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THE HYDROLOGIC
CYCLE
The Hydrologic Cycle
The Hydrologic Cycle - Fresh Water Storage
Reservoir % of Total Fresh Water
Glaciers (Frozen) 76%
Groundwater 22%
Rivers & Lakes < 2%
Although it only makes up < 2% of total fresh water on earth, surface water is the most utilized and perhaps precious natural resource!
The Hydrologic CycleHow Does Water Move Within The Cycle?
The Hydrologic Cycle
1) RIVER SYSTEMS
A) Important source of fresh water.B) Most important agent of erosion.C) Most abundant continental landform.D) Essential to agriculture & industry
Three Main Parts To A River SystemCollection system; Transportation system; Dispersing system
DIFFERENCES IN RIVER SUB-SYSTEM CHARACTERISTICS
The Collection System – A Drainage Basin
Types of Drainage Basins – Controlled by Geology
The Dynamics of Stream Flow1) Velocity2) Discharge3) Channel Parameters
1) Roughness2) Dimensions
4) Sediment Load5) Gradient and Base Level
The Transportation System
1) VELOCITY – Straight Channel
1) VELOCITY – Curving Channel
High V:Erosion
LowV:Deposition
2) GRADIENT
MEASURING DISCHARGE (Q):Q m3/sec = V (AVG. ) X Width meters X Depth meters
4) SEDIMENT LOAD AND TRANSPORTATION
TRANSPORTING SEDIMENT
Ideal Stream ProfileIncreasing discharge, velocity & sediment load
Decreasing gradient, turbulence & competence
Base level – level of deepest possible erosion.
Dynamic Equilibrium – “You can never change just one thing about a stream.”
• The sensitive, ever-evolving balance between erosion and deposition.
• Graded Stream: erosion = deposition.• If deposition > erosion, stream builds up its
bed, thus increasing gradient and average velocity to restore balance.
• If erosion > deposition, stream erodes bed, decreasing gradient and velocity.
Departures from EquilibriumWaterfalls – signs of a shifting balance: increased
discharge or gradient
Dam That Stream! A System Out of Balance
Dam Effects
Upstream deposition
Discharge of clear, turbulent water & potential erosion.
Elimination of floods (reduced competence);
Choke off down-stream sediment flow.
Disturbed ecosystems
Meandering Streams
Floodplains have a purpose!