EAS 345 HYDROLOGY
Lab #2 Name____________________________________________
Last
First
PRECIPITATION, CONTOURS, AND RIVER DISCHARGE
On All Math Problems, show work
Introduction
The purpose of this lab is to investigate some of the basic relationships between rainfall and runoff or
discharge. To evaluate discharge using the equation of discharge, q = ERA, it is necessary to determine the
area of the catchment basin and the area-averaged rainfall rate. In Lab 1 you learned how to outline the
catchment basin. Now we must learn to estimate area-averaged rainfall. The best way to do this with data
from irregularly spaced rain gages or radar is to perform a contour analysis. In this lab we
1. Use contour lines created by others to calculate average rainfall
2. Construct our own contour analysis
A number of factors affect the runoff efficiency, E in the equation of discharge. They include:
1.
2.
3.
4.
Evaporation
Storage in groundwater
Time lag in reaching the river
Storage as snow or loss of storage due to melting
In the last part of the lab the impact of these and other factors is evaluated by comparing average monthly
runoff of several major rivers to the monthly rainfall.
Problems
1. A tropical depression in the Southeastern Gulf of Mexico produced heavy rains over southwest Florida in
late June, 1992. Four day amounts of 20 to 35 cm were common with the greatest totals up to 58 cm. The
heaviest rains fell on Manatee and Sarasota counties where rivers and small streams flooded homes and
roads. Two deaths resulted from the flooding.
Calculate the average rainfall and total volume of water and mean discharge, q, in two river basins, the
Myakka River and the Peace River using the rainfall contours on the accompanying map and Myakka.ppt.
Procedure
a. Outline the basin of each of the rivers in a distinct color.
b. Use the grid to estimate the area of each basin in m2. The method is simply to count boxes and multiply
by the area of each box (20 km) using the map scale.
Box Length = _____________ m
Box Area = _______________ m2
Basin Area: Myakka River_________________m2 . Peace River__________________m2
c. Use the grid to estimate the average rainfall for each basin. The method is to estimate the rainfall at the
center of each grid box and then average. Convert rainfall to meters.
Rain Depth: Myakka River_________________m Peace River__________________m
d. Calculate the total volume of water assuming a four day period that must flow through the mouth of each
river during the time period assuming all rain reaches the rivers. Then calculate the discharge, q in m3 s-1.
Total Volume: Myakka River_________________m3 Peace River__________________m3
qMyakka_________________m3 s-1 qPeace________________m3 s-1
2. To show the value of contouring, A: Calculate the station average rainfall based on the grid below. B:
Contour the rainfall using an interval of 5. C: In each box enter values of rainfall you expect in each box
based on your contour analysis. D: Calculate the area average rainfall using the values in every box
A: Station Average = ________________
D: Area Average = ___________________
3. Contour the values in the grid on page 4 using a contour interval = 20.
4. Rainfalls and discharges for 4 river basins (Niger, Tiber, Delaware, Yenesei) are included on the last page
of this lab.
a. Use EXCEL or MATLAB to graph the monthly average rainfall and average discharge for each river.
b. For the Niger and Delaware Rivers, find the lag in months at which the maximum correlation between
runoff, q and rainfall, R occurs and the correlation coefficient. Give the reason the maximum correlation
is larger for the Niger than for the Delaware River.
