2.1.3 Temporal variations in river discharge

What is a river regime?

The annual variation in a river’s discharge measured over time.

What factors influence river regimes?

Climate

How does climate influence river regime?

It controls precipitation amount

What is a simple river regime?

A regime with one dominant annual peak in discharge driven by a single main factor.

What causes a simple river regime?

Strong seasonal climates or snowmelt-dominated systems.

What are the characteristics of a simple river regime?

One clear high-flow period

What is a complex river regime?

A regime with multiple discharge peaks or highly variable flow.

What causes a complex river regime?

Multiple precipitation seasons

Why is the Mississippi an example of a complex regime?

It is influenced by snowmelt in the north and rainfall in central and southern regions.

Why is the River Exe described as flashy?

It responds rapidly to rainfall with frequent peaks in discharge.

Why does the River Exe have high winter discharge?

High rainfall and low evapotranspiration lead to saturated soils and increased runoff.

Why does the River Exe have lower summer discharge?

Higher evapotranspiration reduces water reaching the river.

How does geology influence the River Exe’s regime?

Impermeable Devonian rocks reduce infiltration and increase surface runoff.

How does vegetation influence the River Exe’s regime?

Moorland and grassland intercept rainfall and increase infiltration

How does land use influence the River Exe’s regime?

Agriculture and urban areas increase runoff

What role does Wimbleball Reservoir play?

It stores excess water during high flows and releases it during dry periods

What is a storm hydrograph?

A graph showing river discharge response to a rainfall event over a short time period.

What is baseflow?

The normal river discharge sustained by groundwater before a storm.

What is the rising limb?

The increase in discharge as water reaches the river after rainfall.

What is peak discharge?

The maximum flow reached during a storm event.

What is lag time?

The time between peak rainfall and peak discharge.

What is the falling limb?

The decrease in discharge as water drains from the basin after the storm.

What is storm flow (direct runoff)?

The portion of discharge directly caused by the storm event.

How does rainfall intensity affect a hydrograph?

Higher intensity rainfall produces steeper rising limbs and higher peak discharge.

How does rainfall duration affect a hydrograph?

Prolonged rainfall saturates soils

How does antecedent soil moisture affect flooding?

Saturated soils reduce infiltration and increase runoff and peak discharge.

Why are winter hydrographs often flashier in the UK?

Low evapotranspiration and saturated soils increase runoff efficiency.

Why is the River Exe prone to winter flooding?

High rainfall