Tarbuck & Lutgens

Stanley C. Hatfield Southwestern Illinois College

» Illustrates the circulation of Earth’s water supply

» Processes involved in the cycle˃ Precipitation˃ Evaporation˃ Infiltration˃ Runoff˃ Transpiration

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

» 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)

+ Discharge = Depth x Width x Velocity

» Upstream-downstream changes ˃ Profile

+ Cross-sectional view of a stream + From headwaters (source) to mouth

– Profile is a smooth curve – Gradient decreases from the headwaters to the mouth

+ Factors that increase downstream – Velocity– Discharge

» Upstream-downstream changes ˃ Profile

+ Factors that increase downstream – Channel size

+ Factors that decrease downstream– Gradient, or slope – Channel roughness

» The work of streams ˃ Erosion˃ Transportation

+ Transported material is called the stream’s load– Dissolved Particle– Suspended Particle– Bed Particle

» The work of streams ˃ Transportation

+ Load is related to a stream’s – Competence – maximum particle size– Capacity – maximum load – Capacity is related to discharge

» Greater the discharge the greater the capacity.

» 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

» 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

» 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

» Stream valleys ˃ Valley sides are shaped by

+ Weathering + Overland flow+ Mass wasting

˃ Characteristics of narrow valleys + V-shaped+ Downcutting toward base level

» 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

» Stream valleys ˃ Characteristics of wide valleys

+ Floodplain + Features often include

– Meanders– Cutoffs– Oxbow lakes

» Drainage patterns˃ Networks of streams that from distinctive patterns˃ Types of drainage patterns

+ Dendritic+ Radial+ Rectangular+ Trellis

» Floods and flood control ˃ Floods are the most common geologic hazard ˃ Causes of floods

+ Weather+ Human interference with the stream system

» Floods and flood control ˃ Engineering efforts

+ Artificial levees+ Flood-control dams+ Channelization

˃ Nonstructural approach through sound floodplain management

» Largest freshwater reservoir for humans » Geological roles

˃ As an erosional agent, dissolving by groundwater produces + Sinkholes+ Caverns

˃ An equalizer of stream flow

» 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

» 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

» 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

» 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

» 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

» Environmental problems associated with groundwater ˃ Treating it as a nonrenewable resource ˃ Land subsidence caused by its withdrawal ˃ Contamination

» 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

» 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)

» Geologic work of groundwater ˃ Karst topography

+ Formed by dissolving rock at, or near, Earth’s surface + Common features

– Sinkholes – surface depressions– Sinkholes form by dissolving bedrock and cavern collapse– Caves and caverns

+ Area lacks good surface drainage