hydrology runoff and erosion

Question 1

what is effective rainfall and when does it happen

Answer 1

precipitation - interception (held by vegetation leaf storage and then evaporated). losses can be between 6-80%. this is mainly when there is a low rainfall event

Question 2

how do you measure effective rainfall

Answer 2

mm through fall (non intercepted open rainfall) - mm stem flow (intercepted on base of tree/vegetation)

Question 3

what is runoff

Answer 3

effective rainfall - infiltration

Question 4

what is groundwater

Answer 4

deep soil layer that is saturated with water in all pores

Question 5

what is a runoff ratio

Answer 5

it measures the fraction of P that becomes runoff

it is a function of soil and cover (curve number)

Question 6

does Australia have a high runoff ratio

Answer 6

low ratio (8%) compared to global average 35%

Question 7

what is hortonian runoff

Answer 7

infiltration limited runoff occurs when there is quick high-intensity rainfall that exceeds the hydraulic conductivity of the soil. this is more likely to occur on a hill slope

Question 8

what is dunne runoff

Answer 8

saturated/storage limited runoff occurs when there is steady high rainfall that completely saturates soil and water can no longer infiltrate. this is more likely to occur on the lower part of the landscape

Question 9

what is a curve number

Answer 9

range (1-100 less to more runoff) parameter to predict the amount of runoff from the amount of precipitation.
refers to hydraulic condition (amount of cover) and hydrological conductivity number (soil group)

Question 10

limitations of CN and how it is overcome

Answer 10

good first estimate however limitations include unclear data source, not good for short term averages, variation due to moisture and can be adjusted for these variations

Question 11

what is the hydrograph

Answer 11

a plot of discharge/runoff/flow over time

Question 12

what is a quick flow

Answer 12

surface flow runoff can be hortonian dunne runoff, determines peaks in hydrograph heavily influenced by precipitation

Question 13

what is slow flow

Answer 13

water that infiltrates into soil and passes through groundwater runoff into the stream

Question 14

how does a well work

Answer 14

well inserted into an aquifer that is under a confining layer and a lot of fo pressure it releases water by releasing pressure.

Question 15

how does groundwater streamflow input vary with climate (eg humid vs arid)

Answer 15

input can vary from 0-70%.
in humid systems, it is a gaining system meaning the rain is higher than ET therefore continuous draining of groundwater
in arid systems it is a losing system meaning ET is higher than rainfall input therefore groundwater does not flow into the river and can actually be recharged by stream inflows

Question 16

what is an ephemeral river

Answer 16

a dry river system’s only inputs are rainwater no groundwater. characterized by a hydrograph with high peaks only, periods of dry

Question 17

what is a perennial river

Answer 17

a river system with continuous feeding from groundwater with the addition of quick flow, never dry

Question 18

how do measure the contribution of slow and quick flow

Answer 18

1 way is a chemical method, eg salinity is diluted by quick flow input and concentrated by groundwater input, sediments and pollutants carried eg P travels with quick flow and concentration increases with flow peaks

Question 19

what are the 2 ways pollutants can get into the stream

Answer 19

1. dissolution in soluable form eg inorganic N

2. detatchment in suspended form eg sediments and attatched

Question 20

what can erosion cause (3)

Answer 20

1. lack of soil strengh ie more erosion
2. loss of carbon and ferility (thinning)
3. pollution of surface water

Question 21

what is Rusle

Answer 21

E = rainfall erosivity (R) X resistance of environment 
K soil
SL topography 
C plant cover 
P erosion control

Question 22

what is the estimated erosion rate in australia?

Answer 22

average 4 t/ha/year however agricultural areas may be 4-33 higher than natural rate due to poor conservation practices

Question 23

how can erosion impact the stream 3 ways

Answer 23

1. suspended clays increases turbidity decreases O and detrimental to aquatic life
2. sand and sediments can fill water storage
3. particles can transport HM and pollutants causes off site problems

Question 24

name two processes which has increases salinity in AUS

Answer 24

1. clearing of native vegetation to shallow root crops changes the hydrological balance and raises ground water
2. use of irrigation rising ground water table

Question 25

approx how much rainfall is evaporated and how does this contribute to salinity

Answer 25

~90%, salt is left behind however this is a natural part fo teh landscape in equilibrium until humans changed water balance