Environmental engineering: precipitation

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Created by: Chris

What doesn't precipitation consist of?
- Rain
- snow
- sleet
- condensatyion from fog and clouds
- waste water from cities and settlements
which is the fitting general term?
- the water given to land from the atmosphere and an environment
- the general term for the flux of water from the atmosphere to land
- the water that falls from the sky on land
the 'rainfall amount' determines what?
- the local and regional climate and hydrology, resources of water and agriculture
- the total amount of rainfall on an area in a given time
- the amount of rainfall that is needed to allow systems to perfom as ezpected
Define what rainfall intensity determines:
- specific hydrological responses, specifically floods and river discharge
- a wide range of hydrological responses, such as floods, pollution, river discharge etc
- the 'concentration' of rainfall in a area
What is the basic cause for precipitation?
- water condenses due to strong burst of heat from the sun
- warm air mixes with cool air due to wind movements, this causes the air to mix and water to condense
- rising air expands as pressure falls with height, the expansion is accompanied by cooling at a rate known as the lapse rate
More specifically, describe the convection process...
- rising moist air cools, the air can rise for many reasons
- cool air drops from heigher in the atmosphere due to gravity when enough moisture builds up in the clouds, this mixes with the hot air and it then rains
- cold air and hot air mix together, water is created in the form of clouds. This continues until the air reaches its saturation/dewpoint and it rains
describe orographic uplift:
- air is blown against a mountain range, this forces it up and into the colder air
- warm air blown across the sea, the wind chill causes the air to cool and rain
- warm air is forced up and over cold air
describe dynamic ascent:
- cold air forces itself below the warm air, this is caused by wind, it then rains
- warm air forced up and over cold air, this causes it to rain
- warm air front meets a cold air front, the two fronts attempt to force trhu each other and it rains
Which of the following key terms is incorrect?
- Saturation vapour pressure: es- when the air can hold no more water at a given time
- Dewpoint Td- the temperature below which air can hold no more water vapour
- relative humidity U- the ratio of water vapour to the saturated water vapour, expressed as a percentage
- peak amount, considering both temperature and pressure, the point where condensation should occur
In all rainfall mechanisms the following basic concept can be applied, which step does not belong?
- water vapour rises, the temperature decreases with height
- temperature eventually falls below the due point
- the air becomes saturated with water vapour
- the saturation vapour point is reached and condension begins to occur
- its begins to precipitate
- None of these
Saturation vapour pressure is strongly dependant on what?
- temperature
- moistness of air
- rate of rising
What is free convection?
- conditions in the atmosphere that allow air to continue rising
- when the demand for the air to rise is so great the dewpoint and saturation vapour pressure are ignored
- air rises so rapidly that it doesn't condense, it eventually interacts with a cloud and enlarges the cloud
Midlatitude depressions, what are frontal depressions?
- the worlds rarest rainfall system, when to fronts of warm air meet. they combine and rise, they then cool and cause very heavy rain
- when dynamic ascent occurs, warm air forced over cold air, this then rains
- when orographic uplit occurs and upon rising comes into contact with a cold body of air, this then causes rain
What does topography have to do with rainfall? What is wrong?
- seeder and feeder mechanisms, rain falls from a high cloud thru another cloud and grow in size by taking moisture from the feeder cloud
- clouds gather round mountains, because orographic uplift forces warm air over cold air
- clouds get bigger becuase they eat each other
- orographic uplift cuases rainfall
- mountains allow the clouds together and incubate, generating heat and then condensing
It is important to be able to estimate rainfall. Which is not a method for doing this?
- Thiessens polygons
- isoheytal method
- blockmark method
- arithmetic method
describe the arithmetric mean method:
- take means from rain gauges, rain gauges must be uniformly distributed or there is not alot of spatial variability
- all the rainfall readings from rain gauges are gathered and plotted on maps, areas of rainfall can then be predicted
- river and groundwater discharges are observed this gives and idea of the amount of rainfall that has occured
describe thiessen polygons:
- works on the idea that the estimated rainfall at any point is the same as that of the nearest raingauge, the catchment is divided into sectors around the rain guages, these sectors are call thiessen polygons
- polygons are marked on a map, rainfall from rain gauges is then recorded. rain gauge locations are marked on the map. By using a mathematical model the rainfall in each sector can then be calcuated.
- rainfall is described in polygon sizes, this allows the intensity and rainfall amount to be easily observed
desribe the isohyetal method:
- rainfall calculated by taking means of rainfall at different heights, polygons are again used to define the areas
- contours of equal rainfall depth are drawn, isoheyts, rainfall is calculated by taking mean of ereas between the isoheyts
- rainfall is determined by considering the entire rainfall over a catchment, and dividing the catchment into areas. The catchments are decided by physiographic and topographic features. This allows raibnfall to be estiated
How is rainfall frequency often described?
- by its return period, chance of rainfall
- the area and scale of rainfall
- how often rainfall occurs in a given time
a serious event, such as a flood is described in what manner?
- a T-year event, having a return period of T-years
- described regarding the previous record, this is described in a decimal system, much like earthquakes
- the scale of an event, described by the area and damage caused by the event
What is total precipitation?
- sum of all rainfall
