Water 1 Catchments Flashcards
What is a digital elevation model (DEM)?
A model that shows the elevation of each pixel.
What is GIS?
a Geographical Information System.
What is topology?
The pattern of channel networks
what is geomorphology?
the origin of landscape and channels.
what is the drainage density?
the abundance of channels - how many channels there are in an area.
what is the equation for drainage density?
The length of all channels/ area
Ltot/ A
when do you get high drainage density?
areas with low soil conductivity and agricultural zones.
what does the dendritic pattern look like?
a tree
on what type of soil can you find a dendritic channel network?
homogeneous geological formation, either soil or rock. The river network has many tributaries.
What does a radial pattern look like?
When all the streams flow away from a central point.
Where can you find a radial channel pattern?
on mountains or volcanoes.
What does the trellis pattern look like?
Most complicated - a straight fiver flowing down with channel networks between parallel resistant ridges.
Where can you find the trellis pattern?
areas with folds in the earth crust.
What does the parallel channel network pattern look like?
lots of parallel rivers flowing straight down.
where do you find the parallel river network?
on steep slopes, where water flows down the fast. Often on harder rock.
what is the headwater?
the upstream part of a catchment.
how does the headwater behave differently from the main part of the river?
it often runs dry and overflows. The chemistry is determined by only natural conditions.
what is the source?
a point upstream in the river where it starts.
What is order numbering?
when you give orders to parts of the river - you start at the sources and work your way towards the outlet.
What are the most common losses of water in a system?
evapotranspiration (ET) or effective precipitation.
what is effective precipitation?
the precipitation that is no tintercepted or used for evapotranspiration but instead flows through a river.
what are the three most important fluxes in a catchment?
discharge, precipitation, evapotranspiraiton.
what are the forms of precipitation?
rain, snow, hail, fog, dew.
what are the two types of precipitaiton?
stratiform (or frontal)
convective
what is stratiform precipitation?
wide and relatively thin, homogeneous grey/ white.
prolonged periods of low precipitation intensity over large areas.
what is convective precipitation?
short term, intensive precipiation in local areas.
clouds are small and towering, vertical structures formed by upwards movement of water droplets.
what causes spatial variability in precipitation?
size and shape of clouds, downwind of water bodies/ rainforests and wetlands.
why is precipitation high on the windward side of mountains?
clouds are forced upwards, where air is cooler and particles condense.
what is the rain shadow?
the smaller quantity of precipitation on the leeward side of a mountain.
some common vocabulary about rain we use in every day speech?
precipitation events - showers and storms
dry spells.
what is a rain gauge?
a measuring device which collects precipitation in a reservoir. A tipping bucket gauge tips when a certain amount of water is held.
what can a weather radar sense?
location and severity of precipitation events.
evaporation, specific latent heat of vaporization, shortwave incoming radiation, albedo effect.
yes you know this.
What does total evapotranspiration account for?
transpiration, interception evaporation, soil evaporation, open water evaporation,
interception transpiration
evaporation of precipitation which falls on vegetation and evaporates directly
soil evaportation
evaporation from moist soil
open water evaporation
evaporation from lakes.
factors that control evapotranspiration
meteorological factors: temp, air humidity, high wind speeds
land use: vegetation
soil moisture
what is an evaporation pan?
a container with water and you measure how much water evaporates
what is a lysimeter
container filled with soil and local vegetation. The mass is recorded and with the change, evapotranspiration is calculated. It is $$$$$$
reference evapotranspiration
ET that could take place for actual meteorological conditions but with grass (not actual vegetation)
potential evapotranspiration
actual meteorological condtitions and local vegetation.
what is the equation for potential evapotranspiration?
ETref x crop factor
what is the crop factor?
a coefficient that tells you what percentage evaporates depending on the type of vegetation.
rainfall-runoff processes
the processes that determine the route taken from precipitation to surface water network.
interception
storage of precipitation water on leaves, stems, and branches of vegetation
throughfall
rainwater that is intercepted but cannot be stored in vegetation
stemflow
water that is intercepted but moves towards soil
interception capacity
maximum volume of water which the vegetation can intercept and store. This depends on the vegetation type
infiltration
downward movement of water from soil surface through the soil
what does infiltration determine?
the distribution of precipitation between storage on the surface and surface run off.
infiltration speed?
the speed at which water moves through the soil. m cubed per m aquared per time.
infiltration capacity
maximum possible infiltration speed.
how are precipitation intensity and infiltration capacity related?
when precipitation intensity is below infiltration capacity, all rain infiltrates. Otherwise, it stays on the surface.
soil compaction
small soil particles are transported to and deposited on the soil surface, closing pores and hampering infiltration.
On what does infiltration capacity depend?
land cover, soil type, wetness.
when does infiltration capacity decrease?
during a rainfall event, the topsoil becomes wetter
hydrophobic
hehe scared of water i.e. impermeable/ water resistant.
soil matrix
the arrangement of soil particles
pore space
area between soil particles that can fill with air or water
porosity/ pore fraction
ratio between pore space to total volume.
saturated zone of groundwater table
below groundwater table
unsaturated zone
above groundwater table
soil moisture/ water
water in the unsaturated zone above the groundwater table
capillary fringe
the zone above the groundwater table which is completely saturated. This is a fairly thin zone.
percolation
the flow of infiltrated water into the saturated zone due to gravity.
capillary rise
when the groundwater table is shallow, water is sucked upwards by a negative pressure caused by evapotranspiration in the topsoil.
macropores
cracks in clay soils or rocks and animal burrows. These speed up the process of percolation.
what are the reasons for lack of infiltration
impermeable land surface
infiltration excess
saturation excess
seepage
what is saturation excess?
