Chapter 13 Rivers and Streams Streams A stream is a body of water that is confined in a channel and moves downhill under the influence of gravity This definition includes all sizes of running water from a tiny trickle to the Amazon The total area drained by a given stream is its drainage basin Drainage Basins and Divides The line separating one drainage basin from another is a drainage divide The Continental Divide separates drainage basins of rivers that flow to the Atlantic and Gulf of Mexico from those flowing to the Pacific and Gulf of Cortez Gulf of California Floods Flash floods can occur in a matter of hours as a result of a single storm Flash floods are most likely in areas of high gradients Annual floods result from snowmelt or annual rain patterns monsoons Gradient Gradient is the drop per mile km Boulder Creek drops from 8000ft at Nederland to 5600 in Boulder and has a gradient of 160 ft mi 30 m km The Colorado River through Grand Canyon has a gradient of about 10 ft mi 2 m km The lower Mississippi has a gradient of less than 0 5 ft mi 0 1 m km Gradients usually decrease downstream Stream Velocity Velocity is controlled by both gradient and channel size Steep gradients cause high velocities Constricted channels cause high velocities Discharge Discharge is the total flow in ft3 s cfs or m3 s 1 m3 s 35 ft3 s cfs In a section of stream with no tributaries the discharge is constant while the velocity and channel size may vary along the bed Discharge Boulder Creek is typically 20 50 cfs but may be 500cfs or greater in May and June The Colorado at Grand Junction is typically 2000 cfs but may exceed 20 000 in May and June The lower Mississippi is typically 250 000 cfs but exceeded 3 million cfs in 1993 flood Load The load is the amount of material transported by a stream Dissolved load is the material in solution Suspended load is the material in suspension Bed load is the material on the bed Saltation load is the material bouncing along the bottom Traction load is the material dragged along the bottom Deposition and Erosion The amount of bed load and suspended load vary with velocity Where a stream widens and slows it deposits material Where a stream narrows and quickens it erodes material Bars Bars are material deposited by streams A point bar is a bar on the side of a stream A channel bar is a bar in the middle of a stream A braided stream has many channels bars The presence of bars indicates that the steam is depositing
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