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Study Diagram Q4 - Scottish Highers Geography - Question 4 - 2019
Question 4
Study Diagram Q4. For the River Leri on 8th and 9th of June a) describe the changes in discharge level and b) suggest reasons why these changes may have occurred.
Worked Solution & Example Answer:Study Diagram Q4 - Scottish Highers Geography - Question 4 - 2019
Step 1
describe the changes in discharge level
Answer
The flood hydrograph for the River Leri shows distinct changes in discharge levels over the period from 8th to 9th June.
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Increased Discharge: Initially, there is a slow increase in discharge starting at around 12:00 PM on 8th June, indicating beginning rainfall impact.
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Peak Discharge: The discharge reaches a peak of approximately 90 cubic meters per second at around 2:00 AM on 9th June directly following the heaviest rainfall between midnight and 2:00 AM.
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Decreased Discharge: After this peak, there is a rapid decline in discharge evident after this hour, with levels dropping steadily back under 20 cubic meters per second by 6:00 AM on 9th June.
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Lag in Hydrograph Response: A notable lag in the hydrograph is observed; the peak discharge occurs several hours after significant rainfall, indicating the time taken for water to flow through the catchment area.
Step 2
suggest reasons why these changes may have occurred
Answer
Several factors can explain the observed changes in discharge levels:
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Rainfall Intensity: The intense rainfall during the night likely caused rapid runoff into the river system, leading to a swift rise in discharge levels.
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Soil Saturation: Prior to the rainfall, the saturation levels of the soil may have affected how quickly water could infiltrate, resulting in higher runoff and rapid increases in discharge.
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Vegetation Impact: Areas with less vegetation may have experienced higher levels of runoff, contributing to the discharge more rapidly compared to areas with dense vegetation, where water retention is higher.
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Channel Characteristics: The physical characteristics of the river channel itself, such as width and gradient, may influence how quickly water is conveyed through the system. The steepness of the riverbed can facilitate faster flow, contributing to the rapid rise and fall in levels observed in the flood hydrograph.