2. HUMAN IMPACT ON RIVERS

3. HOW RIVERS ARE USED BY HUMANS Transportation A)Some rivers form natural route ways which can be used for transport eg. St. Lawrence, Mississippi –Shipping –Logging Impact -oil spills from ships or other chemicals that may spill from ships B)River valleys often offer fairly easy passage for railroads and highways Impact -road building across steep, bare slopes enhances soil erosion

4. St. Lawrence Seaway

5. HOW RIVERS ARE USED BY HUMANS Supplying water -irrigation (farming) -industrial (logging, mining) -human consumption (urban/rural areas) Impact -more deposition, less erosion

6. Thompson River, Kamloops BC

7. HOW RIVERS ARE USED BY HUMANS Getting rid of waste material -sewers -industrial waste Impact -unclear water if it doesn’t pass through the treatment plant Hydro Power - dams Impact -streamflow evens out and becomes less active in landform change

8. ITAIPU Powerdam, Brazil

9. HOW RIVERS ARE USED BY HUMANS Sheltered Ports - some river mouths contain sheltered water and enable ports to be developed eg. Vancouver, BC Impact -changing of river mouth -freight traffic

10. HOW RIVERS ARE USED BY HUMANS Farming -some flood plains offer soil and flat lands that are excellent for farming Impact - decrease in flooding -contamination of river: pesticides, manure, and fertilizer -building of dykes Recreation - fishing -rafting Impact -business -tourism -contamination: oil spills from boats, garbage

11. Mississippi River

12. FLOODING

13. FLOODS Causes -river flooding -results from long periods of heavy rain or melting snow over large areas ie. The Great Flood of 1993 on the Mississippi -flash floods -caused by short intense storms (thunderstorms) over small river basin producing flood that rises rapidly to a high peak. -common in arid areas and in mountains where intense thunderstorms occur -direct runoff -deforestation reduces infiltration -trees hold soils of forest floor together

14. FLOODS Causes (continued) - increased urbanization -prevents ground absorption of water which increases runoff and contributes to flash flooding -sediment from erosion -settle to river bottom -gradually raises water level -overgrazing -loss of grass cover on hill sides -faster runoff and erosion

15. FLOODS Prevention of floods -dams and reservoirs -dykes -channel improvements - contour plowing Dikes -earth banks built along both sides of river to contain flood flow -other terms: levees, bunds, stopbanks, flood banks

16. 1993 flood along River Des Peres in South St. Louis