- sum of all liquid collected
- the sum of all liquid collected, including groundwater
Why is siting of a rain gauge important? Which description is most appropriate?
- To prevent errors and damage
- to prevent damage and incorrect readings
- to prevent theft and vandalsim
There are many types of gauges... describe the pit gauge and the screens... which is wrong
- pit guages-prevent insplahs
- screens prtect from winds
- snow can be a problem so overcome by protecting with hanging strips
- modern pits are protected from the wind, but can still be subject to snow and dirt problems
- the UK met raingauage includes solar panels to keep the water warm and discourage freezing
- pits can become overgrown with vedgetation
Deescribe the tipping bucket raingauge: which is incorrect
- very rare system
- counts rainfall by buckets and then emptying them once measured
- often used with a datalogger
Measuring snow can be a problem as it is easily blopwn by the wind. Normally a gauge is used, but this may become overcapped if a screen hasn't succesfully protected them. In this case, what method can be used?
- take the depth of the snow and assume this to be 1/3 of the equivilant rainfall
- take the depth of the snow and assume this to be 1/4 of the equivilant rainfall
- gather some samples of the snow and weigh, gather an approximate value for the amount of snow on the ground
- measure the snow depth, weight, snow melt rate and calculate the data
Measuring evaporation is difficult, it can be done as...
- loss of liquid or gain of water vapour in the atmosphere
- loss of liquid from lakes and water beds
- the difference in discharge and rainfall
Measureing water loss thru a catchment... which of the follwoing is incorrect
- E=P-Q
- assumes no loss to groundwater (big assumption)
- subject to large errors
- expensive and only reliable on small simple catchments
- calculated by measuring - precipitaion, run off and soil moisture
- despite simplicity, considers topographic and physiographic features
measuring evaporation thru soil moisture change which is untrue?
- measure the wieght of moist soil and dry soil, the difference is the water mass in the soil
- evaporation and soil moisture can vary spatially
- considers water begin added to the soil via groundwater flow
Another method for calculation the evaporation is the Bowen ratio method. Which best describes this?
- rate of infiltration vs rate of rainfall = evaporation
- Energy in vs energy out, difference = evaporation
- preciptation - discharge = evapoatrion
The eddy correlation method is a method for calculating evaporation. which doesnt belong
- rate of air rise
- vertical components of wind
- humidity
The pennman method is sophiscticated, which of the following is not considered with it?
- Psychrometric constant
- aerodynamic term
- efficeincy factors
- heat budget
- dew point
- slope of temperature vs saturation vapour pressure
Evaporation pans are a cheap and simple way of measuring evaporation, which best describes them?
- subject to errors in readings and water contamination from unwanted sources, cheap and easy to maintain
- widely used and old, easy to maintain and cheap, the water in the pan is the depth measured, this allows evporatino to be calcuated
- usuaully buried to protect from animals interfering with the data
Measuring soil moisture is important, which of the following is not a method for doing this?
- gravimetric method
- conduction probe
- neutron probe
- capacitance probe
- time domaiin reflectrometry
- soil tension
Which best describes the gravimetric method?
- destructive, take a soil sample, store so that no water evaporaters and weight, dry the sample and re weigh it. this gives the water weight
- destructive, bake the soil sample and compare it to a freshly rmoved sample of the same size
- destrcutive, collect a soil sample, allow the water to drip out of the sample under pressure and measure this amount
Which best describes the neutron probe method?
- jam the probe into the ground, the neutrons will or won't bond with the h2o molecules depending on the presence of water, this allows the cobntent to be known
- jam the end of the probe into the ground, the returning neutrons give the soild moisture as the two are proportional
- insert the probe into the bored ground hole and activate, the returning scateered neutrons and proportional to soil moisture
Which best describes the capacitance probe?
- cheaper and safer then neutron probe, meausres the dielectric constant of the soil, this allows the water content to be determined
- much alike the neutron probe but uses electrons instead
- passes and electronic circuit thru the soild from priobe to probe, the resitance of the circuit allows the water content to be valued
Describe the time domain reflectrometry method:
- electronically based techniques meausrung dielectric constant, doesn't measure very deep, but quick and simply requres the probe to be pushed into the ground
- several probes communicate sending signals to each other, the strength of these siganls allow the moisture content to be determined
- takes time to set up, very expensive, but very accurate, the electrical resitance of the soil is measured by a circuit inside the probe
Which the electyrical methods what is it important to remember?
- moisture content is proportional to electrical resistance
- electrical property is proportional to soil moisture
- electrical property is proportional to viods in the soil
Which best describes the soil tension method?
- as moisture changes so does the tension, tension measured using tensiometers and gypsum blocks, soil moisture can be calculated from this
- tension before the soil breaks allows the weight to be determined, the dry weight is then compared. this allows the water content to be determined
- gypsum blocks and tensiometers used to meausre the soil moisture by increasing tension on the soil, if the soil remains unchanged then the soil holds water
in environmental engineering, which is not a factor of key iomportance?
- understanfd the strengths and weaknesses of the instruments
- accuracy of data dependant on quality and nature of the used instruments
- data is vital for understanding
- because data in this area is never exact, errors are acceptable

Environmental engineering: precipitation

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