Water use and productivity of two small reservoir irrigation schemes in Ghana's upper east region

Abstract

To examine the impact of small reservoir irrigation development in Africa, the performance and productivity of two small reservoirs and irrigation schemes in the Upper East Region of Ghana were investigated in this study. Hydrologic data measured included daily irrigation volumes and daily evaporation. Farmer cost inputs, excluding labor, and harvest data were also recorded. There was a strong contrast in water availability between the two systems, the Tanga system having a higher amount of available water than did the Weega system. The concept of relative water supply was used to confirm this disparity; Tanga was an inefficient system with a relative water supply of 5.7, compared to a value of 2.4 for the efficient Weega system. It was also concluded that the dissimilar water availabilities resulted in the evolution of very different irrigation methods and coincided with different management structures. Where there was more water available per unit land (Tanga), management was relaxed and the irrigation inefficient. Where there was less water available per unit land (Weega), management was well structured and irrigation efficient. The productivity of water (US$ m À3 ) of the Tanga system was half that of the Weega system, when analyzed at a high market price for crops grown. In terms of productivity of cultivated land (US$ ha À1 ), however, the Tanga system was 49% more productive than the Weega system. The difference in the productivity of land is primarily a result of increased farmer cash inputs in the Tanga system as compared to the Weega system. The difference in the productivity of water can be attributed to the varying irrigation methods and management structures, and ultimately to the contrasting water availability. Tanga avait un système inefficace avec un taux d'approvisionnement relatif en eau de 5.7 comparé à un taux de 2.4 du système efficace de Weega. Il a été conclu que les différences au niveau de la disponibilité d'eau sont à la base d'une évolution de méthodes et s'accordent avec de concepts de gestion d'irrigation très contrastés. Quand il y avait plus d'eau disponible par unité de surface (Tanga), la gestion était peu organisée et l'irrigation moins efficace. Par contre, quand les ressources en eau étaient limitées (Weega) la gestion était bien structurée et l'irrigation très efficace. En termes d'eau les agriculteurs de Tanga recevaient seulement la moitié du bénéfice économique des agriculteurs de Weega quand le prix du marché était élevé pour les produits récoltés. Par contre, en termes de surface cultivée, les agriculteurs de Tanga faisaient 49% plus de profit par rapport aux agriculteurs de Weega. La différence du bénéfice économique de la terre cultivé est principalement une conséquence des investissements élevés des agriculteurs dans le système de Tanga comparé au système de Weega. La différence du bénéfice économique de l'eau peut être attribuée aux variations des méthodes d'irrigation et des structures de gestion et donc finalement aux disponibilités en eau très contrastées.

Variability in smallholders' irrigation water values: Study in North‐West Province, South Africa

“…This confirms that personal characteristics of the farmers have only a marginal influence on variability in water values. Surprisingly, and in contrast with findings of Faulkner et al (2008) the effect of irrigation technology is even smaller. A possible explanation is that nearly all farmers in the sample use low efficiency technologies like furrow irrigation, bucket irrigation or hosepipes and thus variability in water values cannot be attributed to this factor.…”

“…Hermans et al (2006) and Faulkner et al (2008) suggest that the institutional settings, management and design principles of the schemes can be important explicatory factors for such differences. Figure 1 shows the average water values for the different types of schemes discussed above.…”

“…Knowledge of the economic value of water is necessary when making investment decisions in water resources development, drawing policies for sustainable water use and water allocations or when the socio-economic impacts of water management decisions must be determined (Hussain et al, 2007). It should furthermore be noted that water values are highly variable over space and time (Montazar and Rahimiko, 2008;Faulkner et al, 2008;Hussain et al, 2007;Lange, 2007). A wide range of factors, such as the crops grown, irrigation techniques used, and differences in soils and in management practices, influences irrigation water values.…”

Stochastic control of a micro-dam irrigation scheme for dry season farming

“…Mdemu et al (2009) noticed that the smaller Dorongo scheme, which alone experienced drought, had better water productivity than that in the larger Tono scheme. Faulkner et al (2008) made comparison between another set of two small reservoir irrigation schemes, namely, Tanga and Weega schemes in the Upper East Region of Ghana, where water demand in the irrigated crop fields was estimated to be in the range of 3.7-5.9 mm/ day on weekly basis. In both schemes, the reservoirs' capacities are almost the same with command areas of 1.6 and 6.0 ha in the Tanga and the Weega schemes, respectively.…”

“…It is assumed that h max , the upper limit of tolerable volumetric water content, is equal to 0.35, being a value between h c and h s . Based on the estimation and the observation by Faulkner et al (2008), a reasonably large value of 20 mm/day is assumed for E c , the average water consumption rate. However, there are different small-holder farmers' practices to conserve soil moisture in the semi-arid SSA (Chiroma et al 2006), making it difficult to determine the actual water consumption rate, which may include evapotranspiration varying with different growth stages, deep percolation, conveyance losses, and so on.…”