5.3 water budgets & river systems

Question 1

water budget

Answer 1

the annual balance between precipitation, evapotranspiration and runoff within an area (eg a drainage basin) (balance between inputs and outputs)
calculated through the equation: P= Q + E +/- S
P= precipitation
Q= discharge
E= evapotranspiration
S= change in storage
water budgets can also be displayed in a graph format

Question 2

3a) what scale are water budgets?

Answer 2

they can be calculated at various scales from global to local
budgets at regional/ national scale= useful indication of water available for human use.
budgets at local scale= useful for farmers as they can inform about available soil water (amount of water that can be stored in soil/ available for growing crops)

Question 3

what influences water budgets?

Answer 3

primarily is influenced by climate type (tropical temperate or polar as examples)

Question 4

effective rainfall

Answer 4

= difference between total rainfall and actual evapotranspiration: the amount that the plants/ soil get to use
in simpler terms: the amount of precipitation remaining after evaporation

Question 5

river regime

Answer 5

is the pattern of a rivers discharge over a period of time (usually a year). this can be affected by several factors.

Question 6

factors affecting river regimes

Answer 6

1. size (some rivers cross varied climates- this makes them complex)
2. geology (overlying soils too, porosity and permeability- groundwater in permeable rock is gradually released into river at base flow)
3. precipitation (amount, type and seasonality)
4. temperature ( affects evaporation and plant growth, possible meltwater in summer in some climates)
5. human activities
   - water abstraction
   - dams (controls river flow and water store, flattening the regime)

Question 7

hydrographs

Answer 7

similar to a regime in that it shows discharge over time BUT its over a much SHORTER amount of time usually hours (no more than a few days) after a rainfall event.
the hydrograph plots 2 things: occurrence of short periods of rain over a drainage basin and the subsequent discharge of a river.

Question 8

two types of hydrograph

Answer 8

the shape of a hydrograph depends on the nature of the rainfall event but also the physical characteristics. a combination of these two things can either create a FLASHY or STEADY hydrograph.
flashy= steep rising limbs, high peak discharge and a short lag time.
steady= gentle rising limbs, low peak discharge and a long lag time

Question 9

factors that affect ‘flashy’ and ‘steady’ hydrographs

Answer 9

1. antecedent conditions
   - flashy= prev rainfall may have saturated stores increasing surface run off and decreasing lag time, freezing weather freezes soil, hot summers bake the soil: both reduce infiltration capacity
   steady= high rate of evapotranspiration, stores are depleted therefore increasing storage pot.
2. precipitation
   flashy= prolonged rainfall saturates soils, intense storms- heavy rainfall compacts soil, snowmelt occurs rapidly and cold temp means ground is frozen
   steady= rain falls gently over long period of time, rain falls in form of snow

2.relief
flashy= steep slopes encouraging surface run off
steady= gentle slopes allowing infiltration

3. size of basin
   flashy= small basin, rainfall reaches channel quicker, circular as well
   steady= large or elongated basin means longer lag time, further to travel
4. geology/ soils
   flashy= impermeable rocks eg granite prevents percolation- soils become saturated quicker/ clay soils encourage sr. as they are difficult to infiltrate or thin soils which are easily saturated
5. vegetation
   flashy= deciduous trees lose their leaves during winter/ certain types of land also have reduced interception eg farmland= 10% vs forests= 35% interception rate.
   steady= deciduous woodlands in summer high rates of interception, increasing lag time, also coniferous trees!
6. human activity
   flashy= urbanisation produces impermeable tarmac and concrete surfaces, storm drains massively decrease lag time sending rainfall straight to river, deforestation reduces interception, farming
   steady= afforestation, contour ploughing encourages infiltration,
   conserving rural areas

Question 10

(DEFN.) soil field capacity

Answer 10

max rate of infiltration (rate soil can absorb water)

Question 11

(DEFN.) water deficit and surplus

Answer 11

deficit= water demand is greater than supply surplus= water supply is greater than demand, creating surface run off, can result in flooding

Question 12

(DEFN.) recharge

Answer 12

= process where water moves downward through soil until it arrives at saturated zone, adding to groundwater storage (CAN ALSO be precipitation following a dry period)