Rivers

1. Rivers

2. Where Do Rivers Get Their Water? 466 • Drainage Basin – provides water for the river.

3. Where Do Rivers Get Their Water? 466 • Basin Slope – Runoff from a steep slope is higher than a gentle slope. • Tributaries – Small channels that carry water to rivers.

4. Drainage Patterns 467 • Dendritic Drainage Pattern – Where rocks have about the same resistance to erosion. • Radial Drainage – Occurs on a mountain, drainage flows downhill in all directions

5. Drainage Patterns 467 • Structurally Controlled Pattern – Erosion along faults or fractures. • Trellis • Rectangular Trellis Rectangular

6. How is Material Transported and Deposited? Fine particles can be carried in suspension (floating) in water Soluble ions are dissolved in and carried by moving water Sand grains can roll and bounce along Cobbles and boulders mostly roll and slide during high flows 16.02.a1 Material moving on river bed is bed load

7. How Is Material Transported and Deposited in Streambeds? 468 • Suspended Material - Particles that are small enough to be carried along with a slow current, such as clay (AKA mud) or silt • Saltation – (from the latin word saltus – to leap) the process of larger particles (sand) bouncing off the bottom of the streambed.

8. Transfer of Materials Continued 468 • Larger cobbles and boulders – generally slide but ONLY if there is a high flow • Bed Load – Material that is pushed, bounced, rolled, and slid along the bottom. This sediment exceeds the carrying capacity of the river • Chemicals – dissolve in water and are transported (Calcium and sodium)

9. Transport vs. Deposit 468 • Materials are transported when the river moves quickly. The river then has a high carrying capacity. • When the velocity slows, more material is deposited because the carrying capacity is reduced.

10. Turbulence Viscosity (resistance to flow) and surface tension act to keep water smooth, as in slow-moving water Upward-flowing eddies can pick up loose material Moving water has inertia (tries to keep moving with same speed and direction) At higher velocities or near obstacles, flow becomes more chaotic (turbulent), forming a swirl called an eddy 16.02.c1

11. Turbulence in Flowing water 469 • Viscosity - resistance to flow • Slow rivers = high viscosity and calm water • Fast rivers = low viscosity and chaotic water or turbulent water. • Turbulent rivers have eddies which are horizontal or vertical swirls in the water. • Turbulent water usually increases the amount of grains to be picked up and carried making the water cloudy

12. Erosion in streams 468 • Sand and larger clasts lift because of low pressure created by water flowing over the grain tops or are pushed up by turbulent water. • Once lifted, the clasts collide with obstacles and break off. • Abrasion – when pieces of rock are sandblasted off as a result of material flowing by. • Only happens on upstream side of rock.

13. Erosion in streams 468 • Also occurs when water and sediments swirl in a small area. Creates bowl-shaped pots called, potholes • Turbulent flow loosens and lifts material from the streambed. • Dissolution removes soluble material

14. Erosion, Rivers, and Bedrock 469 • Many rivers are carved into bedrock. If the bedrock is hard, the shape of the river is controlled by the geology. • Waterfalls – The steep gradient (vertical change/horizontal distance) and fast velocity does not allow for erosion on the sides of the river.

15. Erosion, Rivers, and Bedrock 469 • Canyons – originally started where bedrock was softer. Once formed, hard to change the direction of the river.

16. Channel Size, Water Velocity, Discharge, and Sediment Load 470 • As the gradient decreases, sediment size decreases. • Channel size (width x depth) increases • Velocity increases because there are feeder streams adding additional water • Discharge (amount of water flowing through a specific part of the river) increases • Sediment load – increases until it can be deposited at the mouth of the river.

17. River Behavior Through the Year 471 • Peak Discharge - when discharge is the highest. Its usually spring because of the snowmelt.

18. Water Budget – the amount of water evapotransporated and regenerated (in the form of precipitation) during the year. • Surplus – more precipitation than evapotransporation • Deficit – more evapotransporation than precipitation

19. Rivers Through the Year • Perennial Stream – flows all year long. Needs to be fed by groundwater because it doesn’t rain all year.

20. Curves in Rivers and Streams Observe the channels in three rivers 16.05.a2-4 Braided: network of interweaving channels Low sinuosity: gently curved Meandering: very curved; high sinuosity

21. Why do rivers have curves? 474 • Sinuosity – The amount of curves for a given length. • Inside of a curve is shallow so the velocity is slower. Sediment is deposited here, known as the point bar. • Outside of a curve is deeper so the velocity is faster causing erosion on the outer bank or cut bank

22. Landforms in the headwaters of Rivers 476 • Headwaters – The beginning of a stream or river • Waterfalls – A steep gradient formed when hard rock impedes downcutting by the stream. • Rapids – rough, turbulent water along a stream. Form when the gradient steepens and the river is constricted by bedrock or large rocks.

23. Braided Rivers 478 • Braided river – a network of channels that split and rejoin. Usually have a lot of sediment and a steep gradient. • When glaciers melt, there is an abundance of water and sediment and the braided river systems flood and form new rivers. • This allows sediment to redistribute

24. When Rivers Reach Base Level 482 • Base Level – the ocean • Delta – When currents slow, deposit is dropped along the shoreline. • Silt and clay are carried farther out into sea.