Physical Geography 102
Surface Water II


All streams will flood - big or small
During normal discharge or even high discharge all of the water flows within the stream channel
When the volume of water exceeds the channel capacity the stream will flood
Water continues to flow in channel
Excess flows in adjacent areas - flood plain
Flood Stage - level at which the stream floods

Causes of Flooding

Excessive Precipitation - major cause
Extended periods of precipitation
Short bursts of extremely heavy precipitation - flash flooding
Associated with thunderstorms
Most devastating in mountainous terrain

Causes of Flooding

Saturation of the Ground
Normally precipitation runs off as surface and groundwater runoff
When the ground becomes saturated - runoff is forced to flow completely on the surface
Tends to increase severity of flooding

Causes of Flooding

Destruction of Wetlands
Wetlands are marshy areas, swamps, bogs - any place where there is standing water for most or all of the year
Natural water storage areas
Agriculture practices have destroyed many wetland areas
Increased surface runoff adds to flooding, decreases groundwater runoff

Flood Prediction

Prediction of flooding is stream specific
Dependent on annual precipitation, climate, location, topography, bedrock, and man-made alterations
Prediction is primarily based on historical records which indicate when flooding is most likely to occur

100 Year Floods

Floods are classified according to size of the flood (stream dependent)
Based on statistical occurrence of flooding
A 10-Year flood has 10% chance of occurring in any given year
A 100-Year flood has a 1% chance of occurring in any given year


Lakes are bodies of exposed, standing water (includes ponds)
Swamps, bogs, and marshes - wetlands
Short lived features geologically
Formed through tectonic, glacial and erosional processes
Form when the rate of incoming water is greater than or equal to the outgoing water (groundwater and surface runoff)

Lake Destruction

Destroyed easily through natural processes
Reduction in precipitation
Erosion opens natural drainage
Lowering of the water table
Filling of lake with sediment

Pollution of Surface

Water Streams have been natural sources of fresh water for irrigation and drinking
Streams have also been natural waste disposal systems
Three types of pollutant - Solid - Liquid or Chemical - Thermal

Solid Pollutants

Solid pollutants include
- trash
- plastic
- wood
- metals
- styrofoam
- sewage wastes
Anything that is solid that is placed in a stream can be a solid pollutant

Liquid or Chemical - Thermal

Extensive list of liquid pollutants
- industrial solvents
- benzene, acids
- sewage waste
- fertilizers, pesticides, herbicides
- mining waste
- tailings piles, toxic metals
Thermal Pollution
- heat pollution changes the normal temperature of the stream
- Power generation plants