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Earth Science, 13e. Tarbuck & Lutgens. Running Water and Groundwater Earth Science, 13e Chapter 5. Stanley C. Hatfield Southwestern Illinois College.
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Earth Science, 13e Tarbuck & Lutgens
Running Water and GroundwaterEarth Science, 13eChapter 5 Stanley C. Hatfield Southwestern Illinois College
Li River, China’s Guilin DistrictNote karst topography, in which groundwater has dissolved large volumes of limestone (more later).
Earth as a system: the hydrologic cycle • Illustrates the circulation of Earth’s water supply • Processes involved in the cycle • Precipitation • Evaporation • Infiltration • Runoff • Transpiration
Running water • Drainage basin • Land area that contributes water to a river system • A divide separates drainage basins
Drainage basins and divides exist for all streams, regardless of size.
Running water • Streamflow • Factors that determine velocity • Gradient, or slope • Channel characteristics • Shape • Size • Roughness • Discharge – volume of water flowing in the stream (generally expresses as cubic feet per second)
Gradient (slope) • Parts of lower Mississippi: 10 cm/km • Mountain streams: 40 m/km • Steeper gradient has more energy, more velocity
Discharge • Measured in m3 or ft3 per second • Changes over time due to amount of precipitation in drainage basin
Measuring stream velocity 1 kph – 30 kph Straight – highest at center Curved– highest at outer bank
Running water • Upstream-downstream changes • Profile • Cross-sectional view of a stream • From head (source) to mouth • Profile is a smooth curve • Gradient decreases from the head to the mouth • Factors that increase downstream • Velocity • Discharge
Running water • Upstream-downstream changes • Profile • Factors that increase downstream • Channel size • Factors that decrease downstream • Gradient, or slope • Channel roughness
Running water • The work of streams • Erosion • Transportation • Transported material is called the stream’s load • Dissolved load • Suspended load • Bed load
Running water • The work of streams • Transportation • Load is related to a stream’s • Competence – maximum particle size • Capacity – maximum load • Capacity is related to discharge
Running water • The work of streams • Transportation • Deposition • Caused by a decrease in velocity • Competence is reduced • Sediment begins to drop out • Stream sediments • Known as alluvium • Well-sorted deposits
Running water • The work of streams • Transportation • Features produced by deposition • Deltas – exist in ocean or lakes • Natural levees – form parallel to the stream channel • Area behind the levees may contain back swamps or yazoo tributaries
Running water • Base level • Lowest point a stream can erode to • Two general types • Ultimate – sea level • Temporary, or local • Changing causes readjustment of the stream – deposition or erosion
Running water • Stream valleys • Valley sides are shaped by • Weathering • Overland flow • Mass wasting • Characteristics of narrow valleys • V-shaped • Downcutting toward base level
Running water • Stream valleys • Characteristics of narrow valleys • Features often include • Rapids • Waterfalls • Characteristics of wide valleys • Stream is near base level • Downward erosion is less dominant • Stream energy is directed from side to side
Running water • Stream valleys • Characteristics of wide valleys • Floodplain • Features often include • Meanders • Cutoffs • Oxbow lakes
Running water • Drainage patterns • Networks of streams that from distinctive patterns • Types of drainage patterns • Dendritic • Radial • Rectangular • Trellis
Running water • Floods and flood control • Floods are the most common geologic hazard • Causes of floods • Weather • Human interference with the stream system
Running water • Floods and flood control • Engineering efforts • Artificial levees • Flood-control dams • Channelization • Nonstructural approach through sound floodplain management
Satellite view of the Missouri River flowing into the Mississippi River near St. Louis
Water beneath the surface (groundwater) • Largest freshwater reservoir for humans • Geological roles • As an erosional agent, dissolving by groundwater produces • Sinkholes • Caverns • An equalizer of stream flow
Water beneath the surface (groundwater) • Distribution and movement of groundwater • Distribution of groundwater • Belt of soil moisture • Zone of aeration • Unsaturated zone • Pore spaces in the material are filled mainly with air
Water beneath the surface (groundwater) • Distribution and movement of groundwater • Distribution of groundwater • Zone of saturation • All pore spaces in the material are filled with water • Water within the pores is groundwater • Water table – the upper limit of the zone of saturation
Water beneath the surface (groundwater) • Distribution and movement of groundwater • Distribution of groundwater • Porosity • Percentage of pore spaces • Determines storage of groundwater • Permeability • Ability to transmit water through connected pore spaces • Aquitard – an impermeable layer of material • Aquifer – a permeable layer of material
Water beneath the surface (groundwater) • Features associated with groundwater • Springs • Hot springs • Water is 6–9° C (10–15° F) warmer than the mean air temperature of the locality • Heated by cooling of igneous rock • Geysers • Intermittent hot springs • Water turns to steam and erupts
Water beneath the surface (groundwater) • Features associated with groundwater • Wells • Pumping can cause a drawdown (lowering) of the water table • Pumping can form a cone of depression in the water table • Artesian wells • Water in the well rises higher than the initial groundwater level
Water beneath the surface (groundwater) • Environmental problems associated with groundwater • Treating it as a nonrenewable resource • Land subsidence caused by its withdrawal • Contamination
Water beneath the surface (groundwater) • Geologic work of groundwater • Groundwater is often mildly acidic • Contains weak carbonic acid • Dissolves calcite in limestone • Caverns • Formed by dissolving rock beneath Earth’s surface • Formed in the zone of saturation
Water beneath the surface (groundwater) • Geologic work of groundwater • Caverns • Features found within caverns • Form in the zone of aeration • Composed of dripstone • Calcite deposited as dripping water evaporates • Common features include stalactites (hanging from the ceiling) and stalagmites (growing upward from the floor)