Low flow estimation in the UK

Question 1

How do we define the term ‘baseflow’?

Answer 1

The portion of streamflow that comes from subsurface water storage.

Question 2

Be able to explain the impact of permeability on the baseflow contribution to discharge. And explain the differences in FDC due to geology.

Answer 2

Higher permeability = higher baseflow contribution to discharge. High permeability means more infiltration and less runoff.

Question 3

What is a Flow Duration Curve (FDC)?

Answer 3

a plot that shows the percentage of time that flow in a stream is likely to equal or exceed some specified value of interest.

Question 4

What are the steps of calculating the FDC for and ungauged catchment?

Answer 4

Step 1: Sort (rank) average daily discharges for period of record from the largest value to the smallest value, involving a total of n values.

Step 2: Assign each discharge value a rank (M), starting with 1 for the largest daily discharge value.

Step 3: Calculate exceedance probability (P) as follows: P = 100 * [ M / (n + 1) ]