Unit 6: Rivers

1. Unit 6: Rivers Delta Types

2. Today’s Class • River Delta Quiz • River Delta’s • Homework assignment will be emailed to you on Sunday

3. Deltas: Definiton • Delta is a low lying area at mouth of river formed by deposition of silt deposition occurs because river slows as it enters ocean or lake.

4. How Deltas Form • As a river is moving, it carries eroded material with it. The eroded material continues to flow downstream until it reaches still water of an ocean, sea, lake, or bay.

5. How Deltas Form • When the river reaches the still water, the heavy particles are first to settle out. • The lighter particles are carried further from shore. This process is then repeated farther out and a delta forms.

6. Delta’s • Deltas are often popular areas for farming due to the presence of fertile alluvial soils

7. Four Main Types of Delta’s • Bird's Foot or Digitate Delta • Arcuate Delta • Estuarine delta • Cuspate Delta

8. Bird's Foot or Digitate Delta • A bird's foot delta forms where sediment is deposited in relatively calm offshore waters. An example of a bird's foot delta is the Mississippi river delta • Large amounts of sediment

9. The Mississippi Delta Jetties have been built and dredging occurs to allow large vessels to navigate the delta channel Note the large amounts of sediment that surrounds the delta A bird’s foot delta located in Louisiana adjacent to the Gulf of Mexico

10. Arcuate Delta • when a river meets the sea in a place where the waves, currents, and tides are strong. It is often bow shaped and has a number of distributaries flowing across it. An example is the Nile delta of Egypt.

11. Nile

12. Estuarine Delta • When the mouth of a river enters the sea and is inundated by the sea in a mix with freshwater and very little delta, it is called an estuary. An example of a estuarine delta is the Seine river delta in France or the Mackenzie river delta in Canada.

13. Estuarine Delta

14. Cuspate Delta • is formed when a river drops sediment onto a straight shoreline with strong waves. Waves force the sediment to spread outwards in both directions from the river's mouth making a pointed tooth shape with curved sides. An example is the Tiber delta in Italy. • Usually has one distributary

16. River Life Cycles •  Rivers change over time and seem to go through three stages: • Youth • Maturity • Old Age

17. River Life Cycles • Youth: • Are usually found in highland or mountain regions. • Tend to have a steep slope (high gradient) • Usually have a small volume of water • Have a rapid flow of water • Usually very rapid erosion especially vertically • A narrow ‘V’ shaped valley is characteristic • Water falls and rapids are common

18. River Life Cycles • Maturity/Late Maturity: • Most high relief is eroded • Gentler slope • Many well developed tributaries • Broad flat river valley • Well developed flood plain • More lateral erosion than vertical • Meandering results

19. River Life Cycles • Old Age: • Almost no slope • Very little relief • Elaborate meandering • Oxbow lakes develop • Often swampy areas around river • Very muddy due to slow speed • Most susceptible to flooding because of a large flood plain

20. River Life Cycles • Evaluating Evidence to Determine the Age of Rivers • There are six common pieces of evidence you can look for to determine the stage of a river. • Slope of the river (steeper = younger) • Relief of the banks (steeper = younger) • Width of the valley (wider = older) • Meandering (more = older) • Size of flood plain (wider = older) • Rapids or water falls (more = younger)