Geoscience Reference
In-Depth Information
Tanzania. Besides farming, livestock keeping is also a major activity in the region. Cattle,
goats and sheep are the major domesticated animals. Modern diary farming and poultry
keeping are confined to urban centers
Tabora region is among the areas of Tanzania which are in moderate climatic zones. Tabora
region is located in the mid-western part of Mainland Tanzania. Tabora is characterized as
tropical type of climate with clearly distinguished rainy and dry seasons. According to
meteorological statistics the average temperature for the region is about 27
0
C. Tabora
receives Mean Annual Rainfall of 892 mm/annum or 74 mm/month. In Tabora, about 76%
of the population are farmers, and thus agriculture is the largest single sector in the
economy directory producing about 80 percent of Tabora region's wealth of goods and
services. Main cash crops grown are tobacco, cotton and paddy. Tobacco and cotton are
mainly grown for export markets. Principal food crops are maize, sorghum, cassava, sweet
potatoes and legumes.
Arusha region lies in moderate climatic zone. With the exception of a few spots the region is
in the high altitudes ranging from 800 to 4,500 meters above sea level. Because of the high
altitude the region experiences moderate temperatures with rainfall varying with the
altitude. The average annual temperature is 21
0
C in the highlands and 24
0
C in the low lands.
Arusha region has two types of rainfall patterns: unimodal and bimodal. The southern
district of Karatu normally enjoys unimodal rainfall which usually starts in November and
ends in April. The rainfall in this district is usually reliable, ranging from 800 to 1,000
mm/annum. The major crop produced is cereals. Soils have been classified by colour into
grey, brown and red brown. The extensive soils which originate from recent volcanic ash are
found to the north-western parts of the region, west of the rift valley and in the Ngorongoro
massif. Brown soils cover large areas in the central part and western side of the region. The
southern- eastern areas are characterised by grey brown and red-brown soils. Soil erosion is
particularly severe in the heavily settled central part of the region. Generally soil erosion is
widespread throughout the region and is deemed to be an environmental disaster in the
making.
2.2 Data type and sources
This study collected readily available secondary data from reports of Ministry of Water and
Irrigation (Husebye and Torblaa, 1995) as adopted in Tables 2.2.1 & 2.2.2. However, data
from Arusha in Table 2.2.2 were sourced from a recent study by Malisa (2007). They include
name of the dam, full supply level of the dam, capacity of the dam at full supply level, year
of construction, accumulated sediment volume in the dam (Sed Fill ), dam survey Year (Year
Data Collected), volumetric rate of sediment accumulation in the dam (Sed Fill per Year),
catchment area, and Sediment yield. It should be noted also that important data such as
geographical locations of these dams are missing. The dams were built for various purposes,
including and not limited to irrigation, domestic water supply, livestock watering, flood
control and fishing.
It should be noted that most of these sedimentation data presented in Tables 2.2.1 and 2.2.2
were collected using mainly two approaches, namely, direct measurement of transported
materials (
i.e.
, suspended sediment concentration) and measurement of the rate of siltation
of reservoirs/dams. The author would like to note that the first procedure has some
setbacks, especially, when practiced in tropics. For instance, a majority of sediment would
be transported in one or two days. Typically for Tanzania, most of sediment samples had
been taken at medium or low stage. The high stages were hardly sampled. This might have
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