Storm Hydrograph

Which of the following is a key factor affecting the shape of storm hydrographs?

• Economic Growth

• Political Stability

• Cultural Diffusion

• Urbanisation

Answer explanation

Urbanisation significantly impacts storm hydrographs by increasing impervious surfaces, leading to faster runoff and altered flow patterns. This makes it a key factor in shaping how stormwater is managed and observed.

Which of the following best describes a 'flashy' hydrograph?

• Short lag time, high peak discharge

• Steady discharge over time

• Long lag time, low peak discharge

• No significant changes in discharge

Answer explanation

A 'flashy' hydrograph is characterized by a short lag time and high peak discharge, indicating rapid runoff and quick response to rainfall. This contrasts with steady or low discharge scenarios.

Which type of rock is associated with high surface runoff in storm hydrographs?

• Metamorphic rocks

• Permeable rocks

• Sedimentary rocks

• Impermeable rocks

Answer explanation

Impermeable rocks do not allow water to infiltrate, leading to increased surface runoff during storms. This results in higher peaks in storm hydrographs compared to permeable, sedimentary, or metamorphic rocks.

What is the main impact of urbanisation on flood risk?

• Decreases flood risk

• Reduces water quality

• Increases flood risk

• Has no impact

Answer explanation

Urbanisation increases flood risk due to the expansion of impervious surfaces like roads and buildings, which prevent water absorption and lead to higher runoff, overwhelming drainage systems and increasing the likelihood of flooding.

Which of the following is a characteristic of a 'flat' hydrograph?

• Rapid changes in discharge

• Consistent discharge levels

• Short lag time, high peak discharge

• Long lag time, low peak discharge

Answer explanation

A 'flat' hydrograph is characterized by a long lag time and low peak discharge, indicating that the flow response to rainfall is slow and less intense, unlike rapid changes or high peaks.

What does the term 'lag time' refer to in the context of storm hydrographs?

• Time between peak rainfall and peak discharge

• Duration of rainfall

• Time taken for water to evaporate

• Interval between floods

Answer explanation

The term 'lag time' in storm hydrographs refers to the time between peak rainfall and peak discharge. This interval indicates how quickly the rainfall translates into increased river flow, making it crucial for flood forecasting.

Which of the following factors can lead to increased surface runoff?

• Deforestation

• Soil conservation

• Reforestation

• Wetland restoration

Answer explanation

Deforestation removes trees that absorb water, leading to less infiltration and more surface runoff. This increases the volume of water flowing over the land, making deforestation a key factor in increased runoff.

How does a high water table affect the infiltration capacity of soil during heavy rainfall?

• No effect on infiltration capacity

• Infiltration capacity is only affected by vegetation

• Increases infiltration capacity

• Decreases infiltration capacity

Answer explanation

A high water table saturates the soil, reducing its ability to absorb additional water during heavy rainfall. This leads to decreased infiltration capacity, as the soil is already near its saturation point.

What is the primary consequence of saturated soil conditions on surface runoff?

• Soil erosion

• Increased evaporation

• Decreased surface runoff

• Increased surface runoff

Answer explanation

Saturated soil cannot absorb more water, leading to excess water flowing over the surface. This results in increased surface runoff, making it the primary consequence of saturated soil conditions.

Which of the following factors is most likely to lead to flooding in a basin with pre-existing wet conditions?

• Increased vegetation cover

• High rainfall intensity

• Low rainfall intensity

• Dry soil conditions

Answer explanation

High rainfall intensity can overwhelm the soil's capacity to absorb water, especially in already wet conditions, leading to flooding. In contrast, increased vegetation cover and low rainfall intensity would reduce flood risk.