River Systems Chapter 15

15.1 – The Water Cycle

Water Cycle Evapotranspiration Evapotranspiration increases Total loss of water by an area Evaporation + transpiration by organisms Evapotranspiration increases With temperature With vegetation With wind

Water Budget Precipitation = Evapotranspiration + Runoff Globally balanced Locally not balanced Factors affecting local water budget Temperature Vegetation Wind Rainfall amounts

Global Water Oceans (97%) – too salty too use Ice caps (2%) Ground Water (<1%) Rivers, lakes, reservoirs…(<0.01%)

Water Use in U.S. ~ 100 – 150 gallons/day/person (municipal) ~ 2000 gallons/day/person total use Agriculture, hydroelectric, industry

15.2 – Stream Erosion

How rivers develop A river system begins to form when precipitation exceeds evapotranspiration in a given area. After soil soaks what it can hold, excess water moves downslope as runoff. Runoff erodes rock & soil & may form a ditch called a gully Eventually develops into a permanent stream

River System Parts Tributaries Feeder streams into main stream

River System Parts Lake Lanier Watershed Area Watershed Area that drains into a particular stream White Lumpkin Dawson Habersham Lake Lanier Watershed Area Hall Forsyth

River System Parts Divide Separates watersheds

Channel Erosion Headward Erosion Channel erodes at river head in opposite direction of flow

Headward Erosion

Headward Erosion

Headward Erosion Niagara Falls

Stream Piracy One stream takes over and begins to drain an area Pirate stream erodes faster Pirate stream

Stream Load Suspended load Bed load Dissolved load Fine sand and silt Larger materials bouncing down stream Dissolved load Transported in liquid form

Stream Load Suspended load: particles of fine sand and silt Bed load: larger, coarser materials (sand, gravel, pebbles) Dissolved load: mineral matter suspended in liquid solution

More River System Parts Stream Discharge Volume of water that a stream transports Higher velocity = higher discharge

More River System Parts Stream gradient Steepness Generally steeper near headwaters Steeper means higher velocity

Gradients Steep Gradient Gentle Gradient Yellowstone River, WY Near headwater Gentle Gradient Far from headwater Yellowstone River, WY Mississippi River, New Orleans

Meandering Channels Slow moving streams tend to wander They form meanders Winding patterns of wide curves Slowness causes bank erosion as opposed to bed erosion

Meander on the Mississippi Near Baton Rouge

Louisiana Meander

Meandering Stream Rocky Mountain National Park

Meanders and Lakes Oxbow Lakes: A meander curves and forms a narrow neck. When this narrow neck is cut off, the meander is isolated from the river and forms an oxbow lake. Oxbow lakes

Braided Streams Stream with multiple channels that divide and rejoin around sediment bars Result of large sediment load

15.3 – Stream Deposition

Deltas Fan-shaped mass of deposited material at the mouth of a stream or river

Alluvial Fan Deltas formed on land Caused by temporary streams (run off)

Floodplains The part of a valley floor that may be covered with water during a flood.

Natural Levees When a stream overflows its banks and spreads out over the floodplain, the stream slows down and deposits coarse sediment on the river banks. This sediment builds up and raises the height of the river banks. This is a natural levee. Finer sediments are washed out into the floodplain.

Flood Control Human activities contribute to flooding: logging & clearing land of vegetation lead to increased erosion. Natural events like fires can increase likelihood of flooding.

Flood Control Direct: Building artificial structures that redirect flow of water Examples: dams, levees

Flood control Indirect methods: structures are not specifically built and natural methods are used like soil & forest conservation These prevent excess runoff during periods of heavy rainfall

Living in Floodplains Sediments deposited during floods are rich in minerals and nutrients. Rich soils draw people to live there for farming. Convenient access to river for shipping, fishing, and transportation also make people want to live here.

Life Cycle of Lakes Precipitation forms in a depression and forms a lake. A lake loses water as it drains or evaporates. A common cause of excess drainage? An outflowing stream erodes its bed below the level of the lake basin. As water is lost, the lake basin may eventually become dry land. Lakes can also fill up with sediment and disappear. Sediments are carried by streams or in runoff from land.