Running Water and Groundwater Chapter 5 Earth Science Running Water and Groundwater Chapter 5

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

Sources of Earth’s water Figure 5.2

Running Water Surface water is crucial for humans. Running water is surface water – rivers, lakes, etc. Surface water is crucial for humans. Drinking water Agricultural irrigation Fertile soils Transportation Waste disposal

Running water Drainage basin Land area that contributes water to a river system A divide separates drainage basins

Running water Streamflow Factors that determine velocity Gradient, or slope Channel characteristics Shape Size Roughness Discharge – volume of water flowing in the stream (generally expressed as cubic feet per second)

Running Water Gradient (slope) – Vertical drop over a unit horizontal distance. “Rise over run” Example: Fall of 91 feet over 22 miles = 91 feet = 91 feet 22 x 5280 feet 116160 feet = a gradient of 0.00078

Running Water Channel characteristics - shape, size, roughness. Higher velocities with… Uniform channel shape. Smallest channel perimeter. Smooth channels.

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 Discharge – The volume of water moving past a given point per unit time (cfs). Measured by Cross-sectional area Flow velocity Discharge changes due to seasonal variation in precipitation and runoff.

Running water Upstream-downstream changes Profile Factors that increase downstream Channel size Discharge Factors that decrease downstream Gradient, or slope Channel roughness

Running water The work of streams Erosion Transportation Transported material 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 backswamps or tributaries

Formation of natural levees by repeated flooding Figure 5.21

Formation of a Delta

Running water Base level Lowest point to which a stream can erode Two general types Ultimate – sea level Temporary, or local Changing causes readjustment of the stream – deposition or erosion

Adjustment of base level to changing conditions Figure 5.15

Base Level W. W. Norton

Raised Base Level W. W. Norton

Lowered Base Level W. W. Norton

Stream Terraces Remnants of a former floodplain. Rivers adjust to a relative drop in base level by downcutting. Many US streams preserve terraces formed during glacial maximum.

Running water Stream valleys Characteristics of narrow valleys Valley sides are shaped by Weathering Overland flow Mass wasting Characteristics of narrow valleys V-shaped Downcutting toward base level

A narrow, V-shaped valley Characteristics of narrow valleys Rapids Waterfalls Figure 5.17 A

Continued erosion and deposition widens the valley Figure 5.17 B

A wide stream valley is characterized by meandering on a well-developed floodplain Stream is near base level Downward erosion is less dominant Stream energy is directed from side to side Figure 5.17 C

Running water Stream valleys Characteristics of wide valleys Floodplain Features often include Meanders Cutoffs Oxbow lakes

Erosion and deposition along a meandering stream

A meander loop on the Colorado River Figure 5.18

Running water Drainage patterns Networks of streams that form distinctive patterns Types of drainage patterns Dendritic Radial Rectangular Trellis

Drainage patterns Figure 5.22

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

What is Ground Water? Water that infiltrates the surface. A component of the hydrologic cycle.

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

Groundwater Largest freshwater reservoir for humans Geological roles As an erosional agent, dissolving by groundwater produces Sinkholes Caverns An equalizer of streamflow Gaining Losing

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

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

Groundwater Permeability 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 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

Old Faithful geyser in Yellowstone National Park Figure 5.29

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

Formation of a cone of depression in the water table Figure 5.31

Artesian systems Figure 5.32

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

Caverns Most caverns are created by limestone dissolution at or just below the water table.

Cavern Features Composed of dripstone (travertine) calcite deposited as dripping water evaporates. Collectively, they are called speleothems. Stalactites (ceiling) and stalagmites (floor).