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The Usangu wetland (Ihefu) is a wetland of great importance for its biodiversity and acts as
regulator for downstream flows for the Great Ruaha River through the Ruaha National Park.
While recognizing the importance of this wetland, little is known about the effects of land use
and cover changes on the wetland itself and the flow regime of the Great Ruaha River in the
downstream. Recognizing that, a study was conducted using remote sensing and GIS techniques
to inventory land use/cover changes in the watershed over the years. Hydrological data were
analyzed to reveal the alterations and trends at three periods (pre-1974, 1974-1975 and post
1985) from 1958 to 2004. It was revealed that there was a steady increase in cultivated area,
from 121.2 km2 to 874.3 km2 between 1973 and 2000 while the woodland area decreased
significantly over years. The minimum dry season area of the wetland declined significantly,
with more changes occurring between 1984 and 2000 at 67% reduction. The river was found to
be sensitive to land use/ cover changes and highly variable on an intra annual (seasonal) and
inter-annual (year to year) basis. There was a slight shift in the peaking for the post-1985 period
with high flows attained earlier in February instead of April. The Q50 flow progressively declined
from 19.23m3s-1 in the pre-1974 to 16.51 m3s-1 and 9.04 m3s-1 for 1974-1975 and post-1985
period respectively. The Q95 (low flow) declined from 2.84 m3s-1 to 0.11 m3s-1 and 0.0 m3s-1 for
pre-1974, 1974-1975 and post-1985 period respectively. The study concludes that the
modification of the land use and cover has resulted into changes in time distribution of runoff
within the catchment. The study highlights the effects of land use /cover changes on ecosystems
and water resources for an informed decision on proper catchment planning and management. |
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