Flood Hydrograph Flashcards
(37 cards)
Define Hydrograph
A graph that shows river discharge and rainfall over time
Define Flood
When the capacity of a river to transport water is exceeded and water flows over its banks
Define Base Flow
The normal day to day discharge of the river and is the consequence of groundwater seeping into the river channel
Define Bankfull Dischatge
The maximum discharge that a particular river channel is capable of carrying without flooding
Define Peak Discharge
The point of a flood hydrograph when rainfall is at its greatest
Define Lag Time
Period of time between the peak rainfall and peak discharge
Define Peak Rainfall
The point on the flood Hydrograph when rainfall is at its greatest
Define Falling Limb
The fall in discharge back to base level
Define Rising Limb
Discharge rates increasing when storm water enters the drainage basin
How long does flood Hydrograph show?
Covers a relatively short time period usually days or hours
True or False? The shape of a Hydrograph varies in each river basin and each individual storm event
True
What are the physical features of the Drainage Basin which affects Flood Hydrographs?
- Basin size
- Drainage density
- Rock type
- Land use
- Relief
- Soil water
- Rainfall intensity
What are the different types of flood Hydrograph and what are their characteristics?
- flashy = short lag time, high peak, steep rising + falling Limb (fast response = high discharge)
- Subdued = long lag time, low peak, gently rising and falling limbs (slow response = lower discharge)
What type of Basin Size creates a “Flashy” Hydrograph and why?
Small basin, as it leads to rapid water transfer
What type of Basin Size creates a “Subdued” Hydrograph and why?
Large basin, as it leads to a relatively slow water transfer
What type of Drainage Density creates a “Flashy” Hydrograph and why?
High density, speeds up water transfer
What type of Drainage Density creates a “Subdued” Hydrograph and why?
Low density, slows down water transfer
What type of Rock Type creates a “Flashy” Hydrograph and why?
Impermeable rocks - encourages rapid Overland flow with less slower throughflow and infiltration
What type of Rock Type creates a “Subdued” Hydrograph and why?
Permeable rocks = encourages slow transfer by Overland flow with more throughflow and infiltration
What type of Relief creates a “Flashy” Hydrograph and why?
Steep slopes = leads to rapid water transfer
What type of Relief creates a “Subdued” Hydrograph and why?
Gentle slopes = slow down water transfer
What type of Soil Water creates a “Flashy” Hydrograph and why?
Saturated soil = leads to rapid water transfer
What type of Soil Water creates a “Subdued” Hydrograph and why?
Dry soil = soaks up water and slows down its transfer
What type of Rainfall Intensity creates a “Flashy” Hydrograph and why?
Heavy rain = exceeds the infiltration capacity of vegetation and leads to rapid Overland flow
