Browsing by Author "Kakembo, Vincent"

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    Analysis of topographic parameters underpinning landslide occurrence in Kigezi highlands of southwestern Uganda
    (Natural Hazards, 2019) Nseka, Denis; Kakembo, Vincent; Bamutaze, Yazidhi; Mugagga, Frank
    An assessment of the influence of topography on landslide occurrence in the Kigezi highlands of southwestern Uganda was conducted. Whereas the frequency and magnitude of landslides in these highlands are on the increase, the topographic attributes underpinning landslide occurrence are not well understood. Sixty-five landslide scars were surveyed and mapped to produce landslide distribution maps. Specific topographic parameters, namely slope gradient, profile curvature, topographic wetness index (TWI), stream power index (SPI), and topographic position index (TPI), were assessed on landslide slope sites. The attributes were parameterized in the field and GIS environment using a 10-m DEM. Landslides were noted to concentrate along narrow topographic hollows, as opposed to broad concave slopes in the landscape. The occurrence is dominant in slope zones where slope gradient, profile curvature, TWI, TPI, and SPI are 25°–35°, 0.1–5, 8–18, − 1–1, and > 10, respectively. It was established that profile curvature and slope gradient are the most and least significant topographic parameters in landslide occurrence (R2 = 0.802, p value = 0.088 and R2 = 0.5665, p value = 0.057), respectively. An understanding of these topographic underpinnings would serve to identify and predict potential landslide zones within the landscape and enhance landslide hazard mitigation.
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    Characterization of artisanal gold mining activities in the tropics and their impact on sediment loading and stream flow in the Okame River catchment, Eastern Uganda
    (Environmental Earth Sciences, 2016) Barasa, Bernard; Kakembo, Vincent; Karl, Tiller
    Artisanal gold mining activities continue to degrade water resources in the tropical watersheds. In this study, we examined the spatial distribution of artisanal gold mining activities and their impact on sediment and mercury concentration in the Okame River catchment, Eastern Uganda. The spatial distributions of mining activities were assessed using both a TerraSAR-X radar satellite image of 2008 and Landsat image of 2013. Water samples and river bed deposits were collected on a monthly basis for a period of 1 year to assess the impact of mining activities on the streamflow variations and sediment concentration. Our results showed that the distribution of gold mining activities increased from 4.5 km2 in 2008 to 19.9 km2 in 2013. Human-induced sediment loading due to gold stone washing in the sampled tributaries of Okame River was responsible for the high concentration of suspended sediments (CSS), mercury and low water levels than prior to gold stone washing. River Omanyi (0.0191 mg l-1) was the most highly contaminated stream with mercury followed by Nankuke River (0.0163 mg l-1) and Nabewo River (0.0158 mg 1-1) in the Okame. There was also a significant concentration and trend of soluble mercury contamination from the sampled rivers (R2 = 0.8). The average concentration of mercury was found to be 0.004 ± 0.0009 mg l. This paper notes that artisanal mining activities have led to the reduction in streamflow rates, change of streamflow course and colonization of stream banks by riparian vegetation.
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    Effects of heterogeneous land use/cover types on river channel morphology in the Solo River catchment, Eastern Uganda
    (Geocarto International, 2015) Barasa, Bernard; Kakembo, Vincent; Mwololo Waema, Tim; Laban, Macopiyo
    In the tropics, unmonitored land use/cover types cause significant effects on the narrowing and widening of river channels which affects the integrity of water resources. River channel planform extent was characterised using Landsat images while water and bedload samples were collected and analysed for a period of one year. The results revealed that in 1986 the channel planform covered 3.7sq.km in length than in 2013 where it increased to 4.2sq.km. Wetland (537.1mgl-1) and bushland (186.3mgl-1) cover types had the highest concentration of suspended sediments. Fine-sand (0.25mm), silty-sand (1mm) and silty-clay (0.125mm) bedload particle types dominated the riverbed along the channel from the sampled land use/cover types. The high concentration of sediments, bedload materials, bank-instability, and stream-flow were significant contributors to the narrowing and widening of the channel (P<0.05). Agricultural landuse was the major contributor of channel aggradation (0.8m) and degradation (0.25m) compared to treeplantations, bushlands, forest and wetland cover types.
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    Land Use Cover Types and Forest Management Options for Carbon in Mabira Central Forest Reserve
    (African Handbook of Climate Change Adaptation, 2020) Jjagwe, Aisha; Kakembo, Vincent; Barasa, Bernard
    Mabira Central Forest Reserve (CFR), one of the biggest forest reserves in Uganda, has increasingly undergone encroachments and deforestation. This chapter presents the implications of a range of forest management options for carbon stocks in the Mabira CFR. The effects of forest management options were reviewed by comparing above-ground biomass (AGB), carbon, and soil organic carbon (SOC) in three management zones. The chapter attempts to provide estimates of AGB and carbon stocks (t/ha) of forest (trees) and SOC using sampling techniques and allometric equations. AGB and carbon were obtained from a count of 143 trees, measuring parameters of diameter at breast height (DBH), crown diameter (CW), and height (H) with tree coordinates. It also makes use of the Velle (Estimation of standing stock of woody biomass in areas where little or no baseline data are available. A study based on field measurements in Uganda. Norges Landbrukshoegskole, Ås, 1995) allometric equations developed for Uganda to estimate AGB. The strict nature reserve management zone was noted to sink the highest volume of carbon of approximately 6,771,092.34 tonnes, as compared to the recreation zone (2,196,467.59 tonnes) and production zone (458,903.57 tonnes). A statistically significant relationship was identified between AGB and carbon. SOC varied with soil depth, with the soil surface of 0–10 cm depth registering the highest mean of 2.78% across all the management zones. Soil depth and land use/ cover types also had a statistically significant effect on the percentage of SOC (P ¼ 0.05). A statistically significant difference at the 95% significance level was also identified between the mean carbon stocks from one level of management zones to another. Recommendations include: demarcating forest boundaries to minimize encroachment, enforcement of forestry policy for sustainable development, promote reforestation, and increase human resources for efficient monitoring of the forest compartments.
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    Streamflow responses to changes in land use and climate in a tropical catchment: Malaba River Catchment, Eastern Uganda
    (Geosciences, 2018) Barasa, Bernard; Kakembo, Vincent; Mwololo Waema, Tim; Macopiyo, Laban
    The hydrological cycle over most tropical catchments is mainly influenced by changes in land use and climate. This study explored the trend of precipitation and streamflow to evaluate the sensitivity of the catchment to land use and climate. A Mann-Kendall test and the concept of streamflow elasticity were adopted to determine the trend of precipitation and sensitivity of the catchment to climate. Changes in land use on the streamflow were evaluated using a spatially distributed SHETRAN hydrological model. The model calibration period was 1995-1998, while 2009-2012 was the validation period. The highest change in the gain of land were mainly experienced from the agricultural land use (crop growing) (36.7%) and tropical forest-regeneration (2.2%); while the highest loss in land were experienced from the wetlands (24.6%) and bushlands and thickets (15.3%) land cover types. The calibration period had a Nash-Sutcliffe Efficiency (NSE) of 0.78 whilst 0.81 during validation. The high frequency of flood re-occurences and growth in agricultural land use were the major contributors of streamflow in the catchment.