Sculpting the Earth’s Surface Running Water AndGroundwater

The Hydrologic Cycle  Water Basics –Sea water 97.2% –Fresh Water 2.8%  Polar ice & glaciers 2.15%  Groundwater 0.62%  Lakes and Rivers 0.01%

The Hydrologic Cycle  The Three Fates of Precipitation –Infiltration  The movement of water into rocks or soil through cracks and pore spaces –Runoff  Water that flows over the land –Transpiration/Evapotranspiration  the release of water vapor to the atmosphere by plants

The Hydrologic Cycle  Infiltration capacity of the soil is controlled by: –Intensity and duration of rainfall –Soil saturation –Soil texture –Slope of the land –Nature of the vegetative cover

Main Sources of Water  Surface Water –Lakes, rivers, reservoirs  Ground Water –In the Earth, flows through fractures and pores

Surface 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)

Surface Water  Most important agent sculpturing Earth’s land surface –Begins as sheetflow –Sheetflow develops into tiny channels called rills –Eventually flows into streams, rivers & lakes

Profile of a Stream

Surface Water - Streams  Upstream –Higher velocity –Smaller discharge –Smaller channel  Downstream –Lower velocity –Greater discharge –Larger channel Upstream-downstream characteristics

Local and Ultimate Base Level

Surface Water - Streams  Erosion = transportation of sediments –AKA load  Dissolved load  Suspended load  Bed load

Surface Water - Streams  Erosion = transportation of sediments –Load is related to a stream's  Competence - maximum particle size  Capacity - maximum load  Capacity is related to discharge

Surface Water - Streams DepositionDeposition Caused by a decrease in velocityCaused by a decrease in velocity Competence is reducedCompetence is reduced Sediment begins to drop outSediment begins to drop out

Surface Water - Streams  Stream sediments –Known as alluvium –Well-sorted deposits

Surface Water - Streams  Features produced by deposition –Deltas –Natural levees –Back swamps –Yazoo tributaries

Surface Water – Streams  River Erosion –Vertical erosion  Upstream portion  Produces deep, V-shaped valleys with rapids –Lateral erosion  Downstream portion  produces broad valleys, flood plains, and meandering streams

Meanders

Oxbow Lakes

Surface Water – Stream Valleys  Drainage basins and patterns A divide separates drainage basin Types of drainage patterns

Surface Water – Stream Valleys  Flood Plains –Periodic floods deposit rich soils  Agricultural production on floods plains is followed by urbanization –Natural levees  Forms as floods deposit coarse detritus near the river  Naturally constraint the river except in the larger floods

Surface Water – Flooding  Floods and flood control –Floods are the most common geologic hazard –Causes of floods  Weather  Human interference with the stream system

What is Groundwater?  Water found in the pores and fractures of soil and bedrock  Largest reservoir of fresh water  Tends to be less polluted than surface water

What is Groundwater?  An important erosional agent –Groundwater is often mildly acidic –Contains weak carbonic acid –Forms caverns at or just below the zone of saturation –Karst topography on the surface

Groundwater Terminology

 How does water get from the stream to the water table? –Gaining streams – gain water from the inflow of groundwater through the streambed –Losing streams – lose water to the groundwater system by outflow through the streambed –Interactions - A combination of the first two

Groundwater Movement & Storage  Factors –Porosity  Percentage of total volume of rock or sediment that consists of pore spaces –Determines how much groundwater can be stored –Variations can be considerable over short distances –Permeability  The ability of a material to transmit a fluid

Groundwater Movement & Storage  Factors (continued) –Specific retention  The portion whish is retained as a film on particles, rock surfaces, and pore spaces –Specific yield  The portion which will drain under gravity –In general,  Porosity = Specific retention + Specific yield

Groundwater Movement & Storage  Factors (continued) –Aquifer - A zone of Earth material capable of supplying groundwater at a useful rate from a well

Groundwater Movement & Storage  Factors (continued) –Aquitard - A zone of Earth material that holds water but cannot transmit it fast enough to pump from a well

Getting Groundwater Out of the Ground  Extraction Methods –“Natural” Methods  Springs, Hot Springs, & Geysers

Getting Groundwater Out of the Ground  Extraction Methods (continued) –Man-made Methods  Wells

Getting Groundwater Out of the Ground  Artesian well/spring –A situation in which groundwater under pressure rises above the level of the aquifer –Types of artesian wells  Nonflowing – pressure surface is below ground level  Flowing – pressure surface is above the ground –Not all artesian systems are wells, artesian spring also exist

Getting Groundwater Out of the Ground  Problems with groundwater removal –Non-renewable resource –Subsidence –Contamination

Sources of Contamination  Natural Sources –Biologic activity / organisms  Bacteria and viruses –Naturally occurring elements  Uranium, radium, arsenic, and fluoride –Often naturally occurring in rock formations

Geologic Work of Groundwater  Groundwater dissolves rock –Groundwater is often mildly acidic –Contains weak carbonic acid  Forms when rainwater dissolves carbon dioxide from the air and from decaying plants  Carbonic acid reacts with calcite in limestone to form calcium bicarbonate, a soluble material –Forms caverns at or just below the zone of saturation

Geologic Work of Groundwater  Caverns –Composed of dripstone (travertine)  Calcite deposited as dripping water evaporates –Collectively, they are called speleothems –Includes:  Stalactites (hanging from the ceiling)  Stalagmites (form on the floor of a cavern)

Geologic Work of Groundwater  Karst topography –Landscapes that to a large extent have been shaped by the dissolving power of groundwater –Some common features include  Irregular terrain  Sinkhole or sinks (formed by groundwater slowly dissolving the bedrock often accompanied by collapse)  Striking lack of surface drainage (streams)

Karst Topography

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