IGCSE Geography: Storm Hydrograph of a river and River Regimes Hydrographs A Hydrograph is a popular way of representing data for geographers, and to get good understanding in the RIVERS topic, you must be able to know its features. Definition: A Hydrograph shows the discharge of a river as well as its total rainfall over a period of time, before, during and after the storm. Linkages and analysis can thus be made, eg. More rainfall, faster discharge? Etc. Discharge: Volume of water passing a certain point in a given time frame. Measured in Cumecs (its good to know this!) =Cubic m/s *Total rainfall is just the Volume of rain during the storm event, usually measured in (mm). Characteristics of a Hydrograph 1. Peak Discharge: This tells us what time there was the maximum level of discharge by a river. 2. Peak Rainfall: Likewise, the time where there was maximum rainfall. 3. THE LAG TIME: This is simply the time and differential between the two peaks, between the occurrence of maximum rainfall and maximum discharge. A HIGH DISCHARGE and a SHORT LAG TIME=High flooding possibility This means when there is rain, there is immediate discharge (short lag time), and likelihood of flooding. 4. The Rising limb shows the increasing discharge, from this we can calculate how fast it reaches a certain level over time. 5. The Falling limb tells us the recession of discharge, showing decline. This can be used for calculations too. Features you should remember
● Higher rainfall= High Discharge ● Large Basin Size= Greater Discharge *References to base flow and storm flow within the graph should be irrelevant for GCSE, as it is more evident in IB* RIVER REGIMES Definition: Variability/Change in RIVER DISCHARGE and flow of a river in its upper/lower course. This is useful in Geography as is notes patterns connecting how the gradient of a river affects its level of discharge. FACTORS AFFECTING RIVER REGIMES ● Precipitation- A high volume of Rain or other forms of precipitation could result in high discharge in the Upper course, where the speed of the river (velocity) is high . ● Different forms of Precipitation, Ice, Hail could have different impacts on River Discharge. ● Temperature- Seasonal changes in climate affect River flow, Winter( Will water be slower, as part of the river course freezes?), Summer -Autumn (The rainy season results in high precipitation, high Discharge) ● Water Abstractions-Human Contact and usage of water affects discharge too. Building tarmac (non absorbent) means water is quickly discharged in the event of a storm, rainfall. ● Rock Type and Infiltration Capability- How Absorbent and ability to allow water to infiltrate into soil, rock, vegetation could determine how varied discharge is. (High Infiltration rate of soil- Much rain is absorbed by soil, low discharge) ● Slope Gradient- How steep land is determines discharge levels. (You will need to know a few factors to write in your exam, remember some of the ones above) Simple Regime– Within a period of time, there is only one pattern and distinction of high/ low water discharge.(High discharge followed by lower levels of discharge)
Complex Regime– Two or more distinctions between high/ low discharge. eg. (High, low then low, then high levels of discharge, varied levels) Complex regimes are seen in rivers that flow through different land types, affected by River Regime factors.