17. River Flows Flashcards
are droughts natural?
Yes
What does a river normally show?
A flow regime
Where do we often see high flows in the uk?
Spring melt and autumn floods
How do river reigimes vary in the Southern Hemisphere?
Large peaks in winter floods little flow in the summer
What can droughts be considered as?
A disturbance effect
Why might flow be lower in winter?
water is frozen
Why do we expect low flows?
they occur naturally, expected to happed
Can low flows be due to human activity?
Yes, diversion of water, agriculture ect
What is a drought
extreme low flow periods
Are fresh water systems resilient to drought effects?
Yes they can often bounce back
How long can droughts last?
From a few weeks to a few months
Which animals could be effected by dorught
fish, different time of year can effect damage to orgaisms
How can the type of river determine flow
perennial, temporay, bed fed, consecutive
What can excaserbate drought
human impact
Why are droughts more complex than floods
can be longer, supra seasonal, more regional effect
What is a press disturbance
a single disturbance, with one response
What is ramp disturbance
continuing disturbance overtime
Which year did we see a very dry summer followed by a wet winter?
1976
What is a supraseasonal drought
long periods over time of drought
Which type of river was more effected due to drought,
bed fed rivers
how do we decided how low a river flow is in the summer
summer low flow, qL, lowest average of severn consequtive summers
How do droughts affect river organisms
reduced depth and wetted area, reduction in current veolocity
how can reduced veolocity effect organims
could effect breathing, now given enough oxygen, less food for fishes
If there is low flow, how are sediments effected
sediments get stuck in gravels and reduced breeding fish
what do droughts commonlly bring
increased temperature, variability, changes in development rates
Can species richness increase during drought
yes, dome detrivoures may be able to find more food, intermediance disturbance theory
How can invertebrates adapt during drought conditions
breath atmospheric oxygen, adapted gills, can survive damp conditions eg wood/substrate
What can invertebrates go into during hot and dry conditions
aestivation, hibernation for warmer temperatures
Where can invertebrates go during times of low flow
hyperheos, or permanent systems, or will just leave the catchment
What is the main impact for fish during droughts
low oxygen
How can we see areas in drought
some rivers with drought will have very low fish return in upcoming years
how can filamentos algae resond to drought
can bloom during drought, negative response to high flows
How are diatoms effected by droughts
positive response to light
Which river saw a huge fish impact in 1976
the Welsh Wye
What happend with oxygen levels in 1976
huge loss of oxygen down to less than 2
What are dams built for
public water supply, irrigaiton, hydro electric, flood control
How many of the worlds rivers are regulated
2/3
where is most dam building taking place
china
Of all the rivers capable of making power in africa, how many have been regulated
100%
What impact in the construction phase are there on a river
channing from a riverine to a lacustrine environment
how many people where resettled in terms of the lake kariba dam
40-80million
What do reservoiurs result in
reduction in the variability in flow
What does the dam trap behind it
sediment, less fine material moving downstream, temperature will be more variable
If the lake stratisfied and the water is taken from the bottom of the dam what happens
water taken from anoxic conditions
what life will cling to rocks in low flows
mosses
How much of the sediment load gets past the aswan dam
12%
What will settle in a lake system
CPOM, coarse particulate organic matter
what flow does the snake river have behing it
no flow
WHat are anadromous fish
fish that return to fresh water
what is the major dam in china
three gorges
how many of the worlds largest dams are in china
over 50%
how many people have river blindness
15.5 million
what is schistosomaisis
snail fever
