Spatial And Temporal Change Flashcards
What is the water budget?
Balance between inputs and outputs in a system, affects how much water stored in a system
What is water surplus?
When precipitation > evaporation. Occurs in wet seasons, allows for groundwater to recharge
What is water deficit?
When evaporation > precipitation. Drier seasons, groundwater stores depleted
What is the water balance formula?
Precipitation = Run-off + evapotranspiration +/- change in storage
What is the river regime?
The variability in discharge throughout the course of a year in response to precipitation, evapotranspiration, and drainage basin characteristics
What influences on the river regime are there?
Precipitation
Evapotranspiration
Drainage basin characteristics and land use
Geology
Tributaries
What is utilisation?
Plants using water stores
What is the recharging period?
Groundwater stores refilling after a water deficit
What is the water balance equation?
Precipitation = evaporation + transpiration + river flow +/- storage
What is river discharge measured in?
Cumecs (cubic meters per second)
What are characteristics of a flashy hydrograph?
Short lag time (hour of peak discharge - hour of peak rainfall). Steep rising limb. Falling limb falls slower than rising limb because throughflow and groundwater flow reach the river, adding to discharge
What are characteristics of a subdued hydrograph?
long lag time, gradual rising limb
What physical factors affect hydrographs and discharge?
Shape and size of drainage basin
Slope of angle surrounding land
Intensity of rainfall
Soil/rock type
Vegetation cover
Antecedent conditions
What human factors affect hydrographs and discharge?
Deforestation
Agriculture
River flood management
Water abstraction rates
How do storm events affect water cycle?
Flash floods
Increased temps cause more evaporation, causing more water in atmosphere, so stronger rainstorms
As vapour condenses, heat energy given off, increasing strength of storm
How do seasonal changes affect water cycle?
Wet seasons - precipitation > evaporation so water surplus. Groundwater stores fall causing more surface runoff
Dry seasons - evapotranspiration > precipitation, groundwater stores depleted and humans and plants use water so water deficit
Effects of localised deforestation on the water cycle
Evapotranspiration lower
Less interception so increased overland flow and throughflow
River discharge higher, and chance of flood higher
Effects of extensive deforestation on water cycle
Most water leaves area in channel flow rather than being recycled through evapotranspiration.
Less water vapour in atmosphere, so less precipitation, so lower river levels
What is soil drainage and what effects does it have on water cycle?
- When water table is high, tubes drain water from soil improving aeration and this improves soil structure
- increases throughflow and surface layer can dry out
What is water abstraction and how can it affect water cycle?
- Groundwater abstraction removes from ground source. Most water used for irrigation or drinking
- Can lead to rivers drying up, damage to wetland ecosystems, sinking water tables, empty wells
Effects of water abstraction in SE England chalk bedrock.
- water table fell allowing saline water to contaminate freshwater aquifers
- During 19th and 20th century, due to industrialisation the water table was lowered 88 meters below sea level
- This causes a threat to buildings as water table rises again so soil become moist and unstable.
How does deforestation affect the water cycle?
- Less transpiration due to less trees, which reduces water vapour, so less rainfall and drier climates
- More throughfall as less interception, and more overland flow leading to a flashy hydrograph
What are the short term effects of deforestation?
- Reduced transpiration so less water vapour in atmosphere
- Decreased rainfall/hotter drier climates
- Increased overland flow
- Less infilitration into aquifers
What are the long term effects of deforestation?
- Disruption of regional rainfall
- Drought and desertification
- Increased carbon emissions
- Altered climate patterns regionally/globally
Effects of deforestation in the Mekong Basin?
- Deforested catchments have seen a 15-30% decline in infiltration rates, and an increase in overland flow
- Disrupted rainfall, so farmers reliant on consistent precipitation have further water stress
Effects of soil drainage on the Aral Sea?
- It was the 4th largest lake in the world
- In 1960s, it’s 2 main rivers were diverted for irrigation to grow cotton
- Now it only covers 10% of what it used to and was replaced by a salty, arid desert
Describe the river catchment of the River Tweed
- Horseshoe shaped basin, mainly sedimentary rock (large groundwater sotres)
- Upper course has many trees so high interception rates
- Many dammed tributaries by beavers
Describe the river management of the River Tweed
Do nothing - flooding of wetlands allowed to decrease river discharge downstream
Willow Soiling - Willow’s Eco-Shutters have stopped the erosion of the bank after 18 month
Channelisation - downstream to increase river capacity
When and where were floods of the River Tweed
1956 - the Till floodplain completely flooded
2014 - flood embankment breached and roads in Merlindale completely underwater
What land uses along the Tweed are there?
- Mostly for farming and crops, especially upper course which is prone to flooding
- 80% of land is used for agriculture
- Some water is pumped to Edinburgh as there is a sustainable supply, which decreases discharge
