chapter 16

What are the two paths that rainfall can take after it reaches the land surface?

Rainfall is either soaked into the ground where it becomes ground water (below earths surface) or it can become surface runoff.

Define "base level". What processes cause base level to change?

Rivers have the ability to erode there beds down to a specific elevation, which is called the base level. Changes in the base level happen when changes in land-surface slope, water discharge, or sediment supply knock the streak out of adjustment, then it erodes or deposits sediment.

How does sediment get into a stream?

1. Surface runoff after rainfall or snowmelt picks up loose sediment and washes it into streams. 2. Mass movements deliver regolith and rock from hillslopes directly to the steam. 3. Streams pick up sediment where they erode horizontally into the banks or erode vertically downward through their beds.

Define and describe the formation of an alluvial fan. How does it differ from a delta?

Alluvial fans form where water flowing in a confined channel abruptly spreads out on an unconfined valley floor. While a delta is just the landform produced by deposition of sediment where a stream enters a lake, reservoir, or sea.

What is the difference between bedload and suspended load? What is the dissolved load?

Bedload consists of particles that are large grains that roll, slide, and bounce along the bed and spend most of their time touching the bed. The suspended load consists of small sediment grains that mix with the flowing water and are transported above the bed, which they rarely touch. Dissolved load are invisible ions that have mixed with the water.

What are some of the ways that human activities affect rivers?

Dams can be built on rivers and sediment deposition is increasing in rivers as well. One of the reasons being that vegetation is being cleared for different reasons, like farming for example.

Define "discharge." How is discharge measured?

Discharge is the volume of fluid that passes a location within an interval of time. Discharge is measured by multiplying measurements of the flow velocity and the cross-section area of the flowing water.

Why does flooding occur?

Flooding occurs because the discharge exceeds the channel depth. Usually due to excessive snow melt or rainfall.

What is a floodplain? How does it form?

Floodplain is the land surface adjacent to the channel that is made by the river and is inundated during floods. The floodplains are formed because streams are almost always flanked by flat areas that, together with the channel, form a valley bottom, leaving flat areas along streams.

Define and describe the hydrologic cycle.

It is a concept for describing the movement of liquid water and water vapor through all parts of Earth system. It is when precipitation occurs followed by some water going through infiltration into ground water and the rest being surface runoff, in which both go into the stream or lake/ocean. From that it goes through transpiration where the water has evapotranspiration until it becomes condensation. Once it becomes condensation it becomes a matter of time until it turns into precipitation, and thus, the cycle repeats itself.

What is a drainage basin? Describe how water moves through the drainage basin.

It is the area from which a stream gathers water. Water from below ground along with surface run off runs into the drainage basin where it eventually runs through a mouth that drains the basin into another steam, lake, or ocean.

Streams are important agents of transport for sediments. Define "sediment load" and explain the link between sediment load and drainage-basin climate.

Sediment load is the particles carried by the stream. The composition of the sediment corresponds to the types of rocks and soils observed in the drainage basin.

Define "steam power". What is the link between steam power and sediment deposition?

Stream power is a combination of shear stress, which picks up sediment, and the average flow velocity, which transports sediment. Areas that stream power decreases are areas that sediment will be deposited.

Define "steam." What role do streams play in distributing sediment on Earth?

Stream: Flowing water that moves through a channel and simultaneously transports dissolved and particulate products of rock weathering. Streams erode, transport, and deposit sediment liberated from rocks by weathering and mass movement. Streams transport 10cubic kilometers of weathered material to oceans and lakes annually.

Describe the processes that naturally form lakes.

Surface run off flows downslope into an accumulation of water in a low part of the landscape. Water also fills lakes in which the "bowl" is deeper than the water table, causing water to seep into the bowl.

What are terraces and what do they tell us about the past?

Terraces are step-and-bench landforms alongside and above a river channel. They inform us that the river occupied a higher position in the landscape. Each terrace informs us of former position of the valley bottom.

What processes cause rivers to erode incised valleys and canyons?

The rivers actively erode bedrock, even where a meandering pattern suggests that the stream was once an alluvial river before cutting into the rock. Another possibility is that streams were affected by climate change that increased power and caused a downward adjustment of base level.