1. Hydrology and Fluvial Geomorphology Flashcards
What is hydrology
the scientific study of the properties, distribution and effects of water on the Earth’s surface, in the soil and underlying rocks and in the atmosphere
Hydrological cycle
The continous process by which water is circulated throughout the Earth and its atmosphere
Open system
A region seperated from its surroundings by a boundary that admits a transfer of matter or energy across it
Closed system
a region that is isolated from its surroundings by a boundary that admits no transfer of matter or energy across it
Input
the addition of matter, energy or information into a system
Output
the movement of matter, energy or information out of a system
Watershed
a ridge of high land dividing two areas that are drained by different river systems
Drainage basin
an area drained by a river system, including all areas that gather precipitation and direct it to a particular stream, stream system, lake or other body of water
catchment area
area of land bounded by watersheds draining into a river, basin or resevoir
Precipitation
conversion and transfer of moisture in the atmosphere to the land
Interception
the capture of precipitation by the plant canopy and its subsequent return to the atmosphere via evaporation or sublimation
Throughfall
the process of precipitation passing through the plant canopy and landing on the ground
Stemflow
the process that directs precipitation down plant branches and stems into the ground
Overland flow, surface runoff
When water flows over the surface of the ground
Discharge
the volume of water passing through a certain point of a river at a given time
Infiltration
the absorption and downward movement of water into the soil layer
Infiltration capacity
the maximum rate at which rain can be absorbed by soil in a given condition
Throughflow
the flow of water through soil or regolith via natural pipelines and percolines
Baseflow
the normal level of a river fed by groundwater seeping into the bed of the river
Groundwater
water stored underground in permeable rock, e.g limestone
Recharge
The refilling of groundwater levels following abstraction
Water table
the upper layer of permanently saturated pore spaces in the groundwater zone
spring
a natural flow of water from rock or soil onto the land surface or into a body of water
Evaporation
The process by which liquid is converted into a Gaseous state
Transpiration
the process by which water vapour escapes from a living plant, principally the leaves and enters the atmosphere
evapotranspiration
the combined losses of evaporation and transpiration
Aquifers
rocks that contain significant quantities of water
soil moisture
the subsurface water in the soil
field capacity
the amount of water held in the soil after the excess water drains away
Gauging station
a site on a body of water where observations and data are obtained
Infiltration excess flow, Hortonian flow
when water enters a soil system faster than the soil can absorb or move it
River regime
Annual variation in the flow of a river
Storm hydrograph, flood hydrograph
Graph that shows how a drainage basin responds to a period of rainfall
Time lag
the time between the height of the storm and the maximum flow in the river
Rising limb
the section of the storm hydrograph that shows how quickly the waters begin to rise
falling limb
section of the storm hydrograph that shows the speed with which the water level in the river declines after the peak
Peak Flow
Maximum discharge of the river as a result of the storm
Quickflow
the water that gets into the river as a result of overland runoff
Drainage density
the total length of all the streams and rivers in a drainage basin divided by the total area of the drainage basin
antecedent moisture
the amount of moisture in the soil before a rainfall event
porosity
the fraction of open space in a rock
permeability
measure of the ability of soil, sediments and rock to transport water horizontally and vertically
Load capacity
the largest amount of materiel that a stream can carry
load competence
the diameter of the largest partical that can be carried
critical erosion velocity
the lowest velocity at which grains of a given size can be moved
laminar flow
when water flows in sheets or lamina parallel to the channel bed
turbulent flow
a series of fast eddies and vertical movemnt caused by the roughness of the channel
helicoidal flow
the corkscrewing spiral flow within a river responsible for the formation of meanders
abrasion/corrasion
the physical wearing away of the river channel by the abrasive action of the load carried by the river
solution
the chemical dissolving of particles carried by a river
Hydraulic action
the ability of moving water to dislodge and transport materiels from its bed and banks
transportation
the movement of a rivers load downstream, carried by the force of the river
traction
the rolling or sliding of larger particle on the riverbed by the rivers current
suspension
when fine, smaller particles are carried downstream by a rivers current without making contact with the bed
saltation
when medium sized particles bounce along the riverbed as they are too heavy to be entirely suspended
cavitation
a process of intense erosion due to the surface collapse of airbubbles found in constricted, rapid flows of water
deposition velocity
the velocity at which the river can no longer support a load of a given size and thus begins to deposit it on the river bed
bed load
particles that are transported along the riverbed by rolling sliding or saltation
solute load
the dissolved particles which make up part of a rivers load
floodplain
flat area found alongside the stream channel that is prone to flooding and recieves alluvium deposits when flooding occurs
braiding
when a river channel is divided by reoccuring islands or bars formed by deposition
eyot/ait
small island in a river or lake
meander
a significant bend in a sinous river
overbankful discharge
the overflowing of a river channel caused by too much water flowing for the channel to contain it all
plunge pool
a pool at the foot of a waterfall formed by the erosion of the riverbed
riffle
rocky sandbar lying below the surface of a waterway
rapids
part of a river where the current is very rough and turbulent due to the bumpy nature of the riverbed.
