STREAMS AND THE EARTH Water Erosion
2. Running Water Running water is the dominate agent of erosion Obtain sediments by Direct lifting of particles Collisions between carried sediments and stream bed (Abrasion) Receiving dissolved minerals from groundwater flow or by directly dissolving the stream bed
Streams Carry Sediment Three Ways Dissolved minerals carried in solution Solid sediments small size carried in suspension Larger sediments carried by rolling, and bouncing along the bed
AFFECTS ON EARTH’S SURFACE RUNNING WATER Streams and Erosion Average velocity is controlled by: 1. Slope (gradient) 2. Discharge (volume) Earth Science Reference Tables
Sediment Transport!
STRAIGHT CHANNELS
MEANDERING CHANNELS
LIFE HISTORY OF STREAMS 3 Stages of Development Youthful Mature Old age
Youthful Stage of Stream High Energy High Potential High Kinetic Erosion Dominates All sediment sizes moved V-Shaped valley Downcutting Rapids, Waterfalls
Characteristics of Youthful Stream
Mature Stage of Stream Decrease in kinetic energy (and lower potential) Less erosion down-cutting and an increase in side-cutting (widening of stream channel) Smaller particles eroded Ex. Meandering Development of Floodplain Deposition of larger sediments
Reduced Gradient
Meandering Sacramento Valley
Old Age of Stream Over meandering (Oxbow lakes) Very little Kinetic Energy Over meandering (Oxbow lakes) Well-developed Floodplain Deposition Dominates
Mature/Old Age Stage
Natural/Artificial Levees
STAGES REVIEW
DAMS
DEPOSITION “Sedimentation” Process by which sediments are released, settled from, or dropped from an erosional system. Erosion and Deposition are opposite processes. When kinetic energy is high, erosion dominates. Where slope is gradual or kinetic energy minimal, deposition dominates.
Sediment Characteristics Sediments become rounded and smaller with increased time spent in running water Abrasion (Mechanical Weathering) Dissolving (Chemical Weathering)
Sediment Distribution and Deposition Larger particles deposited close to the mouth (high energy environment) and finer sediments are carried out further away from shore (lower energy environment).
Graded Bedding Unsorted sediment dumped into quiet body of water. Heavy/Dense settle first Round settle faster than disc shaped
Watershed The land area from which a stream gets its water ‘Divides’ separate drainage basins Bathtub analogy
Continental Divide