1.1 Drainage Basin System Flashcards
What is a System, Inputs, Outputs, Transfers and Stores?
A system is a group of interacting entities which act and form as a unified whole.
Inputs are what enters a system e.g. precipitation
Outputs leave the system e.g. evt, runoff, discharge
Stores are stored within the system e.g. channel, groundwater
Transfers are the transfer of inputs between components.
What are the open/closed systems of the hydrological cycle?
The drainage basin is a closed system, as it is confined within the watershed and water technically does not leave the system but it recycled from one state to another.
The hydrological cycle is seen as an open system as water flows in and then out of the system and the system responds to changes in its inputs. It also contains inputs, outputs, transfers and stores which vary depending on each other.
What is the composition and distribution of global water supply?
97% is found in the sea
- 1% is found in snowpack and ice
- 8% is found in freshwater in rivers
- 1% is found in the atmosphere.
Describe in short the features and hydrological cycle of the drainage basin
A closed system as all flows go through the stores and circulate. It is driven by gravity and the sun.
It has a source(s), a watershed (area of catchment), tributaries which meet at the main river at a confluence and then flow downstream to the mouth.
Precipitation falls to the earth where it either is caught by trees by interception or lands on the earth where it is stored as surface storage. Some of the intercepted water is evaporated off the tips of the leaves or transpired out the stomata. The remaining water falls down to the surface through stemflow or leaf drip.
The water on the surface either is evaporated, infiltrates into the soil or is transferred to the channel by surface runoff.
Moisture in the soil then either gets absorbed by plants who evaporate/transpire the water, it is transferred to the channel via through flow or it percolates further into the bedrock by percolation.
The water in the bedrock is called groundwater storage which flows to the channel by baseflow. The channel flow is an accumulation of all the flows which make up the river discharge.
What are the 4 outputs of the drainage basin?
Evaporation: water evaporates from leaves, puddles and rivers due to heat, humidity and windspeed which then leaves the system.
Transpiration: Plants draw water from the soil into the leaves where it evaporates out of their pores known as the stomata
Evapotranspiration: Total water loss from both processes. The potential EVT is the EVT if there were unlimited soil moisture, used for comparison. EVT makes up for 80% of outputs
Channel flow: movement of water in channels - directly through precipitation and flows out of the system.
What is the ‘first’ store and its related processes?
Interception is when vegetation catches falling precipitation and stores it within the plant or on the leaves. There are 3 types of process:
Interception loss: water retained by plant surfaces and then evaporated or absorbed then transpired.
Through fall: water falls through gaps in the leaves and drops from them, due to saturation
Stem flow: water trickles along branches and down the main trunk to the surface.
What is the ‘second’ store?
Surface storage - small puddles, seasonal lakes, wetlands, swamps, bogs, marshes
What is the ‘third’ store and what properties may affect this?
Soil storage is when water is stored in the pores in the soil and subsurface layers above the water table. Examples may be clay or sandy soils:
Clay - small pores, not porous but holds water well
Sandy - large pores and permeable/porous, loses water fast
Permeable soils allow water to pass through percolation and throughflow.
Seasonal variations may occur in the moisture budget, a deficit being below field capacity and surplus being above field capacity.
Recharge occurs when the rate of precipitation is greater than the outputs, the utilisation is the amount brought up by capillary action.
What is field capacity?
The amount held in water after excess is drained away.
The wilting point is the range of water content in which wilting may occur in plants
What is the ‘fourth’ store?
Groundwater is the water present under the surface in soil pore spaces. Water flows through the rocks until it reaches the level of saturation, or the water table. If the water table reaches the surface, this forms a spring.
Groundwater may remain in rocks for thousands of years.
What is the water table and what is it influenced by?
This refers to the layer of the upper surface of groundwater - below it is fully saturated rock known as the phreatic zone. The vadose zone is the unsaturated bit between soil and the water table. Capillary action allows soil moisture to move in all directions.
The water table is influenced by precipitation, porosity and permeability of the rock.
What are springs and aquifers? Why are aquifers useful?
When the water table reaches the surface, it may form a spring as water naturally emerges from the Earth’s surface and may be significant enough to be a source of water.
Aquifers are natural bodies of groundwater which come in layers of saturated rock, percolated beyond the soil and remains within empty spaces in the bedrock. Aquifers are able to regulate water which would otherwise quickly reach the river to slow down flooding, depending on the porosity. Groundwater accounts for 96% of extracted freshwater.
There are 2 types:
Unconfined - Under permeable rock
Confined - Under impermeable rock
What may cause loss of groundwater? What is groundwater recharge?
Groundwater accounts for 96% of freshwater, so often boreholes are used to abstract it. If this exceeds recharge rate (time for it to replenish), then water tables will fall and wells can dry up. The abstraction may also lead to salt water intrusion into the empty spaces, reducing the purity.
Further losses may be due to evapotranspiration as roots take up water, natural discharge, leakage and outflows, abstraction.
Groundwater recharge is the time taken for groundwater to be replaced in an aquifer. It may be due to infiltration, seepage through banks or rivers, groundwater leakage, artificial recharge from irrigation, reservoirs, etc.
Explain the flows in the drainage basin:
Through fall: Through gaps in the leaves
Leaf drip: Off leaves
Stem flow: Down branches and trunk
Overland flow - water that flows over the land’s surface. May be accelerated in two ways:
Saturated overland flow: ground fully saturated so can no longer infiltrate
Hortonium overland flow: short and high rainfall exceeds infiltration rates so the water flows over as if saturated. Often happens in cities, on slopes and on concrete.
Infiltration - water soaking into/absorbed by soil. The capacity is the maximum amount of moisture able to enter. Porosity is the capacity of rock to hold water and permeability is the ability for water to move through the rock.
Throughflow: water moves through the soil in natural pipes through the pores
Percolation: Water flows into the bedrock from the soil, where it becomes groundwater
Baseflow: River discharge from groundwater seeps into the river bed.
What influences the rate of infiltration?
Infiltration decreases with time and capacity. Vegetation increases rates as it slows surface speeds.
Overland flow - Less infiltration, more overland flow
Antecedent - wet ground has less infiltration
Porosity - more porous, more infiltration, less surface runoff
Vegetation cover - reduced surface runoff, increased infiltration
Rain size - bigger increased surface runoff, less infiltration
Higher slope angle - more surface runoff, less infiltration
