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1 Fujii, H.; Dawuni, B.; Kulawardhana, Wasantha; Thenkabail, P. S.; Namara, Regassa E. 2009. Features of river flow in inland valleys in semi-deciduous forest zone in Ghana. Transactions of the Japanese Society of Irrigation, Drainage and Rural Engineering, 77(6):637-644.
Watersheds ; Rivers ; Stream flow ; Hydrology ; Runoff ; Forest land ; Rice / Ghana / West Africa / Mankran Watershed / Offinso Watershed
(Location: IWMI HQ Call no: e-copy only Record No: H043148)
(0.96 MB)
There are about 2.8 million ha of inland valleys in Ghana and 20 million ha of inland valley in West Africa. Although inland valleys are suitable for lowland rice due to the abundance of water resources and higher soil fertility compared with the upland, they have not been well utilized as agricultural land in West Africa. Further utilization of inland valley for lowland rice will improve the productivity of rice in West Africa. In this study water resources of small rivers in inland valleys in West Africa are evaluated. Two study watersheds with 1,400-1,500mm of annual rainfall in Semi-Deciduous Forest Zone in Ghana were selected and analyzed on slope distribution in the study watershed to grasp suitable area for lowland rice and on hydrological characteristics such as specific discharge and runoff ratio. The following findings are obtained from the study. 1) Most of the rivers in the study watershed are seasonal rivers. Non-flow period of some rivers were shown for around five months from middle of December to early May. However the term of non-flow period varies much depending on characteristics of sub-watersheds. 2) Runoff ratio for 5 years from 2000 to 2004 in Offinso watershed which is a typical watershed in semi deciduous forest zone in Ghana was indicated only 12%. It ranges from 0.08 to 0.16 depending on the year. The monthly runoff ratio indicated little value in March, April and May which is beginning of rainy season and high value in November and December which is beginning of dry season. 3) The gentle slope area with less than 2%, which seems suitable area for lowland rice, occupies 22 % of inland valley.
2 Fujii, H.; Gumma, M. K.; Thenkabail, P. S.; Namara, Regassa E. 2010. Suitability evaluation for lowland rice in inland valleys in West Africa. In Japanese. Transactions of the Japanese Society of Irrigation, Drainage and Rural Engineering, 78(4):47-55.
(Location: IWMI HQ Call no: e-copy only Record No: H043176)
(2.83 MB)
A GIS based model developed by the authors are applied for selecting suitable rice cultivation area in inland valleys that has high potential for rice production in West Africa where rice consumption is increasing very rapidly. The model has the following features. 1. The model is to evaluate the suitability of the land for lowland rice based on score distribution maps respectively made by the data of 29 evaluation parameters. 2. The parameters are classified into 4 categories; bio-physical, technical, socio-economic and health-environmental parameters. 3. Each scored map(layer)is integrated to obtain total scores by multiplying a weight which is determined by the importance of parameters. The suitability for rice in two study sites was evaluated using the model. Mankran and Jolo-Kwaha watershed selected as the study sites from different agro-ecological zone in Ghana. Applying the data of 12 parameters acquired in the study sites to the model, “very suitable” or “suitable” occupies around 30% in Mankran study site and around 60% in Jolo-Kwaha study site.
3 Dawuni, B. N.; Namara, Regassa; Kizito, Fred; Fujii, H. 2012. Evaluation of surface water availability for inland valleys rice production: the case of Mankran Watershed in a deciduous forest zone of Ghana. Journal of Environmental Science and Engineering, 1(2B):250-259.
Surface water ; Water availability ; Valleys ; Rice ; Case studies ; Watersheds ; Forests ; Rain ; Rivers ; Flow discharge / Ghana / Ashanti Region / Ahafo-Anosouth District / Mankran Watershed / Deciduous Forest Zone
(Location: IWMI HQ Call no: e-copy only Record No: H044832)
(0.37 MB)
In Ghana, inland valleys have been found to be suitable for rice cultivation and could potentially increase lowland paddy rice production. This study estimated the temporal variations of surface water resources and their spatial distribution in the Mankran watershed of Ghana through the collection of recorded hydro-meteorological data in the bench mark watershed from 1998 to 2010. Since most inland valley rice cultivation highly depends on rainfall, the watershed precipitation data over a decadal period showed sufficient wet years with a potential to sustain a high cultivation of paddy rice. Peak wetness occurred in June and October over a bi-modal precipitation pattern. Rating curve data for the Mankran-kesse river-up stream depicted generally low discharge values despite having a higher stream order suggesting that stream order alone is not sufficient to estimate water resources potential. It was presumed that the geomorphology and lithology of the highly porous river bed and the presence of high sub-surface water resources stored in this zone may be implicated for this observation. Provision of water storage options for zones like Kesse-upstream seems a feasible option in order to cater for supplementary irrigation while indirectly tapping on subsurface water resources stored in the porous aquifers through basin interflows. Baseflow data also showed that the discharge from upstream locations to the downstream exit of the watershed was high through direct surface river discharge and subsurface interflow. The temporal patterns of the hydrology indicate that annual paddy rice cultivation is ideal between May and October.
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