floodplain
• area of low-lying land across which a river flows that is covered with sediment as a result of frequent flooding
• Floodplain zoning
the division of a floodplain, so 10,25, 50, 100 year flood zone. Some building will be needed to help after the flood or during the flood, so we want those in areas where they are least going to be hit.
What factors are considered in floodplain zoning
• Recurrence interval and discharge
What is the general trend of the size of floods and their frequency?
• Larger floods occur less frequently
What is meant by the term “recurrence interval”?
• The frequency of occurrence of a flood of a given sixe, or the average number of years between two floods of the same size
Describe the term ‘peak discharge’
• The volume of water that flows through a river at a given time
Describe what is meant by “10–‐year flood,” “25–‐year flood,” “50–‐year flood,” and “100–‐year flood.”
• A flood of a certain discharge may be found to occur, on average, once in a decade.
What is the probability of each of the above floods occurring in a given year?
• 10 year= every year 1 in 10 change or 10%, 25 year= every year 1 in 25 chance or 4%, 50 year= every year 1 in 50 chance or 2%, 100 year= every year 1 in 100 chance or 1%
Which zone should have the greatest building restrictions and why?
• Closes to the river
Describe Cutbank and point bar
- Outside of the bed, where erosion
* Inside of the bend, where deposition is occurring
How are these symbolized on a map?
- Cut bank= lines
* Point bar= dots
Be able to predict where streams will deposit sediments
• On the opposite side
How will a stream change over time?
• It will shift the river the in the direction of the curt bank over time
Which side of a stream is steeper and why
• The cut bank side because its eroding
Which side of the stream is shallower and why
• Point bar because it is depositing
Be able to define porosity and describe how it relates to the 3 sediments we used in class
- How much can be stored
- Sand- High porosity because it has tiny spaces but a lot of them so it can hold a lot
- Gravel- Medium porosity because it has laager spaces but not as many
- Mixed-Low the sand filled in the gravels spaces taking room away from the water
Be able to define permeability and describe how it relates to the 3 sediments we used in class
- Material refers to its ability to transmit water or other fluids
- The flow
- Gravel- High permeability because the large spaces are well connected to flow through
- Sand- Medium permeability because the sand has tiny spaces but there is a lot of them for water to flow through
- Mixed- Low permeability because the spaces are not well connected
Be able to list all of the factors that comprise the DRASTIC index
- D- depth to water
- R- Net Recharge
- A- Aquifer Media
- S- Soil Media
- T- Topography
- I- Impact of the Vadose Zone Media
- C- Conductivity (Hydraulic of the Aquifer)
How does the drastic number relate to the likelihood of the ground becoming polluted?
• Higher drastic # means more likely to be polluted
What is meant by a hydrogelogic setting?
• A collection of subsettings each of which depend on hydrogeologic factors the affect the occurrence and availability of groundwater.
What is a pollution potential index?
• Relative rating system used a combination of weights and rating to produce a quantitative value
