5.3 The water balance and river regimes Flashcards
What is a water budget?
In the short term, water availability varies from day to day, month to month and year to year. Over a longer period, there is usually a natural rhythm that balances out times of surplus and times of deficit. This balance is called the water budget and reflects the differences between inputs and outputs in any given area
How else can the water budget be expressed?
as the water balance equation:
Precipitation (P)
runoff/river discharge (Q)
Potential evapotranspiration (E)
soil moisture and groundwater storage (S)
Each year, whatever falls as precipitation should be balanced out by the other components
P = Q + E +/- S
What are the inputs of a water budget?
-precipitation
-Water diversion into the area
-Groundwater flow into the area
-Surface water flow into the area
-Surface runoff into the area
What are the outputs of a water budget?
Evapotranspiration
Water diversion, groundwater flow, surface water flow/runoff out of the area
Industrial or residential uses within the area
What is the field capacity?
at this point, the soil is full of water and cannot hold anymore
Look at the components of a water budget source… what does part A show?
Precipitation exceeds potential evapotranspiration. Soil water is full with a surplus for plants, runoff and groundwater recharge
Look at the components of a water budget source… what does part B show?
Potential evapotranspiration exceeds precipitation. Soil moisture is used up by plants, or used by evaporation (called soil moisture utilisation)
Look at the components of a water budget source… what does part C show?
Soil moisture store is now used up. Precipitation is likely to be absorbed by the soil, rather than produce runoff. River levels will fall or dry up completely
Look at the components of a water budget source… what does part D show?
Deficiency of soil moisture, as the store is used up. PE exceeds precipitation. Plants must adapt to survive and crops need irrigation
Look at the components of a water budget source… what does part E show?
Precipitation exceeds PE. Soil moisture is recharged
Look at the components of a water budget source… what does part F show?
Soil moisture is now full and field capacity is reached. Additional rainfall will percolate to the water table, and groundwater stores will be recharged
What does the amount of water reaching a river depend on?
both local and drainage basin wide factors, as well as climatic control
What is a river regime?
The annual pattern of a river’s flow (or discharge) which reflects local, drainage basin wide and climatic factors
What is a tropical river’s regime like?
Generally have fairly uniform flow patterns, especially in areas where rain falls every month.
What are worldwide river regimes like?
They tend to have a seasonal pattern whereby they directly respond to the amount of precipitation
What are the two types of river regimes?
Simple and complex
What are simple river regimes?
Where the river experiences a period of seasonally high discharge , followed by low discharge
What are examples of where you would find a simple river regime
- They are typical of rivers where the inputs depend on glacial meltwater, snowmelt or seasonal storms (monsoon).
-Rivers with temperate climates, which rise in mountainous regions where summer snowmelt occurs, tends to be like this (e.g. the Rhone)
What is a complex river regime?
Where larger rivers cross several different relief and climatic zones, and therefore experience the effects of different seasonal and climatic events
What are two rivers that have complex river regimes?
Mississippi
Ganges
What else causes rivers to have complex regimes?
-human factors, such as damming rivers for energy or irrigation
-The longer the river, the more complex the variables (land use, precipitation, evapotranspiration) - making it more complex
What are flow patterns like in the Yukon river in Alaska, US?
high flow in spring and summer, caused by snowmelt
low flow in winter when precipitation is frozen
Large seasonable variability
Relatively few human influences apart from some HEP use for mining industries
What are major influences on the Yukon river?
Tundra, taiga and mountain climates
What are flow patterns like in the Amazon, Brazil?
High flow in wetter season
Low flow in drier season
Moderate seasonable variability- fed by Andean rivers outside rainforest region
Human influences are increasing as large dams are used by Brazil’s cities for irrigation and HEP
