1.1 Hydrology and fluvial geomorphology: the drainage basin system Flashcards
What is a drainage basin
A drainage basin is the area drained by a river and its tributaries.
What are inputs to a drainage basin
Inputs are the addition of water to a drainage basin in the form of precipitation. It can occur in a number of forms (rain, snow, hail, etc.)
What are stores in a drainage basin
Stores are where water is held in some part of the drainage basin for any length of time.
What are flows in a drainage basin
Flows refer to the movement/transfer of moisture in a drainage basin
What are outputs in a drainage basin
Outputs are the losses of water from a drainage basin
Define precipitation
Precipitation is any liquid or frozen water that forms in the atmosphere and falls back to the Earth.
Define evapotranspiration
Evapotranspiration refers to the combined loss from both evaporation and transpiration.
Define evaporation
Evaporation is the loss of water from the land surface and bodies of water as it transfers from a liquid to a gaseous sate (water vapour) by application of heat.
Define transpiration
Transpiration is the loss of water vapour from the stomata in the leaves of plants and trees.
Define river discharge
River discharge is the volume of water being discharged by a river.
Normally expressed as the volume of water passing a point in the river channel in a given unit of time. This is commonly the number of cubic metres per second – “cumecs”
Define interception
Interception is the precipitation which is intercepted on its way to the land surface by leaves, plants, and trees
Define soil water
Soil water is water retained within the gaps and pore spaces in the soil.
Define antecedent moisture
Antecedent moisture is the moisture retained in the soil before a rainfall event
Define surface water
Surface water is water that is stored on the surface in the form of puddles, streams, and lakes – often above impermeable surface or saturated ground
Define groundwater stores
Groundwater stores is water that has percolated downwards and is held in gaps such as cracks, joints, bedding planes, fault lines, and pore spaces in rocks in the underground aquifer.
Define channel store
Channel store is the volume of water contained in the river channel.
Define throughfall
Throughfall is precipitation that makes it directly to the land surface without being intercepted by the plant canopy. Some of this throughfall may be intercepted by leaves and this water may then flow off the leaves and drip to the ground as dripflow – some plants have developed shiny surfaces on their leaf surface to get water off the leaf surface quickly.
Define stemflow
Stemflow is the flow of water from precipitation down the stems of plants. If they reach the trunks of larger trees the water will flow down the trunks of trees, termed trunk flow, to reach the land surface.
Define overland flow
Overland flow is when water flows over the land surface… 2 types: channel flow and sheet flow
Define channel flow
Channel flow is when the water if flowing in small channels, rills, which are less than 30cm in width/depth, in a defined stream of in a river channel.
Define sheet flow
Sheet flow is normally a relatively rare event and takes place when there is a layer/sheet of water on the ground surface. It may occur in two ways:
o Firstly when there is excess overland flow, when rainfall or water arrives too quickly on the land surface and does not have enough time to infiltrate the soil.
o Secondly, it may occur when water flows onto a relatively impermeable surface, such as a clay soil.
Define infiltration
Infiltration is when water enters small openings and pores in the ground from the surface
Define percolation
Percolation is when water flows down through the soil and underlying rock pulled down by gravity
Define throughflow
Throughflow is the lateral movement in soil of infiltrated water. It occurs when water that has infiltrated the surface is retained in the soil. The water then moves horizontally through the soil, down a slope towards a river channel, usually along well-defined lines of seepage (called percolines) that have been formed in the soil or above an impermeable layer.
Define baseflow (groundwater flow)
Baseflow (groundwater flow) is water that has infiltrated and percolated into the bed rock below the soil that then moves laterally under gravity or hydrostatic pressure in a downslope direction to feed springs and river channels.
Define recharge
Recharge of the groundwater takes place when water is added to the aquifer. Recharge takes place when precipitation on the land surface exceeds evapotranspiration and water then infiltrates the ground and percolates down to the aquifer.
Define aquifer
An aquifer is a body of porous rock or sediment saturated with groundwater.
Define water table
Water table is the top of the saturated zone (TF the top of the aquifer = water table)
Define phreatic zone
Phreatic zone is a zone of permanent saturation within an aquifer.
Define spring
Spring is a place where water naturally flows out of the ground.
