6.3 Water Beneath the Surface Chapter 6 6.1 Running Water 6.2 The Work of Streams 6.3 Water Beneath the Surface

The Water Cycle Illustrates the circulation of Earth’s water supply Processes involved in the cycle Precipitation Evaporation Infiltration Runoff Transpiration >Water cycle drawing worksheet

Sources of Earth’s water

Running water Streamflow Factors that determine velocity Gradient, or slope Channel characteristics Shape Size Roughness Discharge – volume of water flowing in the stream

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 Channel size

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

Longitudinal profile of a stream

Running water Base level Lowest point to which a stream can erode Two general types Ultimate – sea level Temporary, or local

Adjustment of base level to changing conditions

The Work of Streams Stream channels are eroded through Abrasion Grinding Dissolving soluble materials Sediment transport Dissolved load Suspended load Bed load

The Work of Streams Transportation of sediment Load is related to a stream’s Competence – maximum particle size a stream can transport Capacity – maximum load Capacity is related to discharge… The greater the volume of water in a stream, the greater its capacity for carrying sediment

The Work of Streams Deposition Caused by a decrease in velocity Competence is reduced Sediment begins to drop out Stream sediments Known as alluvium, or well-sorted deposits from a stream

The Work of Streams Deposition Features produced by deposition Deltas – exist in ocean or lakes Natural levees – Form parallel to the stream channel

Formation of natural levees by repeated flooding

The Work of Streams Stream valleys Characteristics of narrow valleys V-shaped Downcutting toward base level Features often include Rapids Waterfalls

A narrow, V-shaped valley

The Work of Streams Stream valleys Characteristics of wide valleys Stream is near base level Downward erosion is less dominant Stream energy is directed from side to side Floodplains Features often include Meanders Cutoffs Oxbow lakes

Continued erosion and deposition widens the valley

A wide stream valley is characterized by meandering on a well-developed floodplain

Formation of a cutoff and oxbow lake

Erosion and deposition along a meandering stream

A meander loop on the Colorado River

The Work of Streams Floods and flood control Floods are the most common geologic hazard Causes of floods Weather Rapid spring snow melt Storms / heavy rains Human interference with the stream system Dam or levee failure Building / developing on wetlands

The Work of Streams Floods and flood control Engineering efforts Artificial levees Flood-control dams Minimizing development on floodplains, allowing floodplains to naturally absorb floodwaters

Satellite view of the Missouri River flowing into the Mississippi River near St. Louis

Same satellite view during flooding in 1993

The Work of Streams Drainage basin Land area that contributes water to a stream A divide separates drainage basins

Drainage basins and drainage divides

Water beneath the surface (groundwater) Largest freshwater reservoir for humans Geological roles As an erosional agent, dissolving by groundwater produces Sinkholes Caverns Helps to maintain a steady streamflow

Water beneath the surface (groundwater) Distribution and movement of groundwater Distribution of groundwater Belt of soil moisture (close to the surface) Zone of saturation Zone of Aeration (unsaturated zone) Pore spaces in the material are filled mainly with air

Water beneath the surface (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

Features associated with subsurface water

Water beneath the surface (groundwater) Distribution and movement of groundwater Movement Porosity Percentage of pore spaces Ability to store water Permeability Ability to transmit water through connected pore spaces (water can flow through) Aquitard – an impermeable layer of material Aquifer – a permeable layer of material

Water beneath the surface (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

Water beneath the surface (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

Artesian systems

Water beneath the surface (groundwater) Environmental probs with groundwater Treating it as a nonrenewable resource Removing it faster that it can be replenished Land subsidence caused by its withdrawal San Joaquin Valley, California Contamination Septic, Farm waste, inadequate or broken sewers

Water beneath the surface (groundwater) Geologic work of groundwater Groundwater is often mildly acidic 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 / Travertine Calcite deposited as dripping water evaporates Common features include stalactites (hanging from the ceiling) and stalagmites (growing upward from the floor)

Cave Features in Lehman Caves, Great Basin National Park, and Carlsbad Caverns National Park

Water beneath the surface (groundwater) 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 (few streams if any, water is mostly funneled underground)

Features of karst topography