Running Water = water that falls in the form of snow, rain, hail, or other precipitation.

• gets its energy from the sun
• The sun evaporates the water - that keeps the cycle moving
• Wears down the land in two ways

1. it breaks up the bedrock
2. removes weathered rock and soil material

• Using sand, pebbles, etc. as its cutting tools, the water wears away the rock by Abrasion
• Even the cutting tools get worn down and this causes the rocks and pebbles to become nicely rounded stones (also commonly smooth)
• Water will also dissolve soluble minerals - any rocks that are held together with calcite cements can be affected

Water Removes Weathered Rock

• Even slow moving rain water flowing down a gentle slope will carry particles away
• Rivers carry material in three ways:

1. Solution - material dissolved in the water; gives water a cloudy or colored look
2. Suspension - clays, silts, and fine sands that are carried by the river water; generally gives water a real muddy look
3. Bed Load - materials like pebbles, rocks, and boulders that are pushed along the river floor by rushing water

• Rivers carry 25% of load in solution, 50% in suspension, and 25% in bed load
• Smaller streams would have much more solution and less suspension and no bed load
• The power of a stream or river to carry materials is known as its Carrying Power.
• Carrying Power is determined by the speed of the stream and its total discharge ability
• Discharge refers to the volume of water flowing past a given point at a given time
• Thus, the carrying power of a stream increases as the speed and discharge increase

The River Valley

• River valleys form in a couple of ways
• Young streams typically form V-shaped valleys because they are often fast moving and wear away at the ground and bedrock quickly
• These steep valleys are called Canyons or Gorges or Chasms
• Over time, you may see these canyons widen because their exposed rock walls weather away by weathering processes
• Streams can only cut their valleys as low as the body of water they flow into
• This level is called Base Level - the ocean is the base level for many rivers of the world and large lakes are base level for many streams that flow from mountainous areas
• Simply as the stream approaches its base level, its erosional water force decreases, slowing the weathering affect on the stream floor
• Rains also play a role in the formation of small stream valleys - they often create a Gully
• Gullies grow in length, width, and depth every time it rains
• Many river systems of the world began as gullies! This happens when a gully becomes so large and deep, that it penetrates a water table and a river system is born.

Divides and Drainage

• The high lands that separate one gully from the next or one valley from another are called Divides
• The Rocky Mountains contain the Great Continental Divide, separating west from east U.S.
• All water flows either west or east of the Rocky Mountains - water either ends up in the Pacific or the Atlantic Ocean
• All the land that drains to either ocean is then called a Water Shed (Drainage Basin)
• The largest water shed in the U.S. is the Mississippi River system - takes almost 3/4 of the U.S. to the Gulf (Atlantic Ocean)

Stream Piracy

• Stream Piracy is the result of the lengthening of a river by headward erosion
• As erosion continues, river A wears through the divide of nearby river B and joins, often stealing water from river B, cause it to dry up

Water Gaps and Wind Gaps

• A narrow cut called a Water Gap forms in the ridge through which the river runs, often looking like an island in the middle of the river
• Wind Gaps simply form in the river bed when the river dries up

River Deposits

• As rivers or streams run over irregular stream beds, whirlpools form and swirl particles around
• These particles grind away at the rock and form Potholes - almost perfectly circular hollows in the rock
• Very large potholes are called Plunge Pools, which often form at the base of water falls, etc.
• Water Falls of course form wherever rivers run over steep cliffs or into lower lying canyons
• Because of the concept of undermining and erosion, the movement of water falls is somewhat rapid over time
• Water weathers the rock of the stream bed at the water fall and causes the water fall to recede backward
• Niagara Falls for example has receded from Lake Ontario about 11 km over the last 11,000 years! (about 1 km per 1000 years)

Other River Features

• At times of heavy rainfall, rivers may overflow their banks and cover part of the valley floor, creating what is called a Flood Plain
• Flood plains change size over time due to flood sediment
• River sediment also causes rivers to change in shape
• This change in shape usually produces a river that winds throughout the region it is found in
• This winding of the river is called a Meander
• Meanders are limited in size
• As the curves become greater, the loop that is created breaks through and produces a cutoff of the stream of water
• The deposits of sediment in the river block off the meander and produce an Oxbow Lake

River Deposits

• As rivers flow, they carry a variety of deposits in solution, suspension, and bed load
• As rivers slow their speed, they will decrease their carrying power, depositing sediments
• You will see that the river will begin to drop its suspension as it nears an open body of water - like a river flowing into a lake
• Often, a Delta is formed at the mouth of the river - area where river meets lake
• A Delta is a fan-shaped deposit of sediment at the mouth of a river
• Alluvial Fans form at the base of mountains or hills where water runoff has carried material down slope and deposits it in much the same way as a delta

Flood Plains

• Large rivers carry a great amount of water during certain times of the year
• If flooding occurs, major devastation happens
• A Levee is often constructed to increase the size, height, and strength of the natural river banks or walls to keep as much river water in the river instead of flooding the flood plain -(area around the river that floods during the wet season)
• Levees form naturally or are man-made in many areas to hold back flood waters
• Back Swamps are low lying wet areas behind the levees

Causes of River Floods and Prevention

• Long lasting rain or winter snow melt can cause major flooding in most areas
• Sudden cloud bursts of pouring rain will create a Flash Flood
• Larger rivers typically never have flash floods because they can handle rain water, but suffer from winter melts annually
• Floods can also be created by ice jams, dam failure, landslides, or even volcanoes!
• Prevention can occur by constructing spillways for the excess water to flow; making sure surround land is vegetated; and construction and proper management of dams