Physical Geography 102
Surface Water

Surface Water

Surface water is water found above the ground surface
This includes streams, lakes, ponds, oceans, seas, and swamps.
This section will concentrate on surface water found on continental land masses


Streams are channeled flow of surface water moving downhill under the force of gravity
No size distinction - small and large channeled flows are streams
Common names for streams tend to imply size
Rivers - largest streams
Creeks, streams - medium sized streams
Brooks, streamlets, rivulets and runnels - smallest streams

Overland Flow

Water precipitates onto the ground surface
Some of this water will infiltrate to become groundwater
The remainder must flow overland - flow which occurs on the surface
Two forms of overland flow are common - Sheet flow and Thread/Rivulet flow

Overland Flow

Sheet Flow - a continuous, thin film of water which flows downhill
Thread/Rivulet Flow - water gathers into tiny threads of water which flow downhill
Overland flow only occurs over fairly short distances, until the water collects in a depression or trough where the water is concentrated and flows in a larger mass

Stream Flow

Stream flow is the movement of surface water in a channel
A channel is a narrow trough (note: channels can be large or small)
Flow within the channel is characterized by a number of flow parameters
- Flow velocity, Stream discharge, Stream gradient, and Load

Flow Velocity

Flow velocity is a measure of the speed of the flow - typically measured in meters or feet per second
Velocity is not constant for the entire stream
The flow velocity will be greatest in the center of the stream, and toward the top of the stream but not at the surface

Stream flow velocities

Stream Discharge

Stream discharge is the amount of water moving through the channel
This is calculated using the equation: Q = wdv
Q is the discharge
w is the width of the stream
d is the depth of the stream
v is the flow velocity

Stream Discharge

Problems with calculation of discharge
1) width of the stream changes from location to location
2) depth of the stream is not constant from location to location - also they're not flat bottomed (curved or irregular is the norm)
3) velocity can change due to precipitation and channel width

Stream Gradient

Stream gradient is the rate of fall in elevation of the stream surface per unit distance
- feet/mile, meters/km, % grade, degree
How steep is the slope of the stream?
Generally, the steeper the gradient, the higher the flow velocity

Steam Load

Streams transport more than just water
Clay, silt, sand, gravel, and organic material are all moved
The stream load is the amount of sediment carried by the stream

Stream Drainage Systems

Drainage systems deal with how the water gathers together or is organized into larger systems of flow
Streams are separated by Divides - boundary between drainage basins

Drainage basin divides diagram

Drainage Basins

An area on a map outlined by a divide is known as a drainage basin
All of the water within this basin will drain down to a stream then flow out of the basin
No size restrictions on basins - can be large or small
Drainage basins can contain a single stream or multiple streams
Continental Divide - the boundary between drainage basins on a continental scale - For North America water to the west flows to the Pacific Ocean, water to the east flows to the Atlantic Ocean, Gulf of Mexico, Hudson Bay and Arctic Ocean