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Hydrological modeling of the Congo River basin: Asoil-water balance approach

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par Bahati Chishugi Josue
University of Botswana - Masters of Sciences (M.Sc.) 2008
  

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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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