Classroom presentations to accompany Understanding Earth , 3rd edition

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

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 Rivers and streams

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. Stream behavior

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

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

Laminar flow Fig. 13.1a

Turbulent flow Fig. 13.1b

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

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

Sediment Transport Fig. 13.2

Saltation Fig. 13.3

Grain Size and Flow Velocity Fig. 13.1

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 Stream terms

Lower Velocities Form Ripples ripple 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

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. Two important stream types

Incised Meanders, Utah Fig. 13.9 Tom Bean

Meandering River Over Time Fig. 13.10

Lateral migration by erosion at the outside & deposition on the insideof 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

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 Discharge

River at Low Discharge Fig. 13.14a

River at High Discharge Fig. 13.14b

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/ Flooding

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

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 Recurrence interval

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 as a lake or ocean Base level

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

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

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

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

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

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

Alluvial Fans Fig. 13.19 Michael Collier

Formation of River Terraces Fig. 13.20

Drainage divides separate adjacent drainage basins Fig. 13.21

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

Drainage Basin of the Colorado River Fig. 13.22

Typical Drainage Networks Fig. 13.23

Classroom presentations to accompany Understanding Earth , 3rd edition