Water balance and Hydrographs Flashcards
What is Bankfull?
The maximum discharge that a river channel is capable of carrying without flooding
Define Baseflow
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
What is Discharge?
The amount of water ina. river flowing past a particular point expressed as m^3s^-1 cumecs.
What is lagtime?
Lag time is the time between the peak rainfall and peak discharge
What does Peak Discharge mean?
The point on a flood hydrograph when river discharge is at its greatest.
What does storm flow mean?
Discharge resulting from storm precipitation involving both overland flow, throughflow and groundwater flow.
What is a Storm Hydrograph?
A graph of discharge of a river over the time period when the normal flow of the river is affected by a storm event.
What is a River Regime?
The variability in its discharge throughout the course of a year in response to precipitation, temperature, evapotranspiration and drainage basin characteristics.
How many river systems are in the UK?
1,500
Why are storm hydrographs important?
They can predict how a river might respond to a rainstorm, which can help in managing the river.
What is the rising limb?
The rising limb indicates how quickly a river responds to a ‘storm’
What is the Receding limb?
Bankfull discharge. It is at this point a river will begin to overflow
What is Lag time?
The time between peak discharge and peak rainfall
Drainage basins that are more circular in shape lead to what type of hydrograph and why?
A more flashy hydrograph because each point in the drainage basin is roughly equidistant from the measuring point on a river
Drainage basins with steeper sides tend to have what type of hydrograph and why?
A more flashy hydrograph because water flows more quickly on the steep slopes, as either throughflow or overland flow.
Basins that have a high drainage density (they have a lot of surface streams acting as tributaries) have what type of hydrograph and why?
A flashy hydrograph because all the water arrives at the measuring stations at the same time.
What happens if the drainage basin is already saturated by antecedent rainfall?
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
What could make overland flow higher and reduce infiltration and throughflow?
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
What impact does thick vegetation cover in drainage basins have on storm hydrographs?
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
How can the amounts and intensity of precipitation affect storm hydrographs?
Heavy water entering the drainage basin over a short time result in higher discharge
