171 
1921.] Mead.—Impounding-dams for Multiple Functions. 
In concluding, the writer expresses the hope that this theory of the 
multiple-function dam will be considered worthy of test on several of our 
rivers ( e.g .-, Waikato, Wanganui, Waihou, and others) in which at present 
the various problems of navigation, power, and flooding are being tackled 
separately without attempt at co-operation. The organization suggested 
is a river authority for each watershed, having a certain measure of control 
over all works which may affect stream-flow ; and the immediate duty of 
the authority would be to conserve the natural storage, and to establish 
gauge-stations at suitable points in order to obtain accurate data for design 
of future works. 
APPENDIX I.—CALCULATION OF PERENNIAL YIELD. 
The daily gaugings are tabulated, a rate of daily draw-off assumed, and 
the difference added to or deducted from the quantity in the reservoir from 
day to day. The volume of full reservoir is taken as zero, and the greatest 
deficiency represents the required storage. For small reservoirs there is no 
need to analyse the whole of the gaugings ; inspection will reveal the periods 
of low water when the reservoir would be taxed, and calculation may begin 
from a slightly antecedent date when it was obviously full. The gaugings 
here used are those of the Nihotupu Stream, from which fig. 2 was calculated, 
and, the unit of quantity is the day’s flow at 1 cusec. To save unnecessary 
arithmetic, when the flow is low and uniform it is summed in periods of 
ten days. The minimum recorded flow is 2-1 cusecs, and the mean about 
14 cusecs. By inspection of available gaugings the longest dry period 
occurred in autumn of 1919, and the reservoir would be full till about the 
end of February. 
To calculate capacity required to yield 3 cusecs :— 
1. 
Date. 
1919. 
2. 
Flowing 
in. 
3. 
Drawn 
out. 
4. 
Gain or 
Loss. 
5. 
Quantity in 
Reservoir. 
l. 
Date. 
1919. 
2. 
Flowing 
in. 
3. 
Drawn 
out. 
4. 
Gain or 
Loss. 
5. 
Quantity in 
Reservoir. 
Feb. 25 
3-2 
3-0 
+ 0-2 
Overflows. 
April 4 
3-0 
3-0 
0-0 
- 1-2 
26 
3-0 
3-0 
0-0 
Full. 
5 
3-2 
3-0 
+ 0-2 
- 1-0 
27 
30 
3-0 
0-0 
6 
3-0 
3-0 
0-0 
- 1-0 
28 
3-0 
3*0 
0-0 
9 9 
7-16 
24-4 
30-0 
— 5*6 
- 6-6 
Mar. 1 . 
2-6 
30 
- 0-4 
- 0-4 
17-26 
22*7 
30-0 
- 7-3 
- 13-9 
2-11 
24-3 
30-0 
- 5-7 
- 6-1 
27 
21 
3-0 
- 0-9 
- 14-8 
10-21 
24-3 
30-0 
- 5-7 
- 11-8 
28 
2-4 
3-0 
- 0-6 
- 14-4 
22 
3-5 
3-0 
+ 0-5 
- 11-3 
29 
41 
3-0 
+ 11 
- 14 3 
23 
41 
3-0 
+ 1-1 
- 10-2 
30 
4-5 
3-0 
+ 1-5 
- 12 8 
24 
3-2 
3-0 
+ 0-2 
- 10-0 
May 1 
3-0 
30 
0-0 
- 12-8 
25 
2-8 
3-0 
- 0-2 
- 10-2 
■ 2-11 
24-2 
30-0 
- 5-8 
- 18-6 
26 
7-3 
3-0 
+ 4-3 
- 5-9 
12 
. 2-2 
3-0 
- 0-8 
- 19-2 
27 
8-8 
3-0 
+ 5-8 
- 01 
13 
2*2 
3-0 
- 0-8 
- 20-0 
28 
4-5 
. 3-0 
+ 1-5 
Overflows. 
14 
2-2 
3-0 
- 0-8 
- 20-8 
29 
3-5 
3-0 
+ 0-5 
99 
15 
21 
3-0 
-0-9 
- 21-7 
30 
3-2 
3-0 
+ 0-2 
16 
21 
3-0 
- 0-9 
- 22-6 
31 
3-0 
3-0 
0-0 
Full. 
17 
21 
3-0 
- 0-9 
- 23-5 
April 1 
2-6 
3-0 
- 0-4 
- 0-4 
18 
13-0 
3-0 
+ 10-0 
- 13-5 
2 
2-6 
3-0 
- 0-4 
- 0-8 
19 
100-0 
3-0 
+ 97-0 
Overflows. 
3 
2-6 
30 
1 
- 0-4 
- 12 
i 
20 
162-0 
3-0 
! + 159-0 
99 
The reservoir is at its lowest on May 17. The required capacity is 
23-5 X 84,400 = 2,030,000 cubic feet, equivalent in this case to 0-24 in 