Reason = ______________________________________________________________________________
15
20
25
30
35
MYAKKA
45
50
55
40
PEACE
18
18
18
19
19
19
19
18
18
18
17
17
17
16
15
15
14
13
13
12
35
35
35
35
35
34
34
33
32
31
30
28
27
25
23
22
20
18
16
14
51
51
51
50
50
49
48
46
45
43
41
39
36
34
31
28
25
22
19
16
65
65
65
64
63
62
60
58
56
54
51
48
45
41
38
34
30
26
22
18
78
77
77
76
75
73
71
69
66
63
60
56
52
48
43
39
34
29
24
19
87
87
86
85
84
82
80
77
74
70
66
62
58
53
48
43
37
31
26
20
94
94
93
92
90
88
86
83
79
75
71
66
61
56
51
45
39
33
27
20
98
98
97
96
94
92
89
86
82
78
74
69
63
58
52
46
40
33
27
20
99
98
98
96
94
92
89
86
82
78
74
69
63
58
52
46
39
33
26
19
96
96
95
94
92
90
87
84
80
76
72
67
61
56
50
44
38
31
25
18
90
90
89
88
86
84
82
79
75
71
67
62
57
52
47
41
35
29
23
16
81
81
80
79
78
76
74
71
68
64
60
56
52
47
42
37
31
25
20
14
70
69
69
68
67
65
63
61
58
55
52
48
44
40
35
31
26
21
16
11
55
55
55
54
53
52
50
48
46
44
41
38
35
31
28
24
20
16
12
8
39
39
39
38
38
37
36
34
33
31
29
27
24
22
19
16
13
10
7
4
21
21
21
21
21
20
20
19
18
17
16
14
13
11
9
8
6
4
2
0
2
2
2
3
3
3
3
2
2
2
1
1
1
0
-1
-1
-2
-3
-3
-4
-18 -18 -17 -17 -16 -16 -15 -15 -14 -14 -13 -13 -12 -12 -11 -11 -10 -10
-9
-9
-38 -37 -36 -36 -35 -34 -33 -31 -30 -29 -27 -26 -25 -23 -21 -20 -18 -16 -15 -13
-57 -56 -55 -54 -53 -51 -50 -48 -46 -44 -42 -39 -37 -34 -31 -29 -26 -23 -20 -17
-75 -74 -73 -71 -70 -68 -66 -63 -61 -58 -55 -52 -48 -45 -41 -37 -33 -29 -25 -21
-91 -90 -89 -87 -85 -83 -80 -77 -74 -71 -67 -63 -59 -54 -50 -45 -40 -35 -30 -25
-106 -104 -103 -101 -99 -96 -93 -90 -86 -82 -78 -73 -68 -63 -57 -52 -46 -40 -34 -28
-117 -116 -114 -112 -110 -107 -104 -100 -96 -91 -86 -81 -76 -70 -64 -58 -51 -44 -38 -31
-126 -125 -123 -121 -118 -115 -112 -108 -103 -98 -93 -87 -81 -75 -69 -62 -55 -48 -41 -33
-132 -131 -129 -127 -124 -121 -117 -113 -108 -103 -98 -92 -85 -79 -72 -65 -58 -50 -43 -35
-135 -133 -132 -129 -126 -123 -119 -115 -110 -105 -100 -94 -87 -81 -74 -67 -59 -52 -44 -36
-134 -133 -131 -129 -126 -123 -119 -115 -110 -105 -100 -94 -87 -81 -74 -67 -60 -52 -45 -37
-130 -129 -127 -125 -122 -119 -116 -112 -107 -102 -97 -91 -85 -79 -73 -66 -59 -52 -45 -37
-123 -122 -120 -118 -116 -113 -110 -106 -102 -97 -92 -87 -82 -76 -70 -64 -57 -50 -44 -37
Rainfall and Discharge for Several Rivers Around the World
Niger River at Koulikoro (K), Mopti-Nanta Ka (M) and Dire (D). Rain at Kayes (Y) and Timbuktu (T)
Jan
Feb
Mar
Apr
May
Jun
July
Aug
Sep
Oct
Nov
Dec
R(Y)
0.1
0
0
0
1.0
3.8
6.3
9.5
7.4
1.7
0
0
q(K)
403
196
101
67
98
359
1250
3230
5380
4680
2130
880
q(M)
992
400
185
130
82
194
708
1760
2580
2840
2690
2000
R(T)
0
0
0
0
.1
.8
2.3
3.2
1.4
.1
0
0
q(D)
2030
1550
967
434
141
82
259
841
1490
1890
2150
2300
Jan
Feb
Mar
Apr
May
Jun
July
Aug
Sep
Oct
Nov
Dec
R
2.7
2.3
1.5
1.7
2.0
1.0
0.6
0.9
2.7
3.7
3.8
2.8
q
301
343
325
272
242
168
137
123
134
177
264
234
Jan
Feb
Mar
Apr
May
Jun
July
Aug
Sep
Oct
Nov
Dec
R
2.6
2.2
2.9
3.0
3.7
3.6
3.6
3.2
2.6
3.1
2.7
2.6
q
351
353
611
653
387
235
197
170
157
179
292
334
Tiber River at Rome
Delaware River, NJ
Yenesei River Igarka
Precipitation at Irkutsk
Jan
Feb
Mar
Apr
May
Jun
July
Aug
Sep
Oct
Nov
Dec
R
0.4
0.3
0.3
0.2
1.5
2.2
3.5
3.1
1.7
0.7
0.7
0.6
q
4840
4510
4190
3980
30200
76000
27900
18900
17900
14700
6120
4880
Internet Source for World River Discharges http://www.rivdis.sr.unh.edu/