Assessment of the hydrological and land use/land cover changes in Mutonga watershed, Kenya
Mutonga watershed, in the Tana basin has over time experienced significant changes in its hydrology and land use/cover characteristics which have implications on its resources. The nature of the changes in the hydrology and land use have, however not been adequately examined, and so there is no sufficient information regarding hydrological and land use/cover trends. This study examined trends in hydrological and land use/cover variables over a 30-year period. The specific objectives of the study were to examine hydrological variables over the period 1974-2004; examine changes in land use in the watershed over the same period; determine the relationships between discharge and land use changes and assess the current soil and water management approaches in the watershed. Both primary and secondary data were used. Primary data was collected on land use through direct observations and use of a questionnaire. Secondary data was collected by reviewing documented information. The data obtained was analyzed using Statistical Package for Social Sciences (SPSS), GIS arc view 3.2 and MS Excel computer packages. Data on rainfall, river discharge and land use was analyzed through trend and regression analysis by use of MINITAB computer package. The major findings of the study show that there have been changes in discharge trends in the watershed over the study period. Annual discharge levels were found to have decreased by 0.12m3 per year whilst annual rainfall was found to have decreased by O.2mm per year. The findings also show significant land use changes over the period with closed forest cover and shrub land cover having decreased by 21 % and 41.7%, respectfully, while grassland cover and the area under agriculture increased by 99% and 296%, respectfully, due to unsustainable land use practices. Such changes are likely to lower the watershed's water table thereby negatively impacting on future water resource development programmes that depend on water from rivers and underground water sources. The study further reveals that the current soil and water conservation practices do not adequately address soil and water degradation problems in the watershed. It is therefore recommended that planting of drought resistant and early maturing crops be done to minimize over-dependence on rain fed agriculture; sustained soil and water conservation programmes that include replanting of indigenous trees and vegetation within critical water catchment areas be promoted through up-scaling soil and water conservation practices through farmer sensitisation and improvement of farm income. Further, research should be done to establish and quantify the level of sediment yields in River Mutonga over the period; and also the effect of changing land use on ground water resources in the watershed. There is also need to review soil and water management programmes with a view to involving all stakeholders in planning, implementation, monitoring and sharing of responsibilities including funding to ensure those benefiting from conservation efforts contribute towards sustainable watershed management. Future government policies on watershed management need to take cognisance of the hydrological and land use trends in various regions of the Tana basin.