Storm Hydrograph

Question 1

Define Storm and Rainfall Event

Answer 1

. A storm event is a rainfall period separated by dry intervals of at least 24 hours

. A rainfall event is a rainfall period separated by dry intervals of at least 4 hours

Question 2

Define Hydrograph

Answer 2

. A graph of RIVER DISCHARGE of a river over a period of time

Question 3

Define Storm Hydrograph

Answer 3

. A graph of discharge of a river over a period of time when the normal flow of the river is affected by a storm event

Question 4

Define River Discharge

Answer 4

. The volume of water flowing past a particular point

. Measured in cumecs or cubic metre per second

Question 5

How is River Discharge calculated?

Answer 5

. Multiplying the cross - sectional area of the river by its velocity

Question 6

Another name for Storm Hydrograph

Answer 6

Flood Hydrograph

Question 7

Components of Hydrograph

Answer 7

. Lag time
. Base flow
. Rising Limb
. Falling Limb
. Peak Discharge
. Peak Rainfall
. Baseflow
. Bankfull Discharge
. Overland Flow
. Throughflow

Question 8

Define Peak Discharge

Answer 8

. Highest point on the discharge graph

. When river discharge is at its greatest

Question 9

Define Peak Rainfall

Answer 9

. When rainfall is at its greatest

Question 10

Define Lag time

Answer 10

. The delay between peak discharge and peak rainfall

Question 11

Define Rising Limb

Answer 11

. Part of the graph up to peak discharge

. The river discharge increase as rain water flows into the river

Question 12

Define Falling Limb

Answer 12

. Part of the graph after the peak discharge

. Discharge is decreasing as less water is flowing into the river

Question 13

Define Bankfull Discharge

Answer 13

.the maximum discharge that a river channel is capable of carrying without flooding

. On a hydrograph, it is the point a river will begin to overflow

Question 14

Significance of Storm Hydrograph

Answer 14

. Use for predicting how a river may respond to a rainfall

. It can help in managing the river

Question 15

Define Baseflow

Answer 15

. Groundwater flow that feeds into rivers through river banks and river beds

. In the context of the hydrograph, it is the amount of water that would be in the river without the addition of the storm water

Question 16

What is rainfall measured in on a hydrograph?

What is discharge measured in a hydrograph?

Answer 16

. Rainfall measured in millimetres (mm)

. Discharge measured in cubic metres per second

Question 17

Explain the hydrograph in context to a flood

Answer 17

1. ) The storm hydrograph beings with baseflow
2. ) A storm or rainfall results the river is fed by throughflow if water infiltrates into the soil
3. ) The slow movement of throughflow into the river means that the changes in discharge are small. The volume of the river increases
4. ) Eventually, the soil stores are fully saturated and full of moisture, so overland flow on a slope occurs.
5. ) Since overland flow is faster than throughflow, due to less obstacles, the discharge begins to rise higher, increasing the volume of the river. This is shown by the rising limb of the hydrograph
6. ) There is flooding if discharge exceeds bankfull discharge
7. ) It eventually reaches a peak discharge
8. ) The lag time is the delay between peak rainfall and peak discharge
9. ) Discharge beings to fall eventually, This is shown by the receding limb of the graph
10. ) When all of the storm water has passed through, the river returns to its base flow