WJEC (B) GCSE Geography Theme 2 Topic 2 Click to continue Hodder Education Revision Lessons Understanding hydrographs

WJEC (B) GCSE Geography Theme 2 Topic 2 Understanding hydrographs In an exam question you will need to show you can interpret a hydrograph. In other words, what does the hydrograph tell us? Click to continue

WJEC (B) GCSE Geography Theme 2 Topic 2 What could make the lag time longer (i.e. what would slow down the journey of rainfall to the river)? Lag time Lag time is the time between peak rainfall and peak discharge. The longer the lag time, the longer it has taken for the rainfall to reach the river. Click to continue

WJEC (B) GCSE Geography Theme 2 Topic 2 Click to continue Longer lag time Trees could intercept the water by holding it on their leaves. Trees could soak up the water through their roots. The water could soak into the soil and travel to the river as throughflow or groundwater flow. The water could be held in a reservoir and slowly released by a dam. The water could be used by farmers or industry and then put back into the river later.

WJEC (B) GCSE Geography Theme 2 Topic 2 Lag time What could make the lag time shorter (i.e. what could speed up the journey of rainfall to the river)? Click to continue

WJEC (B) GCSE Geography Theme 2 Topic 2 Click to continue Shorter lag time What could make the lag time shorter (i.e. what could speed up the journey of rainfall to the river)? There might not be any plants to intercept the rainfall due to deforestation or after crops have been harvested. The soil could be frozen so the water cannot infiltrate. The ground could have been tarmacked so that water cannot infiltrate. The soil could have been compacted, e.g. by cattle, so rain cannot infiltrate. The ground could be hard after a dry spell, so it is hard for the rain to infiltrate.

WJEC (B) GCSE Geography Theme 2 Topic 2 A short lag time can lead to flooding. Copy the diagram and complete it to show which factors might increase the risk of flooding. What might increase flood risk? Click to continue Lag time

WJEC (B) GCSE Geography Theme 2 Topic 2 Compacted soil Dry ground Frozen ground Impermeable rock Heavy rain Deforestation Lots of tarmac What might increase flood risk? Click to continue Factors that might increase the risk of flooding

WJEC (B) GCSE Geography Theme 2 Topic 2 Match the key terms and definitions. Just write the letters and numbers. 1 Lag time 2 Peak discharge 3 Discharge 4 Base flow 5 Rising limb 6 Falling limb 7 Impermeable 8 Permeable 9 Store 10 Flow A Water being held or kept B Time between peak rainfall and peak discharge C Rock that allows water to flow through D The transfer of water E Normal discharge of a river FIncrease in discharge shown on a hydrograph G Decrease in discharge shown on a hydrograph H Rock that doesn’t allow water to flow through IAmount of water at a point on a river at a given time, measured in cumecs JThe maximum amount of water held by a river after a storm Click to continue Key terms

WJEC (B) GCSE Geography Theme 2 Topic 2 1 Lag time = B Time between peak rainfall and peak discharge 2 Peak discharge = J The maximum amount of water held by a river after a storm 3 Discharge = I Amount of water at a point on a river at a given time, measured in cumecs 4 Base flow = E Normal discharge of a river 5 Rising limb = F Increase in discharge shown on a hydrograph 6 Falling limb = G Decrease in discharge shown on a hydrograph 7 Impermeable = H Rock that doesn’t allow water to flow through 8 Permeable = C Rock that allows water to flow through 9 Store = A Water being held or kept 10 Flow = D The transfer of water Click to continue Key terms