Q1) Regarding the EMOS RH and precipitation data for September 2223, 2021:
a. Deconstruct the precipitation events into two events anchored around
the peak values of the 5-min precipitation rate. Complete the table below
as follows [12 marks]:
Name
Duration (hrs)
(i) 04:40
(Sep 22)
(ii) 08:00
(Sep 23)
04:40 -08:10=
3 hrs, 30 mins
8:00 – 00:10 =
4hrs 10 mins
Peak 5-min
precipitation
rate (mm/hr)
13 mm/hr
Accumulated
Precipitation
(mm)
11 mm
34 mm/hr
26 mm
Precipitation
Efficiency
(mm/hr)
22/7 =
3.14mm/hr
6.24 mm/hr
b) Based upon the data in the Question 1(a) table, compare and/or
contrast these two precipitation events.
According to the table, we can observe that 8:00pm (EST) event lasts
longer than the former.
The second event is much more intense as compared to the first.
c) Precipitation events can be characterized in terms of their intensity,
duration, and areal coverage
1(a) table provides the data for two of these three dimensions.
Add the data for the two events (from Question 1(a) table) to the Figure 1
plot - indicate roughly where on the Figure 1 axes the duration and peak
precipitation rate plot.
ii. Based upon the Question 1(c)(i) result, is the precipitation style more
consistent with stratiform of cumuliform precipitation? Why? [2 marks]
A) (i) 4:40 – This event signifies a stratiform style of precipitation. It has a lower
intensity and it’s more widespread.
(ii) 8:00 - This event signifies cumuliform style of precipitation. This is because it has a
very high intensity and is comparatively less widespread. It lasts for a longer time.
iii. Based upon the question 1(c)(i) and 1(c)(ii) results, state the type of
storm most consistent with this precipitation event. [2 marks]
A) Since (i) is a stratiform, it is likely to be a less severe thunderstorm and a warm
front.
Similarly, (ii) is cumuliform, it is more likely to be an intense thunderstorm and a cold
front.
2. Regarding the hydrometric data here:
a. By adjusting the date parameters, ensure hydrometric data is available
for September 19-21, 2021. Assume that the data captured at this time
(before the peaks) represents average values for this time of the year.
i. Determine the average value for the water level (m) and discharge
(m3 /s).
A) The average water level for September 19-21 seems to be 0.1 m and the average
discharge is 6.5 m3/s.
ii. If the stream has a semi-circular cross section whose radius is equal to
the water level:
1. Estimate the corresponding cross-sectional area. [2 marks]
A) r = 0.1 m
CA = ½ * 3.14 * (0.1)2 = 0.0157 m2
2. Using the measured discharge (Question 2(a)(i)) together with the
cross-sectional area (Question 2(a)(ii)(1)), estimate the average flow
speed of the stream.
VA = D/ CA
= 6.5/ 0.0157 = 414.012 m/s
b. By adjusting the date parameters, ensure hydrometric data is available
for the precipitation events identified in Question 1(a). For one of these
events:
i. Determine the peak value for the water level (m) and discharge (m3 /s)
as well as the corresponding time.
A) On 2021-09-22 at 22:00, the peak value for the water level is at 2.05 m
and the discharge is at 55.1 m3/s.
ii. If the stream has a semi-circular cross section whose radius is equal to
the peak value for the water level:
1. Estimate the corresponding cross-sectional area. [2 marks]
A) CA = ½ * 3.14 * (2.05)2 = 6.5 m2
2. Using the measured peak discharge together with the cross-sectional
area, estimate the peak flow speed of the stream. [3 marks]
A) VA = D/ CA
= 55.1 / 6.5 = 8.4 m/s
3. Provide a screenshot of hydrometric data used - just the graph.
c. Compare average and peak scenarios (for the chosen event) as
follows:
i. Divide the peak water level by the average water level. [1 mark]
Peak water level = 2.05m, Average water level = 0.1m
= 20.5 m
ii. Divide the peak discharge by the average discharge. [1 mark]
Peak discharge = 55.1 m3/s, Average discharge = 6.5 m3/s
= 55.1/ 6.5 = 8.4 m3/s
iii. Divide the peak flow speed by the average flow speed. [1 mark]
Peak flow speed= 8.4 m/s, Average flow speed= 414.012 m/s
= 0.020 m/s
iv. If the stream’s kinetic energy is proportional to the square of the flow
speed, how much more energetic is the stream at its peak versus at the
average scenario?
A) At average value= (414.12) 2 = 171,495.3744 J
At peak value = (8.4)2 = 70.56 J
3. How much of a lag exists between the timing of the peak precipitation
event and the peak discharge event? [2 marks]
On analyzing the hydrometric graph and the EMOS data, there is at least
an hour’s gap between the two events that took place on September 22.
4. To what might this lag be attributed to?
A) This lag could be because the water usually takes time find its way to a
river channel and thus change the water level.