Water balance and Hydrographs

Question 1

What is Bankfull?

Answer 1

The maximum discharge that a river channel is capable of carrying without flooding

Question 2

Define Baseflow

Answer 2

The normal day-to day discharge of the river and is the consequence of slow moving soul throughflow and groundwater seeping into the river channel

Question 3

What is Discharge?

Answer 3

The amount of water ina. river flowing past a particular point expressed as m^3s^-1 cumecs.

Question 4

What is lagtime?

Answer 4

Lag time is the time between the peak rainfall and peak discharge

Question 5

What does Peak Discharge mean?

Answer 5

The point on a flood hydrograph when river discharge is at its greatest.

Question 6

What does storm flow mean?

Answer 6

Discharge resulting from storm precipitation involving both overland flow, throughflow and groundwater flow.

Question 7

What is a Storm Hydrograph?

Answer 7

A graph of discharge of a river over the time period when the normal flow of the river is affected by a storm event.

Question 8

What is a River Regime?

Answer 8

The variability in its discharge throughout the course of a year in response to precipitation, temperature, evapotranspiration and drainage basin characteristics.

Question 9

How many river systems are in the UK?

Answer 9

1,500

Question 10

Why are storm hydrographs important?

Answer 10

They can predict how a river might respond to a rainstorm, which can help in managing the river.

Question 11

What is the rising limb?

Answer 11

The rising limb indicates how quickly a river responds to a ‘storm’

Question 12

What is the Receding limb?

Answer 12

Bankfull discharge. It is at this point a river will begin to overflow

Question 13

What is Lag time?

Answer 13

The time between peak discharge and peak rainfall

Question 14

Drainage basins that are more circular in shape lead to what type of hydrograph and why?

Answer 14

A more flashy hydrograph because each point in the drainage basin is roughly equidistant from the measuring point on a river

Question 15

Drainage basins with steeper sides tend to have what type of hydrograph and why?

Answer 15

A more flashy hydrograph because water flows more quickly on the steep slopes, as either throughflow or overland flow.

Question 16

Basins that have a high drainage density (they have a lot of surface streams acting as tributaries) have what type of hydrograph and why?

Answer 16

A flashy hydrograph because all the water arrives at the measuring stations at the same time.

Question 17

What happens if the drainage basin is already saturated by antecedent rainfall?

Answer 17

Overland flow increased because infiltration capacity has been reached.

This results in reduced lag time, meaning peak discharge is higher resulting in a flashy hydrograph

Question 18

What could make overland flow higher and reduce infiltration and throughflow?

Answer 18

A soil or rock type within the river that is impermeable, resulting in a flashy hydrograph.
The same can be said for hard surfaces ,e.g. sun baked ground or frozen surfaces

Question 19

What impact does thick vegetation cover in drainage basins have on storm hydrographs?

Answer 19

Vegetation intercepts the precipitation, holding water on its leaves , slowing the movement of water to the ground and river channels.
Water is also lost due to transpiration and evaporation, increasing lag time and reducing peak discharge

Question 20

How can the amounts and intensity of precipitation affect storm hydrographs?

Answer 20

Heavy water entering the drainage basin over a short time result in higher discharge