Rivers

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

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

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

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

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

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

Transfer of Materials Continued 468 Larger cobbles and boulders – generally slide but ONLY if there is a high flow 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 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) Chemicals – dissolve in water and are transported (Calcium and sodium)

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

Turbulence Viscosity (resistance to flow) and surface tension act to keep water smooth, as in slow-moving water 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 Upward- flowing eddies can pick up loose material c1

Turbulence in Flowing water 469 Viscosity - resistance to flow Viscosity - resistance to flow Slow rivers = high viscosity and calm water Slow rivers = high viscosity and calm water Fast rivers = low viscosity and chaotic water or turbulent 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 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 Turbulent water usually increases the amount of grains to be picked up and carried making the water cloudy

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. 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. 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. Abrasion – when pieces of rock are sandblasted off as a result of material flowing by. Only happens on upstream side of rock. Only happens on upstream side of rock.

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

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. 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. Waterfalls – The steep gradient (vertical change/horizontal distance) and fast velocity does not allow for erosion on the sides of the river.

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

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

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

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

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

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

Why do rivers have curves? 474 Sinuosity – The amount of curves for a given length. 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. 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 Outside of a curve is deeper so the velocity is faster causing erosion on the outer bank or cut bank

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

Braided Rivers 478 Braided river – a network of channels that split and rejoin. Usually have a lot of sediment and a steep gradient. 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. 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 This allows sediment to redistribute

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