• Discharge

– Process moving groundwater to the surface

Discharge

Groundwater Stores

• Aquifer– Water saturated

rock– Porous and

permeable

• Aquiclude– Layer of

impermeable rock confining aquifers

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Groundwater Stores• Artesian well

– Well accessing water from a confined aquifer– Water rises in artesian wells without pumps

• Due to release of confining pressure

Groundwater Stores• Spring

– Groundwater flowing out where the water table is at the surface

Groundwater Depletion and Contamination• Groundwater mining

– Removal of groundwater faster than it is replenished

– Results in a cone of depression

– Eventually causes depletion of aquifers and subsidence

• Decline in land surface elevation

• Can destroy water carrying capacity of aquifers due to compaction

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Groundwater Depletion and Contamination

• Groundwater contamination– From industrial and

agricultural chemicals– Often difficult to discern and

control

Karst regions: Caves and sinkholes• The slight acidic nature of groundwater

– Dissolves soluble carbonate rocks• Example: Limestone

– Creates karst topography• Caves

– Underground spaces carved by groundwaterg p y g• Sinkholes

– Sunken surface region created by dissolution of underground support rock

Chapter Summary• Water in the Earth System

– The hydrologic cycle, its reservoirs and its processes– The hydrologic cycle is closed with open interacting sub-systems

• The effects of flowing water– Erode, and carry and deposit sediment– Drain land areas– Feed lakes and reservoirs, and serve to close the water cycle

• Floods– Are hazardous to life, and property

• Prediction and control important to human society

• Underground water– Can be mined but at the cost of depletion and environmental

degradation– Is in danger of difficult to detect contamination due to human activity– Forms geological landforms: karst topology of caves and sinkholes

mer1e ch05 lecture.ppt · groundwater stores •spring – groundwater flowing out where the water...

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