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!