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Table 4.6 Final equations for South lsland regions.
Region
West Coast. Nelson
East Coast
lnland Marlb, Canty
McK, lnland Otago, Sthld
No.
Stns
19
11
13
15
õ
õ
õ
õ
B€st Fh Equations R2
Se
est
= 0,0233 AREAo...l224o.e¡
= 1,1 1 x lo-e AREAo ¡e MARA|N3.o
= 0.964 AREAo.¡o
=o.oo1 90 AREAo.el 12241,3
o.971
o.989
0.992
o.963
0.94
o.98
0.98
o.93
Factorial
se €8t
0.1 48 1 .41
0.117 1.30
0.1 09 1 .28
o.1 46 1 .40
catchm€nt drain former glacial moraines on s,hich the
surface drainage network is ill-defined. Considerable
surface storage occurs in swamps and, in the case of
the South Ashburton, the drainage divide with Lake
Heron is ill-defined. Therefore, flood-flow levels are
expected to be substantially reduced and it is uûeal_
istic to use data from these catchments to estimate
flows for other catchments where similar ponding does
not occur. On this basis the data are omitted from the
final analysis.
The central area of the Taieri catchment (Station
74314) is a flat plain through which the river channel
follows a meandering course. The recording station is
situated downstream of a narrow gorge in which flood
waters back up and inundate large areas of the plain.
This ponding occurs to a much greater extent thãn on
most other catchments. The resulting reduction in
peak discharge is reason for rejecting data from this
catchment in the final analysis. Note that this catch_
ment is an outlier in the Q against AREA plot in Fig_
ure 4.3
(iv) Station wlth unreliable rating
Because flow records for Station 9ll0l (Taramakau at
Gorge) were derived using a theoretical rating the re_
cord qualìty was expected to be only fair andihe esti_
mate of Qo6, subject to more error than most values
for most other stations. As the value used appears to
result in a large error, the station is excludeã in the
final analysis.
(v) Remaining outliers
(vi) Snowmelt
Although snowmelt is not an important flood-producing
mechanism in New Zealand, when it combines with
rainfall it may cause floods greater than would occur
through rain alone. However, snowmelt catchments do
not appear aniongst the catchments listed earlier as
outliers. Although data on the extert, depth, and
water-producing capabilities of snowpack are sparse in
New Zealand, it is known that in the Fraser catchment
(Station 75259) five of seven annual flood maxima
us€d in this study occurred in October, November or
Decernber, and are likely to have been associated with
snorvmelt. This may account for any underestimation
of Q for this catchment (residual error equal to 0. 16).
Snowmelt may also be a contributory factor to the
underestimation of Q for other catchments in the
island, paticularly 71116 (Ahuriri at South Diadem)
and75276 (Shotover at Bowens peak).
The final estimation equations were derived after shifting
the boundary between the West Coast and Inland Marlborough/Canterbury
regions slightly lo include the catchment
for Station 64ó06 in the West Coast region, and excluding
Stations 65902, 68806, 71122,74314 and 9ll0l for the reasons
stated.
4,5.4 Final equations for South lsland
estimate is decreased compared with the first trial equations
in Table 4.5.
The geographic distribution of residual errors for the fin_
4.7. Yery good fit has been
Inland Marlborough/Cantrs
are +0.22, and their disdom.
The fÏt for the W€st
Coast and Inland Otago and Southland regions is satisfactory;
one error exceeds 0.30 and t$¡o more exceed O.A.
Although most errors appear randomly distributed in
sDace, several positive errors clustered in the southern part
of the Inland Otago and Southland region suggest ihat
some consistent underestinnation of Q has occuried there.
Table 4.7 correration malrix for rogs of North rsrand charact€rist¡cs.
o
AREA
MARAIN
t224
LENGTH
FOREST
STMFCY*
s1 085*
€LEVT
1.OOO
o.830
o.294
o.2ö7
o.815
o.342
-o.117
-0.413
o.247
AREA MARAIN LENGTH FOREST STMFCY. S1085. ELEV'
1.0O0
o.040
-o.110
0.944
0.189
-o.121
-o.576
0.303
l.OOO
0.296
o.o44
0.506
o.o69
0.332
0.454
l.OOO
-o.101
o.312
o.o60
o.o09
-0.149
l.OOO
0.191
-o.187
-0.598
o.278
1.000
o.178 l.OOO
o.o77 o.196
0.348 o.157
l.OOO
0.348
l.OOO
¡ lncomplete Sample
&
Water & soil technical publication no. 20 (1982)