River Catchment: River Tamar Flashcards
Location
- Largest river in the south west of the peninsula
- Bounded by Dartmoor ( east) and Bodmin moor ( west)
- The catchment area is 915.9km^2
Geology (5)
- Bodmin moor and Dartmoor are made up of granite ( impermeable)
- The river valleys have aluminium ( a fluvial deposit)
- Superficial deposits ( loose un consolidated material on bed rock)
- Bed rock- vey low permeability
- high drainage density- tributaries can increase rapid flow of water so reducing lag time
Relief (3)
- Flows from a maximum altitude of 580.3 MACD
- The river Tamar is a ria( coastal inlet formed by submergence of an unglaciated river valley) - flood risk
- Overall relief ( moderate)
Weather and climate (4)
- High rainfall in the tamar’s drainage basin (1000-1500 mm a year)
- High rates of orographic rainfall( warm moist air from the south west and is forced to rise up over high ground eg Bodmin moor, where it reaches due point)- condensation, cloud formation and then relief
- Predominant air stream south easterly ( tropical maritime air mass from the Azores)
- Mild wet climate
Land use (2)
- Predominantly rural
- 2/3 of the catchment is livestock, grassland farming and horticulture
Population distribution
Low population density ( lower course has an area of high population density)- 280,000 people
Sustainable water supply ( south west water- Road ford reservoir and drought/ catchment management)
- Flood management ( cal stock flood defence scheme)
. Farming is a dominant land use in the Tamar drainage basin ( livestock)- can cause soil compaction, reduce soil moisture. Less water is infiltrated therefore higher risk of surface runoff
. Animal waste is a big factor for water quality ( slurry)- can be an effective fertiliser because it’s thick in nitrate
. Cyanobacteria- slurry gets moved in rivers and the river turns green ( algae)- algae stops sunlight form rescuing organisms, reducing oxygen
. Chemical fertilisers( arable farming)- can cause soil acidification, reducing content of organic matter
. Grazing animals keep vegetation level low (suppress vegetation growth) - increase rates of rapid surface runoff which will cause more slurry to flow into rivers
Arable farming
- In the summer when soil moisture deficit is due-irrigation in the lower course of the river Tamar
- Slope ploughing- 🔴
. It is easy and safe
. there is no interception since it channels the water into drains ( soil erosion)
. it pollutes rivers and streams( from residue and agrichemicals) - Contour ploughing-🟢
More sustainable and reduces soil erosion ( doesn’t generate surface runoff)
Flood management- creek network
- During the construction of the creek network, the materials extracted were used to make the existing embankment, which was then breached to allow water to flow in and out of the area.( a bridge was put over this breach to ensure the public)
- A large change in farmers and locals hand over their land
- Brackish marsh attracts all kinds of animal species such as crabs, snail and fish( improve water quality)
- Increasing biodiversity of the area by attracting and planting as many species as possible.
- Reed beds could improve water quality- sewage works upriver of the defence often release raw sewage but reed beds filters the bacteria
Deforestation
There is less interception by trees so surface runoff increases ( decreasing lag time and increase peak discharge)- flashy hydro graph. The soil is no longer held together by roots, so soil water storage decreases.( there are fewer plants so transpiration decreases)
Storm events
. Large amount of rainfall saturate the ground up its field capacity. No more water can infiltrate the soil, increasing surface runoff, decrease lag time and increase peak discharge- (flashy hydrograph).
. Storm events are therefore less effective at recharging water stores than prolonged rainfall
Seasonal changes
. Spring: more vegetation growth so more interception which decreases flood risk, but exposed areas will transfer to the river more rapidly, decreasing lag time.
. Summer: less rain so Ground may be harder and therefore more impermeable encouraging surface runoff ( greater levels of through flow)
. Autumn: Less vegetation growth so less interception( more surface runoff therefore greater flood risk) .
. Winter: frozen ground may be impermeable and encourage runoff. Snow discourages runoff and takes time to melt slowly down the processes that occur within the water cycle
Agriculture
. Pastoral farming relates to livestock ( pigs, cattle, goats etc.) reduce infiltration
. Arable farming relates to crops. Ploughing increases infiltration by creating a looser soil, which decreases surface runoff. However digging drainage ditches increase surface runoff and streamflow
. Irrigation( the movement of water from human intervention ) can lead to groundwater depletion
Urbanisation
. Creating roads and buildings which have impermeable surfaces and are likely to have drains which reduce infiltration and increase surface runoff, reducing lag time and increasing the flood risk
Seasonal variation of the soil water budget
. Autumn: greater input from precipitation than there is an output from evapotranspiration as deciduous trees lose their leaves and the cooler temperatures mean that the plants photosynthesis less. Soil moisture levels increase and water surplus occurs
. Winter: evapotranspiration from plants reaches a minimum due to the colder temperatures and the precipitation continues to refill the water store. Infiltration and percolation also refill the water table.
. Spring: around February and march, plants start to grow again as evapotranspiration increases when temperatures get higher so plants start to photosynthesis. There is still water surplus in this time
. Summer: the hotter weather leads to utilisation of soil water as evapotranspiration peaks rainfall at a minimum. The output for evapotranspiration is greater than the input from precipitation so the soil water stored are depleting. ( water deficit may occur)
