hydrology runoff and erosion Flashcards
what is effective rainfall and when does it happen
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
how do you measure effective rainfall
mm through fall (non intercepted open rainfall) - mm stem flow (intercepted on base of tree/vegetation)
what is runoff
effective rainfall - infiltration
what is groundwater
deep soil layer that is saturated with water in all pores
what is a runoff ratio
it measures the fraction of P that becomes runoff
it is a function of soil and cover (curve number)
does Australia have a high runoff ratio
low ratio (8%) compared to global average 35%
what is hortonian runoff
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
what is dunne runoff
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
what is a curve number
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)
limitations of CN and how it is overcome
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
what is the hydrograph
a plot of discharge/runoff/flow over time
what is a quick flow
surface flow runoff can be hortonian dunne runoff, determines peaks in hydrograph heavily influenced by precipitation
what is slow flow
water that infiltrates into soil and passes through groundwater runoff into the stream
how does a well work
well inserted into an aquifer that is under a confining layer and a lot of fo pressure it releases water by releasing pressure.
how does groundwater streamflow input vary with climate (eg humid vs arid)
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
what is an ephemeral river
a dry river system’s only inputs are rainwater no groundwater. characterized by a hydrograph with high peaks only, periods of dry
what is a perennial river
a river system with continuous feeding from groundwater with the addition of quick flow, never dry
how do measure the contribution of slow and quick flow
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
what are the 2 ways pollutants can get into the stream
- dissolution in soluable form eg inorganic N
2. detatchment in suspended form eg sediments and attatched
what can erosion cause (3)
- lack of soil strengh ie more erosion
- loss of carbon and ferility (thinning)
- pollution of surface water
what is Rusle
E = rainfall erosivity (R) X resistance of environment K soil SL topography C plant cover P erosion control
what is the estimated erosion rate in australia?
average 4 t/ha/year however agricultural areas may be 4-33 higher than natural rate due to poor conservation practices
how can erosion impact the stream 3 ways
- suspended clays increases turbidity decreases O and detrimental to aquatic life
- sand and sediments can fill water storage
- particles can transport HM and pollutants causes off site problems
name two processes which has increases salinity in AUS
- clearing of native vegetation to shallow root crops changes the hydrological balance and raises ground water
- use of irrigation rising ground water table
approx how much rainfall is evaporated and how does this contribute to salinity
~90%, salt is left behind however this is a natural part fo teh landscape in equilibrium until humans changed water balance
