Edexcel IGCSE Geography 复习笔记 1.1.3 River Regime & Hydrographs
Edexcel IGCSE Geography 复习笔记 1.1.3 River Regime & Hydrographs
River Regimes & Storm Hydrographs
River regimes
- The discharge of a river changes over time
- The river regime is a record of these changes over a year
- Many factors can influence the river regime including temperature, vegetation, land use and human activity
Storm hydrographs
- A storm hydrograph shows the changes in river discharge after a storm event
- The graph shows a short period of time, usually 24 hours
- The storm hydrograph has a number of features:
- Base flow
- Peak rainfall
- Rising limb
- Peak discharge
- Lag time
- Recessional limb
Storm hydrograph in an urban area
Worked Example
Study Figure 1 which shows storm hydrographs for rivers A and B
Figure 1 Storm Hydrograph
What is the lag time for river A? (1)
- To work out the answer you need to calculate the difference between the peak rainfall and peak discharge:
- The peak rainfall is between 2 and 3 hours from the start of the storm, taken at the mid point this would be 2 hours and 30 minutes.
- The peak discharge is at 6 hours from the start of the storm
- 6 hours - 2 hours and 30 mins = 3 hours and 30 mins
Answer
Lag time = 3 hours and 30 mins (1)
Exam Tip
Remember a hydrograph shows the changes in discharge over a short period after a storm event, whereas the river regime shows changes in discharge over a long period, usually a year.
Factors Affecting Regimes
- There are many factors which affect the discharge or regime of a river
- The shape of storm hydrographs is also affected by these factors
- Factors which increase overland flow lead to:
- shorter lag times
- increased discharge
- steeper rising limb
Factors which Influence River Regimes
| Factor | Effect |
| Climate | Snow and ice melt leads to higher discharge - usually in the spring months
High temperatures increase evaporation and reduce river discharge Higher rainfall in autumn and winter increases river discharge Convectional rainfall in summer or hot, moist climates increases river discharge |
| Vegetation | Vegetation increases interception and infiltration leading to reduced overland flow and so lower river discharge
Deciduous trees lose their leaves in winter decreasing interception, increasing overland flow and river discharge |
| Land Use | Concrete and tarmac in urban areas and built environments are impermeable leading to high overland flow - this is rapidly taken by drainage systems to the rivers/streams, increasing river discharge |
| Geology | Permeable rocks increase infiltration and percolation which reduces overland flow and decreases river discharge |
| Soils | Soils which are compacted or frozen reduce infiltration, increasing overland flow and river discharge |
| Abstraction | Water taken for irrigation and domestic use decreases the river discharge |
| Dams | Dams control the flow of water, so can both increase and decrease river discharge
Reservoirs experience higher levels of evaporation which can decrease river discharge |
| Relief | Steep slopes increase overland flow which leads to increased river discharge |
| Drainage Density | High drainage density leads to increased discharge, particularly after a rainfall event |
Exam Tip
Remember all the factors which affect river regimes also affect the risk of flooding. Any factor which increases overland flow and discharges also increase the risk of flooding.
转载自savemyexams
国际竞赛真题资料-点击免费领取！
美高学分项目重磅来袭！立即了解
AMC8备考管家服务全新上线！
