Classroom presentations to accompany Understanding Earth, 3rd edition prepared by Peter Copeland and William Dupré University of Houston Chapter 13 Streams: Transport to the Ocean

Streams: Transport to the Ocean Gary D. McMichael/Photo Researecher

Rivers and streams Stream : body of water flowing in a channel The floor of the channel is called the bed. When rainfall is very heavy or snow melts rapidly, bodies of water overflow their banks and water covers the adjacent land called the floodplain.

Rivers and streams Carry away runoff to lakes and seas Erode land (degradation) Transport and deposit sedimentary debris

Stream behavior Mostly determined by velocity and shape of channel. These factors combine to allow either laminar or turbulent flow. Turbulent flow is much more erosive. Stream velocities may vary from 0.25 to 7 m/s.

Laminar flow Smooth sheet-like flow at a low velocity Usually confined to edges and top of stream

Turbulent flow Irregular swirling flow Occurs at most rates of stream flow Keeps particles in suspension

Laminar flow Fig. 13.1a

Turbulent flow Fig. 13.1b

Laminar to turbulent transition Laminar flow Turbulent flow ONERA Fig. 13.1c

Streams move material in three forms Dissolved load Suspended load Bed load (traction and saltation)

Sediment Transport Fig. 13.2

Saltation Fig. 13.3

Grain Size and Flow Velocity Fig. 13.1

Stream terms competence: measure of the largest particles a stream can transport proportional to v2 capacity: maximum quantity of sediment carried by stream proportional to Q and v

Lower Velocities Form Ripples Fig. 13.5a

Higher Velocities Form Dunes ripples dune dune Fig. 13.5b

Pebbles Caught in Eddies Form Potholes Fig. 13.6 Carr Clifton/Minden Pictures

Waterfall Retreating Upriver Fig. 13.7 Donald Nausbaum

Parts of a River System Fig. 13.8

Two important stream types 1. Meandering Streams Gentle gradients, fine-grained alluvium Minimizes resistance to flow and dissipates energy as uniformly as possible (equilibrium) Examples: point bars,oxbow lake, migrating meanders

Two important stream types 2. Braided Streams Sediment supply greater than amount stream can support. At any one moment the active channels may account for only a small proportion of the area of the channel system, but essentially all is used over one season. Common in glacial, deserts, and mountain regions.

Incised Meanders, Utah Fig. 13.9 Tom Bean

Meandering River Over Time Fig. 13.10

Lateral migration by erosion at the outside. & Lateral migration by erosion at the outside & deposition on the inside of the river Fig. 13.10a

Meandering River Point Bar Fig. 13.11 Peter Kresan

Braided River Fig. 13.12 Tom Bean

Formation of Natural Levees Fig. 13.1

Discharge Total amount of water that passes a given point in a stream per unit time Q = w d v

Discharge Discharge (m3/s) = width (m)  depth (m)  average velocity (m/s) In the U.S., this is expressed as cubic feet per second (cfs): 1 m3/s = 35.9 ft3/s

River at Low Discharge Fig. 13.14a

River at High Discharge Fig. 13.14b

Flooding Water in the stream is greater than the volume of the channel. Interval between floods depends on the climate of the region and the size of the channel/

City Built on a Floodplain Xie Jiahua/China Features/Sygma

Recurrence interval Average time between the occurrences of a given event The recurrence interval of a flood of a given size at a given place depends on: • climate of the region • width of the floodplain • size of the channel

Annual Flood Frequency Curve Fig. 13.1

Longitudinal Stream Profile of the Platt and South Platt Rivers Fig. 13.16

Elevation at which a stream enters a large body of water such Base level Elevation at which a stream enters a large body of water such as a lake or ocean

Role of Base Level in Controlling Longitudinal Profile of Rivers Fig. 13.17

Effects of Building a Dam Original Profile Graded to Regional Base Level Fig. 13.18a

Effects of Building a Dam Dam Forms New Local Base Level Fig. 13.18b

Effects of Building a Dam Deposition Upstream and Erosion Downstream Fig. 13.18c

Graded stream Stream in which neither erosion nor deposition is occurring, due to an equilibrium of slope, velocity, and discharge.

Geologic evidence of changes in stream equilibrium Alluvial fans Terraces: erosional remnants of former floodplains

Alluvial Fans Fig. 13.19 Michael Collier

Formation of River Terraces Fig. 13.20

Drainage divides separate adjacent drainage basins Fig. 13.21

Drainage basin Area of land surrounded by topographic divides in which all the water is directed to a single point

Drainage Basin of the Colorado River Fig. 13.22

Typical Drainage Networks Fig. 13.23

Stream was present before deformation Antecedant Stream Deformation causes gorge to form Stream was present before deformation Fig. 13.24&b

A Superimposed Stream Downcutting causes gorge to form Deformation occurred before stream was present Fig. 13.25

Delaware Water Gap A Superimposed Stream Fig. 13.24c Michael P. Godomski/Photo Researchers

Location of significant sedimentation where a river meet Delta Location of significant sedimentation where a river meet the sea.

Mississippi Delta Fig. 13.26 Landsat 2 image annotated by Moore, 1979

Typical Large Marine Delta Fig. 13.27

Shifting Mississippi River Delta Over the Past 6000 Years Fig. 13.28