734 
these proceedures provide the only flow estimates 
against which those obtained from LANDSAT imagery can 
be compared. 
An estimate of the return period of the 1979 rain 
fall was made, as was an estimate of the flow peaks 
of the 1979 event, as obtained from the unit hydro 
graphs. An interesting conformity was seen and is 
presented below in table 2. 
Table 2. Rainfall and synthesised flow peak return 
periods 
Station 
Rainfall 
Peak flow 
Non-floodplain 
station I 
II 
years 
9.3 
years 
Non-floodplain 
station 2 
9 
years 
8.5 
years 
Big F'alls 
Ranch 
9 
years 
3.7 
x 10 years 
Bermudan 
Landing 
9 
year's 
9.6 
x IC? years 
Davis 
Bank 
9 
years 
9.2 
x years 
In all cases, rainfall returns approximated to nine 
years as did the flows of the non-floodplain stations. 
In contrast, the floodplain stations' return periods 
were extremely high. 
It was clear that by applying a nine years return 
limit to the hydrographs of the floodplain stations, 
a good estimate of their true maximum discharges for 
the 1979 event could be found. The difference between 
this and the synthesised flood flow would provide 
estimates of loss from the Belize river to the flood- 
plain. Table 5 below presents these losses and also 
includes a value of the runoff contribution from the 
floodplain catchment (Fiddes 1977)« 
Table 5. Belize river losses to the floodplain 
Station 
Loss (m^) to floodplain 
Big Falls Ranch 
Bermudan Landing 
Davis Bank 
0.63 x 10 
1.48 x 10 
2.02 x 10 
Local catchment 
contribution 
1.04 x 10 
Total Flood Volume 
5.37 x 10 
8 
While these values cannot be substantiated by other 
means and are obtained from a series of calculation 
methods, these methods are based on well tried 
hydrological principals. F'rom the study of the flow 
hydrographs of the 1979 event it was apparent that 
the LANDSAT scene was taken between 14 and 16 days 
after the start of the flooding which first occured 
at or around Big Falls Ranch. 
2.3. LANDSAT estimates of the 1979 flood 
Preliminary investigations of the LANDSAT flood scene 
showed that slides of computer compatible tapes 
could provide the most information if projected at a 
scale of 1:30,000. Ground control point measurements 
were made to assess the distortional effects of the . 
projections and indicated that while they were indeed 
present, they were not great. It was not possible to 
identify these distortional effects in terms of their 
vertical and horizontal components due to the distri 
bution of the ground control points. The overall rel 
ationship of the distortions can be described by: 
Map scale = 0.99898 + 0.00283 x Slide scale 
F'rom 1:50,000 scale topographic maps, spot heights 
were transposed onto the base map obtained from the 
LANDSAT flood scene. Sufficient were present at the 
flood margins to identify a maximum flood level of 
between six and seven metres above sea level. The 
overall extent was estimated as 265.6 square km. Not 
all the flood extent was observable due to the dense 
vegetation cover and the maximum level was extrapola 
ted to identify flooded areas under dense vegetation. 
Sufficient spot heights to provide average flood 
depths, were present only in the basinal areas close 
to permanent lagoons. This depth was three metres, 
obtained from cross-sections through the area but the 
consideration of the wider spread of spot heights 
indicated an average flood depth of two metres, or 
possibly less. 
In these circumstances, a range of depth/volume est 
imates were made to provide a comparison with that 
obtained by the flow hydrograph study. They are given 
below in table 4• 
Table 4. LANDSAT estimated flood volumes 
r lood depths (metres) 
-z 
Flood volumes (nr ) 
1.5 
3.98 x 10® 
5.3I x 10° 
2.0 
2.5 
6.63 x 10° 
3.0 
7.97 x 10 
hydrograph 
estimate 
5.I3 x I0 b 
It can be seen that the estimates from both sources 
are close and while no direct ground measurement of 
the flood is available, the correlation is clear. It 
is possible that during the later stages of the flood 
process, that water could flow back to the Belize 
river. However, the observation of the floodwater 
distribution shows it concentrated in the area of the 
river still in active flood, the area providing 85% 
of the floodwater. Any return to the river is likely 
to have been relatively small. 
3. THE LOWER FLOODPLAIN 
3.I LANDSAT investigations 
The information of flood plain inundation can be 
summarised, as obtained from the LANDSAT scene, by 
figure I. The identification of both source and dist 
ribution can be made, as can the areas of its influe 
nce upon the Western highway. In the lower floodplain 
river flows are not recorded, spot height information 
is very restricted and so flood estimates are not 
attempted. The distribution of the floodwaters and 
their effects on the Western highway is the most 
significant factor under study. 
While local catchment and Belize river contributions 
to flooding have been identified, the lower floodplain 
is shared with the Sibun river, another source of 
floodwater. Figure I shows the areas of flooding as 
presented by false colour composite slides. The posi 
tion of the flooding- can be located to about + 150 
metres according to ground resolution and slide dist- 
-17° 50' N 
Figure I. 
ortion con 
not easily 
Belize riv 
around the 
contributi 
tions. The 
lagoons (a 
is clearly 
spread sou 
spread as 
image proc 
nnels, foe 
Band 7» un 
and manipu 
ing. A his 
ined and t 
boundaries 
severity w 
of lagoon 
within the 
features a 
river was 
Figures 2 
tches, res 
ibutions o 
4, 5 and 6 
taken by t 
any contri