Rivers and Groundwater

SURFICIAL PROCESSES n Erosion, Transportation, Deposition on the Earth’s Surface n Landscapes created and destroyed n Involves atmosphere, water, gravity n Agents: –Mass wasting (gravity), Running water (streams), glaciers (ice), wind, water waves, ground water

MASS WASTING n Masses of debris (mud, sand, gravel) or bedrock moving downhill n Landslides and slower movements n Driven by GRAVITY

Controlling Factors n Slope angle- gentle vs steep n Local relief- low vs high n Thickness of debris over bedrock- slight vs great n Planes of weakness ( in bedrock) –bedding planes; foliation; joints –planes at right angle to slope vs parallel to slope most dangerous

The Hydrologic Cycle n n Powered by the Sun n n Evaporation primarily from tropical oceans n n Evapotranspiration- from surface water & plants n n Condensation- clouds n n Precipitation n n Runoff- from the land n n Infiltration/Percolation into soil and rocks

Water Reservoirs n Oceans- 97% n Ice caps and Glaciers- 2.15% n Groundwater- 0.62% n Lakes % n Soil Moisture % n Streams % n Atmosphere %

Drainage Basins n n Tributary n n Divide

Drainage Patterns n n Dendritic n n Radial n n Rectangular n n Trellis

Factors Affecting Stream Erosion and Deposition n n Velocity n n Gradient n n Channel Shape and Roughness n n Discharge

Factors Affecting Stream Erosion and Deposition n n Velocity n n Gradient n n Channel Shape and Roughness n n Discharge

Meandering Streams and Point Bars n n Meanders n n Point Bar n n Meander Cutoff – – Oxbow Lake n n Flood Plains – – Natural Levees

Meandering Streams and Point Bars n n Meanders n n Point Bar n n Meander Cutoff – – Oxbow Lake n n Flood Plains – – Natural Levees

Meandering Streams and Point Bars n n Meanders n n Point Bar n n Meander Cutoff – – Oxbow Lake n n Flood Plains – – Natural Levees

DELTAS

Flooding n n Flooding n n Urban Flooding n n Flash Floods n n Controlling Floods n n The Great Flood of 1993

Flooding n n Controlling Floods n n The Great Flood of 1993

The Great Flood of 1993 n Excessive rain in upper midwest n 6.6 million acres in 9 states flooded n Discharge exceeded 100-year discharges on many rivers –At St. Louis Mississippi Q=1,000,000 cfs –River Stage 20 ft above flood stage n 38 deaths n $17 billion in losses

Groundwater n What happens to precipitation once it reaches the ground –infiltration –percolation n Water filling pore space, cracks & crevices in rocks- Porosity n Aquifer- Geologic unit that can store, transmit and yield appreciable amounts of water

Porosity and Permeability n Porosity – % of rock or sediment that is open (void spaces) – ability to hold water n Permeability- ability to transmit water

Movement of ground water n Moves in response to differences in water pressure & elevation n Velocity influenced by – Slope of water table – Permeability

Aquifers n Geologic unit that can store, transmit and yield appreciable amounts of water n Highly permeable & saturated with water – Good aquifers n Aquitards- impermeable n Unconfined aquifer –open to atmosphere n Confined aquifer –under pressure –artesian- flows w/o being pumped

Wells n Penetrate aquifer within the saturated zone n Water table rises and falls during seasons – Recharge n Cone of depression – Drawdown n Artesian well- no need to pump – Artesian aquifer

Springs and Streams n Spring –Water table intersecting hillside n Gaining stream= Effluent Stream n Losing stream= Influent Stream

Springs and Streams n Spring –Water table intersecting hillside n Gaining stream= Effluent Stream n Losing stream= Influent Stream WT

Pollution of Ground Water n Pollutants –Chemicals »Gasoline » Pesticides & herbicides » Fertilizers » Heavy metals – Bacteria, viruses, parasites- Sewage – Acid mine drainage – Radioactive waste – Natural pollution

Balancing Withdrawal & Discharge n Overpumping results in: – Falling water table – Ground subsidence n Artificial recharge

Subsidence of land caused by extraction of groundwater in the San Juaquin Valley, CA The land sank 9m or 30 ft in 52 years

Effects of Groundwater Action n Karst topography -Caves – Rock usually limestone – Dissolves by weakly acidic water n rainwater pH 5.5 and carbonic acid from humus – Dripstone- Speleothem » stalagtite » stalagmite – Flowstone –Sinkholes

Hot Water Underground n Hot springs – Near magma or cooling igneous rocks – Deep-circulating groundwater or n Geyser n Precipitation of dissolved ions – Travertine- calcite – Sinter- silica n Mudpot n Geothermal Energy

Hot Water Underground n Hot springs – Near magma or cooling igneous rocks – Deep-circulating groundwater or n Geyser n Precipitation of dissolved ions – Travertine- calcite – Sinter- silica n Mudpot n Geothermal Energy