Option A: Freshwater - Part 2: Flooding and mitigation

Question 1

Flood Hydrograph

Answer 1

Shows a river’s discharge against time during a period of storm or run-off.

Question 2

Rising Limb

Answer 2

Speed of increase.

Steep in flash-floods or small drainage basins.

Question 3

Peak Discharge

Answer 3

Highest amount of discharge.

Larger basins = higher discharge.

Question 4

Lag time

Answer 4

Time between peak rainfall and peak discharge.

Question 5

Run-off curve

Answer 5

Relationship between overland flow and through flow

Question 6

Base flow

Answer 6

Seepage of groundwater into the channel supplying river discharge.

Question 7

Falling Limb

Answer 7

Time for discharge to decrease after peak flow.

Question 8

Hydrograph size (area underneath curve)

Answer 8

High rainfall + large basin = high discharge

Question 9

Mississippi Case Study

Answer 9

Flows through 10 states.
Drains 1/3 of USA.
Control flooding by: Stone and earthen levees to raise banks, holding dams, straightening channel to remove water speedily.

10 billion spent on controlling 
200m spent on maintenance annually
1993 Heavy rainfall led to levees collapsing.
Damage = 12 billion 
43 deaths
25,000 km cubed flooded.
Led to hurricane katrina.
Flood relief: Waterway from New Orleans to the Gulf of Mexico

Atchafalaya River carries 1/4 water

Dredging of AtchaFalaya and Mississippi rivers
Morganza floodway between atch and miss.