All the soil is already saturated and further storage of water is no longer possible.
Depression storage
when excess water that can not infiltrate is stored in ponds in relatively low lying areas.
surface run off
water which flows overland during and just after a rain shower. This water ends up in channels
saturation excess overland flow
surface run off flows overland when the soil is wet (usually close to a riveR)
infiltration excess overland flow
surface run off due to high precipitation intensity.
interflow
water infiltrates but cannot percolate due to low soil permeability close to the surface. The soil above this becomes saturated and the water follows teh slope of this semi-permeable layer. ‘This only occurs during and just after a rain shower as small water layer empties quickly.
drainage
groundwater flows towards the surface water of a river. This is not visible to the eye.
upward seepage
water enters an area via deeper soil layers and subsequently moves upward towards soil surface.
downward seepage
water infiltrates in teh soil and is transported to another area via groundwater flow. Also infiltration.
weirs
strucutres that block water flow
brackish seepage
the upwelling of deep salty groundwater.
salinization
the water becomes salty
groundwater storage
the groundwater table rises, saturating part of the unsaturated zone and storing water in the soil. This happens after a rainfall event.
specific storage
volume of water in the soil per unit of area. It is increased by infiltrating rain water percolating and decreaseed by evaporation.
storativity
(storage coefficient) the ration between the change in specific storage and the change in groundwater level.
equation for storage coefficient
mew = delta S/ delta h
= specific storage/ change in height of groundwater level.
field capacity
the wetness of the upper soil layer when the soil has lost its surplus of water to the groundwater after a wet period.
piezometer
(groundwater tube) measures the groundwater level.
surface water systems that can store water?
river, brook, floodplains, natural and man-made lakes, retention basins, reservoirs.
snow water equivalent
the amount of water there is in a certain volume of snow
runoff (NOT surface runoff)
water flows through or over the ground to channels that drain the catchment.
streamflow
channels transport water out of catchment
formula for discharge
Q=va
formula for velocity
v= C sqrt(S A/P)
S = slope
A = area
P - wetted perimeter
Q=AC sqrt(slope *A/P)
stationary flow
water flow in an open channel does not change in time
uniform flow
water flow in an open channel does not change in space
Chezy constant
measure of the conductivity of the channel bed and banks
hydraulic radius
the ratio between the cross sectional area and the wetted perimeter
ADCP
Acoustic Doppler Current Profiler
To measure discharge, sound waves are reflected off transported sediment and it’s super expensive.
stilling wells
used to measure water level continuously and thus discharge. Vertical tubes connected to the river using horizontal tubes.
rating curve, Q-h-relation, stage discharge relaiton
converts water level to discharge. accuracy is helped by a weir or flume.
hydrograph
discharge time series, providing informationo about the behaviour of a catchment
discharge dynamics
temporal variability of discharge
attenuation
reduction of precipitation signal due to the catchment.
mixed rivers
fed by snow and rain.
baseflow
the minimum discharge. Mainly originates from groundwater in the catchment. It is a flow that responds very slowly to changes.
recession
the slow reduction of baseflow during the drier season.
perennial streams
carry water year-round
ephermeral streams
streams that run dry part of the year.
quickflow
the fast reaction in discharge due to events in the catchment.
direct runoff
other term for quickflow
why is quickflow so quick?
it flows over ground and therefore has a path with less resistance. Floods and inundations are caused by quickflow
which factors increase the probability of quickflow?
steep topography
low infiltration capacity
high drainage density
hydrophobic soil
high precipitation intensity
uneven precipitation distribution (local soil saturation occurs)
wet initial conditions
rain on snow
concentration time
time taken for surface water at the most upstream point to reach the catchment outlet.
response time
time difference between a rainfall event and the resulting discharge peak. Also called lag time.
width function of a channel network
plot of the number of network links as a function of distance to the catchment.
what are retention basins used for?
store water during flood peaks and release it when the river water levels drop.
water budget/ water balance.
total amount of water which moves in and out of a catchment in a period of time.
what is the really long equation for water balance?
P - ET ± Q ± Us ± Ul ± X = delta S
what do all the letters in the water balance equation stand for?
P - precipitation
ET - evapotranspiration
Q - inflow minus outflow of surface waters
Us - upward (+ve) or downward (-ve) seepage
Ul - lateral inflow (+ve) or outflow (-ve) of horizontal groundwater.
X - additional sources
delta S - storage change
What is the simplified equation for water balance?
P - ET - Q = delta S
balance area
like the catchment of a channel. The boundaries are chosen so that the inflows and outflows are easiest to measure.
balance period
the time through which the water balance is measured. Usually, an entire year is used.
when does the hydrological year start in Netherlands?
April 1st as soil is at field capacity. It depends on the country.
what is the equaiton for residence time for water in a lake when inflow = outflow
Tr = V/ Qin = V/ Qout
Tr - residence time
V - volume of lake
Q in/ out - sum of all fluxes into and out of lake.
