Fluvial Morphology: Landforms Made by Running Water

RUNNING WATER  Rivers and Streams What is the most important geomorphic agent shaping the physical landscape? RUNNING WATER  Rivers and Streams What is the work of rivers and streams? Erosion Transportation Deposition Fluvial Morphology: Study of Landforms Made by Running Water FLUVIAL: from the Latin fluvins for ‘running water’ or streamflow

SOURCES OF WORLD’S WATER Source % of Supply Oceans 97.2 Ice Sheets and Glaciers 2.15 Ground Water 0.62 Lakes (Fresh) 0.009 Inland Seas / Salt Water Lakes 0.008 Soil Moisture 0.005 Atmosphere 0.001 Rivers* 0.0001  * Running water or streamflow is the most significant agent sculpting the Earth’s land surface

Sources of stream flow 25 - 40% of total precipitation runs off as storm flow, and becomes stream flow The rest of stream flow comes from groundwater discharge, as base flow

River Quiz: Amazon: http://www.youtube.com/watch?v=ta35C488dnE http://www.ilike2learn.com/ilike2learn/Rivers/Longest%20Rivers.html Amazon: http://www.youtube.com/watch?v=ta35C488dnE

Stream Order, Drainage Basin, Watershed and Drainage Divide Rills  Gullies  Streams  Stream Order, Drainage Basin, Watershed and Drainage Divide

Mississippi-Missouri Drainage Basin Lake Itasca is a small glacial lake, approximately 1.8 square miles in area, in the Lake District of Northwestern Minnesota. It is the source of the Mississippi River.

Southern California Watersheds

3-D Drainage System and Stream Model Fig. 17-3, p. 472

Drainage Patterns and Topography

The Long Profile of Streams At their headwaters, the grade of a stream is usually steep At mid-course, the grade becomes more gently sloping Near the mouth of the stream, the grade becomes almost flat

Stream Gradients Fig. 17-11, p. 480

Stream Stages Streams also show three stages of gradation from the mountains to the sea, with associated erosional and depositional features: Youth Maturity Old Age

Stream Stage 1 – Youth Characteristics of Youthful Streams Steep, irregular profile Headward erosion  Waterfalls, rapids, and plunge pools River is deepening its channel Cutting into bedrock – Vertical erosion* V-shaped cross-section  *Reflects the propensity of streams to try and reach their ultimate base levels (i.e., sea level) or secondary base levels

V-shaped Valleys

Waterfalls

Stream Stage 2 – Mature Valley Characteristics of Mature Valley Streams Valley widening begins Meandering stream  lateral erosion + deposition Braided channel  deposition (sand bars) Floodplains

Meandering Streams

Meandering Stream Fig. 17-24a, p. 489

Braided Stream Channel of the Brahmaputra River in Tibet

Tectonic Uplift, Stream Rejuvenation and Alluvial Terraces Downcutting, and the Grand Canyon

Stream Stage 3 - Old Age Characteristics of Old Age Streams Wide Alluvial Valley Stage The channel is quite large and U-shaped Stream discharge at a maximum and sediment load composed of finer materials Natural Levees, parallel to the stream channel on both banks Other depositional features, including Delta

Floodplain Features Fig. 17-26, p. 491

Mississippi Floodplain

 Delta Large deposit of alluvial sediment located at the mouth or estuary of a stream where it enters a body of standing water, usually a ocean or a lake. http://www.youtube.com/watch?v=AjZLAw_lgZ4&feature=related Deltas are created when the sediment load carried by a stream is deposited because of a sudden reduction in stream velocity. Delta surface is characterized by distributaries Some deltas, like that of the Nile, have a typical triangular shape, like the Greek letter 

Mississippi Birdfoot Delta Source: NASA

Ganges-Brahmaputra River Delta From Landsat 7 WRS Path 137 Row 44, center: 23.12, 90.37. Image taken 2/28/2000

Fluvial Processes and Landscapes at Different Stream Stages Youthful Steep hillsides, drainage divides predominant, V-shaped valleys Headward erosion, stream downcutting – vertical erosion Mature Rounded hills, valley walls predominant, graded streams, broad floodplains Lateral erosion, streams adjust to discharge/load Old age Floodplains, ox-bow lakes, deltas and alluvial plains, very low relief Deposition, sluggish stream flow, poor drainage

Los Angeles River Now! 2005 Flood