CHAPTER SIX
6.0 CONCLUSIONS AND RECOMMENDATIONS 6.1
Conclusions
The hydrogeomorphologic model has caracterised the Congo Basin
in term of its topography, hydrography and hydrology. The major subwatershed
(Sangha, Ubangi, Ouesso, Congo and Lualaba) are identical if considering the
stream development characteristics. Slopes values are generally more or less
negligible all over the basin. As observed from both the Hydrosheds and Hydro1k
DEM maps used, more than 60 percent of the basin is covered by a flat area
where slopes are obviously derived negligible. This flat area is surrounded by
mountainous zones in the eastern, southern and northern part of the basin. The
spatial resolution of 1000 meters used will definitely hide some ground
realities such as hill slopes of a length less than 1000 metres, surrounded by
flat area, will not be observed on the map.
Furthermore, a distributed GIS-based hydrological model,
namely Hybrid Atmospheric Water Balance (HATWAB) was developed using GIS and
computational hydrology techniques. The model is based on the combined,
NDVI-based interception abstraction of precipitation, CN method of overland
runoff and soil-moisture accounting technique for runoff generation for
specific geo-referenced grids.
Besides, rainfall and climatological data, the inputs to the
model are the GIS based agronomic soils and vegetation cover information over
the region has been reclassified into appropriate textural soils and rooting
depth and used to derive the soil moisture parameters such as field capacity
(FC), wilting point (WP) and available water content (AWC).
This enables one first to establish the hydrologic regimes of
the region, and for various drainage basins (subwatershed). It ultimately
permits a through assessment of the region's water resources availability.
The simulated annual runoff using HATWAB for the Congo basin
is found to be within 5% error margin compared to the observed mean annual
runoff, which is quite a commending outcome of the study.
Developed for the water balance studies of drainage basins in
the various climatic regimes of Africa, which is being successfully tested in
different basins, HATWAB model is a regional scale hydrological model which is
capable of estimating the spatial and temporal variation of the major
components of water balance such as the soil moisture, the actual
evapotranspiration and runoff.
First, the model has been used to create a GIS-based high
resolution data sets of soil moisture, evapotranspiratiom, grid runoff for
grids that represent the land catchment of the region at 12 km (6 minutes)
spatial resolution.
This work is the first comprehensive distributed hydrological
model in the region that utilises the hydro-climatology and hydrologic soil
information using the state of the art GIS technique computing the water
balance for the whole Congo River basin. The model and the findings of the
study reveal important information to assess the water resources potential of
the various sub-catchments and the whole Congo basin in one environment.
6.2 Recommendations
Even though the HATWAB model has simulated some realistic
parameters for the Congo basin water balance, the following recommendations are
made:
1. The soil texture data was not verified on the field. For
the entire basin, only 6 textural soil groups were classified from 133
agronomical FAO soil groups. This may also introduced some error in estimation
hydrological soil properties and therefore, in the simulation of water balance
components.
2. The NDVI data was extracted from a map of 1987 while the
climate change is affecting the Africa continent. There is a possible change in
land cover/use distribution over the area.
3. Although the above mentioned deficiencies, one will need
to point out that their influence would be negligible for such a HATWAB Model
applied simulating the water balance for a large watershed such the Congo River
basin. However, for further calibration of HATWAB model, observed or recoded
discharge data for the various sub-catchment outlets as well as the main Congo
basin outlet point need to be used.
4. With the advent of increasing computing power of the
current computers, HATWAB can give an impetus to and can throw light towards
development of refined and data intensive hydrological model as high resolution
spatial and temporal hydroclimatic information are becoming increasingly
affordable from satellite-data sources. Furthermore, this approach provides an
operational hydrological tool to deal with national, or regional planning and
developing decision support systems, with possible linkage with the
inter-related multi-sectoral nature of the natural resources and socioeconomy
of the region or the globe at large.
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