Sculpting the Earths Surface Running Water And Groundwater
- Slides: 44
Sculpting the Earth’s Surface Running Water And Groundwater
The Hydrologic Cycle § Water Basics – Sea water – Fresh Water § Polar ice & glaciers § Groundwater § Lakes and Rivers 97. 2% 2. 8% 2. 15% 0. 62% 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-downstream characteristics § Upstream – – – Higher velocity Smaller discharge Smaller channel § Downstream – – – Lower velocity Greater discharge Larger channel
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 • Deposition • Caused by a decrease in velocity • Competence is reduced • Sediment 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
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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