Surface Water

Chapter 9 Notes

The Water Cycle

Runoff

• Surface water flowing downslope is called runoff.

• Factors affecting runoff/infiltration:– Soil composition– Soil saturation – Rate of precipitation– Vegetation– Steepness of slope

Stream Systems

• All streams flow downhill• Rivers that flow into other streams are called

tributaries.• A watershed or drainage basin is the land area

whose water flows into a stream system.• A divide is an elevated land area that

separates two watersheds.

Watersheds

Stream Load/Carrying Capacity

• Moving water carries sediment• The amount of sediment (carrying capacity)

depends on the amount of water and its velocity

• Sediment can be– Suspended (silt, clay, and sand)– Bed load (sand, pebbles, and cobbles)– Dissolved (salts and minerals)

Discharge of a Stream

• Discharge is the volume of water that flows past a point in a given amount of time

• Discharge = width x depth x velocity

• Mississippi: 17,000 m3 per second

• Amazon: 170,000 m3 per second

Floods

• Floods occur when water spills over the stream’s banks

• The broad, flat area covered by flood waters is known as a floodplain

• Floodplains develop very fertile soil due deposits of nutrients

Natural Levees

• Sediment carried by flood water is deposited along the banks

• Natural ridges called levees are formed

Stream Development

Deposition of Sediment• When streams slow down,

sediment they are carrying is deposited

• Deltas: triangular deposit where a stream enters a lake or ocean

• Alluvial fans: sloping, fan-shaped deposits in dry stream beds

Stream Rejuvenation

• A change in base level can cause an “old” stream to begin downcutting again.

• Meanders can become deep canyons (entrenched meanders)

• example: Colorado River

Lakes

• Most lakes in Europe and North America are in recently glaciated areas

• A meandering river can form an oxbow lake through erosion and deposition of sediment

Eutrophication

Wetlands

• Wetlands play an important role in improving water quality

• Wetlands serve as a filtering system that traps pollutants, sediment and pathogenic bacteria

• Wetlands provide important habitat for wildlife