undercutting
a steep slope created on the outside of a meander bend by erosion
slip off slope
the slope on the inside of the meander bend formed by the deposition of the rivers load in slower flowing water
waterfall
cascade of falling water from a height formed where the river erodes a band of softer rock after flowing over an area of more resistant materiel
gorge
steep sided rocky valley formed by the retreat of a waterfall upstream
levee
river embankments build by the deposition of a river as it floods
bluff
a steep cliff of rock bordering a river or its floodplain
ox bow lake
a meander that has been cut off from the rest of the river to form a small lake
alluvial fan
fan shaped deposit of sediments found where the erosional stream channels meet the valley floor, depositing the stream load
delta
a river mouth choked with sediment causing the main channel to split into smaller branching channels or distributaries
recurrence interval
the average time period that seperates natural events
hard engineering
the controlling of the natural processes of a river by the construction of manmade structures such as dams
soft engineering
use of ecological principles and practices (afforestation) to reduce the effects of a rivers natural processes in a manner that preserves the natural environment
Dam
barrier constructed across a waterway to constrict its flow
Levees(artifical)
man made embankments to prevent a river from overflowing
How does groundwater recharge occur
Infiltration of precipitation
Seepage of water through the banks and beds of surface water bodies
Groundwater leakage and inflow from adjacent rocks and aquifers
What influences the river regime
Amount and nature of precipitation Local rocks, porosity and permeability shape or morphology of the drainage basin area soil cover and soil type vegetation cover and type
How does precipitation type and intensity influence the flood hydrograph
Intensive rainfall produces overland flow and a steep rising limb and high peak flow. Low intensity rainfall is likely to slowly infiltrate into the soil and percolate, increasing time lag and reducing peak flow. Rapid melting of snow can lead to high overland flow and peak flows
How does temperature and evapotranspiration influence the flood hydrograph
High temperatures lead to more evaporation, warm air can hold more water so the potential for high peak flows in warm areas are raised
How does antecedent moisture influence the flood hydrograph
If the ground is near saturation, additional rainfall will produce overland flow, high peak flow and short time lag
How does drainage basin and shape influence the flood hydrograph
Smaller drainage basins respond quickly to rainfall conditions. Circular drainage basins respond more quickly than linear drainage basins
How does drainage density influence the flood hydrograph
High drainage density e,g urban areas with sewers respond very quickly. Short time lag
How does porosity and impermeability of soils influence the flood hydrograph
Impermeabililty causes water to flow over land. Causes greater peak flows
Urban areas have large areas of impermeable surfaces
Rocks like chalk or gravel are permeable and allow water to inflitrate and percolate. Reduces peak flow and increases time lag
How do slopes influence the flood hydrograph
Steeper slopes create more overland flow, shorter time lags and higher peak flows
How does vegetation type influence the flood hydrograph
Broad leafed vegetation intercept more rainfall, especially in summer, and so reduce the amount of overland flow, peak flow and increases time lag. In winter, decidous trees lose their leaves and intercept less
How does land use influence the flood hydrograph
Land use that creates impermeable surfaces or reduces vegetation cover, reduces interception and increases overland flow. However, if more drainage channels are built, the water is carried to rivers very quickly. This increases peak flow and reduces time lag
Examples of flows
rainfall
rivers
evaporation
surface runoff
Examples of stores
Resevoirs Ice Snow Clouds Groundwater Vegetation
Degradation
The lowering of a riverbed over a period of time
Aggradation
Build-up of the level of any land srface by the deposition of sediment
How are pools and riffles formed
Turbulence cause the deposition of coarse sediments at high velocity points
