CIVL253 - HYDROLOGY
Suggested Exercises (Precipitation Analysis)
1.
2.
The following incremental rainfall data were recorded at gage 1-WLN in Austin,
Texas, on May 24, 1981. Plot the rainfall hyetograph. Compute and plot the
cumulative rainfall hyetograph. Calculate the maximum depth and intensity of
rainfall for 5, 10, 30, 60, 90, and 120 minutes for this storm.
Time (min)
Rainfall (in)
0
-
5
0.09
10
0.00
15
0.03
20
0.13
25
0.10
30
0.13
35
0.21
40
0.37
Time (min)
Rainfall (in)
45
0.22
50
0.30
55
0.20
60
0.10
65
0.13
70
0.14
75
0.12
80
0.16
85
0.14
Time (min)
Rainfall (in)
90
0.18
95
0.25
100
0.48
105
0.40
110
0.39
115
0.24
120
0.41
125
0.44
130
0.27
Time (min)
Rainfall (in)
135
0.17
140
0.17
145
0.14
150
0.10
Test the consistency of a record of 25 years of annual rainfall of a raingage designated
as A. Mean annual rainfall for five neighboring stations located in a meteorologically
homogenous region is available. This mean and rainfall data for raingauge A are as
follows:
Year
Gage A
5-Gage
Mean
Year
Gage A
5-Gage
Mean
Year
Gage A
5-Gage
Mean
1956
142
114
1966
113
125
1976
104
117
1957
115
106
1967
126
131
1977
130
129
1958
142
117
1968
116
124
1978
125
140
1959
130
118
1969
106
114
1979
140
133
1960
155
129
1970
76
92
1980
145
163
1961
134
124
1971
118
108
1962
157
122
1972
114
130
1963
115
94
1973
112
108
1964
128
102
1974
104
114
1965
157
154
1975
110
104
Indicate the year in which the change in rainfall regime occurred. Adjust the annual
rainfall of raingage A, and compute the difference between the recorded and the
adjusted rainfall for this gage. (Use least-squares method to find the best slopes of
each segment in the double mass curve to calculate the adjustment factor.)
3.
Refer to Figure P.1 which shows the hourly rainfall hyetographs of 8 Geotechincal
Engineering Office (GEO) raingages in Kowloon area for the 13 June, 1983 storm
event. From the relative positions of these gages (as shown in the map of automatic
raingauges, in class notes), could you tell how the storm move through this area?
4.
Refer to Table P.1 containing the information of elevation and mean annual
precipitation (MAP) at 25 raingauges in Hong Kong.
(1)
Plot the MAP (on vertical axis) against elevation (on horizontal axis) and
make assessments about orographic effect on precipitation amounts in Hong
Kong area.
(2)
By examining the MAP vs. Elevation plot, what type of model can be used to
describe the relationship between them? Then, use the least squares method to
determine the model parameters.
5.
Refer to Table P.2 showing the annual and monthly correlation coefficients of rainfall
amounts at 10 raingauges in Hong Kong area.
(1)
Identify the locations of the 10 gauges on the map and estimate the distances
between each pair of gages (a total of 45 pairs). Then, prepare the distance
matrix similar to the correlation matrices as shown in Table P.2.
(2)
Based on the correlation and distance matrices, construct separately the plots
of annual and monthly correlation against distance for the corresponding gage
pair. Then, discuss what your observations about the spatial correlation of
rainfall amounts in Hong Kong area.
6.
Refer to Figure P.2 showing the isohyetal map of rainstorm occurred on July 18, 1992
over the north western New Territory, Hong Kong. The rainfall depths observed at
the 5 raingauge stations in the neighbourhood of Basin 9 are given in the following
table.
Gage Name
Yuen Long
Tuen Mun
Tin Shui Wai
Ta Mo Shan
Rainfall Depth
280 mm
275 mm
205 mm
420 mm
Sheung Shui
235 mm
Estimate the aerial average rainfall depth the storm event by (a) arithmetic average
method; (2) Thiessen polygon method; and (3) isohyetal method.
7.
Referring to Figure P.1, the total rainfall depths corresponding to each of the 8 GEO
raingauges in Kowloon area for the 17th June 1983 storm event are listed below.
(1)
Propose a technique to evaluate the relative performance (in term of
estimation accuracy) of the following methods for estimating the missing
rainfall at a point: (a) arithmetic average method; (b) normal ratio method; and
(c) inverse distance method with the exponent value b=1.
(2)
Carry out your proposed performance evaluation technique by using the 8
GEO gauges in Kowloon area and draw your conclusions.
Sta. Code
Station Name
Rainfall (mm)
K01
K02
K03
K04
K05
K06
K07
Ho Man Tin
Lung Cheong Court
Sau Mau Ping
Jordan Valley
Yau Tong
So Uk
Tsz Wan Shan
249
234
291
291
371
276
224
K08
Lam Tin
357
Figure P.1