Surface Hyrology Flashcards
(43 cards)
What does surface hydrology allow us to describe?
The fate of a water droplet once it hits the earth (identify –> Characterise –> quantify
How much water is used per person per day in the UK?
140 Litres/day
How much rainfall does London recieve in a year?
650mm/year
What can the water availability in London be described as?
Water scarce
What is the average volumetric flow rate of the Thame?
65 cubic meters a second
How much water is needed to produce 1 kg of beef
15,000L
What is the main assumption in hydrology for the global water cycle?
The total amount of water on Earth is constant
What is the error of a ‘good’ measurement in surface hydrology?
5-10%
What is the easiest flux to measure in the hydrological cycle? Why?
River Discharge
One-Dimensional problem, all the discharge flows in a distinct channel, dimensions of channel can be measured.
Why are fluxes such as precipitation and evaporation so difficult to measure?
They are two-dimensional problems, measuring at specific points is accurate and straight forward, however, spacial averages are much more challenging.
Groundwater and soils have similair limitations but can also become three-dimensional problems
What is the direct method for meauring the volumetric flow rate (m^3 s^{-1})?
Q = change in Volume/ Change in time = Delta V/ Delta T
What is the indirect method for meauring the volumetric flow rate (m^3 s^{-1})?
Integrate the velocity over the cross sectional area (multiply the average velocity by the cross sectional area Q =UA (Y1 fluids))
Lecture 1 slide 19/39
Name one method for caculating the mean flow rate in a river.
Mean-section method
What are some ways of measuring the velocity profile in a river?
- Valeport propellor meter (density of data is very important)
- Acoustic Doppler Velocity Profilers
- Preasure transducer (automatic - multiple data points)
- Staff gauge (easy to check at regular intervals)
What measurement does the water stage give you?
The water height
How are the water stage and the discharge related?
Stage-Discharge relationship
- Often represented graphically
- Formed using manual volumetric flow rate measurements at different water stages
- result must be read off graph
Lecture 1 slide 24/39
What factors affect the stage discharge relationship?
- Vegetation cycles
- Ice cover
- Erosion or sedimentation of channel
What civil engineering structures can allow a reliable stage discharge relationship to be defined?
Weirs and flumes
Weir: rise in the channel bed, creates a sub-critical upstream flow and super-critical downstream flow. Flow over the top of the Weir is critical - allows a reliable relationship to form
Flume: induces a critical flow by reducing the width of a section of the river (sometimes raises the bed). Reduces the risk of the sedimentation behind the control. Critical flow allows for reliable relationship
Lecture 1 slides 26–> 28 /39
What are the main types of weir?
- Sharp-crested
- Broad-crested
- Crump weirs
- Special Weirs
Lecture 1 slides 26 &27/39
Why does the South Tyne have a larger normalized river flow than the River Kennet?
The River Kennet has a permeable chalk layer, water flows through into the aquifer, and so the overall flow rate is lower
What can be said about the dominant flow rate in a river? What does this say about the distribution of the flow rate when plotted on a histogram?
The low flow dominates.
This results in a positively skewed flowrate when plotted on a histogram
Lecture 1 slide 31/39
How do you determine the start of the stormflow?
The local minima after the start of precipitation
How do you find the time lag?
T_L = time@max flow - time @ max precip
How do you find the end of the stormflow
time at end of the preciptiation + the time lag*N
N is usually == 4
