River systems
Runoff vs. Infiltration Factors determining runoff, or infiltration 1.Soil composition & pore space Coarse-grains & lots of humus = good infiltration Very fine-grains & poor humus = bad infiltration 2.Rate of precipitation Hard fast rain won’t soak in easily Slow steady rain infiltrates 3.Vegetation Abundant vegetation allows water to soak in 4.Slope steepness Steep slopes = more runoff
Tributaries- the main stream and feeder streams Water shed- the land from which the water runs off into the stream Divides- The elevated regions of land that separate watersheds.
Drainage Basins DDrainage basins and patterns Drainage basin: land area that contributes water to the stream A divide separates drainage basin Types of drainage patterns Dendritic Radial Rectangular Trellis
Illinois Drainage Basins
The drainage basin of the Mississippi River
Drainage patterns
Stream and Channel Erosion Stream load- the materials carried by a stream Suspended load: Consists of fine particles like sand and silt Dissolved load: Mineral matter that’s dissolved and transported in the water solution Bed load: the larger more coarse material carried by the stream (sand, pebbles, rock)
Important River Terms Discharge - the volume of water moved by a stream in a given time Gradient - the change in elevation of a stream over a given horizontal distance Headwaters - the beginning of a stream Mouth- end of the stream system
Stages of a River - Youthful River Has a V-shaped valley with steep sides Waterfalls and rapids are common features Steep gradient High Velocity water (high discharge)
Stages of a River - Mature River Has well established tributaries and caries a large volume of water. Developing floodplain Meanders - a series of wide curves in river channel Oxbow lake - water that remains when meander is cut off from new river channel
Stages of a River - Old River The gradient and velocity decrease (flat land) Wide river bed Well established floodplain More meanders develop
Floods & Flood Control Occur when discharge exceeds channel capacity Floods are the most common geologic hazard Causes of floods Weather Human interference with the stream system
Floods and flood control Engineering efforts Artificial levees Flood-control dams Channelization Nonstructural approach through sound floodplain management
Satellite view of the Missouri River flowing into the Mississippi River near St. Louis
Same satellite view during flooding in 1993
Comparison of 1988 & 1993