River Systems

watershed•land from which water runs off into streams (drainage basin)

Surf your watershed

http://www.epa.gov/surf/

Know your watershed

http://ctic.purdue.edu/kyw/kyw.html

tributaries•feeder streams that flow into a main river

divide•ridges or elevated regions of high ground that separate watersheds

headwaters•beginning of a stream

Stream Erosion

channel•the path that a stream follows

bank

bed

headward erosion

•process of lengthening and branching of a stream

stream piracy•the capture of a stream in one watershed by a stream with a higher rate of erosion in another watershed

Stage 1 - Beaverdam Creek, Gap Run, and Goose Creek flow eastward through the Blue Ridge and enter the Potomac.

Stage 2 - As the land is eroded downward, the three east flowing creeks do not have the power to erode as far through the Blue Ridge as the Shenandoah, Potomac system. The Shenandoah extends itself southward by headward erosion through the relatively high land west of the Blue Ridge. It eventually captures Beaverdam Creek.

Stage 3 - The capture of Beaverdam Creek added more discharge to the Shenandoah which was able to therefore erode more. Headward erosion leads to the capture of Gap Run. The water gaps where Beaverdam Creek and Gap Run used to flow through the Blue Ridge are left as wind gaps.

Stage 4 - Eventually Goose Creek is captured as well. Snicker's Gap, Ashby Gap, and Manassas Gap are left as wind gaps. As the land on either side of the ridge is eroded down together with the ridge summit, the relative elevation of the wind gaps becomes higher and higher.

channel erosion5 things that affect the rate

stream load:

material carried

by a stream

dissolved load: mineral matter transported in liquid solution

suspended load: particles of fine grains and silt

bed load: made of larger, coarser sand, gravel, and pebbles

Bed

Observe how sediment is

transported by flowing water.

discharge•volume of water moved by a stream within a given time

gradient•steepness of a stream slope

water gap

•notch formed where the stream has eroded its channel

Stream Valleys

Youthful river•straight •erodes rapidly•V-shaped•few tributaries•has waterfalls and rapids

Mature river

•meandering (winding)•slow erosion•U-shaped •lots of tributaries •holds lots of water

Old river

•gradient and velocity decreases

•no more erosion•more meandering

Observe changes in the channel of a

meandering river.

rejuvenated river

•a river whose gradient increases due to movement in the Earth’s crust (form a step-like terrace) or velocity increases due to more water movement

Stream Deposition

as the velocity of a stream decreases, it drops the sediment it was carrying

Observe how sediments are

deposited.

delta•underwater deposit of sediment at the mouth of a river or stream

alluvial fan

•fan-shaped deposit at the base of a slope on land

floodplain

•part of the valley floor that may be covered with water during a flood

natural levee

•raised riverbank that results when a river deposits its load at the river’s edge

Flood Control

Artificial Levee – Earthen mounds built on the banks of a river

Flood Control Dams – store floodwater and

let it out slowly