Drainage Basin Characteristics- Inputs, Outputs, Stores, Flows Flashcards
Stemflow
water which trickles along twigs and branches and finally falls down the main trunk
Precipitation
Conversion and transfer of moisture in the atmosphere to the land via rainfall, hail, dew and snow.
Interception loss
water that is retained by plant surfaces and is later evaporated away or absorbed by the plant. Interception loss varies with different types of vegetation.
Less from grasses (shoots have smaller surfaces) than from woodland trees such as beeches. For agricultural crops (cereal). In the winter coniferous trees intercept more than deciduous in winter (lose their leaves in autumn and winter and therefore have a lower SA)
Aquifers
rocks which contain significant quantities of water and are permeable providing a reservoir for water. Natural Regulator in hydrological cycle as water moves very slowly and absorbs water which would otherwise reach streams quickly. Also maintain stream flow in dry periods.
Field Capacity
Amount of water held in the soil after excess water drains away-saturation or near saturation.
Channel storage
all water that is stored in rivers, streams and other drainage channels. Some are seasonal and may disapear underground naturally (in areas with carboniferous limestone) or in urban areas where they are culverted
Throughflow
the lateral movement of inflitrated water in soil. The water moves parallel to the surface (horizontally) down the slope to the river channel along percolines (defined lines of seepage).
Soil Moisture Budget
the annual balance between precipitation, evapotranspiration, and runoff i.e. annual balance between the inputs and outputs. It is calculated from the formula:
P = E + R +/- S
(Where P is precipitation, E is evapotranspiration, R is runoff and S represents changes in storage over a period of time, usually one year)
Aeration Zone
zone which is seasonally wetted and seasonally dries out.
Drainage Basin Definition
An area of land drained by a river and its tributaries. Is an open system as it allows for the movement of matter and energy across its boundaries
Groundwater
subsurface water stored in rocks. Accounts for over 96% of all freshwater on earth.
Interception and its 3 main components
when water is caught and stored by vegetation. The 3 main components are Interception loss, Throughfall, and Stemflow.
Water Table
Water table is an underground boundary. It marks the point below which the soil or rocks are permanently saturated with water.
Surface Runoff
water that flows over the lands surface when :
- precipitation exceeds infiltration rate
- the soil is saturated
Saturation
refers to a soil’s water content when practically all pore spaces are filled with water. If precipitation continues on a saturated soil, it will result in surface runoff, water percolation down to the water table & groundwater stores being recharged. If soil is poorly drained and/or compacted so that water is unable to drain away, it can lead to the soil becoming waterlogged.
Inflitration Capacity
The maximum rate at which water can be absorbed by the soil. Is influenced by
- Duration of Rainfall (decreases with time) ie; 0-4mm/hr on clays, 3-12mm/hr on sands
- Vegetation-(increases inflitration as the speed at which water reaches the surface is reduced) IE; bare soils w/rainsplash impact = 10mm/hr, vegetation cover= 50-100mm/hr
-Antecendent soil moisture
-soil porosity
-raindrop size
-slope angle
Variations in Seasonal Soil Moisture Budget
Soil Moisture Deficit- SM falls below field capacity. Temperate areas- late Winter/ early Spring SM is low as a result of high levels of precipitation and limited EVT.
SM Recharge- precipitation exceeds evapotranspiration
SM surplus- soil is saturated and water cannot enter resulting in surface runoff
SM utilization- water is drawn up to the surface by capillary action ( the process of a liquid flowing in narrow spaces without the assistance of, or even in opposition to, external forces like gravity.)
Below Ground
Infiltration
Percolation
Throughflow
Baseflow
Surface Water
Temporary or permanent stores of water. Temporary- small puddles and turloughs (seasonal lakes in the west of ireland)
Permanent stores- marshes, swamps, lakes
Channel Flow
movement of water in channels such as rivers
Soil Moisture
subsurface water in the soil and subsurface layers above the water table.
Water can be
-absorbed
-held
-transmitted downwards towards the water table
-transmitted upwards towards the soil surface and the atmosphere.
Groundwater Recharge
Infiltration
Seepage- through banks and beds of surface water
Groundwater leekage inflow-from adjacent rocks and aquifers
artificial recharge- irrigation and reservoirs
Pheratic Zone
lays below the water table and is the permanently saturated zone within rocks and sediments.
Throughfall
when water falls through gaps in vegetation or when it drops from leaves or twigs
Input of Drainage Basin system
The addition of water to the drainage basin through precipiation or leekage.
available soil water
is the amount of water that can be stored in the soil and is available for growing crops. This is valuable to users, such as farmers, who can use it to identify when irrigation might be required, and how much.
EVT accounts for how much precipitation loss?
100% in arid areas
75% in humid areas
Groundwater Recharge
refilling of water pores in dry areas or hwere water has been extracted by humans
Stores
Interception
Soil Water
Surface Water
Groundwater
Channel Store
Baseflow
Water which has percolated into the bedrock and then moves laterally down slope to seep into the bed of the river. Constant flow though may increase slightly after a wet period.
Factors affecting precipitation and its effects on the drainage basin system,
FACTORS AFFECTING PRECIPITATION
- temporal variability
- climates of different countries (polar and temperate climates snow-melt is a significant input.
FACTORS AFFECTING LOCAL DRAINAGE SYSTEM
-The amount of precipiation
- the type of precipitation
-intensity of precipitation (mm/hr)
-geographical distribution of precipitation
Water Table
an underground boundary. It marks the point below which the soil or rocks are permanently saturated with water.
Varries seasonally - Temperate zones- higher in the winter after increased levels of precipitaion
Above ground flows
Throughfall
Stemflow
Surface Runoff
Evapotranspiration
the combined loss of evaporation ( process of transforming liquid water from the earths surface into water vapour) and transpiration (the loss of water through vegetation and to the atmosphere)
losses of groundwater
EVT- in low-lying areas where water table is close to surface
Natural Discharge- seepage
Groundwater outflow- into adjacent aquifers
Artifical Abstraction- Saudi Arabia- groundawter reserve in 2010 was 42% less than in 1985
Percolation
Water moves slowly downwards from the soil into the bedrock
Wilting point
Range of moisture content in which
permanent wilting of plants occurs.
Potential Evapotranspiration PEVT
evapotranspiration that would occur if there was an unlimited water supply for vegetation use in the soil. For example, Egypt has 250mm of EVT due to low rainfall but PEVT is 2000mm
Outputs
Evapotranspiration
