Works of Streams Steams doing work

Erosion  Erosion is transportation of minerals and materials by use of mobile agent  Usually water, wind or ice  Rivers erode their channel by water physically moving rocks and sediments or dissolving soluble minerals  Sand and gravel carried by the steam can act like sandpaper

Sediment Transport  There are three different ways sediments are transported down river  In Solution  Dissolved load  In Suspension  Suspended load  Scooting or rolling along the bottom  Bed load

Dissolved Load  Most of the dissolved load enters streams through groundwater  The amounts can vary depending on climate conditions  Most materials are different forms of salts  The amounts tend to be small in comparison and are measured in units of Parts Per Million (ppm)  The world average is ppm

Suspended load  Most streams carry the largest part of it’s load in suspension  The visible cloudiness of materials floating in the water  The faster the velocity the more material will be able to be carried  Suspension increases when floods occur

Bed Load  This is the part of a stream’s load of solid material that is made up of sediment too large to be carried in suspension  These are larger rocks or boulders that are “scooted” across the bottom of the river bed  These materials are NOT always moving like suspended and dissolved  These rocks provide a lot of erosion to the channel of the stream

Competence and Capacity  Competence  The largest particles the steam can move  If the river’s velocity doubles it’s competence quadruples  Capacity  This is the maximum load it can carry  Related to discharge (how much water)

Deposition  Deposition is the depositing of a rivers sediments  As a river slows down the competence decreases and larger particles are deposited on the floor of channel floor  Material that is dropped in this process are called alluvium  These can be dropped at any point in a river’s life

Delta? I prefer Southwest  As a river enters an ocean or lake the velocity for the most part stops  As a result the alluvium is dropped at a fairly fast rate  Deltas are an accumulation of sediment formed where a stream enters a lake or ocean  The alluvium builds up and “dams” off the channel  This forces the river to change its direction

Mississippi River Delta

Natural Levees  A Levee is a natural landform that runs parallel to a stream or river  When a stream overflows it’s banks  As the river overflows it’s banks it’s velocity decreases which causes it’s competence to decrease leaving behind sediments  As this occurs over time the sides of the river build up  Humans sometimes build levees in hope of preventing flooding

Stream Valleys  Since water always flows down hill, rivers are usually found at the bottom of a Valley  Narrow Valleys  Narrow V-shaped valleys results from a river cutting straight down towards it’s base level  Waterfalls are also dominant features  Wide Valleys  Usually result when a river is closer to it’s base level  Create “flood planes” areas around a river that will take on water when the river floods

Floods  Floods occur when the waters of a stream overflow their banks  They are the most common and destructive natural disaster in the world  They have many causes  Usually rapid rain or snow melting and storms  Flash floods occur and recede quickly usually due to rapid rain fall

Controls of floods  Artificial levees  Are earthen mounds built on the bank of a river by people  The goal is to give added protection if a river overflows it’s natural levees  Flood-Control Dam  These dams stop flood water and lets it out slowly  Dams can cause ecological damage

Drainage Basins  A drainage Basin is the land area that contributes water to a stream