Week 2 Part 2

Question 1

Manning’s equation

Answer 1

Manning’s equation estimates runoff in m3s-1.
Q = 1/n (AR2/3 S1/2)

n is the roughness coefficient (0.013 for concrete, 0.112 for weedy and sluggish).
A is the cross-sectional area (m2)
R is the hydraulic radius (given by A divided by the wetted perimeter).
S is the channel slope (m/m).

Question 2

Stream Mass Load

Answer 2

Streams carry “loads” of dissolved and particulate substances, including salt, nutrients, sediment, contaminants etc.
Load = Flow x concentration
g/s = m3/s x g/m3

Question 3

Flood Frequency

Answer 3

• Average Recurrence Interval (ARI) is a statistical estimate of the average period of year in between the occurrence of a flood of a given size or larger.
ARI = 100 means that a flood will occur once every 100 years.
• Annual Exceedance Probability (AEP) is the likelihood of a flood of a given size or larger in any year.