Land alterations including deforestation, unsustainable land management practices and an increase in cultivated areas have occurred in the Upper Ruvu watershed in recent decades threatening water and natural resources. This study, which used a combination of remote sensing techniques, field experiments, watershed monitoring, and modeling was designed to investigate impacts of environmental changes on hydrology and soil erosion. The objectives were to: map the extent of land use and land cover change and its influence on soil erosion; correlate the contribution of climate variability and human activities to the changes in hydrology at headwater and watershed scales; estimate surface runoff, sediments and Curve Number at plot scale, and model streamflow responses to changes in land use and land cover using the SWAT watershed model. Results indicate that areas covered by forest decreased from 17% in 1991 to 4% of the total watershed area in 2015. However, areas covered by cropland increased from 14% to 30% of the total watershed area from 1991 to 2015, respectively. Further, results indicate that site characteristics affect runoff and sediment yield as higher soil loss was estimated from cropland with a mean of 28.4 tha-1 in 2015 from 19.8 tha-1 in 1991. Results from monitoring show high sediment loads were from the most disturbed watersheds, compared to Mbezi. Analysis of trends for the long term records at the watershed showed that rainfall had significant decreasing trends. At annual scale, climate variability contributed 46% and human activities contributed 54% of the changes in streamflow. Results from the rainfall simulation experiments show upland rice had higher runoff (48 mmh-1) and soil loss (94 gm-2) compared to grassland and forest. Results from the model outputs showed that average streamflow decreased by 13% between 1991 and 2015. Average peak flows increased by 5% and 12% for 2000 and 2015, respectively compared to the baseline. Land alterations had impacts on surface runoff which increased by 75% and baseflow decreased by 66% in 2015 from the baseline. These results highlight the main areas of changes and provide quantitative information to decision makers for sustainable land and water resources planning and management. / Ph. D. / Deforestation, unsustainable land management practices including cultivation in marginal areas, slash and burn, illegal forest harvest; and bush fires have been common threats to the landscapes of the Upper Ruvu watershed in recent decades. These practices have contributed to the deterioration of water and natural resource base and jeopardize sustainability. Our study was designed to investigate the impacts of environmental changes on the hydrology and soil erosion. We used a combination of methods including experiments in the field, remote sensing and mathematical modeling to investigate the extent of the problem and provide useful information for sustainable management of resources. The objectives were to understand the extent and dynamics of land use and land cover change and subsequent influences on soil erosion; to correlate contribution of climate variability and human activities to hydrology at different scales; to estimate surface runoff and sediments at plot scale; and to model and predict streamflow responses to changes in land use and land cover. Our results indicate that the watershed has been characterized by a loss of forest cover which decreased from 17% in 1991 to 4% of the total watershed area in 2015. Areas of the watershed occupied by cropland increased from 14% to 30% of the total watershed area from 1991 to 2015, respectively. Further, results indicate that the changes had effects on runoff and sediment yield as a high increase ofsoil loss was estimated from cropland which increased from 19.8 t ha<sup>-1</sup> in 1991 to 28.4 t ha<sup>-1</sup> in 2015 and areas occupied by forest were least contributors to soil erosion. The assertion is supported by results from a stream-monitoring which revealed that watersheds with least human interferences generated less sediments, and upland rice had higher soil loss compared to grassland and forest. Analysis of rainfall trends showed significant decreasing trends and fluctuations in climate contributed 46%, and human activities contributed 54% of the changes in streamflow signifying impacts on water availability. Results from the model outputs showed that average streamflow decreased by 13% between 1991 and 2015, with increase in peak flows and decrease in baseflow. Results highlight the changes and subsequent consequences on the hydrology of the watershed and water availability. The information is useful for watershed planning and water resources management.
| Identifer | oai:union.ndltd.org:VTETD/oai:vtechworks.lib.vt.edu:10919/83863 |
| Date | 10 January 2017 |
| Creators | Mbungu, Winfred Baptist |
| Contributors | Biological Systems Engineering, Heatwole, Conrad D., Sridhar, Venkataramana, Galbraith, John M., Easton, Zachary M. |
| Publisher | Virginia Tech |
| Source Sets | Virginia Tech Theses and Dissertation |
| Detected Language | English |
| Type | Dissertation |
| Format | ETD, application/pdf |
| Coverage | Tanzania |
| Rights | In Copyright, http://rightsstatements.org/vocab/InC/1.0/ |
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