hydrology flooding and water quality

Question 1

3 reasons why floods occur

Answer 1

1. excess rainfall due to cyclone activity or low-pressure systems (dunne flooding)
2. locally intense rainfall (hortonian flash flooding)
3. changed catchment conditions eg land cover, obstruction, development in flood plains

Question 2

what are 3 predictions of climate change due to an increase in CO2 related to precipitation

Answer 2

1. increase in global precipitation due to Clausis claperon equation that states warm air holds more water (7% per K)
2. strong spatial and temporal variation meaning increase in tropics and decreases in arid.
3. a higher maximum daily precipitation leading to more flooding

Question 3

3 ways climate change will impact flooding

Answer 3

1. higher probability of floods
2. change in ENSO more intense periods of rainfall
3. rise in sea level will cause bigger tides leading to compound risk of flooding

Question 4

what is a flood risk

Answer 4

combination of exposure and probability, flood risk has increased due to population growth and development which has increased exposure

Question 5

how can increasing Warragamba dam wall affect the water balance

Answer 5

might increase flooding on back end therefore shifted issue from downstream to upstream flooding. what is really needed is to have capacity for flooding downstream (storage)

Question 6

what 5 things describe a flood

Answer 6

1. frequency
2. duration
3. rates of change ie slope of limbs
4. magnitude
5. flow history

Question 7

what is the flow duration curve and how do you read the shape

Answer 7

flow probability of the occurrence of a flood level (100% being always) (1% being rare)
the flood behaviour can be measured by the shape of the curve
the flatter the curve the more regular the flows
the steeper the curve the more variable

Question 8

how can flood duration curve measure the flow regime

Answer 8

flow regime is flood timing duration and magnitiude, the before and after of the flood duration cruve and measure these effects of flow regulation

Question 9

Q01 =

Answer 9

1% chance of occurring in a year

1:100 reaccurance interval

Question 10

how to predict higher ARI

Answer 10

to get 1:100- 1:1500 data limited used linear regression etc using distributions

Question 11

what is river routing and what are the two types

Answer 11

river routing predicts the movement of water through the channel and how its impacted by storage

1. hydrological
2. hydrualic (difficult)

Question 12

what is attenuation

Answer 12

reduction of magnitude/height of flood peak as it makes downstream ie depression AND spread

Question 13

what is translation

Answer 13

change in time of flood peak as it moves downstream (shift)

Question 14

what is a linear reservoir

Answer 14

move runoff through a series of storages which delays flow as each store has a different retention time

Question 15

what is the difference between the linear storage model and the Muskingum equation

Answer 15

linear storage is only a function of outflow whereas Muskingum is a function of inflow and outflow

Question 16

what does the Muskingum and linear storage model tell us in terms of flood risk mitigation

Answer 16

more storage = less impact. it changes the decreases flood peak and increases the width

Question 17

what are the 4 types of flow that have ecological benefits

Answer 17

1. base (minimum long-term flows)
2. freshes (allows fish movement and feeding)
3. bank full (can trigger breeding)
4. over bank (wetland recharge)

Question 18

how can flooding impact dissolved oxygen

Answer 18

sudden increases in flow decreases DO and increases dissolved carbon which can lead to hypoxia which kills organisms.

Question 19

how can flooding increase P in surface water

Answer 19

P can be transported via sediment in floods, in water the absorbed P can be released due to the exchange coefficient

Question 20

how can flood effect nutrients in soil

Answer 20

flooding can activate mircobes and other biologucal acitvies, flooding can decrease soil P and N and increase soil ammonium

Question 21

how can droughts affect water quality (5 examples)

Answer 21

concentration effects 
1. salinity increases
2. turbidity decreases
3 organic c increases
4 metal increases 
5. dissolved oxygen decreases

Question 22

describe the process of eutrophication

Answer 22

an instream process where water becomes enriched with nutrients due to high turbidity, this enhances the growth of bacteria which can be toxic in high concentrations. this process is more likely in higher temps

Question 23

6 main cuases of agal blooms

Answer 23

1. low flow
2. high turbidity
3. increased salinity
4. high temperatures
5. high nurtients
6. stratification of the water column

Question 24

how do fish kills occur eg meindee lakes 2019

Answer 24

eutrophication of water causing agal blooms when these died the bacteria feeders used all the oxygen which drowned the fish (lack of O2)

Question 25

how is risk defined in relation to water quality

Answer 25

toxicity *exposure

need a load and concentration threshold

Question 26

how is toxicity defined

Answer 26

D50 threshold where 50% of pop has died (lab rats)

for humans this is D01 (1%)

Question 27

how are thresholds for toxicity defined

Answer 27

concentration ie micro seimens/cm

load ie tons/year